Very wide dynamic range SWIR sensors for very low background applications

This paper describes a high performance 320 by 256 readout integrated circuit (ROIC) designed for P-on-N short wave infrared (SWIR) detectors including InGaAs and HgCdTe, which also has the ability to operate at low input current levels with N-on-P detectors. The ROIC/FPA will support a wide range of system requirements from very low background applications (nightglow) to daytime high illumination conditions. To accommodate the wide scene dynamic range requirements, two selectable integration capacitors are used to control the input circuit transimpedance gain. A 10fF integration capacitor is used for low noise and low flux levels down to 10(-5) Lambert, corresponding to approximately 2x10(10) ph/cm(2)-sec for 0.9 mu m to 1.7 mu m spectral band using f/1.5 optics, assuming a 2856 Kelvin blackbody distribution. For higher flux levels, a 0.21pF integration capacitor can be selected, thus providing over a factor of 20 dynamic range. A capacitive feedback transimpedance amplifier (CTIA) provides a low noise detector interface circuit capable of operating at low input currents without frame-to-frame image lag. A sample and hold capacitor is also part of the input unit cell architecture, which allows the FPA to be operated in full frame snapshot mode and provides the maximum integration time available. The integration time is electronically controlled (gated) by an external clock pulse, and is adjustable from 0.5 mu sec to approximately the frame time of 33.3msec for 30Hz operation. This produces an additional factor of 66,000 to the total system dynamic range. The combination of integration time control and selectable integration capacitors accommodates over nine orders of magnitude in scene dynamic range.