TRANSISTORS

Point-Contact Transistor – first transistor ever made

“The Wonder child of electronics world”

By

AJAL.A.J ( ASSISTANT PROFESSOR)ECE DEPARTMENTMAIL: [email protected]: 8907305642

What is a transistor?A transistor is a 3 terminal electronic device

made of semiconductor material.Transistors have many uses, including

amplification, switching, voltage regulation, and the modulation of signals

This session will help you to understand the,

1.Evolution of transistor  2.Importance of transistor  3.Definition & transistor types  4.Transistor symbol & operation  5.Advantages of transistor

6.Latest in transistor technology

History of transistors In 1906, an American inventor and

physicist, Lee De Forest, made the vacuum tube triode or audion as he called it.

Used in radios Used in early computers

Picture shows the workbench of John Bardeen (Stocker Professor at OU) and Walter Brattain at Bell Laboratories. They were supposed to be doing fundamental research about crystal surfaces.

The experimental results hadn't been very good, though, and there's a rumor that their boss, William Shockley, came near to canceling the project.  But in 1947, working alone, they switched to using tremendously pure materials. 

It dawned on them that they could build the circuit in the picture. It was a working amplifier!  John and Walter submitted a patent for the first working point contact transistor. 

Interesting story…

Shockley was furious and took their work and invented the junction transistor and submitted a patent for it 9 days later. The three shared a Nobel Prize in 1955. Bardeen and Brattain continued in research (and Bardeen later won another Nobel).

Shockley quit to start a semiconductor company in Palo Alto. It folded, but its staff went on to invent the integrated circuit (the "chip") and to found Intel Corporation.

By 1960, all important computers used transistors for logic, and ferrite cores for memory.

Interesting story…

Qualitative basic operation of point-contact transistor

Problems with first transistor…

First Bipolar Junction TransistorsW. Shockley invented the p-n junction transistorThe physically relevant region is moved to the bulk of the material

Moore’s Law

It’s an observation made by Gordon E. Moore, in which he predicted that the number of transistors, inside an Integrated Circuit, could be doubled every 24 months.

At the density that also minimized the cost of a transistor.

Transistor DefinitionTransistor is an electronic device made of three layers of semiconductor material that can act as an insulator and a conductor.

The three layered transistor is also known as the bipolar junction transistor.

Basic models of BJT

BJTs – Basic Configurations

pnp BJT npn BJT

Bipolar Junction Transistors (BJT’s)

The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structure

There are two types of BJTs, the NPN and PNP

Origin of the namesthe Emitter 'emits' the electrons which pass

through the device the Collector 'collects' them again once

they've passed through the Base ...and the Base?...

Transistor operation

force – voltage/currentwater flow – current - amplification

Architecture of BJTsThe bipolar junction transistor (BJT) is

constructed with three doped semiconductor regions separated by two pn junctions

Regions are called emitter, base and collector

Basic construction

Architecture of BJTsThere are two types of BJTs, the npn and pnpThe two junctions are termed the base-emitter

junction and the base-collector junctionThe term bipolar refers to the use of both holes and

electrons as charge carriers in the transistor structureIn order for the transistor to operate properly, the two

junctions must have the correct dc bias voltagesthe base-emitter (BE) junction is forward

biased(>=0.7V for Si, >=0.3V for Ge)the base-collector (BC) junction is reverse biased

Regions of a transistorA transistor has three regions namely,

Emitter- heavily doped

Base- lightly doped

Collector- moderately doped

Transistor symbols Transistor symbols

How does IC vary with VCE for various IB?

Note that both dc sources are variable

Set VBB to establish a certain IB

Transistor biasing The base-emitter (BE) junction is forward

biasedThe base-collector (BC) junction is reverse

biased.

