A 16 bit linear passive-charge-sharing SAR ADC in 55nm CMOS

This paper presents a first reported passive-charge-sharing SAR ADC that achieves 16 bit linearity. It is known that on chip passive-charge-sharing suffers from poor linearity due to the unregulated reference voltage during bit trials. The proposed unique ADC architecture and calibration technique addresses the issue of signal dependent reference voltage droop during SAR ADC bit trials and orthogonalize the bit weights to achieve 16bit linearity. In addition, the proposed architecture maximizes SNR by sampling on to the bit cap, the first reported in this type of SAR ADC. Measurement result from a prototype test chip shows +/-0.8 LSB (16-bit level) INL at 1MSPS.