A 16-mW 8-Bit 1-GS/s Digital-Subranging ADC in 55-nm CMOS

This paper presents a digital-subranging (sub-R) analog-to-digital conversion (ADC) architecture to improve the operation speed of sub-R ADCs. Long latency between coarse and fine conversions will slow down the conventional sub-R ADCs. The proposed digital-sub-R uses digital circuits to implement the sub-R function and shorten this latency, thus benefits the CMOS scaling. Furthermore, the dynamic comparators are used to save more ADC power consumption. Their accuracy is improved by the proposed pseudodifferential offset calibration loop. The digital-sub-R also helps to reduce the dynamic offset of the fine comparators caused by the input common-mode variation. Fabricated using a 55-nm CMOS technology, the reported 8-bit 1-GS/s ADC consumes only 16 mW from a 1.2 V supply. Measured signal-to-noise ratio (SNR) and spurious free dynamic range (SFDR) are 46 and 55 dB, respectively. Measured effective number of bits (ENOB) is seven bits at 10-MHz input frequency. At Nyquist input, the ENOB performance of 6.3 bits is still maintained. Its figure-of-merit is 197-fJ/conversion-step.