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ENGR 298
Successive Approximation Analog to Digital
Converter
Presented to
Ali M. Zargar
On
April 30, 2010
By
Team Number 7
Nila Barot
Committee Members
Faculty Reader
Prof. Morris Jones, Retired from Intel Corp.
Industrial Sponsor
Srenik Mehta, Atheros Comm.
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2010
Nila Barot
ALL RIGHT RESEREVED
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APPROVED FOR THE GENERAL ENGINEERING DEPARTMENT
Morris Jones
Srenik Mehta
__________________________________________
Ali M. Zargar
APPROVED FOR THE UNIVERSITY
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ABSTRACT
This master project report contains implementation of design and economic justification of SAR
ADC. The main motivation is to implement design of capacitor array DAC and achieve high
speed with medium resolution using 45nm technology. The current SAR architecture has in built
sample and hold circuit, so there is significant saving in chip area. The other advantage is
matching of capacitor can be achieved better then resistor. The market and cost analysis says
current SAR ADC has better future.
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ACKNOWLEGEMENT
Writing and implementing this master project was a very rewarding for me. I would like to say
thanks to my project guides Prof. Morris Jones and Srenik Mehta for their guidance and support
for design the SAR ADC using capacitor array DAC. I would like to say thanks to Prof. Ali
Zargar for his direction to planning and writing this master project report. Finally, thanks to the
readers of this project report for their suggestions and comments.
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Contents
1. Introduction............................................................................................................................................... 8
1.1 Selection of the right ADC architecture.............................................................................................. 8
1.2.1 SAR ADC Architecture................................................................................................................... 8
1.2.2. Advantages and limitations............................................................................................................. 9
1.3 VNB company................................................................................................................................. 10
2. Objective................................................................................................................................................. 10
2.2 Summary of phenomena................................................................................................................... 10
2.3 Description of Internal Major Blocks............................................................................................... 12
2.3.1 Design of Capacitor array DAC................................................................................................. 12
2.3.2OperationforbinaryweightedcapacitorarrayDAC................................................................. 13
2.3.3 SAR Logic................................................................................................................................. 17
2.3.4 Design of Comparator................................................................................................................ 18
2.4.1 Experimental Procedures............................................................................................................... 23
2.4.1.1Staticparameters.................................................................................................................... 24
2.4.1.2 Dynamic parameters............................................................................................................... 24
2.4.2 Resources Utilized......................................................................................................................... 25
2.4.3 Project Schedule............................................................................................................................. 25
3. Literature Survey.................................................................................................................................... 26
4. Economic Justification............................................................................................................................ 28
4.1 Executive Summary.......................................................................................................................... 28
4.2. Market Survey.................................................................................................................................. 28
4.3. Current SAR ADC........................................................................................................................... 33
4.4 Cost Survey....................................................................................................................................... 34
5. Applications of Data Converters............................................................................................................. 35
6. Cost Analysis.......................................................................................................................................... 36
6.1 Human Resources
.............................................................................................................................
36
6.2 Product Cost...................................................................................................................................... 37
6.3. Product Revenue.............................................................................................................................. 38
6.4 Breakeven Analysis.......................................................................................................................... 39
6.5 Profit & Loss Analysis...................................................................................................................... 42
6.6 SWOT Assessment........................................................................................................................... 44
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7. Relevance of core courses....................................................................................................................... 45
8. Conclusion.............................................................................................................................................. 46
9. Future Work............................................................................................................................................ 46
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1. Introduction
1.1 Selection of the right ADC architecture
The selection of the right architecture is a very crucial decision. The following figure 1 shows
the common ADC (Analog to Digital Converter) architectures, their applications, resolutions and
sampling rates. Sigma Delta ADC architectures are very useful for lower sampling rate and
higher resolution (approximately 12-24 bits). The common applications for Sigma-delta ADC
architecture are found in voice band, audio and industrial measurements. The Successive
Approximation (SAR) architecture is very suitable for data acquisition; it has resolutions ranging
from 8bits to 18 bits and sampling rates ranging from 50 KHz to 50 MHz. The most effective
way to create a Giga rate application with 8 to 16 bit resolution is the pipeline ADC architecture.
(Kester, W. 2005, June)
Figure 1 ADC architecture, applications, resolution, and sampling rates. (Kester, W. 2005, June)
1.2.1 SAR ADC Architecture
The SAR architecture mainly uses the binary search algorithm. The SAR ADC consists of fewer
blocks such as one comparator, one DAC (Digital to Analog Converter) and one control logic.
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The algorithm is very similar to like searching a number from telephone book. For example, to
search a telephone number from telephone book, first, the book is opened and the number may
be located either in first half or in the second half of the book. Further, relevant section is divided
into half. This procedure can be followed until finding relevant number. (Moscovici, A. 2001)
Figure 2 Block diagram of SAR ADC which has a capacitive DAC, a comparator and a digital
logic ( BP Ginsburg, A. C. 2007).
