Infrared focal plane with automatic responsivity control using photodetector bias modulation

摘要

Automatic responsivity control for an array of infrared photodetectors is provided without additional hardware such as a beam chopper or a reference object of known irradiance. The requisite modulated reference signal is provided instead by uniformly modulating the bias voltage applied to each of the plurality of photodetectors in the array. Photodetectors having different responsivities respond to the same bias modulation differently to produce a superimposed sinusoidal component in the photodetector output current which is used to compensate for differences in responsivities of the individual photodetectors. For this purpose, an automatic responsivity control circuit selects the superimposed sinusoidal component from the photodetector output current corresponding to the frequency of the reference signal modulating the bias voltage, and compares the amplitude of the selected sinusoidal component with a reference level to adjust the amplification at the photodetector output in accordance with this comparison, so that the amplified outputs from the plurality of photodetectors respond uniformly to the sinusoidal reference signal applied as a bias voltage to the photodetectors.