VLC

Visible Light Communications using

Wavelength Division Multiplexing

Submitted by:

Talha Ahmed Khan 2006-Elect-128

Supervised by: Dr M.Tahir

Department of Electrical Engineering

University of Engineering and Technology Lahore

Visible Light Communications using


Submitted to the faculty of the Electrical Engineering Department

of the University of Engineering and Technology Lahore

in partial fulfillment of the requirements for the Degree of

Bachelor of Science

in

Electrical Engineering.

Internal Examiner External Examiner

DirectorUndergraduate Studies

Department of Electrical Engineering

University of Engineering and Technology Lahore

i

Declaration

I declare that the work contained in this thesis is my own, except where explicitly stated

otherwise. In addition this work has not been submitted to obtain another degree or

professional qualification.

Signed:

Date:

ii

Acknowledgments

With the blessings of ALLAH Almighty ,I have succeessfully completed my final year

project.

First of all,I would like to extend my deepest gratitude to Dr Muhammad Tahir,my

project advisor, for patronizing the project.The technical support and

encouragement rendered by Dr Muhammad Tahir was very vital in the completion of

this project.

I would like to thank my loving parents for their prayers and financial support.

I would like to acknowledge all my friends and my brother for their moral support and

valuable suggestions.

iii

Dedicated to all the people I love

iv

Contents

Acknowledgments iii

List of Figures viii

Abstract x

1 An Introduction to Visible Light Communications 1

1.1 Visible Light Communications . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.1.2 VLC Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Merits and Demerits of VLC . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 Merits:VLC vs RF Communication . . . . . . . . . . . . . . . . . . 4

1.2.2 Merits:VLC vs IR Communication . . . . . . . . . . . . . . . . . . 4

1.2.3 Demerits of VLC . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.3 Applications of VLC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3.1 Position Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3.1.1 Position Detection using GPS . . . . . . . . . . . . . . . 6

1.3.1.2 Position Detection using RF . . . . . . . . . . . . . . . . 7

1.3.1.3 Position Detection using WiFi . . . . . . . . . . . . . . . 7

1.3.1.4 Position Detection using QR Codes . . . . . . . . . . . . 7

1.3.1.5 Position Detection using VLC . . . . . . . . . . . . . . . 8

1.3.2 Intelligent SuperMart . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.3.3 Image Sensor Communication . . . . . . . . . . . . . . . . . . . . . 10

1.3.4 Intelligent Transport System . . . . . . . . . . . . . . . . . . . . . 10

1.3.5 Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.3.6 Audio Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.3.7 Aesthetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2 Wavelength Division Multiplexing 13

2.1 WDM: A Fibre-Optics Perspective . . . . . . . . . . . . . . . . . . . . . . 13

2.1.1 Evolution of WDM . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1.2 WDM systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.1.2.1 Advantages of WDM systems . . . . . . . . . . . . . . . . 14

2.1.2.2 Types of WDM . . . . . . . . . . . . . . . . . . . . . . . 14

2.2 VLC and WDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.3 LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3.1 Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

v

Contents vi

2.3.2 Practical Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3.3 White LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.3.3.1 RGB LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.3.3.2 Phosphor-based LEDs . . . . . . . . . . . . . . . . . . . . 18

2.3.4 Types of LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.3.4.1 Miniature LEDs . . . . . . . . . . . . . . . . . . . . . . . 20

2.3.4.2 High Power LEDs . . . . . . . . . . . . . . . . . . . . . . 20

2.3.4.3 Medium Range LEDs . . . . . . . . . . . . . . . . . . . . 21

2.3.5 Advantages of LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3.6 Disadvantages of LEDs . . . . . . . . . . . . . . . . . . . . . . . . 22

3 Motivations and Problem Statement 24

3.0.7 LED:Technical Evolution . . . . . . . . . . . . . . . . . . . . . . . 24

3.1 Problem Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4 Implementation 27

4.1 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.2.1 LED Modulation Scheme . . . . . . . . . . . . . . . . . . . . . . . 28

4.2.2 Wavelength Division Multiplexing . . . . . . . . . . . . . . . . . . 28

4.2.3 Demultiplexing using Optical filters . . . . . . . . . . . . . . . . . 28

4.2.4 Data Reception using Direct Detection . . . . . . . . . . . . . . . . 28

4.3 Hardware Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3.1 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3.1.1 Colored LEDs . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3.1.2 MOSFETs . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.3.1.3 RS232 line driver . . . . . . . . . . . . . . . . . . . . . . 31

4.3.1.4 USB to RS232 converter cable . . . . . . . . . . . . . . . 31

4.3.1.5 Voltage Regulator . . . . . . . . . . . . . . . . . . . . . . 31

4.3.2 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.3.2.1 Optical Receiver . . . . . . . . . . . . . . . . . . . . . . . 32

4.3.2.2 Optical Filters . . . . . . . . . . . . . . . . . . . . . . . . 32

4.3.2.3 Voltage Regulator . . . . . . . . . . . . . . . . . . . . . . 33

4.3.2.4 RS232 line driver . . . . . . . . . . . . . . . . . . . . . . 33

4.3.2.5 USB to RS232 converter cable . . . . . . . . . . . . . . . 33

4.4 Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.4.1 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.4.2 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.5 PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.5.1 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.5.2 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.6 Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

5 Performance Evaluation 39

5.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.1.1 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . 39

5.1.1.1 Experiment 1 . . . . . . . . . . . . . . . . . . . . . . . . . 39

Contents vii

5.1.1.2 Experiment 2 . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.2 Conclusion and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 42

A MATLAB Codes 43

B Datasheets 48

References 70

List of Figures

1.1 Visible Light Communication: A historical perspective [9] . . . . . . . . . 2

1.2 A GPS system used for position detection [6] . . . . . . . . . . . . . . . . 6

1.3 RF-IDs based navigation system for handicapped people [6] . . . . . . . . 7

1.4 Pattern generated by QR code captured by a PDA [6] . . . . . . . . . . . 7

1.5 Location related information transfer from a traffic signal (Prototypemade by The Nippon Signal Co., Ltd., JAPAN SHOP 2006 [6]) . . . . . . 8

1.6 (Prototype made by VLCC member companies NEC and MatsushitaElectric works) [16] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.7 A comparison of Position Detection technologies [6] . . . . . . . . . . . . . 9

1.8 Shopping cart and Receiver(Prototype presented by NEC and MatsushitaElectric Works) [6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.9 Photograph from the succesful experiment conducted by Casio Computersfor a transmission distance of 1km [1] . . . . . . . . . . . . . . . . . . . . 11

1.10 A digital audio system where each color transmits a different sound(Prototypepresented by Sony and Agilent technologies [6]) . . . . . . . . . . . . . . . 11

1.11 An audio system using red green and blue LEDs [6] . . . . . . . . . . . . 12

1.12 Yokohama National Exibition:A treat to watch [6] . . . . . . . . . . . . . 12

2.1 This table shows the available colors with wavelength range,voltage dropand material used [3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.2 Combined spectral curves for blue, yellow-green, and high brightness redsolid-state semiconductor LEDs. FWHM spectral bandwidth is approxi-mately 2427 nm for all three colors [3] . . . . . . . . . . . . . . . . . . . . 18

2.3 Spectrum of a white LED clearly showing blue light which is directlyemitted by the GaN-based LED (peak at about 465 nm) and the morebroadband Stokes-shifted light emitted by the Ce3+:YAG phosphor whichemits at roughly 500700 nm [3] . . . . . . . . . . . . . . . . . . . . . . . . 19

2.4 Different types of LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.1 Price vs Performance curve depicting the technical evolution of LEDs [9] . 25

4.1 Block Diagram of project . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.2 IRF 520: NMOS transistor IC (source:Fairchild Semiconductors) . . . . . 30

4.3 7805:Voltage Regulator IC (source:) . . . . . . . . . . . . . . . . . . . . . 31

4.4 TORX 173:Fiber optic Receiving Module by TOSHIBA (source:TOSHIBAwebsite) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

4.5 7805:Voltage Regulator IC . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.6 Schematic Diagram of Transmitter . . . . . . . . . . . . . . . . . . . . . . 34

4.7 Schematic Diagram of Receiver . . . . . . . . . . . . . . . . . . . . . . . . 35

viii

List of Figures ix

4.8 PCB layout of Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.9 PCB layout of Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.1 Average BER vs distance between noise source and receiver . . . . . . . . 40

5.2 Average BER vs noise intensity . . . . . . . . . . . . . . . . . . . . . . . . 41

Abstract

Solid-state lighting is a rapidly growing area of research and applications,due to the reli-

ability, low power consumption and predicted high efficiency of these devices. In Visible

Light Communications (VLC), the LED sources that are typically used for general illu-

mination are used for data transmission. In this project, LEDs are used for wireless data

transmission between two computers using On-Off Keying.Wavelength Division Multi-

plexing is used to transmit multiple data streams simultaneously over the same wireless

channel.The effects of ambient noise on the performance of wireless link are also studied.

On the basis of the empirical results, a performance evaluation of this technique is also

presented.

Chapter 1

An Introduction to Visible Light

Communications

Overview

In the past few years,an unprecedented demand for wireless technologies has been taking

place.Usually,the radio frequency (RF) is used for wireless data transmission, but it has

its bandwidth constraints.In some cases where the distance between transmitter and

receiver is relatively small, RF technology can be replaced by visible light communication

(VLC) to provide high data rates. In addition, this technique not only provides better

security than RF communication, but it is also less prone to interference for indoor

situations. VLC uses spectral region with corresponding wavelengths lying between

450nm-900nm and offers potentially large bandwidths.

High power LEDs used for lighting are simultaneously used to transfer data, over the

wireless channel. On the receiver side a photo sensitive device is used for data reception.

For different data sources, wavelength division multiplexing can be used to transmit

data simultaneously over the same channel. In this technique, a different color (wave-

length) can be reserved for each data stream. The different streams are multiplexed and

are transmitted by modulating the light source. At the receiver, different wavelength

filters are used to separate the desired data stream followed by the light sensing device.

The received signal from the photo sensing device is then demodulated to recover the

transmitted data.

1.1 Visible Light Communications

“Visible light Communication (VLC) is a modern communication technology

which employs visible solid-state light sources (LEDs) for transmitting data

wirelessly as they are used for general illumination at the same time.”

1

Chapter 1. An Introduction to Visible Light Communications 2

1.1.1 History

Though the research and development of visible light communications systems was

started not long ago (2003) ,man has always resorted to some form of communications

employing a light source since stone age (Fig1.1). The age-old techniques of optical

communication are listed in a chronological order:

Heliograph: In bygone times,reflecting mirrors were used to deliver information over a

large distance.This technique is referred to as ‘Heliograph’.

Lamps and Fires: Burning kites were used in the battlefield for communication. Simi-

lary,lamps were used in lighthouses as well.

Ship-to-ship communication: Morse code was used for communication between ships.The

message was transmitted in the form of ‘marks’ and ‘spaces’.

Photophone: In 1880 Graham Bell devised a wireless communication system called a

Photophone in which sunlight was used as the optical source.A vibrating mirror was

used to modulate and reflect light to the receiver consisting of a parabolic mirror.This

system worked for a distance of around 700 ft.

Traffic Signals: Traffic signals also employ visible light communication in principle as

three different colours are used to communicate three different messages to the onlook-

ers.

Figure 1.1: Visible Light Communication: A historical perspective [9]

Visible Light Communication is the most advanced wirelss communication technology

using visible light sources for data transmission.Different lighting devices can be ex-

ploited to incorporate a visible light communications system. For instance,the lighting


used in homes,offices or roads, traffic signals, commercial displays, small lamps on elec-

tronic home appliances including TVs,etc.The use of LEDs in these devices is getting

popular,owing to the improved performance,low power consumption and cleaner light

provided by these devices.Similarly,the use of moile phones equipped with cameras is

also getting widespread acceptance.These cameras can be used to receive the visible

light. By using the visible light for the data transmission, many problems related to

radio and infrared communications are solved.

1.1.2 VLC Characteristics

The merits and demerits of this technology become apparent once we go through the

charactersitics of visible light communication technology:-

• Human Safety : VLC poses no health hazards to human body.Thus,the transmis-

sion power can be kept high if needed.