1.2.2. Advantages and limitations
The main advantage of SAR ADC is good ratio of speed to power. The SAR ADC has compact
design compare to flash ADC, which makes SAR ADC inexpensive. The physical limitation of
SAR ADC is, it has one comparator throughout the entire conversation process. If there is any
offset error in the comparator, it will reflect on the all conversion bits. The other source is gain
error in DAC. However, the static parameter errors do not affect dynamic behavior of SAR
ADC. Furthermore, higher the speed, it is difficult to obtain the dynamic behavior of ADC. One
solution is to use time-interleaved converters. (Moscovici, A. 2001)
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1.3 VNB company
Currently, VNB Company has one student engineer named Nila Barot and two expert guides Prof. Morris
Jones (Ex. VP of Intel) and Srenik Mehta (Director of Analog Design at Atheros). Data convertor is
major product of company. Company has started business during year 2009, and currently company has
implemented the SAR ADC design. Furthermore, performance testing of SAR ADC is under progress.
2. Objective
The Data Converters are widely used in wireless communication, digital audio and video
applications. There are many kind of ADC such as flash ADC, Integrating ADC, pipeline ADC
and SAR ADC. The SAR ADC can be build using resistor string DAC or Capacitor array DAC.
The current SAR ADC design uses capacitor array DAC using 45nm CMOS (Complementary
Metal oxide Semiconductor) technology. (BP Ginsburg, A. C. 2007)
2.2 Summary of phenomena
The main goal of this project is to design a successive approximation (SAR) ADC using binary
weighted split capacitor array DAC. The basic algorithm of binary search is to convert analog
signal into digital signal/quantized form. The conversion process starts after discharging the
capacitors. During sampling mode capacitor array is charged by vIN (input voltage). During
charge redistribution mode, MSB (Most Significant Bit) set to one and remaining bits set to zero.
The MSB capacitor is charge to Vref (Reference Voltage). If Comparator output is high, bottom
plate of MSB capacitor remains connected to Vref. On the other hand, if comparator output is
low, the MSB capacitor connects to the ground. The conversion process continue for the next
largest MSB same way, and the second largest capacitor charges to Vref while the remaining
LSB (Least Significant Bit) capacitor array connect to the ground. If the comparator output is
high, the second largest MSB capacitor connects to Vref otherwise it connects to the ground.
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This process continues until the last conversion. The figure 3 shows the logic over view of SAR
ADC, where Vx is voltage at top plate of capacitor
Figure 3. Logic over view of SAR ADC
Discharge
Sample
Hold
Vx>VCM?
Bi=0
Bitcycle
Start
Y
N
Bi=1
Bitremain
UnchangedBitchanged
toZero
Vx=Vx+Vref/
2^(i+1)
Vx=VxVref/
2^(i+1)
>N
Stop
I=i+1,Bi=1N
Vx=VCM
Vx=VCM
Vx=Vin+VCM
Vx=Vin+VCM+Vref/2
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2.3 Description of Internal Major Blocks
As mentioned in summary of phenomena, the SAR ADC consists of three major blocks such as a
comparator, a successive approximation register (SAR), and a DAC. The current SAR ADC
builds using following blocks:
Capacitor array DAC Comparator Control logic.
2.3.1 Design of Capacitor array DAC
The conventional binary weighted capacitor array has limitation for higher resolution due the
larger capacitor ratio from MSB capacitor to LSB capacitor. To eliminate this problem, one
technique can be applied known as split capacitor technique. (BP Ginsburg, A. C. 2007). For
example, to achieve the 8bits resolution, the capacitor array can be splited as shown in following
figure 4. The attenuation capacitor divides the LSB capacitor array and MSB capacitor array.
Here, the ratio between LSB to MSB capacitor (C to 8Cc) reduces drastically compare to the
conventional binary weighted capacitor array (C to 128C). (Baker, J. R., Li, H. W., & Boyce, D.
E.1998)
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Figure 4. Split capacitor array DAC for 8 bits resolution (Baker, J. R., Li, H. W., & Boyce, D. E.,
1998)
2.3.2OperationforbinaryweightedcapacitorarrayDACThe capacitor array works in four different phases such as
Discharge Sample Charge transfer (Hold) Charge redistribution
The following paragraphs describe all the phases in detail.
2.3.2.1DischargephaseDuring discharge phase, comparator act as unity gain buffer as shown in figure 5, and the reset
switch is on. All bottom plates of capacitor array are connected to VCM. (In this case 0.5V),
C C 2C8C C2C 8C4C
16/15CAttenuation Capacitor
VCM
Vin
Vrefn
Vrefp
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hence voltage across capacitor plate are zero. As shown in figure 5, Vx is voltage at top plate of
capacitor array, and VCM is common mode voltage.
Figure 5. Discharge phase
2.3.2.2SamplingphaseDuring sampling phase bottom plates of capacitor array are connected to Vin as shown in figure
6. The reset switch still on hence the top plate is on VCM; and voltage across capacitor array is
Vin-VCM.
Figure 6. Sampling Phase
2 C
Vin VCM
2 C
VCM VCM
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2.3.2.3Chargetransfer/HoldphaseDuring Charge transfer phase, bottom plates of capacitor array are switched to VCM and top
plates are floating as shown figure 7. In this phase, reset switch is off. Hence, Voltage at top
plate Vx, which is as follows:
Vx= VCM - (Vin-VCM) = -Vin.
