Linearized offset QPSK modulation utilizing a sigma-delta based frequency modulator
First Claim
1. A modulator comprising:
- an offset QPSK modulator, said offset QPSK modulator operative for receiving input data and generating a first output signal representing the modulation to be imposed on a carrier signal to effect offset QPSK modulation of said input signal and a second output signal representing an amplitude of said input data;
a frequency modulator comprising a sigma-delta modulator, said frequency modulator operative for receiving said first output signal generated by said offset QPSK modulator, and generating a control signal representing the desired frequency of said carrier signal such that said carrier signal represents said input signal offset QPSK modulated;
a phase-lock loop circuit comprising a voltage controlled oscillator for generating said carrier signal and a programmable frequency divider, said programmable frequency divider receiving said control signal as an input signal, said programmable frequency divider operative for changing the frequency of the carrier signal in accordance with said control signal, andan amplifier having variable gain for receiving and amplifying said carrier signal output by said phase-lock loop circuit, said second output signal controlling the amount of gain of said amplifier; and
wherein said offset QPSK modulator comprises;
a demultiplexer for receiving said input data and generating I and Q quadrature signals corresponding to said input data;
a delay circuit operative for receiving said Q quadrature signal from said demultiplexer and for delaying the Q quadrature signal relative to the I quadrature signal;
a digital waveform generator operative for receiving said I quadrature signal output by said demultiplexer and said delayed Q quadrature signal output by said delay circuit, and for generating a digital signal indicating the modulation to be imposed on said carrier signal.
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Accused Products
Abstract
A vector modulator including an offset QPSK modulator operative for receiving input data and generating a first output signal representing the modulation to be imposed on a carrier signal to effect offset QPSK modulation of the input signal and a second output signal representing an amplitude of the input data; and a frequency modulator including a sigma-delta modulator, operative for receiving the first output signal generated by the offset QPSK modulator, and generating a control signal representing the desired frequency of the carrier signal such that the carrier signal represents the input signal offset QPSK modulated. The vector modulator also includes a phase-lock loop circuit having a voltage controlled oscillator for generating the carrier signal and a programmable frequency divider for receiving the control signal as an input signal and for changing the frequency of the carrier signal in accordance with the control signal, and an amplifier having a variable gain which is operative for receiving and amplifying the carrier signal output by the phase-lock loop circuit in accordance with the amplitude of the second output signal.
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Citations
19 Claims
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1. A modulator comprising:
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an offset QPSK modulator, said offset QPSK modulator operative for receiving input data and generating a first output signal representing the modulation to be imposed on a carrier signal to effect offset QPSK modulation of said input signal and a second output signal representing an amplitude of said input data; a frequency modulator comprising a sigma-delta modulator, said frequency modulator operative for receiving said first output signal generated by said offset QPSK modulator, and generating a control signal representing the desired frequency of said carrier signal such that said carrier signal represents said input signal offset QPSK modulated; a phase-lock loop circuit comprising a voltage controlled oscillator for generating said carrier signal and a programmable frequency divider, said programmable frequency divider receiving said control signal as an input signal, said programmable frequency divider operative for changing the frequency of the carrier signal in accordance with said control signal, and an amplifier having variable gain for receiving and amplifying said carrier signal output by said phase-lock loop circuit, said second output signal controlling the amount of gain of said amplifier; and wherein said offset QPSK modulator comprises; a demultiplexer for receiving said input data and generating I and Q quadrature signals corresponding to said input data; a delay circuit operative for receiving said Q quadrature signal from said demultiplexer and for delaying the Q quadrature signal relative to the I quadrature signal; a digital waveform generator operative for receiving said I quadrature signal output by said demultiplexer and said delayed Q quadrature signal output by said delay circuit, and for generating a digital signal indicating the modulation to be imposed on said carrier signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A modulator utilizing direct digital offset QPSK modulation, said synthesizer comprising:
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a digital offset QPSK modulator, said digital offset QPSK modulator operative for receiving a digital input data and generating a first digital output signal, said digital output signal representing the modulation to be imposed on a carrier signal to effect offset QPSK modulation of said digital input signal and a second digital output signal representing an amplitude of said digital input data; a frequency modulator comprising a sigma-delta modulator, said frequency modulator operative for receiving said first digital output signal generated by said digital offset QPSK modulator, and generating a digital control signal representing the desired frequency of said carrier signal such that said carrier signal represents said input signal offset QPSK modulated; a phase-lock loop circuit comprising a voltage controlled oscillator for generating said carrier signal and a programmable frequency divider, said programmable frequency divider receiving said digital control signal as an input signal, said programmable frequency divider operative for changing the frequency of the carrier signal in accordance with said control signal; and an amplifier having a variable gain for receiving and amplifying said carrier signal output by said phase-lock loop circuit, said second digital output signal controlling the amount of gain of said amplifier; and wherein said digital offset QPSK modulator comprises; a digital demultiplexer for receiving said input data and generating I and Q quadrature signals corresponding to said input data; a digital delay circuit operative for receiving said Q quadrature signal from said demultiplexer and for delaying the Q quadrature signal relative to the I quadrature signal; and a digital waveform generator operative for receiving said I quadrature signal output by said digital demultiplexer and said delayed Q quadrature signal output by said digital delay circuit, and for generating a digital signal indicating the modulation to be imposed on said carrier signal. - View Dependent Claims (11, 12, 13, 14)
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15. A method for generating an offset QPSK modulated signal at a desired carrier frequency, said method comprising the steps of:
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receiving a input data signal to be modulated; generating a digital output signal representing the modulation to be imposed on said carrier signal to effect offset QPSK modulation of said input data signal; generating an amplitude signal indicative of the amplitude of said input data signal; utilizing a frequency modulator comprising a sigma-delta modulator to receive said digital output signal and to generate a digital control signal representing the desired frequency of said carrier signal such that said carrier signal represents said input signal offset QPSK modulated; controlling a programmable frequency divider forming a portion of a phase-lock loop circuit, said programmable frequency divider receiving said digital control signal as an input signal, said programmable frequency divider operative for changing the frequency of said carrier signal in accordance with said control signal, said carrier signal being generated by a voltage controlled oscillator; amplifying said carrier signal in accordance with the level of said amplitude signal; and demultiplexing said input data signal and generating digital I and Q quadrature signals corresponding to said input data signal; delaying the Q quadrature signal relative to the I quadrature signal; performing an arctangent function on said delayed Q quadrature signal and said I quadrature signal so as to generate an output signal indicating the phase of a modulation signal to be imposed on said carrier signal; and differentiating said output signal so as to generate a digital signal indicating the frequency of said modulation signal to be imposed on said carrier signal. - View Dependent Claims (16, 17, 18, 19)
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Specification