Patent ID: 7903760

Claim:
A circuit for generating a demodulation carrier signal used to demodulate a modulated digital signal, the circuit comprising: an accumulator configured to generate an output by accumulating modulated first and second signals branched from the modulated digital signal, each of the modulated first and second signals containing a first signal having a frequency corresponding to a sum of first and second frequencies and a second signal having a frequency corresponding to a difference between the first and second frequencies, the first frequency being a frequency of a bit clock signal and the second frequency being a frequency of a carrier signal; a band-pass filter directly connected to the accumulator and configured to extract a frequency signal having twice the frequency of the carrier signal from the output of the accumulator; and a carrier signal generator connected to the band-pass filter and configured to divide the frequency signal output from the band-pass filter to obtain the demodulation carrier signal having the same frequency as the carrier signal.