For example: Vin = 0.7V
Vx=0.5- (0.7-0.5)
=0.5-0.2=0.3V
Figure 7. Charge transfer Phase
2.3.3.4ChargeredistributionphaseDuring the Charge redistribution phase, first the MSB is set to high, and the bottom plate of
MSB capacitor is connected to Vrefp (Reference voltage Positive) (In this case 1V) as shown in
figure 8. The other remaining bits are set to zero, hence bottom plates of these capacitors are
connected to Vrefn (Reference voltage Negative) (In this case GND). If the comparator output is
high, the MSB reset to high and bottom plate of MSB capacitor remains connected to Vrefp. If
2 C
VCM
VCM
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Comparator output is low, the bottom plate of MSB is then connected back to the GND. The
voltage at top of the capacitor array Vx is:
Vx = -Vin + Vos + D N-1 * (Vrefp/2)
= 0.3 + Vos+ 1*(1/2)* 1(for time being Vos=0)
=0.8 V
Figure 8. Charge redistribution phase (MSB set to High)
Then, the next largest capacitor is tested in the same manner clearly shown in figure 9. The
conversion process continues until the last bit. (Baker, J. R., Li, H. W., & Boyce, D. E. 1998)
2 C
Vref
VCM
Vrefn
2 C
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Figure 9. Testing second largest bit during charge redistribution phase
2.3.3 SAR Logic
SAR logic is purely a digital circuit, and it consists of three major blocks;
Counter Bit register Data register
The counter provides timing control and switch control. For 8 bits conversion, seven DFFs (D
flip-flops) are used. The following table 1 explains which bit set to high during different phases
of SAR operation.
Phase q0 q1 q2 q3 q4 q5 q6
Discharge/Reset 0 0 0 0 0 0 0
Sample/ Reset 1 0 0 0 0 0 0
Vref
VCM
Vrefn
2 C
Vrefn
2 C
2 C
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Hold (charge Transfer) 1 1 0 0 0 0 0
Test7 [D7] 1 1 1 0 0 0 0
Test6 [D6] 1 1 1 1 0 0 0
Test5 [D5] 1 1 1 1 1 0 0
Test4 [D4] 1 1 1 1 1 1 0
Test3 [D3] 1 1 1 1 1 1 1
Test2 [D2] 0 1 1 1 1 1 1
Test1 [D1] 0 0 1 1 1 1 1
Test0 [D0] 0 0 0 1 1 1 1
Unused 0 0 0 0 1 1 1
EOC (end of conversion) 0 0 0 0 0 1 1
Table 1. Control of switches during different four phases
2.3.4 Design of Comparator
2.3.4.1 Characterization of a comparator
A comparator is a circuit, which has a binary output and its value is based on a comparison of
two analog inputs. The output of the comparator is high (VOH) when the difference between the
non inverting and the inverting inputs is positive. The output is low (VOL) when the difference
is negative, which clearly shown in figure 10. This is an ideal behavior of comparator, which is
impossible in a real time.
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Figure 10. Ideal Transfer curve of comparator (Anonymous)
Ideally, output of comparator is defined as follows:
Practically, comparator cannot achieve infinite gain; hence, the output is defined as follows:
(Anonymous)
Figure 11. Transfer curve of comparator with finite gain (Anonymous)
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Another important characteristic of comparator is slew rate. If the input voltage is larger which
will results into a smaller delay time. However, it has upper limit. (Philips E. Allen 2002)
Another non- ideal characteristic of comparator is input offset. The output of comparator does
not change until the input difference reached the input offset Vos. The figure 12 shows the
transfer characteristic of comparator with input offset. The output is defined as follows:
(Philips E. Allen 2002) and (Anonymous)
Figure 12. Transfer curve of a comparator including input offset voltage (Anonymous)
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Figure 13. Ideal Comparator with gain 1000, Vm (0 10 1V), Vp(0.3V)
Input voltage Vm varies from 0 to 1V while another input Vp is set nearly 500mV. The result of
simulation is shown in figure 14.
Figure 14. Simulation data of ideal comparator with gain 1000
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Furthermore, often a comparator is placed in noisy environment; hence, the output of comparator
is noisy. By adding hysteresis into the comparator, better results can be achieved. The hysteresis
can be added by adding positive feedback externally or internally. For current SAR ADC internal
positive feedback is used. (Philips E. Allen 2002)
2.3.4.2 Regenerative comparator
There are many types of comparator such as two stage open loop comparator, discrete time
comparator and folded cascade comparator. For current SAR ADC design, discrete time
comparator is used. The discrete time comparator works on some portion of time, and it is clock
driven.
The block diagram of comparator is as shown in figure 15. The first stage is pre amplification
stage to amplify the input signal. The second stage is decision circuit or sense amplifier with
latch. The current regenerative comparator uses positive feedback for comparison of two signals.
The latch works on two phases, one disable the positive feedback and other phase enables the
latch. The latch keeps the voltage high or low relative to its value. The last part of comparator is
an output buffer. (Baker, J. R., Li, H. W., & Boyce, D. E. 1998), and (Philips E. Allen 2002)
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Figure 15 Three stage Comparator block diagram (Baker, J. R., Li, H. W., & Boyce, D. E., 1998)
2.4.1 Experimental ProceduresReferred the different internal blocks circuits from literatures, books and online materials, and
applied the concepts to the circuits. The next phase is mathematical calculation which were done
using Microsoft Excel and manually.
The schematic capture is done using the Cadence Composer Tool. The next task was to simulate
the design at circuit level, and to integrate all the circuits to check the functionality. Another
major task was to measure the performance evaluation. The performance parameters are the
essential part of any kind of design to satisfy the design specification. There is two kinds of
parameter of ADC; one is static and other is dynamic. The static parameters are offset error, gain
error, Integral Non linearity (INL), and Differential Non linearity (DNL). While the dynamic
Preamplification
SenseAmplifier
/DecisionCircuit Postamplification
F
r
o
m
c
a
p
a
c
i
t
o
r
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parameters are, signal to noise ratio (SNR), ENOB (Effective Number of Bits), and Total
harmonic distortion.
