Linearization of Active Downconversion Mixers at the IF Using Feedforward Cancellation

A feedforward linearization technique for third-order intermodulation (IM 3 ) distortion cancellation in active downconversion mixers is proposed in this paper. Low-frequency second-order intermodulation (IM 2 ) tones are created and multiplied with the mixer's output to generate low-frequency IM 3 replicas for cancellation. Implemented mostly at the IF band, this technique brings a third-order input intercept point (IIP 3 ) improvement independently of the mixer topology and is robust against parasitic parameters. A 2-GHz current commutating mixer linearized by the proposed technique is designed and fabricated using a 130-nm CMOS process to verify the concept. Experimental results show that the mixer with a unit-gain amplifier delivers 8.5 dB of conversion gain and has an IIP 3 of 2.5 dBm before linearization. The linearization technique improves the mixer's IIP 3 by 12 dB for input signals as large as −15 dBm. The technique has a negligible impact on the mixer's gain and incurs a noise figure penalty of less than 0.2 dB. The mixer with the unit-gain amplifier consumes a current of 8.4 mA, while the proposed technique circuitry consumes an extra current of 4.2 mA, both using a 1.2-V voltage supply.