Photoconductive photodiode built-in test (bit)

Abstract

A Built-In Test (BIT) for a photoconductive photodiode is performed using the health or characteristics of the photodiode's parasitic capacitance as a 'proxy' for the health or characteristics of the photodiode itself. A failure or degradation of the photodiode manifests as a similar failure or degradation of the parasitic capacitance. Under normal operating conditions, the photoconductive photodiode responds to incident photons from a target by generating a photocurrent signal at its cathode. A processor processes the signals from one or more photodiodes to evaluate characteristics of the target. To perform the BIT, a time-varying voltage signal is applied at the photodiode's anode. This signal is coupled through the parasitic capacitance to produce a test current signal at the photodiode's anode. The processor processes the signal to evaluate the health or characteristics of the parasitic capacitance and thus the photodiode.