Digital continuous phase modulation for a DDS-driven phase locked loop
First Claim
1. A transmitter for use in a communication system, comprising:
- a digital synthesizer;
a phase locked loop, an output of said digital synthesizer coupled to an input of said phase locked loop;
a phase modulation generator, an output of said phase modulation generator coupled to an input of said digital synthesizer such that said phase modulation generator phase modulates a signal at said output of said digital synthesizer; and
wherein said phase modulation generator comprises a phase modulation generator means for generating a plurality of phase trajectory signals at said output of said phase modulation generator, said plurality of phase trajectory signals associated with information to be transmitted by said transmitter.
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Abstract
A system and method are provided in which a phase modulation generator is used to modulate the output signal of a DDS with a modulation index, h/N. The phase-modulated. DDS output drives a PLL, which is an upconversion stage for a radio transmitter, with the modulated DDS signal as the PLL'"'"'s reference. The output of the PLL will have a modulation index of h. Consequently, the frequency band of the DDS output is significantly narrower than the frequency band of upconversion stages used in conventional transmitters, and there are significantly less spurious emissions in the transmitted signal. However, a transmitter employing the present phase-modulated DDS-driven PLL topology can still transmit over a relatively wide frequency band.
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Citations
14 Claims
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1. A transmitter for use in a communication system, comprising:
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a digital synthesizer; a phase locked loop, an output of said digital synthesizer coupled to an input of said phase locked loop; a phase modulation generator, an output of said phase modulation generator coupled to an input of said digital synthesizer such that said phase modulation generator phase modulates a signal at said output of said digital synthesizer; and wherein said phase modulation generator comprises a phase modulation generator means for generating a plurality of phase trajectory signals at said output of said phase modulation generator, said plurality of phase trajectory signals associated with information to be transmitted by said transmitter. - View Dependent Claims (2, 3)
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4. A method for modulating an output signal from a phase locked loop in a radio transmitter, comprising the steps of:
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generating signals for supplying a digital synthesizer with a plurality of phase trajectory signals that are associated with information to be transmitted by said radio transmitter; modulating a signal at an output of said digital synthesizer with said plurality of phase trajectory signals; and coupling said modulated signal at said output of said digital synthesizer to an input of said phase locked loop, and thereby modulating said output signal from said phase locked loop. - View Dependent Claims (5, 6)
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7. A transmitter for use in a communication system, comprising:
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a digital synthesizer; a phase locked loop, an output of said digital synthesizer coupled to an input of said phase locked loop a phase modulation generator, an output of said phase modulation generator coupled to an input of said digital synthesizer such that said phase modulation generator phase modulates a signal at said output of said digital synthesizer; and wherein said phase modulation generator is adapted to accommodate a division ratio of N of said phase locked loop. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification