Improving injection efficiency of gate modulation ROIC interface for HgCdTe IR photodiodes

Abstract

A new interface circuit for readout of HgCdTe Infrared photodiodes is proposed that can be used for efficient transfer of photocurrent from the photodiodes to the integration capacitor of the readout integrated circuit (ROIC). This ultimately results in high sensitivity and improved IR images. A high gain amplifier in the feedback path between gate and drain of the input transistor of standard gate modulation interface circuit has been introduced and the circuit has been simulated using SPICE circuit simulator with SCL 0.18 µm standard CMOS technology and the sub-circuit model of HgCdTe photodiodes. The circuit enhances the effective input conductance of interface node by orders of magnitude. This not only improves the bias stability but also enhances the charge injection efficiency even for low dynamic resistance photodiodes, making it suitable for SWIR to VLWIR HgCdTe photodiodes. We have shown that for the detectors of low dynamic resistance, such as ~1 MΩ, the injection efficiency better than 99.999 % can be achieved by using the proposed circuit.