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Light intensity detecting circuit with dark current compensation

  • US 4,916,307 A
  • Filed: 12/12/1988
  • Issued: 04/10/1990
  • Est. Priority Date: 12/15/1987
  • Status: Expired due to Fees
First Claim
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1. A received light intensity detecting circuit with an optical sensor having first and second terminals and a parallel capacitor and being connected at the first terminal with a predetermined potential, first potential applying means connected between the second terminal of the optical sensor and a source of a first potential and rendered conductive at an initial setting, and a comparator having a first input terminal connected to the second terminal of the optical sensor and a second input terminal receiving a comparative reference potential of a level between the predetermined potential and the first potential such that the intensity of received light is detected as the time period between the initial setting and the instant when an output signal is generated from the comparator, comprising:

  • an optically shielded mimic sensor having a first terminal connected to the predetermined potential and a second terminal connected to the second input terminal of the comparator and having the same structure as that of the optical sensor including a corresponding parallel capacitor;

    a source of a second potential having a level between the predetermined potential and the first potential; and

    second potential applying means connected between said second potential source and the second terminal of said mimic sensor and being rendered conductive only at said initial setting.

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