• High Data Rates: VLC inherits high data rates from optical communications.Thus,it

can be used for very high speed wireless communications.

• Bandwidth: Visible light communications exploits the visible region of electromag-

netic spectrum.Thus it offers much larger frequency band ( 300 THz) compared to

that available in RF communications ( 300GHz).

• Ubiquitous Nature: We have a well-established lighting infrastructure throughout

the world.In addition to it, LED based lighting devices are getting widespread ac-

ceptance round the globe.Since VLC uses the already available visible light sources

for wireless communictions,so it is expected to become a ubiquitous technology in

near future.

• Security : As VLC involves line of sight communication,so it is impossible to tap the

communication without breaking the link.So it offers a very secure communication

and can be used in high security military areas where RF communication is prone

to eavesdropping.

• Visibility : It is aesthetically pleasing to see data being communicated by colored

lights.Thus,VLC is also used in many entertainment related activities like silent

concerts,decoration systems,etc.

• Unlicensed Spectrum: As VLC uses the visible region of electromagnetic spec-

trum,so it is free of cost.Contrary to it,the RF communication band is regulated.

1.2 Merits and Demerits of VLC

Although,RF communications is the most popular wireless technology today but it has

its disadvantages as well.VLC can be used for wireless communications in certain areas

where RF communications exibits poor performance.As evident from the characteris-

tics of visible light communications,it offers several advantages over existing wireless


communication technologies.A comparison is drawn between VLC and other wireless

technologies in following subsections:-

1.2.1 Merits:VLC vs RF Communication

• Limited Transmission Power :In RF communications,the electric transmission power

cannot be increased beyond a prescribed level as it poses serious health hazards

for human body.

• Regulated Spectrum:Due to the radio wave restriction,there is no room to use more

radio frequency.In addition,the use of radio spectrum is regulated.

• Banned in Sensitive Areas: The radio wave cannot be used in hospitals and

space stations becauses it adversely affects the performance of precision instru-

ments.These radio wave problems above are easily solved by use of the visible

light communications.

Remedy

All these problems can be solved using visible light communications.This can be accred-

ited to the high available bandwidth,high data rates,high transmission power,health-

friendly operation and lower implementation costs of this technology.

1.2.2 Merits:VLC vs IR Communication

IR(Infra-red) communications is used in many applications including mobile phone and

laptops.Although IR communications offers the same advantages in terms of available

bandwidth but it lags behind VLC in certain areas.

• Limited Data Rates:In IR communications,data rates cannot be increased beyond

a prescribed level as it poses serious threat to human eyes.This can be attributed

to the high energy density created by IrDA due to invisibility.

Remedy

The eye safety problem can be solved using visible light communications.As compared to

IR communication, the visible light communication is suitable to human eyes in terms of

visibility.The system employs LED, which can be transmitted by a few watts, a relatively

high energy for the use of lighting. This means that the VLC is capable of transmitting

data at higher data rates.

1.2.3 Demerits of VLC

• LOS Communication: The greatest disadvantage of visible light communication is

that it requires line of sight communication.

• Short Range: This technology usually works over a short distance range.To increase

the transmission distance, the power of the lighting source must be increased.Image


Sensor communication can be used in conjunction with telescope lenses to realize

long distance ranges.Unfortunately,this range improvement leads to an appreciable

increases in the implementation cost.

• Prone to Interference: The VLC system is prone to interference from other illu-

minating devices.


1.3 Applications of VLC

VLC is not meant for replacing existing wireless communication technologies;its sole

purpose is to complement the existing wireless technologies.VLC offers a very wide area

of research and applications.Some of the major applications are discussed briefly:

• Position Detection

• Intelligent SuperMart

• Intelligent Transport System

• Image Sensor Communications

• Networking

• Audio Applications

• Aesthetics

1.3.1 Position Detection

Different wireless technologies are being used for position detection in local and global

navigation systems.VLC can also also be used in such systems [6]. Some of the popular

technologies are discussed below followed by a comparison chart at the end (Fig 1.7).

1.3.1.1 Position Detection using GPS

In GPS(Global Positioning System),satellites are used to detect the position of a user.

The user of GPS can know his/her position by receiving signals from at least 4 satel-

lites(Fig 1.2). Although, it is the technology of choice for car navigation systems but it

cannot be used in indoor environments.

Figure 1.2: A GPS system used for position detection [6]


1.3.1.2 Position Detection using RF

RF-IDs can also be used in certain position detection systems.The communication dis-

tance ranges from a few millimeters to several meters depending on the application. In

Japan, It is used in navigating handicapped people (Fig 1.3).

Figure 1.3: RF-IDs based navigation system for handicapped people [6]

1.3.1.3 Position Detection using WiFi

In WiFi based position detection systems, radio signal strength from two or more WiFi

base stations alongwith the position information of base stations are used for dseter-

mining user’s position.Positioning accuracy using WiFi is sometimes better than GPS

as shown in the above picture due to non-sufficient signal strength and mutlipath effect

caused by skyscrapers.

1.3.1.4 Position Detection using QR Codes

Figure 1.4: Pattern generated by QR code captured by a PDA [6]


Figure 1.5: Location related information transfer from a traffic signal (Prototypemade by The Nippon Signal Co., Ltd., JAPAN SHOP 2006 [6])

In this technique, a two-dimensional code known as QR code is used to encode a URL in

order to obtain a pattern which is printed and pasted at all the desired locations. Mobile

phones are used to take a snap of the pattern (Fig1.4). It can be used to automatically

access the URLs in order to get location related information like longitude and attitude.

1.3.1.5 Position Detection using VLC

In VLC based position detection systems, the position of the user can be detected if the

light sources are made to send position related information.It is equally effective indoors

as well as outdoors.Several companies have presented protoypes of VLC based position

detection systems [6].Some of the application scenarios are discussed below:

Traffic signal-pedestrian communication

The accompanying figure (Fig 1.5) shows a pedestrian receiving location related infor-

mation from a traffic signal using a PDA[16][4].

Global Navigation System

VLC has been used to demonstrate a prototype of a global navigation service It ac-

cesses the Internet by first obtaining a code from a visible light source such as LED

lights.It then accesses the location server from the cellular phone in order to obtain

location-related information [14](Fig 1.6).


Figure 1.6: (Prototype made by VLCC member companies NEC and MatsushitaElectric works) [16]

Figure 1.7: A comparison of Position Detection technologies [6]


1.3.2 Intelligent SuperMart

In an intelligent super mart,VLC is used to transmit merchandise related information[15].The

VLC receivers are mounted on the shopping carts (Fig 1.8).

Figure 1.8: Shopping cart and Receiver(Prototype presented by NEC and MatsushitaElectric Works) [6]

1.3.3 Image Sensor Communication

A visible light communications system usually employs a photodiode as the receiving

device .However, in Image Sensor Communications, the image sensor used in cameras

is used to serve the purpose. Although it is more expensive to use an image sensor in

place of a photodiode but it has its advantages:

• An image sensor consists of a large number of pixels and each pixel can be used as

an independent receiving channel. Thus, multiple receiving channels are available.

• As all the pixels are spatially separated, so the effects of interference are eliminated.

• As each receiving channel has the location information corresponding to the pixel,

it can specify the position of the transmitter when receiving.

• It can be used for long distance communication as well. Though the size of the

appearance of the source of light becomes smaller at large distances, but it can

still read the information from a far-off transmitter by using telescope lenses (Fig

1.9).

Despite all its advantages, this technology is not used at present owing to its high im-

plementation cost. The developers are eying at the widespread popularity and advances

made in mobile phone technology. As the modern mobile sets come equipped with high

frame rate cameras, it is hoped that these cameras will be used for image sensor commu-

nications in future as they become affordable. Thus, this technology may be employed

in a host of applications related to mobile devices and PDAs.

1.3.4 Intelligent Transport System

This technology can be used to design an intelligent transport system to ensure road

safety. Although red light enforcement cameras are used to catch red light runners but

this technique may lead to an increase in rear-end collisions. Nowadays, solid state

lighting is widely used in traffic signals and vehicle lights. So, these sources can also


Figure 1.9: Photograph from the succesful experiment conducted by Casio Computersfor a transmission distance of 1km [1]

be used for both car-to-car and car-to-traffic signal information communication. For

instance, it has been proposed that a traffic light can be used to transmit the time for

which it would remain yellow to the vehicles as far as 50m away. In addition to it,

car-to-car communication can be used for data logging at the time of accident. This

information can then be used to investigate the nature of the accident [7].

1.3.5 Networking

VLC is used in conjunction with PLC (Power Line Carrier Communications) to convert

the illuminating sources in homes and offices into optical hotspots [8]. Thus, the users

can enjoy high speed network access where the light sources are used to setup a wireless

LAN. Thus, there are no bandwidth bottlenecks owing to the high bandwidth offered

by VLC systems.

1.3.6 Audio Applications

VLC is used to send digital audio using colored LEDs namely red, green and blue.It

is also used in a silent concert where different sounds are transmitted using different

colors.The users have a choice to listen to the musical instruments they like by switching

between the different light beams,while the artists are performing in front of them. In

this way, it is used to provide entertainment to users as well [10].

Figure 1.10: A digital audio system where each color transmits a differentsound(Prototype presented by Sony and Agilent technologies [6])


Figure 1.11: An audio system using red green and blue LEDs [6]

1.3.7 Aesthetics

VLC is also used for for decoration or amusement.In the accompanying picture(Fig 1.12),

an analog sound system is shown.Illumination is synchronized with music sounds, which

are transmitted through the lights(bottom) by VLC to the audience.

Figure 1.12: Yokohama National Exibition:A treat to watch [6]

Wireless data transport by means of light paves the way for new applications in the

home as well as in industry and transportation.It is hoped that VLC systems will be

used in the near future in a host of applications.

Chapter 2


This chapter presents an overview of wavelength division multiplexing.Since the tech-

nique originally belongs to the field of fibre optics,a general introduction is presented

from the perspective of optical fibres followed by the use of wavelength division multi-

plexing in visible light communications.

2.1 WDM: A Fibre-Optics Perspective

In fiber-optic communications, wavelength-division multiplexing (WDM) is

a technology which multiplexes multiple optical carrier signals on a single

optical fiber by using different wavelengths (colours) of laser light to carry

different signals [2].

This allows for a multiplication in capacity, in addition to enabling bidirectional com-

munications over one strand of fiber. This is a form of frequency division multiplexing

(FDM) but is commonly called wavelength division multiplexing.The term wavelength-

division multiplexing is commonly applied to an optical carrier which is typically de-

scribed by its wavelength; whereas frequency-division multiplexing typically applies to

a radio carrier which is more often described by frequency. However, since wavelength

and frequency are inversely proportional, and since radio and light are both forms of

electromagnetic radiation, the two terms are equivalent in this context.[2]

2.1.1 Evolution of WDM

The concept was first published in 1970, and by 1978 WDM systems were being realized

in the laboratory.Early WDM systems were expensive and complicated to run. However,

recent standardization and better understanding of the dynamics of WDM systems have

made WDM less expensive to deploy.The first WDM systems only combined two signals.

Modern systems can handle up to 160 signals and can thus expand a basic 10 Gbpss

fiber system to a theoretical total capacity of over 1.6 Tbps over a single fiber pair [2].

13

Chapter 2. Wavelength Division Multiplexing 14

2.1.2 WDM systems

A WDM system uses a multiplexer at the transmitter to join the signals together, and a

demultiplexer at the receiver to split them apart. With the right type of fiber it is possible

to have a device that does both simultaneously, and can function as an optical add-drop

multiplexer. The optical filtering devices used have traditionally been etalons, stable

solid-state single-frequency FabryProt interferometers in the form of thin-film-coated

optical glass [2]. Most WDM systems operate on single mode fiber optical cables, which

have a core diameter of 9 m. Certain forms of WDM can also be used in multi-mode

fiber cables (also known as premises cables) which have core diameters of 50 or 62.5

m.Optical receivers, in contrast to laser sources, tend to be wideband devices. Therefore

the demultiplexer must provide the wavelength selectivity of the receiver in the WDM

system.

