Patent ID: 7860192

Claim:
A frequency shift keying (FSK) demodulator with build-in band-pass filter, the FSK demodulator comprising: a band-pass filter, which is used as a phase shifter of the FSK demodulator for shifting phase of an FSK signal to generate a revised FSK signal; an auto-calibration loop coupled to the band-pass filter for adjusting a center frequency of the band-pass filter, wherein the auto-calibration loop comprises: an oscillator for generating a reference clock signal; an integrator coupled to the oscillator for generating an output amplitude according to the reference clock signal and a working voltage; an amplitude comparator including a first input end coupled to the integrator, and a second input end coupled to the oscillator, the amplitude comparator used for comparing the output amplitude of the integrator with an amplitude of the reference clock signal of the oscillator and outputting a comparison result; and a working voltage adjuster having an input end coupled to the amplitude comparator and an output end coupled to the integrator, the working voltage adjuster used for tuning the working voltage of the integrator according to the comparison result outputted from the amplitude comparator; a phase comparator including a first input end coupled to an output end of the band-pass filter, and a second input end for receiving the FSK signal, the phase comparator used for comparing the FSK signal with the revised FSK signal for a phase difference and outputting a comparison result; and an analog-to-digital converter coupled to the phase comparator for converting the comparison result into digital data.