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High speed half duplex modem with fast turnaround protocol

  • US 5,001,729 A
  • Filed: 07/17/1989
  • Issued: 03/19/1991
  • Est. Priority Date: 05/26/1987
  • Status: Expired due to Fees
First Claim
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1. An improved method for locking a sampling signal onto a predetermined zero-crossing point of a reference signal having a characteristic frequency, said sampling signal having a sampling frequency and a phase with respect to said reference signal, comprising:

  • (a) sampling said reference siagnal at said sampling frequency to obtain a plurality of sampling points, said sampling frequency being a multiple M of said characteristics frequency, M being an integer greater than three;

    (b) designating one of said sampling points as a primary sampling point;

    (c) using said primary sampling point and a secondary sampling point to determine in which quadrant of said reference signal that said primary sampling point lies;

    (d) using said primary sampling point and said secondary sampling point to calculate a phase difference between said primary sampling point and said predetermined zero-crossing point; and

    (e) adjusting said phase of said sampling signal by a phase step size which reduces said phase difference.

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