2.1.2.1 Advantages of WDM systems

WDM systems are popular with telecommunications companies because they allow them

to expand the capacity of the network without laying more fiber. By using WDM and op-

tical amplifiers, they can accommodate several generations of technology development in

their optical infrastructure without having to overhaul the backbone network. Capacity

of a given link can be expanded by simply upgrading the multiplexers and demulti-

plexers at each end.This is often done by using optical-to-electrical-to-optical (O/E/O)

translation at the very edge of the transport network, thus permitting interoperation

with existing equipment with optical interfaces.

2.1.2.2 Types of WDM

A WDM system cab ne classified into different types on the basis of wavelength spacing,

number of channels, and the ability to amplify the multiplexed signals in the opti-

cal space.WDM systems are divided in different wavelength patterns, conventional or

coarse and dense WDM. Conventional WDM systems provide up to 16 channels in the

3rd transmission window (C-Band) of silica fibers around 1550 nm. DWDM uses the

same transmission window but with denser channel spacing. Channel plans vary, but a

typical system would use 40 channels at 100 GHz spacing or 80 channels with 50 GHz

spacing. Some technologies are capable of 25 GHz spacing (sometimes called ultra dense

WDM). New amplification options (Raman amplification) enable the extension of the

usable wavelengths to the L-band, more or less doubling these numbers.

CWDM in contrast to conventional WDM and DWDM uses increased channel spac-

ing to allow less sophisticated and thus cheaper transceiver designs. To again provide

16 channels on a single fiber CWDM uses the entire frequency band between second

and third transmission window (1310/1550 nm respectively) including both windows

(minimum dispersion window and minimum attenuation window) but also the critical

area where OH scattering may occur, recommending the use of OH-free silica fibers in

case the wavelengths between second and third transmission window shall also be used.


Avoiding this region, the channels 31, 49, 51, 53, 55, 57, 59, 61 remain and these are the

most commonly used [2].

2.2 VLC and WDM

As the demand for ultra broadband wireless access home networks constantly increases,

the radio frequency spectrum is becoming extremely congested and thus, attention is

drawn towards alternative technologies. The abundance of unregulated bandwidth at

the optical frequencies has diverted the attention towards visible light communications

systems as a means of delivering high bit-rate services over short distances.Similar to

fibre optics,wavelength division multiplexing can also be applied to transmit multiple

data streams simultaneously over the same wireless channel.

In this technique, a different color (wavelength) can be reserved for each data stream.

The different streams are multiplexed and are transmitted by modulating the colored

light source. At the receiver, different wavelength filters are used to separate the desired

data stream followed by the light sensing device. The received signal from the photo

sensing device is then demodulated to recover the transmitted data.

In the next section,an overview of LEDs is presented.


2.3 LED

A light-emitting diode (LED)is a semiconductor light source. LEDs are used as indicator

lamps in many devices, and are increasingly used for lighting. Introduced as a practical

electronic component in 1962, early LEDs emitted low-intensity red light, but modern

versions are available across the visible, ultraviolet and infrared wavelengths, with very

high brightness.

2.3.1 Physics

Electroluminiscense

The LED is based on the semiconductor diode. When a diode is forward biased (switched

on), electrons are able to recombine with holes within the device, releasing energy in

the form of photons. This effect is called electroluminescence and the color of the light

(corresponding to the energy of the photon) is determined by the energy gap of the

semiconductor. An LED is usually small in area (less than 1 mm2), and integrated

optical components are used to shape its radiation pattern and assist in reflection.

Like a normal diode, the LED consists of a chip of semiconducting material doped with

impurities to create a p-n junction. As in other diodes, current flows easily from the

p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-

carrierselectrons and holesflow into the junction from electrodes with different voltages.

When an electron meets a hole, it falls into a lower energy level, and releases energy

in the form of a photon.The wavelength of the light emitted, and therefore its color,

depends on the band gap energy of the materials forming the p-n junction. In silicon

or germanium diodes, the electrons and holes recombine by a non-radiative transition

which produces no optical emission, because these are indirect band gap materials. The

materials used for the LED have a direct band gap with energies corresponding to near-

infrared, visible or near-ultraviolet light.LED development began with infrared and red

devices made with gallium arsenide. Advances in materials science have made possible

the production of devices with ever-shorter wavelengths, producing light in a variety of

colors.LEDs are usually built on an n-type substrate, with an electrode attached to the

p-type layer deposited on its surface. P-type substrates, while less common, occur as

well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate [3].

2.3.2 Practical Uses

LEDs present many advantages over incandescent light sources including lower energy

consumption, longer lifetime, improved robustness, smaller size, faster switching, and

greater durability and reliability. However, they are relatively expensive and require

more precise current and heat management than traditional light sources. Current LED

products for general lighting are more expensive to buy than fluorescent lamp sources of

comparable output. They also enjoy use in applications as diverse as replacements for

traditional light sources in aviation lighting, automotive lighting (particularly indicators)

and in traffic signals. The compact size of LEDs has allowed new text and video displays


and sensors to be developed, while their high switching rates are useful in advanced

communications technology. Infrared LEDs are also used in the remote control units

of many commercial products including televisions, DVD players, and other domestic

appliances.

2.3.3 White LEDs

There are two primary ways of producing high intensity white-light using LEDs. One is

to use individual LEDs that emit three primary colors[54]-red, green, and blueand then

mix all the colors to produce white light. The other is to use a phosphor material to

convert monochromatic light from a blue or UV LED to broad-spectrum white light,

much in the same way a fluorescent light bulb works.

2.3.3.1 RGB LEDs

White light can be produced by mixing differently colored light, the most common

method is to use red, green and blue (RGB). Hence the method is called multi-colored

white LEDs (sometimes referred to as RGB LEDs). Because its mechanism is involved

with electro-optical devices to control the blending and diffusion of different colors, this

approach is little used to produce white lighting. Nevertheless this method is particularly

Figure 2.1: This table shows the available colors with wavelength range,voltage dropand material used [3]


interesting in many applications because of the flexibility of mixing different colors,and,

in principle, this mechanism also has higher quantum efficiency in producing white light

[3]. There are several types of multi-colored white LEDs: di, tri, and tetrachromatic

Figure 2.2: Combined spectral curves for blue, yellow-green, and high brightness redsolid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 2427 nm

for all three colors [3]

white LEDs. Several key factors that play among these different approaches include

color stability, color rendering capability, and luminous efficacy. Often higher efficiency

will mean lower color rendering, presenting a trade off between the luminous efficiency

and color rendering. For example, the dichromatic white LEDs have the best luminous

efficacy, but the lowest color rendering capability. Conversely, although tetrachromatic

white LEDs have excellent color rendering capability, they often have poor luminous

efficiency. Trichromatic white LEDs are in between, having both good luminous efficacy

and fair color rendering capability. What multi-color LEDs offer is not merely another

solution of producing white light, but is a whole new technique of producing light of

different colors. In principle, most perceivable colors can be produced by mixing different

amounts of three primary colors, and this makes it possible to produce precise dynamic

color control as well. As more effort is devoted to investigating this technique, multi-

color LEDs should have profound influence on the fundamental method which we use

to produce and control light color. However, before this type of LED can truly play

a role on the market, several technical problems need to be solved. These certainly

include that this type of LED’s emission power decays exponentially with increasing

temperature,[12] resulting in a substantial change in color stability. Such problems are

not acceptable for industrial usage. Therefore, many new package designs aimed at

solving this problem have been proposed and their results are now being reproduced by

researchers and scientists.

2.3.3.2 Phosphor-based LEDs

This method involves coating an LED of one color (mostly blue LED made of InGaN)

with phosphor of different colors to produce white light, the resultant LEDs are called

phosphor-based white LEDs [13]. A fraction of the blue light undergoes the Stokes shift

being transformed from shorter wavelengths to longer. Depending on the color of the

original LED, phosphors of different colors can be employed. If several phosphor layers


of distinct colors are applied, the emitted spectrum is broadened, effectively increasing

the color rendering index (CRI) value of a given LED. Phosphor based LEDs have a

lower efficiency than normal LEDs due to the heat loss from the Stokes shift and also

other phosphor-related degradation issues. However, the phosphor method is still the

most popular technique for manufacturing high intensity white LEDs. The design and

production of a light source or light fixture using a monochrome emitter with phosphor

conversion is simpler and cheaper than a complex RGB system, and the majority of

high intensity white LEDs presently on the market are manufactured using phosphor

light conversion. The greatest barrier to high efficiency is the seemingly unavoidable

Stokes energy loss. However, much effort is being spent on optimizing these devices

to higher light output and higher operation temperatures. For instance, the efficiency

can be increased by adapting better package design or by using a more suitable type

of phosphor. Philips Lumileds’ patented conformal coating process addresses the is-

sue of varying phosphor thickness, giving the white LEDs a more homogeneous white

light.With development ongoing, the efficiency of phosphor based LEDs is generally in-

creased with every new product announcement. Technically the phosphor based white

LEDs encapsulate InGaN blue LEDs inside of a phosphor coated epoxy. A common yel-

low phosphor material is cerium-doped yttrium aluminium garnet (Ce3+:YAG). White

Figure 2.3: Spectrum of a white LED clearly showing blue light which is directlyemitted by the GaN-based LED (peak at about 465 nm) and the more broadbandStokes-shifted light emitted by the Ce3+:YAG phosphor which emits at roughly 500700

nm [3]

LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture

of high efficiency europium-based red and blue emitting phosphors plus green emitting

copper and aluminium doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to

the way fluorescent lamps work. This method is less efficient than the blue LED with

YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted

to heat, but yields light with better spectral characteristics, which render color better.

Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both

approaches offer comparable brightness. Another concern is that UV light may leak

from a malfunctioning light source and cause harm to human eyes or skin.


Figure 2.4: Different types of LEDs

2.3.4 Types of LEDs

The main types of LEDs are miniature, high power devices and custom designs such as

alphanumeric or multi-color

2.3.4.1 Miniature LEDs

These are mostly single-die LEDs used as indicators, and they come in various-sizes from

2 mm to 8 mm, through-hole and surface mount packages. They are usually simple in

design, not requiring any separate cooling body. Typical current ratings ranges from

around 1 mA to above 20 mA. The small scale sets a natural upper boundary on power

consumption due to heat caused by the high current density and need for heat sinking.

2.3.4.2 High Power LEDs

High power LEDs (HPLED) can be driven at currents from hundreds of mA to more

than an ampere, compared with the tens of mA for other LEDs. Some can produce over

a thousand lumens. Since overheating is destructive, the HPLEDs must be mounted on

a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed,

the device will burn out in seconds. A single HPLED can often replace an incandescent

bulb in a flashlight, or be set in an array to form a powerful LED lamp.

Some well-known HPLEDs in this category are the Lumileds Rebel Led, Osram Opto

Semiconductors Golden Dragon and Cree X-lamp. As of September 2009 some HPLEDs

manufactured by Cree Inc. now exceed 105 lm/W (e.g. the XLamp XP-G LED chip

emitting Cool White light) and are being sold in lamps intended to replace incandescent,

halogen, and even fluorescent style lights as LEDs become more cost competitive.

LEDs have been developed by Seoul Semiconductor that can operate on AC power

without the need for a DC converter. For each half cycle part of the LED emits light

and part is dark, and this is reversed during the next half cycle. The efficacy of this type

of HPLED is typically 40 lm/W [12]. A large number of LED elements in series may be

able to operate directly from line voltage. In 2009 Seoul Semiconductor released a high

DC voltage capable of being driven from AC power with a simple controlling circuit.

The low power dissipation of these LEDs affords them more flexibility than the original

AC LED design.


2.3.4.3 Medium Range LEDs

Medium power LEDs are often through-hole mounted and used when a output of a few

lumen is needed. They sometimes have the diode mounted to four leads (two cathode

leads, two anode leads) for better heat conduction and carry an integrated lens. An

example of this is the Superflux package, from Philips Lumileds. These LEDs are most

commonly used in light panels, emergency lighting and automotive tail-lights. Due to

the larger amount of metal in the LED, they are able to handle higher currents (around

100 mA). The higher current allows for the higher light output required for tail-lights

and emergency lighting.

2.3.5 Advantages of LEDs

The main advantages of LEDs are described as follows:

Efficiency

LEDs produce more light per watt than incandescent bulbs.Their efficiency is not af-

fected by shape and size, unlike Fluorescent light bulbs or tubes.

