On I/Q-mismatch in active interference cancellation schemes

The performance of active interference cancellation schemes in RF receiver front-ends can be seriously affected by I/Q-mismatch of the active cancellation filter core. Therefore, the influences of I/Q gain and phase mismatch on active feedforward and feedback cancellation schemes are investigated. It is found that I/Q mismatch leads to an image spectrum at the band of interest. The image can be particularly detrimental when blockers that should be filtered by active cancellation appear at the image band thus desensitizing subsequent circuit blocks in the receive chain. A comparison of feedforward and feedback cancellation reveals that feedforward cancellation is much more sensitive to I/Q mismatch effects than feedback cancellation. Simulation results and measurements from a prototype chip are presented to confirm the theoretical results.