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Optical reader with improved response to change in reflected signal

  • US 5,506,411 A
  • Filed: 12/29/1993
  • Issued: 04/09/1996
  • Est. Priority Date: 12/29/1993
  • Status: Expired due to Term
First Claim
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1. An optical reading device including:

  • a light source;

    means for projecting light from said light source onto an object containing information to be read;

    optic means for imaging light reflected from said object onto an image sensor for converting the reflected light into electric signals having large and rapid peak-to-peak variations and which can be shifted up and down as a function of ambient light; and

    signal processing circuitry connected to said image sensor for receiving said electric signals and producing, at an input point, a signal voltage (Vin) responsive thereto also having large and rapid peak-to-peak variations;

    said signal processing circuitry including;

    first means for charging a first capacitive node to the peak values of the positive going excursions of Vin;

    second means for charging a second capacitive node to the peak values of the negative going excursions of Vin;

    first and second unidirectional conducting elements, each element enabling conduction in a forward direction with an offset voltage drop (VF); and

    means connecting said first unidirectional conducting element between said first capacitive node and an output terminal and said second unidirectional conducting element between said output terminal and said second capacitive node.

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