Color

LEDs can emit light of an intended color without the use of the color filters that tradi-

tional lighting methods require. This is more efficient and can lower initial costs.

Size

LEDs can be very small (smaller than 2 mm ) and are easily populated onto printed

circuit boards.

On/Off time

LEDs light up very quickly. A typical red indicator LED will achieve full brightness

in under a microsecond .LEDs used in communications devices can have even faster

response times.

Cycling

LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike

fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that

require a long time before restarting.

Dimming

LEDs can very easily be dimmed either by pulse-width modulation or lowering the

forward current.

Cool light

In contrast to most light sources, LEDs radiate very little heat in the form of IR that

can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat

through the base of the LED.


Slow failure

LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent

bulbs.

Lifetime

LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours

of useful life, though time to complete failure may be longer. Fluorescent tubes typically

are rated at about 10,000 to 15,000 hours [3], depending partly on the conditions of use,

and incandescent light bulbs at 1,0002,000 hours.

Shock resistance

LEDs, being solid state components, are difficult to damage with external shock, unlike

fluorescent and incandescent bulbs which are fragile. Focus: The solid package of the

LED can be designed to focus its light. Incandescent and fluorescent sources often

require an external reflector to collect light and direct it in a usable manner.

Toxicity

LEDs do not contain mercury, unlike fluorescent lamps.

2.3.6 Disadvantages of LEDs

The disadvantages of LEDs are described below:

High initial price

LEDs are currently more expensive, price per lumen, on an initial capital cost basis,

than most conventional lighting technologies. The additional expense partially stems

from the relatively low lumen output and the drive circuitry and power supplies needed.

Temperature dependence

LED performance largely depends on the ambient temperature of the operating environ-

ment. Over-driving the LED in high ambient temperatures may result in overheating

of the LED package, eventually leading to device failure. Adequate heat-sinking is re-

quired to maintain long life. This is especially important when considering automotive,

medical, and military applications where the device must operate over a large range of

temperatures, and is required to have a low failure rate.

Voltage sensitivity

LEDs must be supplied with the voltage above the threshold and a current below the

rating. This can involve series resistors or current-regulated power supplies.

Light quality

Most cool-white LEDs have spectra that differ significantly from a black body radiator

like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can

cause the color of objects to be perceived differently under cool-white LED illumination


than sunlight or incandescent sources, due to metamerism,red surfaces being rendered

particularly badly by typical phosphor based cool-white LEDs. However, the color

rendering properties of common fluorescent lamps are often inferior to what is now

available in state-of-art white LEDs [12].

Area light source

LEDs do not approximate a point source of light, but rather a lambertian distribution.

So LEDs are difficult to use in applications requiring a spherical light field. LEDs are

not capable of providing divergence below a few degrees. This is contrasted with lasers,

which can produce beams with divergences of 0.2 degrees or less.

Blue hazard

There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding

safe limits of the so-called blue-light hazard [3].

Chapter 3

Motivations and Problem

Statement

LED lighting is going to be the general lighting technology of the 21st century.This can

be accredited to its low price and efficient performance. .Incidentally,LEDs happen to

be very fast switching devices.Thus,these lighting devices can be used as data transmit-

ters for digital data communication while illuminating the suuroundings at the same

time.Photodiodes can be used for data reception at the receiver.As the lighting infras-

tructure is already well established all over the world,so this wireless communication

technology carries alot of promise. Forseeing the future market,the leading consumer

appliance companies(Toshiba,Samsung,NEC,Siemens,etc.) are in the process of devel-

oping and prototyping numerous visible light communications systems.Appreciable re-

search work is underway in leading universities all over the world.Thus,VLC is a rapidly

growing field for research and development.It is for the same reason that i opted for a

project in this field.The following sections disscuss the technical evolution of LEDs and

its advantages,providing sound basis of motivation.

3.0.7 LED:Technical Evolution

In recent past,incandescent and fluorescent light sources were generally used for light-

ing.However,with the advent of efficient solid-state lighting devices,the trend is shifting

in favour of white LEDs.This change can be attributed to the numerous advantages

provided by white LEDs including low power consumption,everdecreasing costs and

high brightness.In addition to it,it is environment friendly and poses no health haz-

ards.Thus,in near future,white LEDs will replace existing technologies used for general

illumination.The major advantages of LED lighting are listed below:

• low power consumption

• high brightness

• low cost

24

Chapter 3. Motivations and Problem Statement 25

• durability

• minimal heat generation

• environment friendly operation

The accompanying graph (3.1) depicts the true picture of the technical evolution of

LEDs.It shows that in a few years,LEDs will outshine all other technologies owing to a

small cost/brightness and a large brightness/power ratio.

Figure 3.1: Price vs Performance curve depicting the technical evolution of LEDs [9]

Chapter 3. Motivations and Problem Statement 26

3.1 Problem Statement

I intend to setup a visible light communications system for wireless data

transmisssion between two nodes over a short range.Wavelength Division

Multiplexing will be used to send multiple data streams from different sources

simultaneously over the same wireless channel.Light filters will be used to

demultiplex the streams at the receiver.Using the results from the hardware

setup,a performance analysis of the technique will also be presented.

Chapter 4

Implementation

High power LEDs used for lighting are simultaneously used to transfer data, over the

wireless channel. On the receiver side a photo sensitive device is used for data reception.

For different data sources, wavelength division multiplexing can be used to transmit

data simultaneously over the same channel. In this technique, a different color (wave-

length) can be reserved for each data stream. The different streams are multiplexed and

are transmitted by modulating the light source. At the receiver, different wavelength

filters are used to separate the desired data stream followed by the light sensing device.

The received signal from the photo sensing device is then demodulated to recover the

transmitted data.

4.1 Block Diagram

The block diagram of the project is shown in figure (4.1).

Figure 4.1: Block Diagram of project

27

Chapter 4. Implementation 28

4.2 Methodology

A computer program, written in MATLAB, is used to write the data to be transmitted

to the serial port. A USB-to-serial converter cable is used to connect the computer via

USB port to a RS232-to-TTL level converter IC (MAX232).The TTL level output of this

IC is then fed to the LED driving circuitry, which consists of MOSFETs. Here, On-Off

Keying (OOK) is used to modulate the LEDs. At the receiving end, the light pulses

are filtered and then received using a digital optical receiver (TORX173).The receiver

output is fed to MAX232 IC for TTL-to-RS232 level conversion. Another serial to USB

converter cable connects the conditioned output to the computer, where a computer

program, written in MATLAB, is used to receive the data from serial port.

4.2.1 LED Modulation Scheme

In visible light communications systems intensity modulation is the most popular modu-

lation technique.In this project,OOK (On Off Keying) is used as the modulation scheme

to modulate the visible light (LED) sources.It is a special type of intensity modulation

where only two intensity levels are used to transmit data, namely 1 and 0.The bitstream

from the computer is interfaced to the gate of a high speed N-type MOSFET,which

drives the LEDs.Thus the data bits are transmitted serially in the form of light pulses.If

the bit is high,a light pulse is transmitted and if the bit is low,no pulse is transmitted.

4.2.2 Wavelength Division Multiplexing

In wavelength division multiplexing,separate wavelengths are used to transmit different

data streams over the same channel.Since,each wavelength corresponds to a specific

frequency,the term wavelength division multiplexing used in optical communications

rhymes with the term frequency division multiplexing used in telecommunications.In

this project,two independent data streams are multiplexed using wavelength division

multiplexing and are transmitted over the wireless channel at the same time.A pair of

wavelengths belonging to the set Red,Green,Blue can be used to serve the purpose.For

example,red LEDs may be used to send one data stream and green to send the other

data stream.There is no interference as both the beams correspond to distinct frequency

bands which have an inherent guard band between them.

4.2.3 Demultiplexing using Optical filters

At the receiving end,narrowband optical filters are used to demultiplex the two data

streams.Each optical filter allows only a specific wavelength,corresponding to a particular

color, to pass through it while blocking all others.For example,if a blue filter is used at

the receiver,only the blue light manages to reach the receiver.In this way, red,green or

blue lights can be selected by using the appropriate filters.

4.2.4 Data Reception using Direct Detection

In visible light communication systems,intensity modulation is used in conjunction with

direct detection for modulation and demodulation at transmitter and receiver.In direct


detection,a photodiode is usually used to receive the transmitted light pulses.The pres-

ence or absence of light pulses switches the photodiode on or off.In this way photo diodes

directly detect the transmitted bit stream.In this project,a fiber optic receiving module

is used to receive the light pulses.Although,this module is designed for fiber optic com-

munication but it can also be used for free space communication over a short range.The

range of the wireless system can be increased using high power LEDs at the transmitter.


4.3 Hardware Setup

The hardware setup for the visible light transmitter and receiver are discussed separately

in the following section:-

4.3.1 Transmitter

The following components are used at the transmitting side:

• Colored LEDs

• Mosfets

• RS232 line driver IC

• USB to RS232 coverter cable

• Voltage Regulator

4.3.1.1 Colored LEDs

An array of Red,Green and Blue LEDs are used at the transmitter end as visible light

sources.They are connected as loads in the transistor circuitry.They are high power and

emit a focussed beam.Each color is used to carry a different data stream.

4.3.1.2 MOSFETs

A high speed N-type power MOSFET IRF 520 (Figure 4.2)is used to modulate the LEDs

using OOK(On Off Keying).The serial output from the computer is converted into TTL

compatible form and is then applied to the gate of the transistor.Thus,it switches the

load (LEDs) on and off in accordance with the input data stream.The datasheet is pro-

vided in Appendix A.

Figure 4.2: IRF 520: NMOS transistor IC (source:Fairchild Semiconductors)


4.3.1.3 RS232 line driver

Since the output of computer is RS232 compatible,a 16 pin RS232 line driver IC MAX

232 is used to make the computer output TTL level compatible to drive the transistor

circuit carrying thr LED load.The datasheet is given in Appendix A.

4.3.1.4 USB to RS232 converter cable

In laptops,serial port is not available.Since data is to be transmitted serially between the

two computers,a USB to RS232 converter cable is used to interface the serial output from

MAX 232 IC to the laptop using the built-in USB port.This cable contains an embedded

controller to conform the RS232 compatible data into USB protocol compatible form.

4.3.1.5 Voltage Regulator

A voltage regulator is used to supply constant voltage (5V) to MAX232 IC.A 3 pin 7805

IC is used to serve the purpose.The datasheets are given in Appendix A.

Figure 4.3: 7805:Voltage Regulator IC (source:)


4.3.2 Receiver

The following components are used at the receiving side:

• Optical Receiver

• Optical Filters

• Voltage Regulator

• RS232 line driver IC

• USB to RS232 coverter cable

4.3.2.1 Optical Receiver

A 6 pin fiber optic receiving module TORX 173 (Figure 4.4)is used as the light sensing

device.On receiving light pulses,it gives a high output wheraes the output goes low in the

absence of light.The datasheets are given in Appendix A.The importannt charecteristics

of this sensor are listed below:

Minimum Receivable Power = -27 dBm

Maximum Receivable Power = -14.5 dBm

Maximum Data rate = 6 Mbps

Operating Voltage = 5 V

Figure 4.4: TORX 173:Fiber optic Receiving Module by TOSHIBA(source:TOSHIBA website)

4.3.2.2 Optical Filters

Red,green and blue light filters are used at the receiver to demultiplex the multiple data

streams.These are sharp narrowband filters.A red light filter allows the frequency band

corresponding to red color to pass through it and blocks all other wavelengths.Thus,when

a red light filter is placed in front of the optical receiver,only the data stream carried by

the red beam falls at the receiver while the other streams are blocked.Similarly,blue or

green light filters can be used to allow the desired data stream to reach the receiver.


4.3.2.3 Voltage Regulator

A voltage regulator is used to supply constant voltage (5V) to TORX 173.A 3 pin 7805

IC (Figure 4.5)is used to serve the purpose.The datasheets are given in Appendix A.

Figure 4.5: 7805:Voltage Regulator IC

4.3.2.4 RS232 line driver

Since the output of TORX 173 is TTL level compatible,a 16 pin RS232 line driver IC

MAX 232 is used to make the output RS232 compatible so that the receiving module

can be interfaced to the computer.The datasheets are given in Appendix A.

