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Clock circuitry for a data communication system

  • US 4,276,651 A
  • Filed: 01/29/1979
  • Issued: 06/30/1981
  • Est. Priority Date: 09/06/1977
  • Status: Expired due to Term
First Claim
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1. A clock circuitry continuously synchronizable to a digital data signal serially transmitted by a data clock signal having a predetermined frequency, comprising:

  • delay means coupled to the digital data signal for providing a delayed digital data signal delayed with respect to the digital data signal by a predetermined time interval;

    first combining means for combining the digital data signal and the delayed digital data signal to provide a bit-transition pulse signal for each bit transition of the digital data signal;

    oscillator means for providing an oscillator clock signal having a free-running frequency substantially the same as the frequency of the data clock signal, said oscillator means further including Schmitt trigger gating means for providing the oscillator clock signal and buffer gating means capacitively coupled to the oscillator clock signal from the Schmitt trigger gating means for providing a clock-transition pulse signal for each predetermined logical state change of the oscillator clock signal; and

    second combining means for combining the bit-transition pulse signals and clock-transition pulse signals to provide a phase correction signal and applying the phase correction signal to the Schmitt trigger gating means for synchronizing the phase of the oscillator clock signal to the phase of the data clock signal.

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