Patent ID: 7224238
Filing Date: 2007-05-29
Classification: H03C,H03L,H03M,H04L

Abstract:
1. A frequency modulator that performs frequency modulation based on digital modulation data, comprising: a sigma-delta modulator for sigma-delta modulating data obtained by adding a fractional part of provided reference frequency division factor data with modulation data; a reference frequency divider for dividing a frequency of a provided reference signal based on data obtained by adding an output of the sigma-delta modulator with an integral part of the reference frequency division factor data; a voltage controlled oscillator operable to control an oscillation frequency; a frequency divider for dividing a frequency of an output of the voltage controlled oscillator; a phase comparator for comparing phases of the reference signal frequency-divided by the reference frequency divider and an output of the frequency divider; a loop filter for smoothing an output of the phase comparator and providing the smoothed signal to the voltage controlled osciliator; and a D/A converter for converting the output of the sigma-delta modulator to an analog signal and outputting the analog signal as a control signal, wherein the voltage controlled oscillator is operable to control the oscillation frequency based on an output of the loop filter and the control signal outputted from the D/A converter.