Patent ID: 7242728

Claim:
A carrier quadrature error detecting method of a quadrature modulator which receives a pair of carrier signals having phases perpendicular to one another, and I and Q signals, quadrature-modulates the pair of carrier signals by the I and Q signals, and outputs a modulating signal, detects a quadrature error based on a phase difference between the pair of carrier signals at a modulator output of the quadrature modulator, the quadrature error detecting method of the quadrature modulator comprising: adding a pair of dc voltages for causing that the modulating signal output from the quadrature modulator is made to be a predetermined reference level, to the I and Q signals, respectively, in a state that signal levels of the I and Q signals are respectively made to be zero; retrieving plural combinations of pairs of dc voltages for causing that a signal level of the modulating signal output from the quadrature modulator is made to be the predetermined reference level, in a state that the pairs of dc voltages are respectively changed and sequentially added to the I and Q signals; and calculating the quadrature error from simultaneous equations in which respective values of retrieved plural combinations of pairs of dc voltages, the signal level of the modulating signal output from the quadrature modulator, and a quadrature error of the carrier signals are variables.