一种用于CMOS图像传感器的采用伪多重采样和校准的分辨率可重构SAR ADCOA

This paper presents a resolution reconfigurable two-step successive approximation register analog-to-digital(A/D)converter(ADC)with the pseudo-multiple sampling(PMS)and gain error calibration method for CMOS image sensors.The proposed ADC can be configured with 10-bit,11-bit and 12-bit by adjusting the number of 10-bit A/D conversions,thereby satisfying various demands in different situations.The PMS method enables the attainment of high-resolution ADC results by summing the conversion outputs of several low-resolution ADCs,thereby reducing the number of unit capacitors and the area of the capacitor array.A compensation technique is proposed to expand the quantization range and improve the effective resolution of the proposed ADC.A calibration method suitable for bottom-plate sampling is proposed,which reduces the gain error between reference voltages.Simulated in a 55 nm process,the proposed ADC in the 12-bit mode achieves a differential nonlinearity of+0.47/-0.50 least significant bit(LSB)and an integral nonlinearity of+0.75/-0.84 LSB at a sampling frequency of 3.497×105 per second with the calibration.The effective number of bits reaches 11.63 bits.The area occupied by a single ADC column is 39.5 µm×119.2 µm and the power consumption is 62.8 µW.