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Dual loop frequency synthesizer having fractional dividers

  • US 5,610,559 A
  • Filed: 03/13/1996
  • Issued: 03/11/1997
  • Est. Priority Date: 09/14/1994
  • Status: Expired due to Term
First Claim
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1. A frequency synthesizer for providing a first output signal programmable over a first frequency band in first frequency steps and a second output signal programmable over a second frequency band in second frequency steps, comprising;

  • first reference divider means for dividing a reference frequency by a first integer to produce a first comparison frequency;

    second reference divider means for dividing said reference frequency by a second integer to produce a second comparison frequency;

    first controlled oscillator means for producing a first output frequency and having an input for a first frequency control signal;

    first fractional-N divider means for dividing said first output frequency by a first programmable quantity having both a first integer part and a first fractional part to produce a first loop frequency;

    first phase and frequency comparator means for comparing said first loop frequency with said first comparison frequency to produce a first error signal;

    first loop filter means for processing said first error signal to obtain said first frequency control signal;

    second controlled oscillator means for producing a second output frequency and having an input for a second frequency control signal;

    mixing means for generating a difference frequency signal having inputs from said first and second controlled oscillator means;

    second fractional-N divider means for dividing said difference frequency by a second programmable quantity having a second integer part and a second fractional part to produce a second loop frequency;

    second phase and frequency comparator means for comparing said second loop frequency with said second comparison frequency to produce a second error signal;

    second loop filter means for processing said second error signal to obtain said second frequency control signal.

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