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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A 2.5V second order RF bandpass filter is presented. A new Q-enhancement structure stacked on a LNA is fabricated in a 65-nm CMOS process with a die area of 1.1 mm x 1.1 mm. The frequency range is adjustable in a 25% range from 1.7 GHz to 2.2 GHz while the Q is adjustable up to 50. Q and the center frequency are adjusted by binary weighted switchable capacitors. The filter draws 42 mA including the buffers from a 2.5 V supply and has an input referred out-of-band 1-dB compression point of 0 dBm. The measured in-band NF is between 5.4 and 6.2 dB.

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