Research on dark level correction method for CMOS image sensors

Abstract

To obtain higher imaging quality, the dark level generated during the operation of CMOS image sensors (CIS) needs to be corrected. In this paper, a dark level correction circuit is designed based on a 4 T active pixel, which includes a dark current cancellation circuit and a switched capacitor amplifier circuit. First, the dark current is collected in real time by using the dark pixels in the periphery of the face array, and the dark current noise is read out and differed from the image signals output from the columns to obtain a more accurate output signal, thus eliminating the dark level caused by the dark current. Then the switched-capacitor amplifier is used to collect and amplify the signals to facilitate the subsequent ADC processing. Based on the 110 nm process for the proposed method of specific circuit design verification, the verification results show that the dark level correction circuit designed in this paper through a real-time sampling of the dark pixels of the periphery of the array can be reduced to the exposure stage of the dark current noise to more than 85% of the original.