Digital I/Q imbalance compensation in a low-IF receiver

Double low-IF receiver architectures avoid the need for expensive image-reject and channel selection filters and so reduce cost. This approach however introduces the need for an accurate in-phase and quadrature version of the first local oscillator. We present a way to digitally measure amplitude and phase imbalances and compensate for them. Simulations show image-reject values round 50 dB with amplitude imbalances of more than 10% and phase imbalances of more than 10 degrees. Although we focus on GSM-like applications, the algorithms are suitable for other low-IF systems as well.