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