Photoconductive photodiode built-in test (BIT)
First Claim
1. 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.
1 Assignment
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Accused Products
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.
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Citations
20 Claims
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1. A detector, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A detector, comprising:
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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 capacitor having a first side coupled to the photodiode'"'"'s anode and a second side; a MOSFET device having a gate, a first contact coupled to the second side of the capacitor and a third contact coupled to first reference voltage; and a resistor coupled between said first contact and a second reference voltage to bias the MOSFET in an off state, wherein said MOSFET device is responsive to a test voltage pulse applied to its gate to switch to an on state for the duration of the pulse to produce a voltage pulse that is coupled through the capacitor to the anode of the photodiode and through a parasitic capacitor between the photodiode'"'"'s anode and cathode to produce a test current pulse at the photodiode'"'"'s cathode, said processor processing the voltage signal produced by the test current pulse to provide a measure of the health or characteristics of the parasitic capacitor as a proxy for the health or characteristics of the photodiode. - View Dependent Claims (15, 16)
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17. A detector for use with a pulsed laser that illuminates a target, comprising:
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a plurality of photodiodes in an array reverse-biased between a common anode at a negative bias voltage and respective cathodes at positive bias voltages to operate in a photoconductive mode in which incident photons from a pulsed laser spot reflected off of the target onto the array of photodiodes produce photocurrent pulses at the photodiodes'"'"' cathodes; a plurality of transimpedance stages that convert the respective photocurrent pulses to respective voltage pulses; a processor that processes the voltage pulses to compute the position of the laser spot on the array to provide a bearing to a target; and a built-in test (BIT) circuit comprising; a circuit element coupled to the photodiodes'"'"' common anode; a solid-state switch coupled to the circuit element, said switch responsive to a test voltage pulse to produce a voltage pulse that is coupled through the circuit element to the common anode and through respective parasitic capacitors between each photodiode'"'"'s anode and cathode to produce test current pulses at the photodiodes'"'"' cathodes, said processor processing the plurality of voltage pulses produced by the test current pulses to provide a measure of the health or characteristics of the parasitic capacitors as proxies for the health or characteristics of the photodiodes. - View Dependent Claims (18, 19)
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20. A method of performing a built-in test (BIT) on a photodiode, comprising:
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reverse biasing the photodiode to operate in a photoconductive mode in which incident photons on the photodiode produce a photocurrent signal at the photodiode'"'"'s cathode; converting the photocurrent signal to a voltage signal; processing the voltage signal to characterize the photons incident on the photodiode; and in response to a BIT request, applying a time-varying voltage signal at the anode of the photodiode, said time-varying voltage signal coupled through a parasitic capacitor between the photodiode'"'"'s anode and cathode to produce a test current signal at the photodiode'"'"'s cathode; converting the test current signal to a test voltage signal; and processing the test voltage 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.
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Specification