2.4.1.1StaticparametersOffset error is defined as the difference between the actual value and theoretical value of input
voltage required to obtain the transition from first code 00000 to next code 00001.
(Moscovici, A. 2001)
Gain error is defined as ratio of difference between actual maximum input voltage and actual
minimum input voltage to difference between theoretical maximum input voltage and theoretical
minimum input voltage. (Moscovici, A. 2001)
Integral Non-linearity (INL) is defined as the difference between the data converter code
transition points and straight line with all other error set to zero. (Baker, J. R., Li, H. W., &
Boyce, D. E. 1998)
Differential Non-linearity (DNL) is defined as difference between the actual code width of a
non-ideal converter and ideal case. (Baker, J. R., Li, H. W., & Boyce, D. E. 1998)
2.4.1.2 Dynamic parametersSignal to Noise Ratio (SNR) is ratio of the value of the highest RMS (Root Mean Square) input
signal to the RMS value of the noise. (Baker, J. R., Li, H. W., & Boyce, D. E. 1998)
Effective numbers of bits (ENOB) specifies the dynamic performance of an ADC at a specific
input frequency and sampling rate. (Maxim Integrated Product 2010)
Total harmonic distortion (THD) is defined as the ratio of the RMS sum of the selected
harmonics of the input signal to the fundamental itself. (Maxim Integrated Product 2010)
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2.4.2 Resources Utilized
For the design and simulation, Microsoft Excel and Cadence tools are used. For the
implementation of the design, Cadence Composer tool is used. In the next step is simulated the
design using the Cadence Circuit Simulator and the performance parameters are checked
2.4.3 Project Schedule
This Project contains two phases; Phase I and Phase II. Both the phases involve the eight major
tasks. Each task has approximately eleven to sixteen days duration. The Table 1 and Gnatt Chart
present the activities of phase II as shown in following.
Task
No
Task Nos. of
Days
Start Time Finish
Time
Status
1 Design of Capacitor array DAC 16 1/22/10 2/12/10 Completed
2 Design of control Logic 11 2/12/10 2/26/10 Completed
3 Design of Comparator 15 2/26/10 3/18/10 Completed
4 Integration of all blocks 4 3/18/10 3/23/10 Completed
5 Simulation of Data Convertor 18 3/23/10 4/16/10 Completed
6 Performance Evaluation 11 4/16/10 4/30/10 Under Progress
7 Final Report 6 4/09/10 4/16/10 Completed
8 Final Report Presentation 6 4/23/10 4/30/10 Under Progress
Table 2 Project Schedule for Project Phase II
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Figure 16. Gnatt Chart for Project Phase II
3. Literature Survey
Several IEEE documents, companys websites and on line newsletters are analyzed. The table 3
shows the summary of performance of a SAR ADC for 65nm CMOS technology.
Table 3. Summary of Performance (BP Ginsburg, A. C. 2007)
Technology 65 nm CMOS 1P6M
Supply Voltage 1.2v
Sampling Rate 500 MS/s
Resolution 5 bits
Input Range 800m Vpp Differential
SNDR(fin=3.3 MHz) 27.8 dB
SNDR(fin=239 MHz) 26.1dB
SFDR(fin=239 MHz) -41.5dB
DNL 0.26 LSB
INL 0.16 LSB
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Texas Instruments have announced the 16, 14, 12 bits six channel simultaneously sampling
analog to digital converter. The maximum data rate per channel is around 500kSPS [3]. The
following data shows the detail features about six channel SAR ADCs. (Incorporated, T. I. 2009,
August).
Features of six channel SAR ADCs
Family of 16, 14, 12 bits, Pin and software Compatible ADC Six SAR ADCs Grouped in three Pairs Maximum Data Rate Per Channel with Internal Conversion Clock and Reference:
ADS8556: 630kSPS (PAR) or 450kSPS (SER)
ADS8557: 670kSPS (PAR) or 470kSPS (SER)
ADS8558: 730kSPS (PAR) or 500kSPS (SER)
Maximum Data Rate with External ConversionClock and Reference:
800kSPS (PAR) or 530kSPS
Pin Selectable or Programmable Input VoltageRanges: Up to 12V
Excellent Signal to Noise Performance:91.5dB (ADC8556)
85 dB (ADS8557)
73.9 dB (ADS8558)
Programmable and Buffered InternalReference: 0.5V to 2.5V and 0.5V to 3.0V
Operating Temperature Range:
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-40 C to +125 C
LQFP -64 Package (Incorporated, T. I. 2009, August)
4. Economic Justification
4.1 Executive Summary
Currently, VNB Company has one full time student engineer from San Jose State University
under the guidance of Professor Morris Jones (Ex. VP of Marketing at Intel Corporation) and
Srenik Mehta (Director of Analog Design at Atheros). The present job of the VNB Company is
to implement the design of SAR ADC using 45nm technology.
To achieve this mission VNB Company, currently uses resources from SJSU Electrical
Department Lab. Additionally, for research VNB company explores the library database, books
and online materials. These equipments and materials are easily accessible and economical.
