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A current mirroring integration based readout circuit for high performance infrared FPA applications

This paper reports a current mirroring integration (CMI) CMOS readout circuit for high-resolution infrared focal plane array (FPA) applications. The circuit uses a feedback structure with current mirrors to provide stable bias voltage across the photodetector diode, while mirroring the diode current to an integration capacitor. The integration capacitor can be placed outside of the unit pixel, reducing the pixel area and allowing to integrate the current on larger capacitance for larger charge storage capacity and dynamic range. The CMI unit cell allows almost rail-to-rail voltage swing on the integration capacitance for low voltage operation. The detector bias voltage can be adjusted independently for various detector requirements-By virtue of current feedback in the CMI structure, very low (ideally zero) input impedance is achieved. The unit-cell contains just nine MOS transistors and occupies 20 mum x 25 mum area in a 0.8-mum CMOS process. The CMI circuit provides a maximum charge storage capacity of 5.25 x 10(7) electrons and a maximum transimpedance of 6 x 10(7) Omega for a 5 V power supply and 2 pF off-pixel integration capacitance.