An Active Feedback Interference Cancellation Technique for Blocker Filtering in RF Receiver Front-Ends

A feedback interference cancellation circuit is presented that uses a control loop to reject blockers in wireless receivers. The concept is based on a feedback translational loop which subtracts a blocker replica from the original blocker signal. In contrast to feedforward methods loop selectivity does not depend on exact gain matching of two paths but on the open loop gain which is easier to adjust. The concept is described including the theoretical derivations of the transfer function and stability. Nonidealities like I/Q mismatch and noise mechanisms are discussed. Finally, measurements from a prototype chip in 65-nm CMOS are presented showing the feasibility of active feedback cancellation. In a desensitization scenario, gain drops by more than 12 dB for a -15 dBm blocker at 20 MHz offset without feedback interference cancellation while a gain degradation of merely 3 dB is measured with feedback interference cancellation enabled.

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