微光CMOS图像传感器读出电路研究

摘要

High performance signal readout circuit is the important component of low-light-level COMS image sensor. How to reduce the readout circuit noise and improve output signal noise radio is the emphasis of the circuit design. This paper projects a kind of readout circuit for low-light-level photo detector with high gain, low noise Capacitive Trans impedance Amplifier and Correlated Double Sampling circuit. CTIA circuit uses a switched capacitor voltage divider feedback circuit to achieve high sensitivity and low read noise. The circuit is fabricated with CSMC 0.5μm CMOS technology, measurement results show that the circuit function is fine when the integratedtimeis 20μs and the light signal current is 20pA~300pA. The SNR reaches 10;it can be used in low-light-level CMOS Image Sensor.%高性能的信号读出电路是微光CMOS图像传感器的重要组成部分，如何降低读出电路噪声，提高读出电路输出信号的信噪比成为读出电路设计的重点。本文设计了一种高增益低噪声的电容反馈跨阻放大器CTIA（Capacitive Trans impedanceAmplifier）与相关双采样电路CDS （Correlated Double Sampling）相结合的微光探测器读出电路。在CTIA电路中，采用T网络电容实现fF级的积分电容，并通过增益开关控制，来达到对微弱光信号的高增益低噪声读出。采用CSMC公司的0.5μm标准CMOS工艺库对电路进行流片，测试结果表明：在光电流信号为20~300 pA范围内，积分时间为20μs，该电路功能良好，信噪比（SNR）达到10，能应用于微光CMOS图像传感器。