Patent ID: 7920652

Claim:
A quadrature demodulator, comprising: a quadrature demodulation circuit section; and an orthogonality detector into which outputs of the quadrature demodulation circuit section are input, wherein the quadrature demodulation circuit further comprises a circuit for compensating phase mismatch between in-phase components and quadrature components from outputs of the quadrature demodulation circuit section based on outputs of the orthogonality detector, wherein the orthogonality detector further comprises a first high pass filter for removing low frequency components of in-phase components of the signal input I from the quadrature demodulation circuit section, a second high pass filter for removing low frequency components of quadrature components of the signal input Q from the quadrature demodulation circuit section, a multiplier for multiplying outputs of the first and second high pass filters with each other, and a low pass filter for removing high frequency components from an output of the multiplier, wherein the orthogonality detector is configured to detect an orthogonality error between the in-phase and quadrature components of the signals input from the quadrature demodulation circuit section based on the output of the low pass filter, and to compensate the output of the quadrature demodulation circuit section based on the orthogonality error, to provide a compensated output of the quadrature demodulator, wherein an output from the first high pass filter is (I−E[I]), an output from the second high pass filter is (Q−E[Q]), E being an average, and wherein the output from the multiplier comprises a covariance E[(I−E[I]) (Q−E[Q])], wherein the quadrature demodulation circuit section comprises a local oscillator, a first mixer outputting in-phase components of the input signal of the quadrature demodulation circuit section, a second mixer outputting quadrature components of the input signal of the quadrature demodulation circuit section, and a variable phase shifter connected between an output terminal of the orthogonality detector and an input terminal of one of the first and second mixers, wherein the variable phase shifter changes a phase shift quantity based on the output of the orthogonality detector, and controls an input phase of the mixer to which the output terminal of the variable phase shifter is connected.