Nyquist-rate ADCs

87 Pages·2012·1.69 MB·English

Erik Jonsson School of Engineering & Computer Science
Recent Advances in Multistep
Nyquist ADC’s
Yun Chiu
Erik Jonsson Distinguished Professor
University of Texas at Dallas
Performance vs. Energy
Efficiency
MWSCAS, 8/5/12 - 2 - © Y. Chiu
Walden Figure-of-Merit (FoM) for ADC
 V nT 
·· D n = 2N  in s 
· out
V
 
ref
P  Joule 
FoM 
 
2BW 2ENOB Conversion - Step
 
FoM “measures” energy efficiency
• P = power consumption
• ENOB = effective number of bits
• BW = min(f /2, ERBW)
s
Ref. [1]
• ERBW = effective resolution BW
MWSCAS, 8/5/12 - 3 - © Y. Chiu
How to compare ADC performance?
• Higher performance with lower cost is the
obvious criterion for comparison
– ADC performance: speed (sample rate) or
bandwidth, resolution
– ADC cost: power consumption, die size
Q: how to define performance quantitatively?
MWSCAS, 8/5/12 - 4 - © Y. Chiu
Definition of PERFORMANCE
• Bandwidth (or speed) performance
– BW = min(f /2, ERBW)
s
• Resolution (or precision) performance
– Effective number of bits (ENOB), or equivalently
effective number of steps (ENOS) = 2ENOB
• Separately, it is easy. But how to combine the
two in one merit? Just take the product?
MWSCAS, 8/5/12 - 5 - © Y. Chiu
Definition of PERFORMANCE
• 2×BW  2×Power, 2×Area (same ENOS) 
Power, area scale linearly with bandwidth
• 2×ENOS  4×Power, 4×Area (same BW) 
Power, area scale quadratically with precision
(for thermal noise or matching limited design)
Power, Area  BW,
Power, Area  ENOS2
MWSCAS, 8/5/12 - 6 - © Y. Chiu
Definition of PERFORMANCE
Power & Area  BW,  ENOS2
Definition:
Performance = 2BW ENOS2
Hz Step2 
 
= 2BW  4ENOB
 
2BW = f 10log 4ENOB = SNR
sample 10
This definition avoids penalizing high-SNR works as Walden FoM does
MWSCAS, 8/5/12 - 7 - © Y. Chiu
Definition of ENERGY EFFICIENCY
Power & Area  BW,  ENOS2
Definition:
P
Energy Efficiency =
2BW ENOS2  J 
 
P Step2
 

2BW  4ENOB
Note: PerformanceEnergy Efficiency
P
= 2BW 4ENOB  =Power
2BW 4ENOB
MWSCAS, 8/5/12 - 8 - © Y. Chiu
Performance–Efficiency (PE) Chart
Constant performance
n
B g
O
i
N s X·Y = Power
E e
4 d
W· st e Con
e c st
B ) B n ant-
2· e a po
= al m cy wer h
nce g sc ncy erfor cien yperbola
ma (lo cie P Effi
i
f
r f
o e
f t Po
r n w
e a er
P t
s
n
o
C
(log scale)
Energy Efficiency = Power/(2·BW·4ENOB)
MWSCAS, 8/5/12 - 9 - © Y. Chiu
Pipeline ADC PE Chart (< 2005)
ISSCC & VLSI data
]
2
p
e
t
S
·
z
H
[
e
c
n
1W
a
m
r
o 100mW
f
r
e
P
10mW
1mW
1μW 10μW 100μW
Efficiency [J/Step2]
MWSCAS, 8/5/12 - 10 - © Y. Chiu