Patent ID: 6345173
Filing Date: 2002-02-05
Classification: H03C,H04L

Abstract:
A frequency modulator for modulating a carrier signal according to a modulation data signal to provide a modulated output signal, the frequency modulator comprising:a reference signal generator coupled to receive the modulation data signal for generating a reference signal modulated according to the modulation data signal; and a main synthesizer coupled to receive the modulated reference signal and the modulation data signal for providing the modulated output signal at an output, and wherein the reference signal generator comprises an auxiliary synthesizer for performing a low frequency modulation process and having a lock-up time which is substantially greater than that of the main synthesizer, the auxiliary synthesizer comprising: an auxiliary phase detector having a first input for receiving a fixed reference signal having a fixed frequency, a second input and an output for providing an error signal representing the difference in phase between the fixed reference signal and a signal at the second input; and an auxiliary VCO coupled to receive the error signal and the modulation data signal for generating the modulated reference signal at an output, the output of the auxiliary VCO being coupled to the main synthesizer and to the second input of the auxiliary phase detector.