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Color demodulation for digital television

  • US 5,815,220 A
  • Filed: 08/30/1996
  • Issued: 09/29/1998
  • Est. Priority Date: 08/30/1996
  • Status: Expired due to Term
First Claim
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1. A digital sampling and color separation unit for a receiver of a composite video signal having a quadrature-modulated color subcarrier signal, comprising:

  • an analog-to-digital converter that samples said video signal at a sampling frequency such that an integer number of samples are acquired in a time equal to an integer number, plus or minus 0.25, times the period of said subcarrier signal, thereby providing sampled video data;

    a digital luminance-chrominance separator that receives said sampled video data and separates said sampled video data into luminance data and chrominance data;

    a digital oscillator for providing phase reference values at said sampling frequency, each phase reference value representing a phase relationship between a sample of said chrominance data and said subcarrier signal, such that each chrominance sample has an associated phase reference value;

    a memory, driven by said digital oscillator, that stores sin and cosine values and that matches said phase reference values to said sin and cosine values; and

    a demodulator that receives said sin and cosine values and said chrominance data, multiplies each chrominance sample by a sin or a cosine value matched to the phase reference value associated with that sample, and low pass filters the product, thereby providing color difference data.

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