Patent ID: 7529313
Filing Date: 2009-05-05
Classification: H03C,H04L

Abstract:
1. An apparatus comprising: an affine transformation portion that subjects complex amplitude signals to affine transformation according to affine transformation coefficients and outputs compensated signals; a quadrature modulation portion that carries out quadrature modulation according to the compensated signals and outputs a modulated signal; a quadrature detection portion that removes a carrier component from one of the modulated signal and a signal based on the modulated signal, and outputs complex feedback signals; and a control portion that updates the affine transformation coefficients based on linear distortions remaining in the complex feedback signals; the affine transformation portion subjects input complex amplitude signals I(t) and Q(t) to the affine transformation according to affine transformation coefficients, and outputs compensated signals a(t) and b(t); the quadrature modulation portion comprises a quadrature modulator, and applies quadrature modulation on a local oscillation signal according to the input compensated signals to output the modulated signal as a real signal; the quadrature detection portion removes the carrier component from one of the input modulated signal and a signal that is the modulated signal having undergone at least one of frequency conversion and amplification, and outputs complex feedback signals I′(t) and Q′(t); the control portion extracts linear distortions remaining in the complex feedback signals I′(t) and Q′(t) as distortion coefficients, and updates the current affine transformation coefficients to new affine transformation coefficients in accordance with updating equations including the distortion coefficients, so that updated affine transformation coefficients are set again in the affine transformation portion; as a function of compensating for a DC offset on each input complex amplitude signal, the affine transformation portion includes a DC offset correction portion, and the control portion includes a level detection portion and a correction value control portion; the DC offset correction portion provides an I-phase correction value and a Q-phase correction value of the DC offset, respectively, to an I-phase component and a Q-phase component of each input complex amplitude signal; the level detection portion feeds back each complex amplitude signal to which the correction values are provided from the DC offset correction portion, and detects a level of a feedback signal; the correction value control portion controls the I-phase correction value and the Q-phase correction value provided from the DC offset correction portion according to the level detected by the level detection portion; and the correction value control portion searches through plural points provided initially on an IQ plane at regular intervals for a point at which the level detected by the level detection portion is minimum when a level of the input complex amplitude signal is 0 in a case where the I-phase component value and the Q-phase component value of each point are set in the DC offset correction portion as the I-phase correction value and the Q-phase correction value, and thereafter, conducts the search once or more using the point searched in a last time as a central point while making the regular intervals smaller than in the last time, so that the I-phase component value and the Q-phase component value of a point searched finally are adopted as the I-phase correction value and the Q-phase correction value and set in the DC offset correction portion.