Offset-free Column Buffer for CMOS image sensor

Abstract

A new column buffer circuit with improved offset mismatch and charge sharing for CMOS image sensor is proposed in this paper. Based on the bottom plate sampling and fixed common level method, this novel design can avoid the offset non-uniformity of the two buffers. Also, it can restrain the charge sharing caused by the varied operating point by using a single buffer and switched capacitor technique. The proposed techniques are experimentally verified in a 1024 × 1024 prototype chip using 55nm low power CMOS process. The simulation results show that the linear range is extended by 20%, and the improved photo response non-uniformity is up to 1.16%.