The Companys progress seems to be satisfactory, and profit of approximately $1.5 million is
expected to be achieved within first five to six years. To accomplish a target the Company is
putting hours of hard work, and it also needs initial funding of approximately $250,000.
The wireless communication and battery powered equipment companies are target user of VNB
products.
4.2. Market SurveyThere are many IC companies, which make different kinds of data convertors. The following is
list of some companies, which make data converters:
Analog Devices National Semiconductors
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Texas Instruments Maxim Cirrus Logic Universal Semiconductor, Inc Accord Solutions, Inc Aimtron Technology Analog Microelectronics Arizona Microtek, Inc CE Infosys GmbH Empire Technology Group Euram Electronics Source, Inc Foresight Technologies, Inc Quickfilter Technologies Inc. Royal Philips Electronics Shanghi Belling Co. Ltd Smith Semiconductor, Inc Swindon Silicon Systems T.D Stringer THine Electronics, Inc Yeeuntech Co. Ltd (Global Spec, 1999-2000)
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Analog Devices announced a few new releases, which have SAR ADC architectures ranging
from 6-bit, 8-bit, and 12-bit up to 28-bits. The newly released data converters are applicable for
low power and high-speed application. (Analog Devices I., 1995-2009)
The table 4 shows important features for currently released AD7985/AD7980, and similar
products.
Table 4. Products and its features (Analog Devices, 2009) and (Analog Devices I., 1995-2009)
Product ID Resolution
bits
Speed
MSPS
Power
Consumption(mw)
AD7985 16 2.5 15.5
AD7980 16 1.0 7.0
AD7450A 12 1 9
AD7450 12 1 9
AD7451 12 1 9.25
AD7440 10 1 9
AD7441 10 1 9.3
AD7983 16 1.33 12
AD7623 16 1.33 55
AD7622 16 2 85
AD7621 16 3 86
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National Semiconductor has a large variety of ADCs, which have sampling rate ranging from
kSPS (Kilo Samples Per Second) to GSPS (Giga Samples Per Second). Here, in table 5, few
products are listed which use SAR ADC architecture. The resolution range is from 8 to 12 bits.
In addition the Graph 1 shows comparison between Analog Devices and National
Semiconductor. (Anonymous, 2009, June)
Product ID Resolu
tion
(bits)
Speed
(kSPS)
Power
Consumption(mw)
3V
Power
Consumption(mw)
5v
Supply
Voltage
ADC081C021 8 5.5 to 189 0.26 0.78 2.7 to 5.5
ADC101C021 10 5.5 to 189 0.26 0.78 2.7 to 5.5
ADC121C021 12 5.56 to189 0.26 0.78 2.7 to 5.5
ADC081C027 8 5.5 to 189 0.26 0.78 2.7 to 5.5
ADC101C027 10 5.5 to 189 0.26 0.78 2.7 to 5.5
ADC121C027 12 5.56 to189 0.26 0.78 2.7 to 5.5
Table 5 National Semiconductor products, resolution, speed, power and supply voltage
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Graph 1 Comparison between Analog Devices and National Semiconductor
National Semiconductor has similar products for ultra high speed and medium resolution;
however, those products use pipeline architecture. The table 6 contains product ID and its
resolution with corresponding speed.
Product ID Resolution bits Speed (GSPS)
ADC081000 8 1
ADC08D1000 8 1
ADC08D1020 8 1
ADC081500 8 1.5
ADC08D1500 8 1.5
0
0.5
1
1.5
2
2.5
3
3.5
8 8 10 10 12 12 12 16 16 16 16
SpeedinMSPS
Resolutioninbits
SpeedVsResolution
SpeedMSPS(National
Semiconductor)
SpeedMSPS(AnalogDevice)
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ADC08D1520 8 1.5
ADC083000 8 3
ADC08B3000 8 3
Table 6 National Semiconductors ultra high speed and medium speed products (Anonymous,
2009, June)
4.3. Current SAR ADC
From the market survey, the SAR ADC has resolution from 8 to 16 bits with sampling rate few
kSPS to few MSPS. The current SAR ADC has resolution of 8 bits and sampling rate more than
50 MSPS. The current SAR ADC will be useful for high speed with medium resolution
application. The following graph 2 shows a clear picture for the current SAR ADCs comparison
with Analog Device and National Semiconductor SAR ADCs in terms of sampling rates and
resolutions.
Graph 2 Analog Devices, National Semiconductor and current SAR ADC
6
8
10
12
14
16
18
1.00E+02 1.00E+04 1.00E+06 1.00E+08
Resolution
SamplingRate
AnalogDevices
NationalSemi
Current
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The design specification mentioned under following table no. 7 is for the current SAR ADC.
Table 7. Targeted and Achieved Design specification for 8 bit SAR ADC
4.4 Cost Survey
The sampling rate of Analog Device products is higher compared to some of National
Semiconductor ADC products, which make Analog Device Products costlier than National
Semiconductor products for same resolution.
Analog Device National
Semiconductor
AD7985BCPZ $30.99 ADC081S021CIMF $0.67
Targeted Achieved
Technology 45 nm 1P6M 45 nm
Supply Voltage ~1v 1v
Sampling Rate >50MSPS >50MSPS
Resolution 8 bits 8 bits
Integral Nonlinearity +/- 0.5 LSB Under progress
Differential Nonlinearity +/- 0.5 LSB Under progress
Power Consumption Future work Future work
Signal to Noise Ratio Future work Future work
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AD7980ARMZ $13.38 ADC12C105CISQ $24.00
AD7980BRMZ $17.85 ADC12C105CISQE $24.00
AD7626BCPZ $34.95 ADC12C105CISQ $24.00
AD7626BCPZ-RL7 $34.95 ADC12C170CISQ $33.00
Table 8. Pricing for Analog device products and National Semiconductor (Analog Device, I.,
2009), and (Anonymous. (2009, Oct))
However, for comparable resolution and speed both companies have more or less same prices.
