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Method and apparatus to center the frequency of a voltage-controlled oscillator

  • US 7,315,218 B1
  • Filed: 12/28/2005
  • Issued: 01/01/2008
  • Est. Priority Date: 12/28/2005
  • Status: Active Grant
First Claim
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1. A Phase Locked Loop (PLL) circuit comprising,a Voltage Controlled Oscillator (VCO) responsive to a digital control signal received on a first input node to set a frequency of the VCO to correspond to a mid-range voltage of an analog control signal received on a second input node;

  • anda frequency calibration circuit responsive to a plurality of input signals received on a plurality of input nodes to drive an output node with the digital control signal to set the frequency of the VCO, the frequency calibration circuit comprising;

    a frequency detector to detect a frequency difference between a feedback signal and a reference signal and drive an output node with an output signal representative of the detected frequency difference;

    a counter responsive to the output signal of the frequency detector to generate and output the digital control signal;

    a controller configured to control a calibration process of the VCO; and

    a clock generator configured to generate a first clock to clock the controller and to generate a second clock to clock the frequency detector;

    wherein a change in the digital control signal represents a frequency shift to set the frequency of the VCO.

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