US3644740A
Expired / Lapsed
US
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Control circuit for biasing a photodetector so as to maintain a selected false alarm rate
Assignee: Raytheon Co
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Filing: 1969-07-22
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Granted: 1972-02-22
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Expires: 1989-07-22
Abstract
Abstract A circuit for controlling the bias supplied to an avalanche photodetector so as to maintain a ''''false alarm'''' rate within acceptable limits, while maximizing the photodetector sensitivity for those limits. The circuit is particularly useful in conjunction with laser-ranging (distance-measuring) equipment in which a timing interval is normally initiated coincident with the transmission of a light pulse and terminated coincident with the receipt of the reflected light pulse. The timed interval is, of course, indicative of the distance of the reflector from the transmitter and receiver. If the detector sensitivity is too high, various forms of noise can produce false alarms, i.e., signals indistinguishable from that attributable to the reflected light pulse. The subject circuit controls the bias on the photodetector to maintain a constant false alarm rate, e.g., 1 percent, during the timing intervals of interest, while permitting the detector sensitivity to be maximized for that rate. The circuit utilizes a pulse shaper which continually responds to input signal excursions exceeding a certain threshold level to control an integrator. If such excursions occur at a rate greater than the desired false alarm rate, the integrator will modify the detector bias to lower its sensitivity. On the other hand, if such excursions occur at a rate lower than the desired rate, the bias is modified to increase the detector sensitivity.
Inventors
- 👤 Burton E Dobratz
- 👤 Robert P Farnsworth
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 17:25
CPC Classifications
H; H10; H10F; H10F77/00; H10F77/95; H10F77/953; H10F77/959; G; G01; G01J; G01J1/00; G01J1/42; G01J1/44; G01S; G01S7/00; G01S7/48; G01S7/483; G01S7/486; G01S7/4861; G01S7/487; G01S7/4873; H03; H03G; H03G11/00; H03G11/04; H03G3/00; H03G3/20; H03G3/30; H03G3/3084; H04; H04B; H04B10/00; H04B10/60; H04B10/66; H04B10/69; H04B10/691; H04B10/6911
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
166 words
1. A circuit for biasing a photodetector so as to substantially maintain a selected false alarm rate, said circuit comprising: threshold means for providing threshold output signals when the signals from said photodetector exceed a predetermined threshold level; a pulse generator coupled to said threshold means for providing current pulses of a predetermined duration in response to said threshold output signals; reference current source means for providing a reference current having an average value which is preselected as a function of said false alarm rate; integrator means for providing an output signal which is a function of the integral of the difference in magnitudes of said current pulses and said reference current; and means responsive to the output signal of said integrator means for applying bias current to said photodetector to cause the sensitivity thereof to decrease when said current pulses occur at a rate in excess of a predetermined rate and increase when said current pulses occur at a rate less than said predetermined rate.
Claim 2
Dependent Claim
166 words
1. A circuit for biasing a photodetector so as to substantially maintain a selected false alarm rate, said circuit comprising: threshold means for providing threshold output signals when the signals from said photodetector exceed a predetermined threshold level; a pulse generator coupled to said threshold means for providing current pulses of a predetermined duration in response to said threshold output signals; reference current source means for providing a reference current having an average value which is preselected as a function of said false alarm rate; integrator means for providing an output signal which is a function of the integral of the difference in magnitudes of said current pulses and said reference current; and means responsive to the output signal of said integrator means for applying bias current to said photodetector to cause the sensitivity thereof to decrease when said current pulses occur at a rate in excess of a predetermined rate and increase when said current pulses occur at a rate less than said predetermined rate.
Claim 3
Dependent Claim
105 words
The circuit of claim 1 adapted for use with a pulsed energy transmission and reception system having an effective maximum range suCh that photodetector output signals, derived from received energy from targets at a greater range than said maximum range, are less than said predetermined threshold level; and wherein said pulse generator is a monostable multivibrator which when triggered by a threshold output signal provides an output current pulse of a duration approximately equal to or greater than the time interval corresponding to the effective maximum range; whereby no more than one current pulse is produced by target signals during each transmission and reception period.
Claim 4
Dependent Claim
44 words
The circuit of claim 1 further comprising a data output terminal; and second threshold means for providing output signals to said data terminal when the signals applied to said second threshold means from said photodetector exceed a level greater than said predetermined threshold level.
Claim 5
Dependent Claim
34 words
The circuit of claim 1 wherein said reference current source means includes a direct current source for providing a reference current having a predetermined magnitude which is a function of said false alarm rate.
Claim 6
Dependent Claim
33 words
The circuit of claim 1 wherein said reference current source means includes a source of current pulses for providing a reference current having an average current value proportional to said false alarm rate.
