A 12-bit SAR ADC with a reversible VCM-based capacitor switching scheme

Abstract

A low-power 12-bit 10 MS/s successive approximation register (SAR) analog-to-digital converter (ADC) with a reversible VCM-based capacitor (RVC) switching scheme is presented in this paper. The switching power consumption of the proposed scheme is 95% and 62.3% lower than that of conventional and VCM-based capacitor switching schemes, respectively. The use of a segmented DAC structure reduces the size of the largest capacitor from 211 unit capacitors in the conventional capacitor array to 24 unit capacitors. This 75% reduction in the capacitor area decreases the settling time of the DAC capacitor network as well as requirements on the bandwidth and driving capability of the reference source VREF. An ADC prototype with an active area of 0.218 mm2is fabricated in 180-nm 1P6M CMOS process. With supply of 1.8 V and sampling rate of 10 MS/s, the ADC achieves a signal-to-noise and distortion ratio (SNDR) of 58.9 dB and consumes power of 0.36 mW, yielding a figure of merit (FOM) of 59.8fJ/conversion-step.