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Dual mode FM and DQPSK modulator

  • US 5,446,422 A
  • Filed: 09/14/1994
  • Issued: 08/29/1995
  • Est. Priority Date: 04/23/1993
  • Status: Expired due to Term
First Claim
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1. A frequency modulator, comprising:

  • means for receiving an injection frequency signal and for regenerating the injection frequency signal to provide at a first output a first injection frequency signal and at a second output a second injection frequency signal, said first injection frequency signal having a non-zero phase shift with respect to said second injection frequency signal;

    first mixer means having a first input coupled to said first injection frequency signal and a second input coupled to a first modulation control signal, said first mixer means having an output for providing a first output frequency signal that is phase modulated in accordance with said first modulation control signal;

    second mixer means having a first input coupled to said second injection frequency signal and a second input coupled to a second modulation control signal, said second mixer means having an output for providing a second output frequency signal that is phase modulated in accordance with said second modulation control signal;

    combining means, having a first input coupled to said output of said first mixer means and a second input coupled to said output of said second mixer means, for combining said first and second mixer means outputs into a modulator output signal; and

    biasing means having a control input for receiving a mode control signal and an output, said output of said biasing means being coupled to at least said first mixer means for selectively enabling said first mixer means, in a first mode of operation indicated by said mode control signal, to output said phase modulated first output frequency signal, said output of said biasing means selectively enabling said first mixer means, in a second mode of operation indicated by said mode control signal, to output a frequency signal that is substantially identical to said first injection frequency signals, said biasing means being comprised of a diode having a first terminal coupled to a transistor switch and a second terminal coupled to at least said first mixer means, said transistor switch having a control terminal coupled to said mode control signal and being responsive to said mode control signal for reverse biasing said diode in the first mode of operation indicated by said mode control signal and for forward biasing said diode in the second mode of operation indicated by said mode control signal, whereby in the second mode of operation said diode conducts a current to at least said first mixer means.

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