Research and System Design of Weak Photocurrent Detection Technology Based on Two-Dimensional Position Sensitive Detector

Aiming at the two-dimensional position sensitive detector(2D PSD) output photocurrent with the characteristics of low signal strength and large noise interference, this paper studies the position measurement principle of 2D PSD, analyzes the noise sources in the circuit, and uses hardware and software filtering to suppress the noise, and designs a weak photocurrent detection device for 2D PSD. The 4-channel weak photocurrent output from PSD is first converted into voltage by I/V conversion circuit, and after hardware filtering, the AD conversion circuit is designed to convert the analog signal into digital signal and pass it to FPGA, which performs mean value filtering and coordinate solving on the 4-channel input signals at the same time, and ultimately transmits the spot position information to the upper computer and drives the VGA display for displaying. In order to verify the performance of the system, the weak current detection performance and the position detection performance of 2D PSD were tested respectively, and the results show that the system can detect weak current signals at the nano-ampere level, and the repeatability of the position measurement reaches 1μm, with a high position detection accuracy.