Direct digital synthesis of precise, stable angle modulated RF signal
First Claim
1. An RF modulator comprising:
- a phase lock loop including a loop filter and receiving as an input signal a baseband modulation signal and producing as an output signal a modulated RF signal;
circuitry for producing an injection modulation signal;
circuitry for injecting the injection modulation signal into the phase lock loop at a point past the loop filter; and
control circuitry, coupled to the circuitry for injecting the injection modulation signal, for controlling the amplitude of the injection modulation signal.
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Abstract
The present invention, generally speaking, provides an RF modulator that allows precise, stable phase shifts to be obtained. The modulator uses a PLL structure including an auxiliary feedforward path used to inject a baseband modulation signal into the PLL at a point past a loop filter of the PLL. A phase demodulator recovers phase information from the output signal of the PLL. The recovered phase information is compared to the phase information of the baseband modulation signal. A resulting error signal is used to control injection of the baseband modulation signal into the PLL, to automatically achieve the correct "dosage." A precise, adaptive, phase-stable modulator results. The adaptation of the modulator compensates for variability of the VCO and other components of the PLL.
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Citations
14 Claims
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1. An RF modulator comprising:
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a phase lock loop including a loop filter and receiving as an input signal a baseband modulation signal and producing as an output signal a modulated RF signal; circuitry for producing an injection modulation signal; circuitry for injecting the injection modulation signal into the phase lock loop at a point past the loop filter; and control circuitry, coupled to the circuitry for injecting the injection modulation signal, for controlling the amplitude of the injection modulation signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method of producing precise, stable phase shifts in a modulated RF signal, comprising the steps of:
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using a baseband modulation signal, producing a modulated signal; applying the modulated signal as a reference signal to a phase lock loop; and automatically deriving an adaptive gain factor and applying the adaptive gain factor to the baseband modulation signal to produce an injection signal and injecting the injection signal into the phase lock loop; wherein the injection signal compensates for the phase lock loop partially removing modulation introduced by the baseband modulation signal. - View Dependent Claims (14)
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Specification