Patent ID: 8265192

Claim:
A multilevel QAM demodulator performing a phase rotation compensation and a phase noise compensation on both a common phase signal and an orthogonal signal which are obtained by quasi-synchronous detection, the multilevel QAM demodulator comprising: a phase difference calculation unit calculating a phase difference signal based on the common phase signal and orthogonal signal after the phase rotation compensation; a phase shift amount calculation unit calculating a phase shift amount indicating a degree of a phase shift based on the common phase signal and orthogonal signal after the phase rotation compensation and phase noise compensation; and a correction unit correcting the phase difference signal based on the phase shift amount, wherein a phase rotation is performed for the phase noise compensation based on the phase difference signal corrected by the correction unit and the phase noise compensation is performed after the phase rotation compensation, and wherein the phase shift amount is an absolute value of a phase difference signal based on the common phase signal and orthogonal signal after the phase noise compensation.