20.3 A 50MHz-Bandwidth 70.4dB-SNDR Calibration-Free Time-Interleaved 4th-Order Noise-Shaping SAR ADC

Noise-Shaping SAR (NS-SAR) is an emerging ADC architecture that offers both high resolution and high energy efficiency. State-of-the-art NS-SAR ADCs eliminate the need for op-amps, which relaxes design complexity and technology scaling issues. However, existing NS-SAR ADCs, with high FoM, are limited in bandwidth [1, 2] (typically in the MHz range). This makes NS-SAR ADCs unsuitable for applications that need bandwidths in the tens of MHz range, such as wireless communications. Traditionally, high-bandwidth, high-resolution applications utilize pipeline or continuous-time sigma-delta (CT-SD) ADCs, but these architectures are much more power hungry than the NS-SAR. Thus, to increase the bandwidth of NS-SAR ADCs and extend their low-power advantages, this work presents a new time-interleaved noise-shaping SAR (TINS-SAR) architecture that enables higher bandwidth. Although time-interleaving of ADCs is difficult for high resolution, interleaving impairments can be avoided when combining interleaving with noise-shaping. Our prototype 40nm CMOS TINS-SAR ADC has a measured SNDR of 70.4dB for a 50MHz bandwidth without calibration. It consumes only 13mW and occupies 0.061mm
²
, making it a potential substitute for CT-SD ADCs.