Current Reference Pre-Charging Techniques for Low-Power Zero-Crossing Pipeline-SAR ADCs

Current pre-charging techniques are introduced to generate the reference in MDACs of pipeline ADCs. They are specifically applied to zero-crossing-based (ZCB) pipeline-SAR ADCs in this paper. The proposed reference pre-charge technique relaxes power and area requirements for reference voltage generation and distribution in ZCB Pipeline ADCs, by eliminating power-hungry low-impedance reference voltage buffers. Dynamic reference loading (DRL), a variant of current reference pre-charging, is further proposed to reduce the loading due to the reference capacitors leading to improvements in the ADC noise performance. A proof-of-principle reference pre-charged DRL ZCB Pipelined-SAR ADC, implemented in 65 nm CMOS, shows an SFDR/SNR/SNDR of 77 dB/70 dB/66 dB at 25 MHz, while consuming 4.8 mW at 50 MS/s for an FOM of 57 fJ/step. The ADC does not require any additional power and/or area for reference voltage generation and distribution.