A readout circuit for QWIP infrared detector arrays using current mirroring integration

This paper reports a current mirroring integration (CMI) CMOS readout circuit for high-resolution Quantum Well Infrared Photodetectors (QWIPs). The circuit uses a feedback structure with current mirrors to provide stable bias voltage across the photodetectors, which can be adjusted between 0 V and 3.5V. The photodetector current is mirrored to an integration capacitor which can be placed outside of the unit pixel, reducing the pixel area and allowing to integrate the current on larger capacitances for larger charge storage capacity and dynamic range. With the current feedback in the CMI structure, very low (ideally zero) input impedance is achieved. The readout circuit integrated with CMI provides a maximum charge storage capacity of 170x10(6) electrons and a maximum transimpedance of 17.6x10(6) for a 5 V power supply and 6.8 pF off-pixel integration capacitance. A 64x64 FPA circuit prototype has been implemented in a 0.8 mum CMOS process and hybrid connected to a 64x64 QWIP FPA. The fabricated chip has 38 mum pixel pitch and results in a total chip area of 3.2mmx4.0mm. The operation of the fabricated circuit together with QWIP FPA is verified. The measured dynamic range of the circuit is more than 96 dB for maximum charge storage case and non-linearity of the circuit is smaller than 4 Least Significant Bit (LSB) for 10-bit resolution.