4.3.2.5 USB to RS232 converter cable

In laptops,serial port is not available.Since data is to be transmitted serially between the

two computers,a USB to RS232 converter cable is used to interface the serial output from

MAX 232 IC to the laptop using the built-in USB port.This cable contains an embedded

controller to conform the RS232 compatible data into USB protocol compatible form.


4.4 Schematic Diagram

4.4.1 Transmitter

Figure 4.6: Schematic Diagram of Transmitter


4.4.2 Receiver

Figure 4.7: Schematic Diagram of Receiver


4.5 PCB Layout

4.5.1 Transmitter

Figure 4.8: PCB layout of Transmitter


4.5.2 Receiver

Figure 4.9: PCB layout of Receiver


4.6 Programming

The transmitting computer can send any type of data (audio,picture,text files) to the

receiving computer via the serial port.The computer programs for the transmitter as

well as receiver are written in MATLAB.The codes are given in Appendix A.

Chapter 5

Performance Analysis

In addition to the hardware implementation of the proposed visible light communica-

tions system,a performance analysis of the designed system is also presented.Using the

hardware testbed, the effect of introducing a noise source in the vicinity of the transmit-

ter was also studied.In addition,the effect of increasing the distance between transmitter

and receiver on system performance was also observed.Using the empirical data,error

performance curves of the system were also plotted.

5.1 Experimental Setup

The experiment was conducted using the designed visible light communications system

in a normally lit indoor environment.The transmitter and receiver were placed in line

at a fixed distance from each other.White LEDs were used at the transmitter and only

a single data stream was transmitted.

5.1.1 Experimental Procedure

At the transmitter,a computer program was used to transmit data(text) repeatedly for

a predetermined number of trials.Another computer program was used at the receiving

end to receive the transmitted data.The total number of bit errors were calculated using

the output of the two programs.This process was repeated multiple times for a given

transmission distance.In this way,average bit error rate was computed for a given dis-

tance.In a similar manner, bit errors were computed for different transmission distances

by moving the transmitter towards the receiver along a fixed axis.

5.1.1.1 Experiment 1

A noise source was intoduced in the system by placing another whire LED near the

transmitter such that the receiver lyed in its field of view.The transmitter and receiver

were placed along a fixed axis at a fixed distance.The noise source was placed at different

points along the fixed axis,while the transmitter and receiver distance was kept constant

throughout the experiment.The bit errors were computed for each position of the noise

source using the experimental procedure as described in an earlier section.The empirical

39

Chapter 5. Performance Evaluation 40

data was used to plot the variations in BER(bit error rate) with distance of noise source

drom the receiver. Another curve was obtained by performing the experiment for a

different value of transmission distance.The MATLAB plots are shown in Fig ??:-

27 28 29 30 31 32 33 34 35 360

0.2

0.4

0.6

0.8

1

distance between noise source & receiver

Ave

rage

BE

R (

Bit

Err

or R

ate)

BER vs distance of noise source from receiver

transmission distance=15cmtransmision distance=30cm

Figure 5.1: Average BER vs distance between noise source and receiver

Result

As the distance between the noise source and receiver is reduced,the average bit error

rate increases.This can be attributed to a derease in the SNR(signal to noise ratio) at

the receiver; the noise power at the receiver increases while the signal power remains the

same because both the transmission power and the relative positions of the transmitter

and receiver do not change. This trend is also depicted in the accompanying plot(Fig

5.1).

If the experiment is repeated for a greater transmission distance,a similar trend is ob-

tained.However,there is an increase in the BER for the same noise source position.This

is because the received signal power reduces due to an increase in transmission distance

while the noise power remains the same.Thus ,the SNR is reduced.

5.1.1.2 Experiment 2

In the first experiment,the position of noise source was changed relative to the receiver

and its effect on BER was observed,for a fixed transmission distance.The second experi-

ment was conducted by keeping the noise source at a fixed distance from the receiver.The

transmitter and receiver are also placed a fixed distance apart.The noise intensity is

changed by changing the current supplied to the LED cting as the noise source.For a

given value of current,average BER is computed as done in the first experiment.The

variation in BER vs noise intensity is shown in Fig 5.2.

Furthermore,the curve shows a sharp transition at some points.It can be accredited to

the receiver characteristics.The receiver has a minimum receivable power of -27 dBm

while a maximum receivable power of -14.5 dBm.As soon as the received power levels


cross these thresholds,the receiver malfunctions,leading to a sudden transition in bit

error rate.

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.80

0.5

1Error Performance Curves

current of noise source(A)

Ave

rage

BE

R (

Bit

Err

or R

ate)

0 1 2 3 4 5 60

0.5

1

normalized intensity of noise source(dB)

Ave

rage

BE

R (

Bit

Err

or R

ate)

BER vs current

BER vs noise intensity

Figure 5.2: Average BER vs noise intensity

Result

As the intensity of the noise source is increased,the average bit error rate increases.This

can be attributed to a derease in the SNR(signal to noise ratio) at the receiver; the noise

power at the receiver increases while the signal power remains the same because both

the signal transmission power and the relative positions of the transmitter and receiver

do not change. This trend is also depicted in the accompanying plot(Fig 5.2).


5.2 Conclusion and Future Work

The use of wavelength division multiplexing was successfully demonstrated by using

colored LEDs for transferring multiple data streams simultaneously in a visible light

communications system.Since each data stream was transmitted using a different color

(wavelength), the effect of interference between transmitted data streams was elimi-

nated.The performance of the VLC system was also evaluated using empirical data.

The impact of noise intensity on the bit error rate was studied and the results were

explained using error performance curves.

Wireless data transport by means of light paves the way for new applications in the home

as well as in industry and transportation.Researchers have achieved a data transfer rate

of up to 500 Mbps over a distance of 5m using a white LED light [5].The researchers were

also able to show that a system combining up to five LEDs is capable of transferring data

over longer distances at rates as high as 100 Mbps [5].Such a system could be used to

transmit data via ceiling lights to a receiver mounted on a desk located anywhere within

a room. The IEEE (Institute of Electrical and Electronics Engineers) has been working

since 2007 to standardize activities in this field [11]. It is hoped that this work will be

completed by the end of 2010 .Keeping the ongoing research in view,it is imperative that

visible light communications has a very bright future ahead.

Appendix A

MATLAB Codes

43

%VLC_TX_AUDIO

%Program to read two audio files and write the data to two serial

ports

clc; clear all;

%Read two audio files [y1,Fs] = wavread('hohoho.wav','native'); [y2,Fs] = wavread('ak47.wav','native');

[row1 col1] = size(y1); [row2 col2] = size(y2);

count1=row1*col1; count2=row2*col2; count=min(count1,count2);

%Convert the read audio files into row vectors Y1=reshape(y1,1,count1); Y2=reshape(y2,1,count2);

%Output Buffer Size k=8191;%511,1023,2047,4095,8191,16383,32767,65535...

%Create serial port objects to open the serial ports s1= serial('COM5','BaudRate',230400,'outputbuffersize',k+1); fopen(s1); s2= serial('COM6','BaudRate',230400,'outputbuffersize',k+1); fopen(s2);

%Code to write the audio file data to the serial ports

tic limit=(k+1)*floor(count/k+1); trials=25; for j=1:trials for i=1:k+1:limit-k-1 fwrite(s1,Y1(1,i:i+k),'uint8'); fwrite(s2,Y2(1,i:i+k),'uint8'); end end toc

%Close the serial ports and delete the serial port objects fclose(s1); fclose(s2); delete(s1); delete(s2);

%VLC_RX_AUDIO

%Program for serial port read and audio playback

clc; clear all;

%Sampling Frequency Fs=11025;

%Input Buffer Size k=8191; %511,1023,2047,4095,8191,16383,32767,65535...

%Create a serial port object to open the serial port s2= serial('COM6','BaudRate',230400,'inputbuffersize',k+1); fopen(s2);

count=31688; limit=(k+1)*floor(count/k+1); trials=10;

%code for reading the serial port & audioplayback tic for j=1:trials for i=1:k+1:limit-k-1 out(1,i:i+k) = fread(s2,k+1,'uint8'); buf(1:k+1,1)=reshape(out(1,i:i+k),k+1,1); buf=uint8(buf); wavplay(buf,Fs,'async'); end end toc

%Close the Serial port and delete the serial port object fclose(s2); delete(s2);

%VLC_TX_IMAGE

%This program reads two images and opens two serial port to send the

%files

clc;

clear;

fclose('all');

%Read two image files

A=imread('codered.png','png');

B=imread('codegreen.png','png');

A=rgb2gray(A);

B=rgb2gray(B);

[a1 b1]=size(A);

[a2 b2]=size(B);

count1=a1*b1;

count2=a2*b2;

count=min(count1,count2);

C1=reshape(A1,1,count1);

C2=reshape(A2,1,count2);

%Create serial port objects to open the serial ports

s1=serial('com6','baudrate',230400,'outputbuffersize',2*count);

fopen(s1);

s2=serial('com5','baudrate',230400,'inputbuffersize',2*count);

fopen(s2);

%Serial Port Write Operation

tic

fwrite(s1,C1(1,1:count1),'uint8');

fwrite(s2,C2(1,1:count2),'uint8');

toc

%Display the images

imshow(A1);

imshow(A2);

%Close the serial port and delete the serial port objects

fclose(s1);

fclose(s2);

delete(s1);

delete(s2);

%VLC_RX_IMAGE

%This program receives the transmitted image and displays it

clc;

clear;

a=55;

b=100;

count=a*b;

D = zeros(1,count);

%Create a serial port object to open the serial port

s2=serial('com5','baudrate',230400,'inputbuffersize',2*count);

fopen(s2);

%Serial port read operation

tic

D(1,1:count) = fread(s2,count,'uint8');

toc

D=reshape(D,a,b);

D=uint8(D);

%Display the received image

imshow(D)

%Close the serial port and delete the serial port object

fclose(s2);

delete(s2);

Appendix B

Datasheets

48

TORX173

2001-08-10 1

FIBER OPTIC RECEIVING MODULE

TORX173 FIBER OPTIC RECEIVING MODULE FOR DIGITAL AUDIO EQUIPMENT Conform to JEITA Standard CP−1201 (For

Digital Audio Interfaces including Fiber Optic inter−connections).

TTL Interface ATC (Automatic Threshold Control) Circuit

is used for stabilized output at a wide range of optical power level.

1. Maximum Ratings (Ta = 25°C)

Characteristics Symbol Rating Unit

Storage Temperature Tstg −40 to 70 °C

Operating Temperature Topr −20 to 70 °C

Supply Voltage VCC −0.5 to 7 V

Low Level Output Current IOL 20 mA

High Level Output Current IOH −1 mA

Soldering Temperature Tsol 260 (Note 1) °C

Note 1: Soldering time ≤ 10 s (More than 1 mm apart from the package). 2. Recommended Operating Conditions

Characteristics Symbol Min Typ. Max Unit

Supply Voltage VCC 4.75 5.0 5.25 V

High Level Output Current IOH ― ― −150 µA

Low Level Output Current IOL ― ― 1.6 mA

Unit: mm

TORX173

2001-08-10 2

3. Electrical and Optical Characteristics (Ta = 25°C, VCC = 5 V)

Characteristics Symbol Test Condition Min Typ. Max Unit

Data Rate NRZ code (Note 2) DC ― 6 Mb / s

Transmission Distance TOTX173 Using APF (Note 3) 0.2 ― 10 m

Pulse Width Distortion (Note 4) ∆tw Pulse width 165 ns Pulse cycle 330 ns, CL = 10 pF Using TOTX173

−20 ― 20 ns

Maximum Receivable Power (Note 5) PMAX 6 Mb / s, Using APF −14.5 ― ― dBm

Minimum Receivable Power (Note 5) PMIN 6 Mb / s, Using APF ― ― −27 dBm

Rise Time tr CL = 10 pF ― 10 30 ns

Fall Time tf CL = 10 pF ― 5 30 ns

Current Consumption ICC ― 22 40 mA

High Level Output Voltage VOH 2.7 ― ― V

Low Level Output Voltage VOL ― ― 0.4 V

Note 2: For data rate > 3 Mb / s, the duty factor must be such as kept 25 to 75%. High level output when optical flux is received. Low level output when optical flux is not received.

