Method of and apparatus for controlling modulation of digital signals in frequency modulated transmissions
First Claim
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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Abstract
A programmable apparatus is disclosed for generating a frequency modulated signal at a selected center frequency in accordance with digital data of at least first and second data levels. The modulating apparatus comprises a modulator having an input and an output and is 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. A circuit is provided for sampling and storing a value of the quiescent voltage. An addressable memory stores a plurality of offsets. A programmable adding circuit adds a downloaded offset voltage to the stored value of the quiescent voltage to output a high modulation voltage. A programmable subtracting circuit subtracts a downloaded offset voltage from the stored value of the quiescent voltage to provide a low modulation voltage. An addressing circuit addresses the memory in accordance with a data transmission parameter for downloading a corresponding offset to the adding and subtracting circuits. A switch or multiplexor is coupled to the subtracting and adding circuits and to receive the digital data for generating and applying to the modulator input an 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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Citations
12 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for generating a frequency modulated signal at a stable center frequency in accordance with digital data, said apparatus comprising:
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a) a voltage controlled oscillator having an input and an output, and being responsive to an input modulation signal for generating the frequency modulation signal at a stable center frequency at said output of said voltage controlled oscillator; b) a phase lock loop interconnected between said input and said output of said voltage controlled oscillator and comprising a reference oscillator for generating at its output a reference frequency signal, a phase detector connected to said reference oscillator output and to said voltage controlled oscillator output for receiving the reference frequency signal and the frequency modulated signal and for providing at its output a signal indicative of the phase difference signal and applying a filtered signal to said input of said voltage controlled oscillator, whereby the center frequency is stabilized; and c) a source for providing the input modulation signal as a sequence of high and low modulation level signals in accordance with the digital data and for inserting the input modulation signal into said phase lock loop, said source comprises a switch inserted into said phase lock loop and operable between a closed state for completing said phase lock loop and an open state for interrupting said phase lock loop. - View Dependent Claims (7)
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8. Apparatus for generating a frequency modulated signal at a stable center frequency in accordance with digital data, said apparatus comprising:
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a) a voltage controlled oscillator 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 modulation signal at the stable center frequency; b) a phase lock loop interconnected between said input and said output of said voltage controlled oscillator and comprising a reference oscillator for generating at its output a reference frequency signal, a phase detector connected to said reference oscillator output and to said voltage controlled oscillator output for receiving the reference frequency signal and the frequency modulated signal and for providing at its output a signal indicative of the phase difference therebetween, and a filter coupled to said phase detector for filtering the phase difference signal and applying a filtered signal to said input of said voltage controlled oscillator, whereby the center frequency is stabilized; c) a source for providing the input modulation signal as a sequence of high and low modulation level signals in accordance with the digital data and for inserting the input modulation signal into said phase lock loop; and d) a track and hold circuit coupled within said phase lock loop and operable in a track mode wherein said phase lock loop is maintained closed and a control voltage applied to said first input of said voltage controlled oscillator is sampled and stored, and a hold state wherein said phase lock loop is opened and the stored sample of the controlled voltage is applied to said input of said voltage oscillator to maintain the center frequency of the frequency modulation signal at its center frequency. - View Dependent Claims (9)
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10. Apparatus for generating a frequency modulated signal at a stable center frequency in accordance with digital data, said apparatus comprising:
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a) a voltage controlled oscillator having a first input serving as a reference modulation port, a second input serving as a voltage controlled oscillator port and an output, and being responsive to an input modulation signal applied for generating at its output the frequency modulation signal at the stable center frequency; b) a phase lock loop interconnected between said input and said output of said voltage controlled oscillator and comprising a reference oscillator for generating at its output a reference frequency signal, a phase detector connected to said reference oscillator output and to said output of said voltage controlled oscillator for receiving the reference frequency signal and the frequency modulated signal and for providing at its output a signal indicative of the phase difference therebetween, and a filter coupled to said phase detector for filtering the phase difference signal and applying at its output filtered signal to said input of said voltage controlled oscillator, whereby the center frequency is stabilized; c) a source for providing the input modulation signal as sequence of high and low modulation level signals in accordance with the digital data and for inserting the input modulation signal into said phase lock loop; and d) a balancing circuit coupled to said source for receiving and apportioning the input modulation signal into a first portion applied to said reference modulation port and a second portion applied to said voltage controlled oscillator modulation port, said balancing circuit apportioning said first and second portions independently of each other based upon a data transmission parameter, whereby the frequency modulation signal may be adjusted to account for variation in the modulation sensitivity over a range of the data transmission parameter. - View Dependent Claims (11)
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12. Apparatus for generating a frequency modulated signal at a stable center frequency in accordance with digital data, the digital data comprises at least first and second data levels, said apparatus comprising:
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a) a voltage controlled oscillator having an input forming a modulation port and an output, and being responsive to an input modulation signal for generating the frequency modulation signal at the stable center frequency at said output of said voltage controlled oscillator; b) a phase lock loop interconnected between said input and said output of said voltage controlled oscillator and comprising a reference oscillator having an output for generating a reference frequency signal at said output of said reference oscillator, a phase detector connected to said output of said reference oscillator and to said output of said voltage controlled oscillator for receiving the reference frequency signal and the frequency modulated signal and for providing at its output a signal indicative of the phase difference therebetween, and a filter coupled to said phase detector for filtering the phase difference signal and applying a filtered signal to said input of said voltage controlled oscillator, whereby the center frequency is stabilized; c) a source for providing the input modulation signal as a sequence for high and low modulation level signals in accordance with the digital data and for inserting the input modulation signal into said phase lock loop; and d) a balancing circuit comprising a first programmable reference modulation shaping circuit and a second programmable voltage controlled oscillator shaping circuit, each of said first and second shaping circuits having an input for receiving the digital data and for generating respectively a first reference modulation signal and a second voltage controlled oscillator modulation signal, each of said first and second modulation signals comprising a sequence of the high and low modulation voltages in accordance respectively with the first and second data levels of the digital data; and e) a controller for programming distinctly the amplitudes of the high and low modulation voltages of the first and second modulation signals, whereby the first and second modulation signals are apportioned between said reference modulation port and said voltage controlled oscillator modulation port.
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Specification