An Oversampling SAR ADC With DAC Mismatch Error Shaping Achieving 105 dB SFDR and 101 dB SNDR Over 1 kHz BW in 55 nm CMOS

Abstract

The successive-approximation-register (SAR) architecture is well known for its high power efficiency in medium-resolution analog-to-digital converters (ADCs). However, when considered for high-precision applications, SAR ADCs suffer from non-linearity resulting from capacitor mismatch and limited dynamic range due to comparator noise. This work presents a mismatch error shaping (MES) technique for oversampling SAR ADCs to achieve 105 dB in-band SFDR without calibration. The capacitor mismatch error is first-order high-pass filtered by simply delaying the reset of LSB capacitor array after sampling. The comparator thermal and flicker noise are also first-order shaped to high frequencies by noise shaping. The prototype in 55 nm CMOS occupies 0.072 mm² and achieves a peak SNDR of 101 dB over 1 kHz bandwidth. It consumes 15.7 $\mu \text {W}$ from a 1.2 V supply at 1 MS/s and can be configured to Nyquist mode up to 5 MS/s. These features enable the application of SAR ADCs in high-precision, multi-purpose sensor readout interfaces.