A Calibration-Free Time-Interleaved Fourth-Order Noise-Shaping SAR ADC

Abstract

Noise-shaping SAR (NS-SAR) is an emerging analog to digital converter (ADC) architecture that offers both high- resolution and high-energy efficiency. Despite these advantages, oversampling limits the useful bandwidth of NS-SAR ADCs. This article introduces a robust and practical interleaving architecture that overcomes this bandwidth limitation. Midway feedback to multiple successive-approximation conversion phases enables a realizable time-interleaved noise-shaped (TINS) system. The inherent delay between channels is harnessed to generate a high- order noise-transfer function (NTF). Redundancy and optimiza- tion of the NTF coefficients eliminate the risk of quantization overload, ensuring robust operation. Error feedback (EF) is realized with a summing pre-amplifier and a shared feedback bus, keeping the architecture simple. Thanks to the low required gain, the pre-amplifier is simply implemented as a single-stage open-loop amplifier. A prototype 40-nm CMOS TINS-SAR ADC has a measured SNDR of 70.4 dB for a 50-MHz bandwidth. It consumes only 13 mW and occupies 0.06 mm 2.T e s t i n go f several devices and evaluation over temperature and supply variations demonstrate robust performance without calibration.