5. Applications of Data Converters
TheapplicationsofDataConvertersarelistedbelow:
Battery powered equipment Wireless Communication Data acquisition systems Medical instruments Test and measurement Industrial imaging (Analog Device I., 2009), and (Analog Device I., 1995-2009)
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Figure 17. Data converters applications (Anonymous, 2009, June)
6. Cost Analysis
6.1 Human Resources
Currently VNB Company has a single employee under the technical guidance from Prof. Morris
Jones (San Jose State University) and Srenik Mehta (Director of Analog design at Atheros
Comm.). VNB Company has already completed the preliminary phase of research. In the
research phase, the company has done literature survey, market survey, and cost survey. The
implementation part of this project has already completed successfully and the testing part is
done partially. Currently, the performance testing part is in progress. The table 9 shows past and
estimated growth from year 2009 to year 2013 of the VNB Company.
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Department 2009 2010 2011 2012 2013
Engineering 1 1 2 3 6
Marketing 1 1 1 2 5
Human
Resources
0 0 Consultant Consultant Consultant
Table 9. Past and Estimated growth of VNB Company
6.2 Product Cost
From the literature survey, the SAR ADC design seems to be challenging, and from the market
survey and cost analysis, it seems marketable and profitable. Currently at the starting point, the
VNB Company has limited resources such as PC, communication tools, and University
resources. As the company expands, it will have more resources such as office space,
workstations, and marketing facilities. For design purpose, company will provide tools like
Cadence, Mentor Graphics, Synopsis Powermill, and Smart Spice etc. The Company will bear
the license cost of the mentioned tools. The table 10 and Graph 3 explain the past and estimated
company product development cost. (Inc., M. , 2006-09), and (Inc., Y. 2009)
Category 2009 2010 2011 2012 2013
Employee Salary 80 90 300 550 740
Marketing 10 10 30 40 600
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Table 10. Past and Estimated VNB company product development cost (in thousand $)
Graph 3. Graphical presentation of development cost of VNB Company
6.3. Product Revenue
From the cost survey and design cost, the price of VNB Companys product is estimated around
$30.00. As the company will expand, there will be similar group of products. The breakeven
point reaches in the year 2011 when the company will start making profit. (Inc., M. 2006-09),
and (Inc., Y. 2009. The table 11 shows the past and estimation of product revenue.
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
2009 2010 2011 2012 2013
Dollorsinthousand
Year
DevlopmentCost
Others
Manufacturing
Marketing
Engineering
Manufacturing 0 20 100 150 3000
Other 0 10 40 50 100
Total 90 140 470 790 3700
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2009 2010 2011 2012 2013
Nos. of Units 0 2500 18,000 32,000 1,206,000
Revenue 0 75 540 960 4,020
Cost 90 140 470 790 3,700
Profit -90 -65 70 150 320
Table 11. Past and Estimation of Product Revenue in thousand dollars
6.4 Breakeven Analysis
Breakeven analysis can be represented graphically or mathematically. Breakeven analysis relates
fix cost and variable cost with number of units produced or number of operation hours.
Breakeven point says when company starts making profit. Breakeven analysis is very important
technique for firms economic evaluation. (Blanchard, B. S., & Fabrycky, W. J. (2006))
It is estimated that VNB Company will sell 2500 units in year 2010 and then next coming years
sale will increase.
The fix cost which must be paid regardless of production. The selling price is estimated $30.00.
Hence, the total revenue is calculated from number of sold units and selling price.
Total revenue = #of units sold * selling price
= 2500 * $30
= $75000
It is assumed that variable cost is around $9 per unit.
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Hence, total variable cost = # of unit sold * variable cost/unit
= 2500 * $9
=$22,500 (for year 2010)
Breakeven =FC / SP VC
Where FC is fix cost, SP is selling price and VC is variable cost.
Breakeven = $63000 / ($30 - $9)
= 3000
Similar way breakeven calculation can be done for following years. The graph 4 shows
breakeven analysis for VNB Company. (S., Patel, K., & Byron, Spring 2009)
Graph 4. Breakeven Analysis
$0
$500
$1,000
$1,500
$2,000
$2,500
$3,000
$3,500
$4,000
$4,500
2009 2010 2011 2012 2013
$inthousands
Year
BreakevenAnalysis
Cost
Revenvebreakeven
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Initial Years VNB Companys profit is negative; however, after year 2011 VNB Company will
first make profit. The total investment is $ 250,000. The return of investment is calculated below.
Return on Investment = Net profit total investment / total investment x 100
= ($385,000 -$250,000) / $ 250,000 x100
= .54 x 100
=54%
The Graph 5 explains the Norden Rayleigh Estimation for each year before VNB Company
makes its first net profit. VNB Company expects approximately $250,000 funding for initial
years.
