US3684378A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Dark current correction circuit for photosensing devices
Assignee: Individual
•
Filing: 1970-09-04
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Granted: 1972-08-15
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Expires: 1990-09-04
Abstract
Abstract In a flicker-type photosensing device, photosensor dark current is corrected for by applying the output of the photosensor to a current-to-voltage mode amplifier including a special dark current correction loop. In particular, the amplifier has connected between its input and output terminals a loop including a resistor, a grounded capacitor, a gating arrangement adapted to close the loop only during those periods when no light beam is applied to the photosensor, and a second resistor for limiting the capacitor charging rate. In operation, the capacitor charges while the gate is closed during the dark period; and, during pulse periods when the gate is open, it discharges to reduce the photosensor current by an amount nearly equal to the dark current.
Inventors
- 👤 Joseph S Lord
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 12:30
CPC Classifications
G; G01; G01J; G01J1/00; G01J1/10; G01J1/16; G01J1/20; G01J1/34; G01J1/36; H; H03; H03F; H03F1/00; H03F1/30; H03F1/303
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
232 words
A flicker-type photosensing device for comparing the intensities of two or more beams of radiation including a beam switcher for applying alternate pulses of different beams to a radiation sensing element, an amplifier for amplifying current generated by said element and circuitry for comparing the current generated by said beams, said device characterized by a gated loop between the input and the output of said amplifier, said loop comprising, in combination: a first resistor, R1, for generating a charging voltage proportional to the current from the output of said radiation sensing element when said gated loop is closed; a grounded capacitor having a capacitance C for charging in response to said charging voltage generated by said resistor R1 when said gated loop is closed and for discharging correction current through said resistor R1 against current from the output of said radiation sensing element when said gated loop is open; a gate arrangement responsive to synchronization pulses from said beam switcher for closing said loop only during the dark period when no beams are directed onto said radiation sensing element, thereby permitting said grounded capacitor to charge, and for opening said loop during the light period when a light beam is applied to said radiation sensing element, thereby permitting said capacitor to discharge; and a second resistor, RL, for limiting the rate at which the capacitor is charged when said loop is closed.
Claim 2
Dependent Claim
232 words
A flicker-type photosensing device for comparing the intensities of two or more beams of radiation including a beam switcher for applying alternate pulses of different beams to a radiation sensing element, an amplifier for amplifying current generated by said element and circuitry for comparing the current generated by said beams, said device characterized by a gated loop between the input and the output of said amplifier, said loop comprising, in combination: a first resistor, R1, for generating a charging voltage proportional to the current from the output of said radiation sensing element when said gated loop is closed; a grounded capacitor having a capacitance C for charging in response to said charging voltage generated by said resistor R1 when said gated loop is closed and for discharging correction current through said resistor R1 against current from the output of said radiation sensing element when said gated loop is open; a gate arrangement responsive to synchronization pulses from said beam switcher for closing said loop only during the dark period when no beams are directed onto said radiation sensing element, thereby permitting said grounded capacitor to charge, and for opening said loop during the light period when a light beam is applied to said radiation sensing element, thereby permitting said capacitor to discharge; and a second resistor, RL, for limiting the rate at which the capacitor is charged when said loop is closed.
Claim 3
Dependent Claim
23 words
A device according to claim 1 wherein the resistance of said first resistor R1 is large compared to that of said second resistorRL.
Claim 4
Dependent Claim
34 words
A device according to claim 1 wherein the product R1C of the resistance of said first resistor and the capacitance of said capacitor is large compared to the period of the longest radiation pulse.
Claim 5
Dependent Claim
53 words
A device according to claim 1 wherein: said amplifier is a current-to-voltage mode amplifier; said first resistor R1 is large compared to said second resistor; and the produCt R1C of the resistance of said first resistor and the capacitance of said capacitor is large compared to the period of the longest radiation pulse.
Claim 6
Dependent Claim
15 words
A device according to claim 4 wherein the gate arrangement comprises a field effect transistor.
Claim 7
Dependent Claim
22 words
A device according to claim 4 wherein said current-to-voltage mode amplifier comprises an amplifier connected in parallel with a third resistor Rf.
Claim 8
Dependent Claim
23 words
A device according to claim 6 wherein the resistance of said third resistor Rf is large compared to that of said first resistor.
Claim 9
Dependent Claim
14 words
A device according to claim 7 wherein said radiation sensing element is a photosensor.
Claim 10
Dependent Claim
36 words
A device according to claim 7 including a second gating arrangement for removing said third resistor, Rf, from the operating circuit during only the dark periods when no beams are directed onto said radiation sensitive cell.
Claim 11
Dependent Claim
236 words
A flicker-type photosensing device for comparing the intensities of two or more beams of radiation including a beam switcher for applying alternate pulses of different beams to a radiation sensing element, an amplifier for amplifying current generated by said element and circuitry for comparing the current generated by said beams, said device characterized by a gated loop between the input and the output of said amplifier, said loop comprising, in combination: a gate arrangement responsive to synchronization pulses from said beam switcher for opening said loop during the light period when one of said two or more beams is applied to said radiation sensing element and for closing said loop during the dark period when none of said beams are applied to said sensing element, thereby permitting the passage of dark current through said loop; a first resistive means, R1, for generating a charging voltage upon the passage of dark current through said loop; capacitive means C for charging in response to said charging voltage generated by said resistor R1 when said gate is closed and for discharging through said resistor, R1, when said gate is open; a second resistive means, RL, for limiting the rate at which the capacitor C is charged when said loop is closed; wherein the values of R1, C, and RL are chosen so that the current produced by the discharge of the capacitor is substantially equal to the dark current.
Claim 12
Dependent Claim
236 words
A flicker-type photosensing device for comparing the intensities of two or more beams of radiation including a beam switcher for applying alternate pulses of different beams to a radiation sensing element, an amplifier for amplifying current generated by said element and circuitry for comparing the current generated by said beams, said device characterized by a gated loop between the input and the output of said amplifier, said loop comprising, in combination: a gate arrangement responsive to synchronization pulses from said beam switcher for opening said loop during the light period when one of said two or more beams is applied to said radiation sensing element and for closing said loop during the dark period when none of said beams are applied to said sensing element, thereby permitting the passage of dark current through said loop; a first resistive means, R1, for generating a charging voltage upon the passage of dark current through said loop; capacitive means C for charging in response to said charging voltage generated by said resistor R1 when said gate is closed and for discharging through said resistor, R1, when said gate is open; a second resistive means, RL, for limiting the rate at which the capacitor C is charged when said loop is closed; wherein the values of R1, C, and RL are chosen so that the current produced by the discharge of the capacitor is substantially equal to the dark current.
Claim 13
Dependent Claim
36 words
The device according to claim 1 wherein R1 is small compared to R1 and C is chosen so that R1C is large compared with the duration of the longest light pulse used in said photosensing device.
References Cited (Backward Citations)
US3025746A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-08-15 | 1976-02-14 | 1976-08-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-08-15 | 1980-02-14 | 1980-08-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-08-15 | 1984-02-14 | 1984-08-15 | $7700.00 | Window Closed / Lapsed |