An Energy-Efficient Time-Domain Incremental Zoom Capacitance-to-Digital Converter
Xiyuan Tang, Shaolan Li, Xiangxing Yang, Linxiao Shen, Wenda Zhao, Randall P. Williams, Jiaxin Liu, Zhichao Tan, Neal A. Hall, David Z. Pan, Nan Sun
Abstract
This article presents an incremental two-step capacitance-to-digital converter (CDC) with a time-domain ΔΣ modulator (TDΔΣM). Unlike the classic two-step CDCs, this work replaces the operational transconductance amplifier (OTA)-based active-RC integrator by a voltage-controlled oscillator (VCO)-based integrator, which is mostly digital and low-power. Featuring the infinite dc gain and intrinsic quantization in phase domain, this TDΔΣM enables a CDC design achieving 76-dB SNDR while requiring only a first-order loop, and a low oversampling ratio (OSR) of 15. Fabricated in 40-nm CMOS technology, the prototype CDC achieves a resolution of 0.29 fF while dissipating only 0.083 nJ/conversion, which improves the energy efficiency by over two times comparing to the similar performance designs.