Digital filter design for I/Q imbalance compensation

All communication receiver structures utilizing I/Q signal processing snare the problem of matching the amplitudes and phases of the I- and Q-branches. In practise, the imbalances are unavoidable and this results in finite and in many cases insufficient attenuation of the image frequency band. Without any additional image rejection, this causes interference and needs to be compensated. We carry out the general signal and imbalance analysis of an I/Q processing based receiver structure and discuss the possibilities of digital imbalance compensation in cases where the dominating part of the imbalance is known in advance. A novel method for fixed imbalance compensation in a wideband approximative quadrature sampling receiver is derived and the performance of the proposed solution is illustrated through an example design.