Patent ID: 8290726

Claim:
A detector, comprising: a photodiode reverse-biased to operate in a photoconductive mode in which incident photons on the photodiode produce a photocurrent signal at the photodiode's cathode; a transimpedance stage that converts the photocurrent signal to a voltage signal; a processor that processes the voltage signal to characterize the photons incident on the photodiode; and a built-in test (BIT) circuit comprising: a circuit element coupled to the photodiode's anode; a solid-state switch coupled to the circuit element, said switch responsive to a control signal to produce a time-varying voltage signal that is coupled through the circuit element to the anode of the photodiode and through a parasitic capacitor between the photodiode's anode and cathode to produce a test current signal at the photodiode's cathode, said processor processing the voltage signal produced by the test current signal to provide a measure of the health or characteristics of the parasitic capacitor as a proxy for the health or characteristics of the photodiode.