Note 3: All Plastic Fiber (970 / 1000 µm). Note 4: Between input of a fiber optic transmitting module and output of TORX173. Note 5: BER ≤ 10−9, rated by peak value.

TORX173

2001-08-10 3

4. Example of Typical Characteristics (Note 6)

Note 6: There give characteristic examples, and its values are not guaranteed.

TORX173

2001-08-10 4

5. Application Circuit

6. Applicable optical fiber with fiber optic connectors.

TOCP172−B

TORX173

2001-08-10 5

7. Precautions during use (1) Maximum rating

The maximum ratings are the limit values which must not be exceeded when using the device. Any one of the rating must not be exceeded. If The maximum rating is exceeded, the characteristics may not be recovered. In some extreme cases, the device may be permanently damage.

(2) Soldering Optical modules use semiconductor devices internally. However, in principle, optical modules are optical components. At soldering, take care that flux dose not contact the emitting surface or detecting surface. Also take care at flux removal after soldering. Some optical modules come with protective cap. The protective cap is used to avoid malfunction when the optical module is not in use. Not that it is not dust or waterproof. As mentioned before, optical modules are optical component. Thus, in principle, soldering where there may be flux residue or flux removal after soldering is not recommended. Toshiba recommends that soldering be performed without the optical module mounted on the board. Then, after the board is cleaned, solder the optical module manually. Do not perform any further cleaning. If the optical module cannot be soldered manually, use non−halogen (chlorine−free) flux and make sure, without cleaning, there is no residue such as chlorine. This is one of the ways to eliminate the effects of flux. In such a case, check the reliability.

(3) Noise resistance Where the fiber optic receiving module case uses conductive resin, shield by connecting the reinforcing pin at a front end of the module to GND. When using this optical module, connect the pin to SIGNAL−GND. Where the fiber optic receiving module case has a resistance of several tens of ohms, take care that the case does not contact power line of other circuits. It is believed that the use of optical transfer devices improve the noise resistance. In principle, optical fiber is not affected by noise. However, especially receiving module which handle signals whose level is extremely small, are comparatively more susceptible to noise. TOSLINK improves noise resistance using a conductive case. However, the current of the signal output from the photodiode of the optic receiving module is extremely small. Thus, depending on the usage environment, shielding the case is not sufficient for noise resistance. When using TOSLINK, Toshiba recommends that you test using the actual device and check the noise resistance. Use a simple noise filter on the TOSLINK fiber optic receiving module power line. If the ripple in power supply used is high, further reinforce the filter. When locating the optical module in an area susceptible to radiated noise, increase shielding by covering the optical module and the power line filter using a metallic cover.

(4) Vibration and shock This module is resin−molded construction with wire fixed by resin. This structure is relatively sound against vibration or shock, In actual equipment, there are some cases where vibration, shock, and stress is applied to soldered parts or connected parts, resultingin line cut. Attention must be paid to the design of the mechanism for applications which are subject to large amounts of vibration.

(5) Fixing fiber optical receiving module Solder the fixed pin (pins 5 and 6) of fiber optic receiving module TORX173 to the printed circuit board to fix the module to the board.

(6) Shielding and wiring pattern of fiber optic receiving modules To shield, connect the fixed pins (pins 5 and 6) of fiber optic transceiving module TORX173 to the GND. Where the fiber optic receiving module uses conductive resin, be careful that the case does not touch wiring (including land). To improve noise resistance, shield the optical module and the power line filter using a metallic cover.

(7) Solvent When using solvent for flux removal, do not use a high acid or high alkali solvent. Be careful not to pour solvent in the optical connector ports. If solvent is inadvertently poured there, clean with cotton tips.

(8) Protective cap When the fiber optic receiving module TORX173 is not in use, use the protective cap.

TORX173

2001-08-10 6

(9) Supply voltage Use the supply voltage within the Typ. operating condition (VCC = 5 ± 0.25 V). Make sure that supply voltage does not exceed the maximum rating value of 7 V, even instantaneously.

(10) Interface TORX173 has a TTL interface. It can be interfaced with C−MOS IC that has compatibility with TTL level.

(11) Output When the receiver output is at low level and connected to the power supply, or when the output is at high level and connected to GND, the internal IC may be destroyed.

(12) Soldering condition Solder at 260°C or less within ten seconds.

(13) Precaution on waste When discarding devices and packing materials, follow procedures stipulated by local regulations in order to protect the environment against contamination.

(14) Precaution on use Toshiba is continually working to improve the quality and the reliability of its products. Nevertheless, semiconductor devices in general can malfunction or fail due to their inherent electrical sensitivity and vulnerability to physical stress. It is the responsibility of the buyer, when utilizing Toshiba products, to observe standards of safety, and to avoid situations in which a malfunction or failure of a Toshiba product could cause loss of human life, bodily injury or damage to property. In developing your designs, please ensure that Toshiba products are used within specified operating ranges as set forth in the most recent product specifications. Also, please keep in mind the precautions and conditions set forth in the Toshiba Semiconductor Reliability Handbook.

TORX173

2001-08-10 7

TOSHIBA is continually working to improve the quality and reliability of its products. Nevertheless, semiconductor devices in general can malfunction or fail due to their inherent electrical sensitivity and vulnerability to physical stress. It is the responsibility of the buyer, when utilizing TOSHIBA products, to comply with the standards of safety in making a safe design for the entire system, and to avoid situations in which a malfunction or failure of such TOSHIBA products could cause loss of human life, bodily injury or damage to property. In developing your designs, please ensure that TOSHIBA products are used within specified operating ranges as set forth in the most recent TOSHIBA products specifications. Also, please keep in mind the precautions and conditions set forth in the “Handling Guide for Semiconductor Devices,” or “TOSHIBA Semiconductor Reliability Handbook” etc..

The TOSHIBA products listed in this document are intended for usage in general electronics applications (computer, personal equipment, office equipment, measuring equipment, industrial robotics, domestic appliances, etc.). These TOSHIBA products are neither intended nor warranted for usage in equipment that requires extraordinarily high quality and/or reliability or a malfunction or failure of which may cause loss of human life or bodily injury (“Unintended Usage”). Unintended Usage include atomic energy control instruments, airplane or spaceship instruments, transportation instruments, traffic signal instruments, combustion control instruments, medical instruments, all types of safety devices, etc.. Unintended Usage of TOSHIBA products listed in this document shall be made at the customer’s own risk.

The information contained herein is presented only as a guide for the applications of our products. No responsibility is assumed by TOSHIBA CORPORATION for any infringements of intellectual property or other rights of the third parties which may result from its use. No license is granted by implication or otherwise under any intellectual property or other rights of TOSHIBA CORPORATION or others.

The information contained herein is subject to change without notice.

000707EAARESTRICTIONS ON PRODUCT USE

©2002 Fairchild Semiconductor Corporation IRF520 Rev. B

IRF520

9.2A, 100V, 0.270 Ohm, N-Channel Power MOSFET

This N-Channel enhancement mode silicon gate power field effect transistor is an advanced power MOSFET designed, tested, and guaranteed to withstand a specified level of energy in the breakdown avalanche mode of operation. All of these power MOSFETs are designed for applications such as switching regulators, switching convertors, motor drivers, relay drivers, and drivers for high power bipolar switching transistors requiring high speed and low gate drive power. These types can be operated directly from integrated circuits.

Formerly developmental type TA09594.

Features

• 9.2A, 100V

• r

DS(ON)

= 0.270

Ω

• SOA is Power Dissipation Limited

• Single Pulse Avalanche Energy Rated

• Nanosecond Switching Speeds

• Linear Transfer Characteristics

• High Input Impedance

• Related Literature- TB334 “Guidelines for Soldering Surface Mount

Components to PC Boards”

Symbol

Packaging

JEDEC TO-220AB

Ordering Information

PART NUMBER PACKAGE BRAND

IRF520 TO-220AB IRF520

NOTE: When ordering, use the entire part number.G

D

S

SOURCE

DRAIN (FLANGE)

DRAINGATE

Data Sheet January 2002


Absolute Maximum Ratings

T

C

= 25

o

C, Unless Otherwise Specified

IRF520 UNITS

Drain to Source Breakdown Voltage (Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .V

DS

100 V

Drain to Gate Voltage (R

GS

= 20k

Ω)

(Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V

DGR

100 V

Continuous Drain Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I

D

T

C

= 100

o

C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I

D

9.26.5

AA

Pulsed Drain Current (Note 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I

DM

37 A

Gate to Source Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .V

GS

±

20 V

Maximum Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P

D

60 W

Dissipation Derating Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.4 W/

o

C

Single Pulse Avalanche Energy Rating (Note 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E

AS

36 mJ

Operating and Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T

J,

T

STG

-55 to 175

o

C

Maximum Temperature for SolderingLeads at 0.063in (1.6mm) from Case for 10s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T

L

Package Body for 10s, See Techbrief 334 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . T

pkg

300260

o

C

o

C

CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of thedevice at these or any other conditions above those indicated in the operational sections of this specification is not implied.

NOTE:

1. T

J

= 25

o

C to 150

o

C.

Electrical Specifications

T

C

= 25

o

C, Unless Otherwise Specified

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS

Drain to Source Breakdown Voltage BV

DSS

I

D

= 250

µ

A, V

GS

= 0V (Figure 10) 100 - - V

Gate to Threshold Voltage V

GS(TH)

V

GS

= V

DS

, I

D

= 250

µ

A 2.0 - 4.0 V

Zero Gate Voltage Drain Current I

DSS

V

DS

= 95V, V

GS

= 0V - - 250

µ

A

V

DS

= 0.8 x Rated BV

DSS

, V

GS

= 0V, T

J

= 150

o

C - - 1000

µ

A

On-State Drain Current (Note 2) I

D(ON)

V

DS

> I

D(ON)

x r

DS(ON)MAX

, V

GS

= 10V (Figure 7) 9.2 - - A

Gate to Source Leakage Current I

GSS

V

GS

=

±

20V - -

±

100 nA

Drain to Source On Resistance (Note 2) r

DS(ON)

I

D

= 5.6A, V

GS

= 10V (Figure 8, 9) - 0.25 0.27

Ω

Forward Transconductance (Note 2) gfs V

DS

≥

50V, I

D

= 5.6A (Figure 12) 2.7 4.1 - S

Turn-On Delay Time t

d(ON)

V

DD

= 50V, I

D

≈

9.2A, R

G

= 18

Ω

, R

L

= 5.5

Ω

MOSFET Switching Times are Essentially Independent of Operating Temperature

- 9 13 ns

Rise Time t

r

- 30 63 ns

Turn-Off Delay Time t

d(OFF)

- 18 70 ns

Fall Time t

f

- 20 59 ns

Total Gate Charge(Gate to Source + Gate to Drain)

Q

g(TOT)

V

GS

= 10V, I

D

= 9.2A, V

DS

= 0.8 x Rated BV

DSS

, I

g(REF)

= 1.5mA (Figure 14) Gate Charge is Essentially Independent of OperatingTemperature

- 10 30 nC

Gate to Source Charge Q

gs

- 2.5 - nC

Gate to Drain “Miller” Charge Q

gd

- 2.5 - nC

Input Capacitance C

ISS

V

DS

= 25V, V

GS

= 0V, f = 1MHz(Figure 11)

- 350 - pF

Output Capacitance C

OSS

- 130 - pF

Reverse Transfer Capacitance C

RSS

- 25 - pF

Internal Drain Inductance L

D

Measured From the Contact Screw On Tab To Center of Die

Modified MOSFET Symbol Showing the Internal Devices Inductances

- 3.5 - nH

Measured From the Drain Lead, 6mm (0.25in) From Package to Center of Die

- 4.5 - nH

Internal Source Inductance L

S

Measured From the Source Lead, 6mm (0.25in) From Header to Source Bonding Pad

- 7.5 - nH

Thermal Resistance Junction to Case R

θ

JC

- - 2.5

o

C/W

Thermal Resistance Junction to Ambient R

θ

JA

Free Air Operation - - 80

o

C/W

LD

LS

D

S

G

IRF520


Source to Drain Diode Specifications

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNITS

Continuous Source to Drain Current I

SD

Modified MOSFET Symbol Showing the Integral Reverse P-N Junction Diode

- - 9.2 A

Pulse Source to Drain Current (Note 3) I

SDM

- - 37 A

Source to Drain Diode Voltage (Note 2) V

SD

T

J

= 25

o

C, I

SD

= 9.2A, V

GS

= 0V (Figure 13) - - 2.5 V

Reverse Recovery Time t

rr

T

J

= 25

o

C, I

SD

= 9.2A, dI

SD

/dt = 100A/

µ

s 5.5 100 240 ns

Reverse Recovered Charge Q

RR

T

J

= 25

o

C, I

SD

= 9.2A, dI

SD

/dt = 100A/

µ

s 0.17 0.5 1.1

µ

C

NOTES:

2. Pulse test: pulse width

≤

300

µ

s, duty cycle

≤

2%.

