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Apparatus and methods for synchronizing a digital receiver

  • US 4,308,619 A
  • Filed: 12/26/1979
  • Issued: 12/29/1981
  • Est. Priority Date: 12/26/1979
  • Status: Expired due to Term
First Claim
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1. A method for synchronizing the transition frequency of a local baud clock digital signal of a receiver in a digital communication system, to the exact baud frequency and phase of a received data bit transition stream, comprising the steps of:

  • (a) generating a first digital signal having a local clock frequency fy which is a first integer multiple of the nominal baud transition frequency of said received data bit transition stream;

    (b) generating a second digital signal having an offset frequency fz which is less than the first digital signal frequency fy ;

    (c) adding said second frequency digital signal to said first frequency digital signal to provide a digital signal having a higher local transition frequency (fy +fz);

    (d) subtracting said second frequency digital signal from said first frequency digital signal to provide a digital signal having a lower local transition frequency (fy -fz);

    (e) selecting one of the higher and lower local transition frequency signals;

    (f) dividing the selected local transition frequency signal by said first integer to obtain said local baud clock digital signal;

    (g) comparing the transition frequency of said local baud clock digital signal to the exact baud clock transition frequency of the received data bit transition stream to obtain an error signal; and

    (h) monitoring the error signal to select the remaining one of the higher and lower local transition frequency signals for division by the first integer to obtain the local baud clock digital signal if the error signal exceeds a predetermined limit.

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