Abstract: 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.