3. Repetitive rating: pulse width limited by Max junction temperature. See Transient Thermal Impedance curve (Figure 3).

4. V

DD

= 25V, starting T

J

= 25

o

C, L = 640mH, R

G

= 25

Ω,

peak I

AS

= 9.2A.

Typical Performance Curves

Unless Otherwise Specified

FIGURE 1. NORMALIZED POWER DISSIPATION vs CASE TEMPERATURE

FIGURE 2. MAXIMUM CONTINUOUS DRAIN CURRENT vs CASE TEMPERATURE

FIGURE 3. MAXIMUM TRANSIENT THERMAL IMPEDANCE

G

D

S

TC, CASE TEMPERATURE (oC)25 50 75 100 125 150 1750

PO

WE

R D

ISS

IPA

TIO

N M

ULT

IPL

IER

0

0.2

0.4

0.6

0.8

1.0

1.2

TC, CASE TEMPERATURE (oC)

50 75 100 17525

10

8

6

0

4

I D, D

RA

IN C

UR

RE

NT

(A

)

2

125 150

ZθJ

C, T

RA

NS

IEN

T 1

0.1

0.0110-210-5 10-4 10-3 0.1 1 10

t1, RECTANGULAR PULSE DURATION (s)

PDM

t1t2

10

NOTES:DUTY FACTOR: D = t1/t2PEAK TJ = PDM x ZθJC + TC

SINGLE PULSE

0.5

0.020.05

0.2

0.01

0.1

TH

ER

MA

L IM

PE

DA

NC

E (

oC

/W)

IRF520


FIGURE 4. FORWARD BIAS SAFE OPERATING AREA FIGURE 5. OUTPUT CHARACTERISTICS

FIGURE 6. SATURATION CHARACTERISTICS FIGURE 7. TRANSFER CHARACTERISTICS

FIGURE 8. DRAIN TO SOURCE ON RESISTANCE vs GATE VOLTAGE AND DRAIN CURRENT

FIGURE 9. NORMALIZED DRAIN TO SOURCE ONRESISTANCE vs JUNCTION TEMPERATURE

Typical Performance Curves Unless Otherwise Specified (Continued)

100

10

1

10001 10 1000.1

I D, D

RA

IN C

UR

RE

NT

(A

)

VDS, DRAIN TO SOURCE VOLTAGE (V)

TC = 25oCTJ = MAX RATEDSINGLE PULSE

10µs

100µs

1ms

10msOPERATION IN THISAREA IS LIMITEDBY rDS(ON)

10V

VDS, DRAIN TO SOURCE VOLTAGE (V)200 50

15

12

9

0

6

I D, D

RA

IN C

UR

RE

NT

(A

)

VGS = 7V

3

30

VGS = 6V

VGS = 8V PULSE DURATION = 80µs

10 40

VGS = 5V

VGS = 4V

DUTY CYCLE = 0.5% MAX

15

12

9

0

6

1 2 3 40 5

I D, D

RA

IN C

UR

RE

NT

(A

)


3

VGS = 6V

VGS = 5V

VGS = 4V

VGS = 7V

VGS = 8V

VGS = 10VPULSE DURATION = 80µsDUTY CYCLE = 0.5% MAX

102

0.12 4 6 80

I D(O

N),

ON

-STA

TE

DR

AIN

CU

RR

EN

T (

A)

VGS, GATE TO SOURCE VOLTAGE (V)

1

10

10

175oC 25oC

VDS ≥ 50VPULSE DURATION = 80µsDUTY CYCLE = 0.5% MAX

ID, DRAIN CURRENT (A)16 320 40

2.5

2.0

1.5

0

1.0

r DS

(ON

), D

RA

IN T

O S

OU

RC

E O

N R

ES

ISTA

NC

E

PULSE DURATION = 80µs

8 24

0.5

VGS = 10V

VGS = 20V


3.0

1.8

0.6

0 60-60

TJ, JUNCTION TEMPERATURE (oC)

NO

RM

AL

IZE

D O

N R

ES

ISTA

NC

E

2.4

1.2

0-40 -20 20 40 80 100 140120 160 180

ID = 9.2A, VGS = 10VPULSE DURATION = 80µsDUTY CYCLE = 0.5% MAX

IRF520


FIGURE 10. NORMALIZED DRAIN TO SOURCE BREAKDOWN VOLTAGE vs JUNCTION TEMPERATURE

FIGURE 11. CAPACITANCE vs DRAIN TO SOURCE VOLTAGE

FIGURE 12. TRANSCONDUCTANCE vs DRAIN CURRENT FIGURE 13. SOURCE TO DRAIN DIODE VOLTAGE

FIGURE 14. GATE TO SOURCE VOLTAGE vs GATE CHARGE

Typical Performance Curves Unless Otherwise Specified (Continued)

1.25

1.05

0.85

0 180

TJ, JUNCTION TEMPERATURE (oC)

NO

RM

AL

IZE

D D

RA

IN T

O S

OU

RC

E

1.15

0.95

0.75-60

BR

EA

KD

OW

N V

OLT

AG

E

60 120

ID = 250µA


C, C

APA

CIT

AN

CE

(p

F)

1000

800

600

400

200

0

VGS = 0V, f = 1MHzCISS = CGS + CGDCRSS = CGDCOSS ≈ CDS + CGD

1 10 102

CISS

COSS

CRSS

ID, DRAIN CURRENT (A)3 6 9 120 15

5

4

3

0

2

gfs

, TR

AN

SC

ON

DU

CTA

NC

E (

S)

1

TJ = 175oC

TJ = 25oC

PULSE DURATION = 80µsVDS ≥ 50


TJ = 175oC

I SD

, SO

UR

CE

TO

DR

AIN

CU

RR

EN

T (

A)

VSD, SOURCE TO DRAIN VOLTAGE (V)

100

10

0.10 0.4 1.2 1.6 2.00.8

TJ = 25oC1

PULSE DURATION = 80µsDUTY CYCLE = 0.5% MAX

Qg, GATE CHARGE (nC)

3 6 9 120 15

20

8

0

VG

S, G

AT

E T

O S

OU

RC

E V

OLT

AG

E (

V)

4

ID = 9.2A

16

12

VDS = 20VVDS = 50VVDS = 80V

IRF520


Test Circuits and Waveforms

FIGURE 15. UNCLAMPED ENERGY TEST CIRCUIT FIGURE 16. UNCLAMPED ENERGY WAVEFORMS

FIGURE 17. SWITCHING TIME TEST CIRCUIT FIGURE 18. RESISTIVE SWITCHING WAVEFORMS

FIGURE 19. GATE CHARGE TEST CIRCUIT FIGURE 20. GATE CHARGE WAVEFORMS

tP

VGS

0.01Ω

L

IAS

+

-

VDS

VDDRG

DUT

VARY tP TO OBTAIN

REQUIRED PEAK IAS

0V

VDD

VDS

BVDSS

tP

IAS

tAV

0

VGS

RL

RG

DUT

+

-VDD

tON

td(ON)

tr

90%

10%

VDS90%

10%

tf

td(OFF)

tOFF

90%

50%50%

10%PULSE WIDTH

VGS

0

0

0.3µF

12VBATTERY 50kΩ

VDS

S

DUT

D

G

Ig(REF)0

(ISOLATEDVDS

0.2µF

CURRENTREGULATOR

ID CURRENTSAMPLING

IG CURRENTSAMPLING

SUPPLY)

RESISTOR RESISTOR

SAME TYPEAS DUT

Qg(TOT)

Qgd

Qgs

VDS

0

VGS

VDD

IG(REF)

0

IRF520

DISCLAIMER

FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHERNOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILDDOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCTOR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENTRIGHTS, NOR THE RIGHTS OF OTHERS.

TRADEMARKS

The following are registered and unregistered trademarks Fairchild Semiconductor owns or is authorized to use and isnot intended to be an exhaustive list of all such trademarks.

LIFE SUPPORT POLICY

FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORTDEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF FAIRCHILD SEMICONDUCTOR CORPORATION.As used herein:1. Life support devices or systems are devices orsystems which, (a) are intended for surgical implant intothe body, or (b) support or sustain life, or (c) whosefailure to perform when properly used in accordancewith instructions for use provided in the labeling, can bereasonably expected to result in significant injury to theuser.

2. A critical component is any component of a lifesupport device or system whose failure to perform canbe reasonably expected to cause the failure of the lifesupport device or system, or to affect its safety oreffectiveness.

PRODUCT STATUS DEFINITIONS

Definition of Terms

Datasheet Identification Product Status Definition

Advance Information

Preliminary

No Identification Needed

Obsolete

This datasheet contains the design specifications forproduct development. Specifications may change inany manner without notice.

This datasheet contains preliminary data, andsupplementary data will be published at a later date.Fairchild Semiconductor reserves the right to makechanges at any time without notice in order to improvedesign.

This datasheet contains final specifications. FairchildSemiconductor reserves the right to make changes atany time without notice in order to improve design.

This datasheet contains specifications on a productthat has been discontinued by Fairchild semiconductor.The datasheet is printed for reference information only.

Formative orIn Design

First Production

Full Production

Not In Production

OPTOLOGIC™OPTOPLANAR™PACMAN™POP™Power247™PowerTrenchQFET™QS™QT Optoelectronics™Quiet Series™SILENT SWITCHER

FASTFASTr™FRFET™GlobalOptoisolator™GTO™HiSeC™ISOPLANAR™LittleFET™MicroFET™MicroPak™MICROWIRE™

Rev. H4

ACEx™Bottomless™CoolFET™CROSSVOLT™DenseTrench™DOME™EcoSPARK™E2CMOSTM

EnSignaTM

FACT™FACT Quiet Series™

SMART START™STAR*POWER™Stealth™SuperSOT™-3SuperSOT™-6SuperSOT™-8SyncFET™TinyLogic™TruTranslation™UHC™UltraFET

STAR*POWER is used under license

VCX™

MAX232, MAX232IDUAL EIA-232 DRIVERS/RECEIVERS

SLLS047I – FEBRUARY 1989 – REVISED OCTOBER 2002

1POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Meet or Exceed TIA/EIA-232-F and ITURecommendation V.28

Operate With Single 5-V Power Supply

Operate Up to 120 kbit/s

Two Drivers and Two Receivers

±30-V Input Levels

Low Supply Current . . . 8 mA Typical

Designed to be Interchangeable WithMaxim MAX232

ESD Protection Exceeds JESD 22– 2000-V Human-Body Model (A114-A)

ApplicationsTIA/EIA-232-FBattery-Powered SystemsTerminalsModemsComputers

description/ordering information

The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to supply EIA-232 voltagelevels from a single 5-V supply. Each receiver converts EIA-232 inputs to 5-V TTL/CMOS levels. Thesereceivers have a typical threshold of 1.3 V and a typical hysteresis of 0.5 V, and can accept ±30-V inputs. Eachdriver converts TTL/CMOS input levels into EIA-232 levels. The driver, receiver, and voltage-generatorfunctions are available as cells in the Texas Instruments LinASIC library.

