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Clock circuit and method for recalibrating an injection oscillator coupled to kick-start a crystal oscillator

  • US 10,673,383 B2
  • Filed: 09/20/2018
  • Issued: 06/02/2020
  • Est. Priority Date: 09/20/2018
  • Status: Active Grant
First Claim
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1. A clock circuit, comprising:

  • a crystal oscillator circuit configured to generate a clock signal at a resonant frequency;

    an injection oscillator coupled to supply an oscillation signal at an injection frequency to the crystal oscillator circuit to reduce a start-up time of the crystal oscillator circuit; and

    a digital frequency calibration circuit coupled to receive the resonant frequency and the injection frequency as inputs, and configured to supply a digital control signal to the injection oscillator to set the injection frequency of the injection oscillator substantially equal to the resonant frequency of the crystal oscillator circuit;

    wherein the digital frequency calibration circuit comprises a digital up/down counter coupled to receive the resonant frequency and the injection frequency; and

    wherein the digital up/down counter is configured to generate a first digital signal based upon an increasing count value and a decreasing count value corresponding to the injection frequency as measured by the resonant frequency.

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