Claim 7
Dependent Claim
66 words
The circuit of claim 1 wherein said means for applying bias current includes a capacitance element coupled to receive the output signal of said integrator means, and a constant current source coupled to said capacitance element and to said photodetector such that the part of the output current from said constant current source applied to said photodetector is controlled by the charge on said capacitance element.
Claim 8
Dependent Claim
44 words
The circuit of claim 2 further comprising a data output terminal; and second threshold means for providing output signals to said data terminal when the signals applied to said second threshold means from said photodetector exceed a level greater than said predetermined threshold level.
Claim 9
Dependent Claim
34 words
The circuit of claim 2 wherein said reference current source means includes a direct current source for providing a reference current having a predetermined magnitude which is a function of said false alarm rate.
Claim 10
Dependent Claim
66 words
The circuit of claim 3 wherein said means for applying bias current includes a capacitance element coupled to receive the output signal of said integrator means and a constant current source coupled to said capacitance element and to said photodetector such that the part of the output current from said constant current source applied to said photodetector is controlled by the charge on said capacitance element.
Claim 11
Dependent Claim
34 words
The circuit of claim 9 wherein said reference current source means includes a direct current source for providing a reference current having a predetermined magnitude which is a function of said false alarm rate.
Claim 12
Dependent Claim
273 words
A circuit for biasing a photodetector so as to substantially maintain a desired false alarm rate; said circuit being adapted for use in a pulsed energy transmission and reception system having an effective maximum range such that photodetector output signals, derived from received energy from targets at a range greater than said maximum range, are less than a predetermined level; said circuit comprising: a first threshold circuit responsive to output signals from said photodetector for providing threshold output signals when the signals from said photodetector exceed a level greater than said predetermined level; a monostable multivibrator coupled to said first threshold circuit so as to provide an output current pulse of a predetermined amplitude and duration when triggered by a threshold output signal, the duration of said output current pulse being approximately equal to, or greater than, a time interval corresponding to the effective maximum range, whereby no more than one current pulse is produced by target signals during any given transmission and reception period; a reference current source for providing a reference current having a constaNt amplitude which is preselected as a function of the desired false alarm rate; an integrator for providing an output signal proportional to the integral of the difference between the magnitudes of said current pulses and said reference current; and means responsive to the output signal of said integrator for applying bias current to said photodetector to cause the sensitivity of said photodetector to decrease when said current pulses occur at a rate in excess of a preselected rate, and to increase when said current pulses occur at a rate which is less than said preselected rate.
Claim 13
Dependent Claim
273 words
A circuit for biasing a photodetector so as to substantially maintain a desired false alarm rate; said circuit being adapted for use in a pulsed energy transmission and reception system having an effective maximum range such that photodetector output signals, derived from received energy from targets at a range greater than said maximum range, are less than a predetermined level; said circuit comprising: a first threshold circuit responsive to output signals from said photodetector for providing threshold output signals when the signals from said photodetector exceed a level greater than said predetermined level; a monostable multivibrator coupled to said first threshold circuit so as to provide an output current pulse of a predetermined amplitude and duration when triggered by a threshold output signal, the duration of said output current pulse being approximately equal to, or greater than, a time interval corresponding to the effective maximum range, whereby no more than one current pulse is produced by target signals during any given transmission and reception period; a reference current source for providing a reference current having a constaNt amplitude which is preselected as a function of the desired false alarm rate; an integrator for providing an output signal proportional to the integral of the difference between the magnitudes of said current pulses and said reference current; and means responsive to the output signal of said integrator for applying bias current to said photodetector to cause the sensitivity of said photodetector to decrease when said current pulses occur at a rate in excess of a preselected rate, and to increase when said current pulses occur at a rate which is less than said preselected rate.
Claim 14
Dependent Claim
64 words
The circuit of claim 11 wherein said means for applying bias current includes a capacitance element coupled to receive the output signal of said integrator, and a constant current source coupled to said capacitance element and to said photodetector such that part of the output current from said constant current source applied to said photodetector is controlled by the charge on said capacitance element.
Claim 15
Dependent Claim
49 words
The circuit of claim 11 further comprising a data output terminal; and a second threshold circuit for providing output signals to said data terminal when the signals applied to said second threshold circuit from said photodetector exceed a level greater than the threshold level of said first threshold circuit.
Claim 16
Dependent Claim
49 words
The circuit of claim 12 further comprising a data output terminal; and a second threshold circuit for providing output signals to said data terminal when the signals applied to said second threshold circuit from said photodetector exceed a level greater than the threshold level of said first threshold circuit.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-02-21 | 1975-08-23 | 1976-02-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-02-21 | 1979-08-23 | 1980-02-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-02-21 | 1983-08-23 | 1984-02-22 | $7700.00 | Window Closed / Lapsed |