Dark current correction circuit for photosensing devices
阅读：798发布：2022-01-31
专利汇可以提供Dark current correction circuit for photosensing devices专利检索，专利查询，专利分析的服务。并且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.，下面是Dark current correction circuit for photosensing devices专利的具体信息内容。
1. 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.
2. A device according to claim 1 wherein the resistance of said first resistor R1 is large compared to that of said second resistorRL.
3. 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.
4. 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.
5. A device according to claim 4 wherein the gate arrangement comprises a field effect transistor.
6. A device according to claim 4 wherein said current-to-voltage mode amplifier comprises an amplifier connected in parallel with a third resistor Rf.
7. A device according to claim 6 wherein the resistance of said third resistor Rf is large compared to that of said first resistor.
8. A device according to claim 7 wherein said radiation sensing element is a photosensor.
9. 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.
10. 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.
11. 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.
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