Abstract: An orthogonal frequency division multiplex signal demodulator circuit includes an analog/digital converter that converts a received signal whose central frequency is non-zero into a digital signal, a digital quadrature signal detector constructed of a digital signal delay circuit that delays the digital signal to generate an in-phase signal and a digital all pass filter that shifts the phase of the digital signal by 90 degrees to generate a quadrature signal, a frequency shifter that shifts the frequencies of the in-phase signal and the quadrature signal to turn the signals into baseband signals having their central frequencies set at zero, and an orthogonal frequency division multiplex detector having a fast Fourier transformer for carrying out fast Fourier transformation on the baseband signals and a digital demodulator for demodulating the digital signal that has been subjected to the fast Fourier transformation, wherein the digital all pass filter is an infinite impulse response digital filter having a pr

Abstract: A digital quadrature signal detecting circuit constituted by a digital signal delay circuit for forming an in-phase (I) signal by delaying a digital signal outputted from an analog/digital conversion part for analog/digital converting a received signal having a non-zero center frequency by a predetermined sampling frequency, and a digital all-pass filter for forming a quadrature (Q) signal by shifting a phase of the digital signal by 90°, wherein the digital all-pass filter is an infinite impulse response digital filter having a definite group delay frequency characteristic, and the digital signal delay circuit has a signal delay amount equal to a group delay amount of the digital all-pass filter.