Graph 5. Norden Rayleigh Estimation for funding
20
0
20
40
60
80
100
120
140
160180
0 1 2 3 4 5 6 7
Dollorsinthousands
Year
NordenRayleighEstimation
Dollorsinthousands
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6.5 Profit & Loss Analysis
Profit and Loss analysis is estimated for year 2009 to 2011.The table 12 to 14 shows profit and
loss with income and expense in tabular form.
Quarter Income Expense Profit/Loss
Qtr 3 '09 0 60 -60
Qtr 4 '09 0 30 -30
Table 12 Past and Estimated Profit and Loss for Qtr 3 09 to Qtr 4 09 ($ in thousands)
The graph 6 shows VNB Company did not make any money in year 2009, however loss is
reduce in following years.
Graph 6 Past and Estimated Profit and Loss for Qtr 3 09 to Qtr 4 09
80
60
40
20
0
20
40
60
80
Qtr3'09 Qtr4'09$inthousa
nds
Quarter&Year
P&LQtr3'09toQtr4'09
Income
Expense
Profit/Loss
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Quarter
Qtr 1 '10
Qtr 2 '10
Qtr 3 '10
Qtr 4 '10
Table 13
Graph 7
As show
Quarter
Qtr 1 '11
$in
thousands
I
1
3
3
Estimated
Estimated P
in table 1
Inco
60
20
10
0
10
20
30
40
50
Qtr
ncome E
0 -2
0 -2
5 50
0 50
rofit and L
rofit and Lo
and graph
e Ex
75
'10
P&
pense P
-2
-2
-1
-1
ss for Qtr 1
ss for Qtr 1
, VNB Co
ense Pr
-15
Qtr2'10
Quarte
L Qtr
43
ofit/Loss
0
0
5
0
10 to Qtr
10 to Qtr 4
pany expe
fit/Loss
Qtr3'10
r&Year
1'10to
10 ($ in th
10
ted first pro
Income
60
Qtr
Qtr4'
ousands)
fit in year 2
4'10
0
11.
Incom
Expen
Profit/
e
Loss
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Qtr 2 '11
Qtr 3 '11
Qtr 4 '11
Table 14
Graph 8
6.6 SW
The SW
briefly s
1
1
2
2
$inthousands
60
190
230
Estimated
Estimated P
T Assessm
T analysis
mmarized.
50
0
50
00
50
00
50
Qtr1
75
160
160
rofit and L
rofit and Lo
ent
performed
'11 Qt
P&L
-15
30
70
ss for Qtr 1
ss for Qtr 3
sing marke
2'11
Quarter&Y
Qtr1'1
44
11 to Qtr
11 to Qtr 2
survey. In
tr3'11
ear
1toQt
60
190
230
11 ($ in t
12
ollowing ta
Qtr4'11
4'11
ousands)
ble 15 SW
Inc
Ex
Pr
T assessme
ome
ense
fit/Loss
t is
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Strengths Weaknesses
1. Current SAR ADC has 8 bits resolution andspeed >50 MSPSs using 45nm technology.
2. Capacitor array DAC is better compare toresistor string DAC. Matching of Capacitorcan be achieved better compare to resistormatching.
1. VNB is small company, so it is difficult togrow in recession time.
Opportunities Threats
1. From market and cost analysis, VNB
Companys product seems marketable and costeffective.
2. In built sample and hold circuit, so there canbe significant saving in chip area.
1. Analog Device and National have released
similar kind of ADCs. They may come up withbetter design.
Table 15. SWOT Assessment
7. Relevance of core courses
The break-even analysis, which was covered in ENGR 202, is useful for this project. Breakeven
analysis is a technique used to find out or analyze when company will make profit. The subject
matter of ENGR 202 is useful to find return of investment and mainly to understand overall
project life cycle. The ENGR 203s contain is helpful for project planning and scheduling using
techniques like Gnatt Chart and CPM (critical path method). The topics covered in ENGR 201
are the Fourier series, time and frequency domain, and transfer function, which are useful to
understand the ADC signal flow. ENGR 200W covered the formatting, how to write the report
and how to present the power point.
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8. Conclusion
As discuss in the introduction, a SAR ADC is suitable for medium resolution with higher speed
ranging from kSPSs to MSPSs. From the literature survey, and current market and cost survey,
the future of SAR ADC using capacitor array DAC is marketable and cost-effective. As
mentioned in the two analog product companies (Analog Devices and National Semiconductor)
are making similar kind of ADC. Furthermore, the SAR ADC has many applications such as
wireless communication, and medical Instruments.
9. Future Work
Future work is to increase the resolution up to 12, 16 and 18 bits with reasonable speed. Current
SAR ADC is designed using split capacitor array DAC. For future design SS capacitor array
(Series Split Capacitor array) can be used. VNB Company will make products using other
architectures such flash ADC or pipeline ADC.
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Bibliography
[1] Analog Devices, I. (1995 - 2009 ). Retrieved from http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7985/products/product.html.
[2] 16-Bit, 2.5 MSPS, PulSAR 15.5 mW ADC in LFCSP. (2009). Retrieved from
www.analog.com.
[3]Device, A. (1995-2009).AD7980: 16-Bit, 1 MSPS PulSAR ADC in MSOP/QFN. Retrieved
from http://www.analog.com/en/analog-to-digital-converters/ad-
converters/ad7980/products/product.html.
[4]Kester, W. ( 2005, June). Which ADC Architecture Is Right for Your Application? Retrieved
from http://www.analog.com/library/analogDialogue/archives/39-06/architecture.pdf.
