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Method and apparatus for synchronizing internal and external video signals

  • US 5,748,252 A
  • Filed: 02/20/1996
  • Issued: 05/05/1998
  • Est. Priority Date: 02/20/1996
  • Status: Expired due to Term
First Claim
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1. A method of synchronizing a programmable sync generator output with an external video signal where the sync generator frequency is controlled by a voltage controlled oscillator comprising the steps of:

  • detecting the beginning of a frame in the video signal by digitizing the video signal,monitoring the digitized signal for determining the beginning of a frame,producing a start pulse for starting the sync generator at the beginning of a frame, andafter one start pulse is produced, inhibiting any additional start pulses so long as the video signal is present;

    starting the sync generator when the frame begins so that initially the sync generator output signal is synchronized with the video signal;

    comparing the phases of the output signal and the video signal and generating a voltage according to phase differential; and

    adjusting the voltage controlled oscillator with the generated voltage to null the phase differential, whereby the output signal is synchronized with the external video signal.

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