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Method of and apparatus for controlling modulation of digital signals in frequency modulated transmissions

  • US 5,912,926 A
  • Filed: 09/10/1996
  • Issued: 06/15/1999
  • Est. Priority Date: 01/18/1990
  • Status: Expired due to Fees
First Claim
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1. Programmable apparatus for generating a frequency modulated signal at a selected center frequency in accordance with digital data of at least first and second data levels, said apparatus comprising:

  • a) a modulator having an input and an output and being responsive to an input modulation signal applied to its input for generating at its output the frequency modulated signal at a center frequency dependent on a quiescent voltage appearing at its input;

    b) a circuit for sampling and storing a value of the quiescent voltage in a register;

    c) an addressable memory for storing a plurality of offsets;

    d) a programmable adder for adding a downloaded offset voltage to the stored value of the quiescent voltage to output a high modulation voltage;

    e) a programmable subtractor for subtracting a downloaded offset voltage from the stored value of the quiescent voltage to provide a low modulation voltage;

    f) a controller for addressing in accordance with a data transmission parameter said addressable memory and for downloading a corresponding offset to said adder and said subtractor; and

    g) a switch coupled to said subtractor and adder and to receive the digital data for generating and applying to said input of said modulator the input modulation signal comprising a sequence of the high and low modulation voltages in accordance respectively with the first and second data levels of the digital data.

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