IE=IB+IC

• Output current can toggle between large and small (Switching Digital logic; create 0s and 1s)

Operating regions of BJT

Cut off region

Linear region

Saturation region

Types of transistor

BJT - Bipolar Junction Transistor

UJT- Unipolar Junction Transistor

FET - Field Effect Transistor

MOS - Metal Oxide Semiconductor

Basic circuits of BJT

Operation of BJTs

BJT will operates in one of following four regionCutoff region (for digital circuit)Saturation region (for digital circuit)Linear (active) region (to be an amplifier)Breakdown region (always be a disaster)

Operation of BJTs

DC Analysis of BJTsTransistor Currents: IE = IC + IB

alpha (DC) IC = DCIE

beta (DC) IC = DCIB

DC typically has a value between 20 and 200

DC Analysis of BJTsDC voltages for the biased transistor:

Collector voltageVC = VCC - ICRC

Base voltageVB = VE + VBE

for silicon transistors, VBE = 0.7 Vfor germanium transistors, VBE = 0.3 V

Q-point

The base current, IB, is established by the base bias

The point at which the base current curve intersects the dc load line is the quiescent or Q-point for the circuit

Q-point

DC Analysis of BJTs

The voltage divider biasing is widely used

Input resistance is:RIN DCRE

The base voltage is approximately:VB VCCR2/(R1+R2)

BJT as an amplifierClass A Amplifiers

Class B Amplifiers

Class A Amplifiers

In a class A amplifier, the transistor conducts for the full cycle of the input signal (360°)used in low-power applications

The transistor is operated in the active region, between saturation and cutoffsaturation is when both junctions are forward biasedthe transistor is in cutoff when IB = 0

The load line is drawn on the collector curves between saturation and cutoff

BJT Class A Amplifiers

BJT Class A Amplifiers

BJT Class A AmplifiersThree biasing mode for class A amplifiers

common-emitter (CE) amplifiercommon-collector (CC) amplifiercommon-base (CB) amplifier

A common-emitter (CE) amplifiercapacitors are used for coupling ac without

disturbing dc levels

BJT Class A Amplifiers

A common-collector (CC) amplifiervoltage gain is approximately 1, but current

gain is greater than 1

BJT Class A Amplifiers

BJT Class A AmplifiersThe third configuration is the common-base (CB)the base is the grounded (common) terminalthe input signal is applied to the emitteroutput signal is taken off the collectoroutput is in-phase with the inputvoltage gain is greater than 1current gain is always less than 1

BJT Class A Amplifiers

BJT Class B Amplifiers

When an amplifier is biased such that it operates in the linear region for 180° of the input cycle and is in cutoff for 180°, it is a class B amplifierA class B amplifier is more efficient than a

class AIn order to get a linear reproduction of the input

waveform, the class B amplifier is configured in a push-pull arrangementThe transistors in a class B amplifier must be

biased above cutoff to eliminate crossover distortion

BJT Class B Amplifiers

When used as an electronic switch, a transistor normally is operated alternately in cutoff and saturationA transistor is in cutoff when the base-emitter

junction is not forward-biased. VCE is approximately equal to VCC

When the base-emitter junction is forward-biased and there is enough base current to produce a maximum collector current, the transistor is saturated

The BJT as a Switch

The BJT as a Switch

An example -- NOR

Transistor as a switch When used as an electronic switch, the transistor is normally operated alternately in cut-off and saturation regions.

Transistor applications

Transistor as amplifierDue to the small changes in

base current the collector current will mimic the input with greater amplitude

Molecular electronicsCarbon nanotube transistorsNano inspiration wire transistorsQuantum computingCMOS devices will add functionality to CMOS

non-volatile memory, opto-electronics, sensing….

CMOS technology will address new markets macroelectronics, bio-medical devices, …

Biology may provide for new technologies bottom-up assembly, human intelligence

Future of Transistors

3D Transistor made using Tri-Gate transistors on its 22nm logic technology.

Advantage of Tri-Gate Transistors ·More than 50% power reduction at

constant performance. ·37% performance increase at low voltage ·Improved performance and efficiency.

What’s new in transistor technology?

BJTs – Practical Aspects

BJTs – Practical Aspects

Heat sink

BJTs – Testing

BJTs – Testing