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Digital compensation for wideband modulation of a phase locked loop frequency synthesizer

  • US 6,008,703 A
  • Filed: 01/31/1997
  • Issued: 12/28/1999
  • Est. Priority Date: 01/31/1997
  • Status: Expired due to Term
First Claim
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1. Apparatus for modulating a phase locked loop, the phase locked loop comprising a voltage controlled oscillator responsive to a control signal for generating an output carrier signal that is modulated by input modulation data and that has a controlled frequency;

  • a reference frequency signal source;

    a phase comparator connected to receive a reference frequency signal and the modulated output carrier signal for generating a difference signal;

    a low pass loop filter connected to filter the difference signal for producing the voltage controlled oscillator control signal; and

    frequency divider means connected between the voltage controlled oscillator output and the phase comparator for dividing the output carrier signal frequency;

    the phase locked loop being characterized by a frequency response having a characteristic cutoff frequency;

    the apparatus comprising;

    means for receiving from a modulation source digital input modulation data having a bandwidth that exceeds the cutoff frequency of the phase locked loop frequency response; and

    means coupled to the modulation data receiving means for digitally processing the input modulation data to amplify modulation data at frequencies higher than the phase locked loop cutoff frequency, and connected to the phase locked loop frequency divider means to modulate the divider means based on the digitally-processed input modulation data, whereby the voltage controlled oscillator is controlled to produce a modulated output carrier signal having a modulation bandwidth that exceeds the phase locked loop cutoff frequency.

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