A 10-bit 120-MS/s SAR ADC With Reference Ripple Cancellation Technique Yi Shen , Xiyuan Tang , Student Member , IEEE, Linxiao Shen , Student Member , IEEE, Wenda Zhao , Student Member , IEEE, Xin Xin, Shubin Liu, Zhangming Zhu , Visvesh S. Sathe, Member , IEEE

Abstract

This article presents a reference ripple cancella- tion technique for high-speed successive approximation regis- ter analog-to-digital converters (SAR ADCs) to address the reference voltage settling issue. Unlike prior techniques that aim to minimize the reference ripple, this article proposes a new perspective: it provides an extra path for the full-sized reference ripple to couple to the comparator but with an opposite polarity, so that the effect of the reference ripple is canceled out, thus ensuring an accurate conversion result. To verify the proposed technique, a prototype 10-bit 120-MS/s SAR ADC is fabricated in a 40-nm CMOS process. The proposed ripple cancellation technique improves the signal-to-noise and distortion ratio (SNDR) by 8 dB and reduces the worst case integrated non-linearity (INL)/differential non-linearity (DNL) by ten times. Overall, the ADC achieves an SNDR of 55 dB with only 3-pF reference decoupling capacitor.