A Low Voltage and Low Power 10-bit Non-Binary 2b/Cycle Time and Voltage Based SAR ADC

Jian Luo, Yang Liu, Jing Li, Ning Ning, Kejun Wu, Zhen Liu, Qi Yu

Abstract: This paper proposes a low power 10-bit 2b/cycle time and voltage based-successive approximation register (SAR) analog-to-digital converter (ADC). At low supply voltage, there will be a significant difference in comparator decision time for different input voltages. By taking advantage of the fact, this ADC converts the reference voltage to the corresponding comparator decision time, achieving 2b/cycle quantization to improve the conversion speed. In addition, by obtaining reference delays with duplicated circuits and using non-binary capacitor arrays, the ADC can tolerate process, voltage and temperature (PVT) variations and decision errors. To validate these concepts, a 10-bit 2MS/s SAR ADC is designed using 130nm CMOS process with 0.5V power supply voltage. Measured results show that the ADC can work normally from 0.5V to 1V supply voltage, with the sampling rate increasing from 2MS/s to 32MS/s. The ADC achieves an SNDR (signal-to-noise distortion ratio) of 56.7dB, corresponding to an ENOB (effective number of bits) of 9.13 bits and consumes <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.4\mu \text{W}$ </tex-math></inline-formula> , resulting in a figure of merit (FoM) of 3.03 fJ/c.-s at 0.5V supply voltage and 2MS/s sampling rate.