ORDERING INFORMATION

TA PACKAGE† ORDERABLEPART NUMBER

TOP-SIDEMARKING

PDIP (N) Tube MAX232N MAX232N

SOIC (D)Tube MAX232D

MAX232

0°C to 70°C

SOIC (D)Tape and reel MAX232DR

MAX232

0°C to 70°C

SOIC (DW)Tube MAX232DW

MAX232SOIC (DW)Tape and reel MAX232DWR

MAX232

SOP (NS) Tape and reel MAX232NSR MAX232

PDIP (N) Tube MAX232IN MAX232IN

SOIC (D)Tube MAX232ID

MAX232I–40°C to 85°C

SOIC (D)Tape and reel MAX232IDR

MAX232I

SOIC (DW)Tube MAX232IDW

MAX232ISOIC (DW)Tape and reel MAX232IDWR

MAX232I

† Package drawings, standard packing quantities, thermal data, symbolization, and PCB designguidelines are available at www.ti.com/sc/package.

Copyright 2002, Texas Instruments IncorporatedPRODUCTION DATA information is current as of publication date.Products conform to specifications per the terms of Texas Instrumentsstandard warranty. Production processing does not necessarily includetesting of all parameters.

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications ofTexas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

LinASIC is a trademark of Texas Instruments.

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

C1+VS+C1–C2+C2–VS–

T2OUTR2IN

VCCGNDT1OUTR1INR1OUTT1INT2INR2OUT

MAX232 . . . D, DW, N, OR NS PACKAGEMAX232I . . . D, DW, OR N PACKAGE

(TOP VIEW)



2 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

Function Tables

EACH DRIVER

INPUTTIN

OUTPUTTOUT

L H

H L

H = high level, L = lowlevel

EACH RECEIVER

INPUTRIN

OUTPUTROUT

L H

H L

H = high level, L = lowlevel

logic diagram (positive logic)

T1IN T1OUT

R1INR1OUT

T2IN T2OUT

R2INR2OUT

11

10

12

9

14

7

13

8




absolute maximum ratings over operating free-air temperature range (unless otherwise noted)†

Input supply voltage range, VCC (see Note 1) –0.3 V to 6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Positive output supply voltage range, VS+ VCC – 0.3 V to 15 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Negative output supply voltage range, VS– –0.3 V to –15 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Input voltage range, VI: Driver –0.3 V to VCC + 0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Receiver ±30 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Output voltage range, VO: T1OUT, T2OUT VS– – 0.3 V to VS+ + 0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

R1OUT, R2OUT –0.3 V to VCC + 0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Short-circuit duration: T1OUT, T2OUT Unlimited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Package thermal impedance, θJA (see Note 2): D package 73°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DW package 57°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N package 67°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . NS package 64°C/W. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds 260°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storage temperature range, Tstg –65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

† Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, andfunctional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is notimplied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

NOTE 1: All voltage values are with respect to network ground terminal.2. The package thermal impedance is calculated in accordance with JESD 51-7.

recommended operating conditionsMIN NOM MAX UNIT

VCC Supply voltage 4.5 5 5.5 V

VIH High-level input voltage (T1IN,T2IN) 2 V

VIL Low-level input voltage (T1IN, T2IN) 0.8 V

R1IN, R2IN Receiver input voltage ±30 V

TA Operating free air temperatureMAX232 0 70

°CTA Operating free-air temperatureMAX232I –40 85

°C

electrical characteristics over recommended ranges of supply voltage and operating free-airtemperature (unless otherwise noted) (see Note 3 and Figure 4)

PARAMETER TEST CONDITIONS MIN TYP‡ MAX UNIT

ICC Supply currentVCC = 5.5 V,TA = 25°C

All outputs open,8 10 mA

‡ All typical values are at VCC = 5 V and TA = 25°C.NOTE 3: Test conditions are C1–C4 = 1 µF at VCC = 5 V ± 0.5 V.




DRIVER SECTION

electrical characteristics over recommended ranges of supply voltage and operating free-airtemperature range (see Note 3)

PARAMETER TEST CONDITIONS MIN TYP† MAX UNIT

VOH High-level output voltage T1OUT, T2OUT RL = 3 kΩ to GND 5 7 V

VOL Low-level output voltage‡ T1OUT, T2OUT RL = 3 kΩ to GND –7 –5 V

ro Output resistance T1OUT, T2OUT VS+ = VS– = 0, VO = ±2 V 300 Ω

IOS§ Short-circuit output current T1OUT, T2OUT VCC = 5.5 V, VO = 0 ±10 mA

IIS Short-circuit input current T1IN, T2IN VI = 0 200 µA

† All typical values are at VCC = 5 V, TA = 25°C.‡ The algebraic convention, in which the least positive (most negative) value is designated minimum, is used in this data sheet for logic voltage

levels only.§ Not more than one output should be shorted at a time.NOTE 3: Test conditions are C1–C4 = 1 µF at VCC = 5 V ± 0.5 V.

switching characteristics, VCC = 5 V, TA = 25°C (see Note 3)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

SR Driver slew rateRL = 3 kΩ to 7 kΩ,See Figure 2

30 V/µs

SR(t) Driver transition region slew rate See Figure 3 3 V/µs

Data rate One TOUT switching 120 kbit/s

NOTE 3: Test conditions are C1–C4 = 1 µF at VCC = 5 V ± 0.5 V.

RECEIVER SECTION

electrical characteristics over recommended ranges of supply voltage and operating free-airtemperature range (see Note 3)

PARAMETER TEST CONDITIONS MIN TYP† MAX UNIT

VOH High-level output voltage R1OUT, R2OUT IOH = –1 mA 3.5 V

VOL Low-level output voltage‡ R1OUT, R2OUT IOL = 3.2 mA 0.4 V

VIT+Receiver positive-going inputthreshold voltage

R1IN, R2IN VCC = 5 V, TA = 25°C 1.7 2.4 V

VIT–Receiver negative-going inputthreshold voltage

R1IN, R2IN VCC = 5 V, TA = 25°C 0.8 1.2 V

Vhys Input hysteresis voltage R1IN, R2IN VCC = 5 V 0.2 0.5 1 V

ri Receiver input resistance R1IN, R2IN VCC = 5, TA = 25°C 3 5 7 kΩ† All typical values are at VCC = 5 V, TA = 25°C.‡ The algebraic convention, in which the least positive (most negative) value is designated minimum, is used in this data sheet for logic voltage

levels only.NOTE 3: Test conditions are C1–C4 = 1 µF at VCC = 5 V ± 0.5 V.

switching characteristics, VCC = 5 V, TA = 25°C (see Note 3 and Figure 1)

PARAMETER TYP UNIT

tPLH(R) Receiver propagation delay time, low- to high-level output 500 ns

tPHL(R) Receiver propagation delay time, high- to low-level output 500 ns

NOTE 3: Test conditions are C1–C4 = 1 µF at VCC = 5 V ± 0.5 V.




PARAMETER MEASUREMENT INFORMATION

≤10 ns

VCC

R1INor

R2IN

R1OUTor

R2OUT

RL = 1.3 kΩ

See Note C

CL = 50 pF(see Note B)

TEST CIRCUIT

≤10 ns

Input

Output

tPHLtPLH

1.5 VVOL

VOH

0 V

3 V

10%90%

50%

500 ns

WAVEFORMS

1.5 V

90%50% 10%

NOTES: A. The pulse generator has the following characteristics: ZO = 50 Ω, duty cycle ≤ 50%.B. CL includes probe and jig capacitance.C. All diodes are 1N3064 or equivalent.

PulseGenerator

(see Note A)

Figure 1. Receiver Test Circuit and Waveforms for tPHL and tPLH Measurements




PARAMETER MEASUREMENT INFORMATION

T1IN or T2IN T1OUT or T2OUT

CL = 10 pF(see Note B)

TEST CIRCUIT

≤10 ns≤10 ns

Input

Output

tPHLtPLH

VOL

VOH

0 V

3 V

10%

90%50%

5 µs

WAVEFORMS

90%50%

10%

RL

90%

10%

90%

10%

tTLHtTHL

SR 0.8 (VOH – VOL)

tTLHor

0.8 (VOL – VOH)

tTHL

NOTES: A. The pulse generator has the following characteristics: ZO = 50 Ω, duty cycle ≤ 50%.B. CL includes probe and jig capacitance.

PulseGenerator

(see Note A)EIA-232 Output

Figure 2. Driver Test Circuit and Waveforms for tPHL and tPLH Measurements (5-µs Input)

EIA-232 Output

–3 V

3 V

–3 V

3 V

3 kΩ

10%1.5 V90%

WAVEFORMS

20 µs

1.5 V90%

10%

VOH

VOL

tTLHtTHL

≤10 ns ≤10 ns

TEST CIRCUIT

CL = 2.5 nF

PulseGenerator

(see Note A)

Input

Output

SR 6 VtTHL or tTLH

NOTE A: The pulse generator has the following characteristics: ZO = 50 Ω, duty cycle ≤ 50%.

Figure 3. Test Circuit and Waveforms for tTHL and tTLH Measurements (20-µs Input)




APPLICATION INFORMATION

VS+

VS–

2

6

14

7

13

8

C1+

C1–

C2+

C2–

1

3

4

5

11

10

12

9

GND15

0 V

VCC

16

5 V

EIA-232 Output

EIA-232 Output

EIA-232 Input

EIA-232 Input

+1 µF

8.5 V

–8.5 V

1 µF

1 µF

1 µF

From CMOS or TTL

To CMOS or TTL

CBYPASS = 1 µF+

–

C1

C2

C3†

C4

† C3 can be connected to VCC or GND.

Figure 4. Typical Operating Circuit

References

[1] Image Sensor Communications, 2008. www.vlcc.net.

[2] Wavelength Division Multiplexing, 2008. www.wikipedia.org.

[3] Light-emitting Diode, 2009. www.wikipedia.org.

[4] S. Arai, S. Mase, T. Yamazato, T. Endo, T. Fujii, M. Tanimoto, K. Kidono,

Y. Kimura, and Y. Ninomiya. Experimental on Hierarchical Transmission Scheme

for Visible Light Communication using LED Traffic Light and High-Speed Camera.

In 2007 IEEE 66th Vehicular Technology Conference, 2007. VTC-2007 Fall, pages

2174–2178, 2007.

[5] J. Grubor, K. Langer, J. Walewski, and S. Randel. High-speed wireless indoor

communication via visible light. ITG FACHBERICHT, 198:203, 2007.

[6] S. Haruyama, V. Chairman, and J. Yokohama. Japan’s Visible Light Communi-

cations Consortium and its standardization activities. Presentation at IEEE, 802,

2008.

[7] S. Kitano, S. Haruyama, and M. Nakagawa. LED road illumination communications

system. In 2003 IEEE 58th Vehicular Technology Conference, 2003. VTC 2003-Fall,

volume 5, 2003.

[8] T. Komine and M. Nakagawa. Integrated system of white LED visible-light com-

munication and power-line communication. IEEE Transactions on Consumer Elec-

tronics, 49(1), 2003.

[9] Dominic O’Brien. Visible Light Communications : A Tutorial, 2008.

[10] G. Pang, K.L. Ho, T. Kwan, and E. Yang. Visible light communication for audio

systems. IEEE Transactions on Consumer Electronics, 45(4):1112–1118, 1999.

[11] J.O. PLENARY. IEEE Cover. AGENDA, 1:1.

[12] E.F. Schubert and J.K. Kim. Solid-state light sources getting smart. Science, 308

(5726):1274, 2005.

70

References 71

[13] S. Tanabe, S. Fujita, S. Yoshihara, A. Sakamoto, and S. Yamamoto. YAG glass-

ceramic phosphor for white LED (II): luminescence characteristics. In Proc. of SPIE

Vol, volume 5941, pages 1–1.

[14] Y. Tanaka, T. Komine, S. Haruyama, and M. Nakagawa. Indoor visible light data

transmission system utilizing white LED lights. IEICE Transactions on Commu-

nications, 86(8):2440–2454, 2003.

[15] J. Vucic, C. Kottke, A. Paraskevopoulos, S. Nerreter, JW Walewski, and K.D.

Langer. High-Speed Optical-Wireless Communications for Indoor Applications.

ITG-Fachberichte-Breitbandversorgung in Deutschland, 2010.

[16] H.B.C. Wook, T. KOMINE, S. HARUYAMA, and M. NAKAGAWA. Visible light

communication with LED-based traffic lights using 2-dimensional image sensor.

VLC

Documents

matsushita

wavelength

bit error

dr muhammad

cl includes

reel tube

max232i dual

inherent electrical