Patent ID: 7751504

Claim:
A frequency modulation-frequency shift keying (FM/FSK) demodulator, comprising: a modulation signal input terminal, which receives a first modulation signal; a phase shifter, which receives the first modulation signal, and then changes its phase to output a second modulation signal; a multiplier, which is coupled to the modulation signal input terminal and the output terminal of the phase shifter for multiplying the first modulation signal and the second modulation signal together and outputting a demodulation signal; an adder, which has a first input terminal, a second input terminal and one output terminal, the first input terminal receiving the demodulation signal; a direct current (DC) compensation unit, coupled to the output terminal of the adder for compensating the DC of the demodulation signal and low-frequency offsets, the DC compensation unit including a Schmitt trigger, a current pump circuit, and a capacitor, the Schmitt trigger receiving a signal from the output terminal of the adder and outputs a control signal, and the current pump circuit receiving the control signal to charge and discharge the capacitor at the second input terminal of the adder; and a demodulation signal output terminal, which is coupled to the output terminal of the adder for outputting the demodulation signal.