Inverter-based noise-shaping SAR ADC for low-power applications

Noise-Shaping (NS) Successive-Approximation (SAR) Analog-to-Digital Converters (ADCs) are one of the most heavily researched ADC topologies in recent years. This high attention is attributed to the advantages of the NS SAR architecture that combines the merits of Sigma Delta and SAR converters. However, the implementation of the NS SAR loop-filter in a passive or an active form imposes challenging tradeoffs among power dissipation, adequacy for scaling with technology, performance, and robustness against process-voltage-temperature (PVT) variations. In this work, a NS SAR ADC realization, based on inverter-based amplification, is proposed that alleviates these design challenges. The proposed implementation is used to design two ADCs in 28 nm CMOS technology to demonstrate its effectiveness. The first ADC employs an active loop-filter and achieves a signal-to-noise-plus-distortion (SNDR) of 62.9 dB, at a sampling frequency of 90 MHz, and an oversampling ratio (OSR) of 4, while consuming 0.59 mW from a 0.9 V supply. The second ADC has a passive loop-filter and provides 61 dB of SNDR for the same OSR and sampling frequency, with 0.58 mW power dissipation.