A dual-exposure in-pixel charge subtraction CTIA CMOS image sensor for centroid measurement in star trackers

In this work, we present a CMOS image sensor for star centroid measurement in star trackers. The analysis of the star tracker system shows that long integration will cause "tail effect" in the star image. It significantly reduces the signal magnitude, which in turn increases the centroiding errors. In order to capture limited photons generated from dim stars within shortened integration time, we propose a new capacitive transimpedance amplifier (CTIA) pixel architecture with a small integration capacitor. On the other hand, bright stars can easily saturate the pixels, which can also induce significant measurement errors. To avoid pixel saturation, the pixel is able to perform in-pixel charge subtraction based on photocurrent thresholding. In order to validate the pixel design, we have fabricated a test chip consisting of a 4×4 pixel array using Global Foundry 65 nm mixed signal CMOS process.