Phase and gain imbalance compensation in low-IF receivers

In this paper, we present a modified image rejection method that uses imbalance compensation techniques for phase and gain in low-intermediate frequency (IF) software-defined radio (SDR) receivers. In low-IF receivers, the image frequency signal interferes with the desired signal owing to the phase and gain imbalances caused by analog devices. Thus, it is difficult to achieve the required image rejection ratio (IRR) of over 60 dB without compensation. To solve this problem, we present modified blind compensation techniques based on digital signal processing using a feedback control loop with a practical computation process. The modified method can reduce the complexity when a hardware logic circuit is used, like an FPGA. The simulation and experimental results verify that the modified method achieves an IRR greater than 50-60 dB for both the carrier and the modulated waves.