15.4b incremental sigma-delta capacitance-to-digital converter with zoom-in 9b asynchronous SAR

An incremental zoom-in capacitance-to-digital converter (CDC) is proposed. By using a 9b SAR, the OSR can be reduced to only 32, significantly improving conversion energy. We show how the OTA in the SAR is bypassed for the CDC further reducing energy and propose a novel matrix based 512-element unit-cap structure for dynamic element matching. The CDC achieves 94.7dB SNR and 33.7µW power consumption with 175fJ/conv-step at 1.4V supply.