Patent ID: 7979037

Claim:
A frequency modulation circuit for frequency modulating and outputting an output frequency modulation signal, the frequency modulation circuit comprising: a bandpass type delta sigma modulation section operable to receive an input modulation signal and perform delta sigma modulation on the received input modulation signal, such that quantization noise is suppressed in a frequency band which requires low noise, and output a first resultant signal; a feedback comparison section operable to receive the same input modulation signal, compare the output frequency modulation signal with the received input modulation signal, control a frequency of the received input modulation signal according to a result of the comparison, and output a frequency-controlled modulation signal; a loop filter operable to suppress a high-frequency component of the frequency-controlled modulation signal and output a second resultant signal; and a voltage controlled oscillator operable to perform frequency-modulation by controlling an oscillatory frequency according to a combination of the second resultant signal outputted from the loop filter and the first resultant signal outputted from the bandpass type delta sigma modulation section, and output the output frequency modulation signal.