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Video signals clamping circuit for maintaining DC level of video signals

  • US 5,341,218 A
  • Filed: 04/07/1992
  • Issued: 08/23/1994
  • Est. Priority Date: 04/09/1991
  • Status: Expired due to Term
First Claim
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1. A video signal clamping circuit for maintaining a DC level of a digital video signal at a fixed level, comprising:

  • an A/D converter for converting an input analog video signal into the digital video signal;

    a first latch circuit for sampling a predetermined part of the digital video signal at a predetermined period and latching the sampled data;

    an average value calculator circuit for taking in a predetermined number of the sampled data items latched by the first latch circuit and calculating an average value of the sampled data;

    a comparison output circuit for comparing the average value obtained in the average value calculator circuit with a reference value and outputting data either added or subtracted by a predetermined width to or from an output signal of a predetermined period before depending on a comparison result;

    a D/A converter for converting the data output by the comparison output circuit into an analog signal; and

    a clamp voltage supply means for supplying a clamp voltage to the input analog video signal on the basis of the analog signal output by the D/A converter, wherein the clamp voltage supply means includes a level compression shift for carrying out a level compression so that a voltage variation amount of the output of the D/A converter corresponding to 1 LSB of change of the input of the D/A converter is less than a voltage variation amount of 1 LSB change of the output of the A/D converter, and for shifting the voltage level to a predetermined level.

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