A, a frequency-to-voltage converter including a calculation module, a quantification module and a signal processing module is disclosed. The calculation module receives a frequency signal and calculates a rotational speed signal according to the frequency signal. The quantification module is coupled with the calculation module and receives the rotational speed signal. The quantification module quantifies the rotational speed signal according to a quantification equation and generates a digital quantified signal. The signal processing module is coupled with the quantification module, receives the digital quantified signal, and converts the digital quantified signal into a digital voltage signal. As such, the proper transition time and ripple magnitude can be endured at the same time.

The present invention discloses BPSK demodulator, which uses a delay circuit to delay a BPSK signal and mixes the delayed BPSK signal with the undelayed BPSK signal to output a demodulated data signal, and which uses a phase rotation circuit and the demodulated data signal to obtain a carrier clock signal. The operating frequency of the delay circuit is the same as or 0.5 times the carrier frequency. Therefore, the present invention consumes less power and is realized by digital circuits and analog circuits.