Adaptive I/Q imbalance compensation in low-IF transmitter architectures

Advanced transmitter architectures based on I/Q signal processing are highly attractive to applications demanding a reconfigurable setting of the transmission parameters, such as carrier frequency and bandwidth. However, unavoidable imbalances between the I- and the Q-branch in the analog part lead to an insufficient suppression of the image signal. A digital predistortion structure is presented to overcome this problem. We show that the adaptation of the predistortion parameters can be performed blindly during the regular transmission mode. With the proposed novel adaptation algorithm, no special training or calibration signal is needed. After 10 iterations, an image suppression of 60-100 dB is achievable, depending on the accuracy of the measured power estimates of the desired transmit signal and the unwanted image signal.