[5] Anonymous. (2009, June).Analog Products selection Guide. Retrieved from
www.national.com.
[6] Anonymous. (2009, Oct). Price & Availability. Retrieved from
http://www.national.com/pf/master_DC.html.
[7] S., Patel, K., & Byron. (Spring 2009).Multicore Microprocessor Interfacing (Propeller). San
Jose State University.
[8] Inc., M. (2006-09).How to calculate Cost of Goods. Retrieved fromhttp://www.marketingmo.com/how-to-articles/marketing-metrics/how-to-calculate-cost-of-
goods/.
[9] Inc., M. (2006-09).How to Calculate ROI Return on Investment. Retrieved from
http://www.marketingmo.com/4-support-tools/how-to-calculate-roi-return-on-investment/.
[10] Inc., Y. (2009). What is revenue? how do i calculate it? and how do businesses generate it?
Retrieved from http://answers.yahoo.com/question/index?qid=20080513102735AAKMSuH.
[11] Baker, J. R., Li, H. W., & Boyce, D. E. (1998). CMOS CIRCUIT DESIGN, LAYOUT, AND
SIMULATION. New York: The Institute of Electrical and Eletronics Engineers, Inc
[12] BP Ginsburg, A. C. (2007). 500-MS/s 5-bit ADC in 65-nm CMOS With Split Capacitor
Array DAC.IEEE Journal of Solid State Circuits .
[13] Incorporated, T. I. (2009, AUGUST ). 16-, 14-, 12-Bit, Six-Channel, Simultaneous
Sampling. Retrieved from http://focus.ti.com/lit/ds/symlink/ads8558.pdf.
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[14 ] Moscovici, A. (2001).High Speed A/D Converters. Kluwer Academic Publishers.
[15] Maxim Integrated Product. (2009). Retrieved from http://para.maxim-
ic.com/en/search.mvp?fam=fast_adc&hs=1.
[16] GlobalSpec. (1999-2009 ). Specialty Data Acquisition and Convertor Chips. Retrieved fromhttp://semiconductors.globalspec.com/SpecSearch/Suppliers/Semiconductors/Analog_Mixed_Si
gnals/Data_Acquisition_Chips/Specialty_Data_Acquisition_Converter_Chips.
[17] Blanchard, B. S., & Fabrycky, W. J. (2006). Systems engineering and Analysis. New Jersey:
Prentice Hall.
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AppendixA
CMOSSwitchRon
ToestimatetheRonresistanceofCMOSswitchfollowingcircuitasshowninfigure3isused.TheDc
operatingconditionissimulatedandresultsaretabulatedintable1.
Figure1. CMOSSwitchRonSchematic
Current1uA
VinV NMOSRon PMOSRon CMOSRon
0.00E+00 3.4150E+03 1.6910E+11 3.4150E+03
1.00E01 3.6280E+03 4.9170E+09 3.6280E+03
2.00E01 3.9870E+03 1.5030E+08 3.9869E+03
3.00E01 4.7050E+03 5.3350E+06 4.7009E+03
4.00E01 6.6680E+03 2.9910E+05 6.5226E+03
5.00E01 1.5610E+04 4.1520E+04 1.1345E+04
6.00E01 1.0230E+05 1.5260E+04 1.3279E+04
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7.00E01 1.8580E+06 9.4920E+03 9.4438E+03
8.00E01 5.1810E+07 7.3410E+03 7.3400E+03
9.00E01 1.6300E+09 6.2470E+03 6.2470E+03
1.00E+00 5.3440E+10 5.5860E+03 5.5860E+03
Table1RonResistanceofCMOSswitch
MOScharacteristics
NMOS
Characteristics
Thefigure2isschematicforcircuitsimulation,andtheoutputcharacteristicsofNMOSsareplottedin
figure3.Thedrainstosourcecurrentsarealmostconstantwhentransistorsareinsaturationregion(for
currentslowerthan30uA).Forhighercurrents,thelengthmodulationeffectissignificant.
Figure2.Circuitforsimulatingoutputcharacteristics
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Figure3. OutputcharacteristicsofNMOStransistor
PMOSCharacteristics
Thefigure4isschematicforcircuitsimulation,andtheoutputcharacteristicsofPMOSsareplottedin
figure5.
Figure4. SchematictomeasureoutputcharacteristicsofPMOS
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Figure5.OutputCharacteristicsofPMOStransistor
Transconductanceparameter
Kn(transconductanceparameterforNMOS)andKp(transconductanceparameterforPmos)are
calculatedfromperformingcircuitsimulationasshowninfollowingfigure4.Thegraphical
presentationisshowningraph1andgraph2.TheKnisapproximately148uA/V2andKpis
approximately78uA/V2 for45CMOStechnology.
Figure6. SchematictofindKnand KpforNMOSandPMOSrespectively
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Graph1. Kn vsL(lengthinnm)fordifferentvalueof W(widthinnm)forNMOS
Graph2KpvsL(lengthinnm)fordifferentvalueofW(widthinnm)forPMOS
0
50
100
150
200
250
300
45 90 135 180
K
n
Lnm
KnvsLKn(w=67.5nm)
Kn(w=135nm)
Kn(w=202.5nm)
Kn(w=270nm)
0
20
40
60
80
100
120
45 90 135 180
K
p
L nm
KpvsLKp(W=67.5nm)
Kp(w=135nm)
Kp(w=202.5nm)
Kp(w=270nm)
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AppendixB
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