Patent ID: 7068983

Claim:
A carrier leak adjustment point detection method for a quadrature modulator for receiving a carrier signal and I and Q signals and quadrature-modulating the carrier signal with the I and Q signals, which detect DC adjustment voltages to be respectively added to the I and Q signals so as to cancel out a carrier leak contained in a modulated signal output from the quadrature modulator, comprising: respectively adding, to the I and Q signals, a first pair of DC voltages which set a signal level of the modulated signal to a predetermined reference level while signal levels of the I and Q signals are set at “0”; sequentially obtaining second and third pairs of DC voltages which set the signal level of the modulated signal to the predetermined reference level by changing the first pair of DC voltages; deciding, based on the first, second, and third pairs of DC voltages, at least three measurement points based on a combination of pairs of DC voltages which sets the signal level of the modulated signal to the predetermined reference level; and assuming that the first, second, and third pairs of DC voltages which provide at least three decided measurement points are located on a circumference of a single virtual circle drawn on a two-dimensional coordinate system with a pair of DC voltages to be respectively added to the I and Q signals being plotted as an ordinate and an abscissa, and calculating coordinates of the center of the virtual circle as the carrier leak adjustment point.