Linearization of Active Downconversion Mixers at the IF Using Feedforward Cancellation

Abstract

A feedforward linearization technique for third-order intermodulation (IM3) distortion cancellation in active downconversion mixers is proposed in this paper. Low-frequency second-order intermodulation (IM2) tones are created and multiplied with the mixer’s output to generate low-frequency IM3 replicas for cancellation. Implemented mostly at the IF band, this technique brings a third-order input intercept point (IIP3) 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 IIP3 of 2.5 dBm before linearization. The linearization technique improves the mixer’s IIP3 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.