Lecture 18 ADC Figures of Merit ADC Rearch
Boris Murmann Stanford University murmann@stanford.edu
Copyright © 2006 by Boris Murmann
B. Murmann
EE 315 Lecture 18
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ADC Figures of Merit (1)
• • • • • Objective – Want to compare performance of different ADCs Can u FOM to combine veral performance metrics into one single number What are reasonable FOM for ADCs? How can we u and interpret them? Trends?
B. Murmann
EE 315 Lecture 18
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ADC Figures of Merit (2)
[R. H. Walden, "Analog-to-digital converter survey and analysis," IEEE Journal on Selected Areas in Communications, April 1999]
FOM 1 = f s ⋅ 2
ENOB
• •
This FOM suggests that adding a bit to an ADC is just as hard as doubling its bandwidth Is this a good assumption?
B. Murmann
EE 315 Lecture 18
水平对齐3
Survey Data
1bit/Octave
[Walden, "Analog-to-digital converter survey and analysis," IEEE J. Selected Areas Comm., April 1999]豆角用英语怎么说
B. Murmann
EE 315 Lecture 18
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ADC Figures of Merit (3)
f ⋅ 2 ENOB FOM 2 = s Power
[R. H. Walden, "Analog-to-digital converter survey and analysis," IEEE Journal on Selected Areas in Communications, April 1999]
• • •
Sometimes inver of this metric is ud In typical circuits power ~ speed – FOM2 captures this tradeoff correctly How about power vs. ENOB? – One additional bit = 2x in power?
B. Murmann
EE 315 Lecture 18
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ADC Figures of Merit (4)
• In a circuit that is limited by thermal noi, each additional bit in – 6dB SNR, 4x less noi power, 4x bigger C – Power ~ Gm ~ C increas 4x Even wor: Flash ADC – Extra bit means 2x number of comparators – Each of them needs double precision – Transistor area 4x, Current 4x to maintain current density – Net result: Power increas 8x
•
B. Murmann
EE 315 Lecture 18
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ADC Figures of Merit (5)
宁夏考试网
• FOM2 in inappropriate for comparing ADCs that are limited by matching or thermal noi – Still the most widely ud FOM "Tends to work" becau not all power in an ADC is noi limited – E.g. Digital power, biasing circuits, etc. To better capture the ca of noi limited circuits, one could u 22ENOB in the numerator – But how about other (non-noi limited) circuits? My suggestion – Avoid using a FOM that assumes a fixed relationship between ENOB and power
•
•
桂花有几个花瓣•
B. Murmann
EE 315 Lecture 18
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ADC Figures of Merit (6)
FOM 3 = Power Conversion Bandwidth
• •
Compare only power of ADCs with approximately same SNR or SNDR (ENOB) Uful numbers (~state-of-the-art):
– 10b (~9 ENOB) ADCs: 1...2 mW/MHz – 12b (~11 ENOB) ADCs: 6...8 mW/MHz拟病毒
B. Murmann
EE 315 Lecture 18
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Trend in ADC Power Dissipation
1.E+06
1.E+05
P/BW [pJ]
1.E+04
1.E+03左手投篮
ISSCC 1998-2001 ISSCC 2002-2005 ISSCC 2006 (OS)
1.E+02
ISSCC 2006 (NYQ) Fit (ISSCC 2002-2005) Fit (ISSCC 1998-2001)
1.E+01 30 40 50 60 70 SNR [dB] 80 90 100 110
•
How much more improvement can we hope for?
EE 315 Lecture 18 9
B. Murmann
Power Limits in "Conventional" ADCs
1.E+06
1.E+06
1.E+05 1.E+05 1.E+04 1.E+04
P/BW [pJ]
P/fsig [pJ]
1.E+03 1.E+03 1.E+02 1.E+02
1.E+01 1.E+00 1.E-01
1.E+01 1.E+00 1.E-01 1.E-02
ISSCC 1998-2001 ISSCC 2002-2005 ISSCC 1998-2001 ISSCC2006 ISSCC 2002-2005 SC-Stage I
SSCC 2006 (OS) Pipeline ISSCC 2006 (NYQ) SC-Stage Gm-C Stage Pipeline Flash Gm-C Stage Fit (ISSCC 2002-2005) Flash Fit (ISSCC Fit1998-2001) (ISSCC 2002-2005)
Fit (ISSCC 1998-2001)
1.E-02 30
30
40
40
50
50
60
60
70 70 SNR [dB]
80
80
90
90
100
110
主观唯物主义100 110
作文万能开头
SNR [dB]
[B. Murmann, "Limits on ADC Power Dissipation," in Analog Circuit Design, Springer, 2006]
B. Murmann EE 315 Lecture 18 10
