Using the Gate–Bulk Interaction and a Fundamental Current Injection to Attenuate IM3 and IM2 Currents in RF Transconductors

Abstract

Two new linearization techniques to attenuate the second-order intermodulation (IM2) and third-order intermodulation (IM3) currents in transconductance stage of CMOS active mixers are proposed. In the first technique, the third-order Volterra kernel of the transconductance stage output current is cancelled using the interaction between the gate and bulk terminals of the input transistors. For this end, a IM2 voltage, with an adjustable magnitude and phase, is produced and applied to the bulk of these transistors. This produces an interaction term in the IM3 current of the stage and attenuates the total IM3 current. In the second technique, a fundamental component is added to the current of the tail source in the transconductance stage. This component produces an IM2 term in the drain current of the input transistors, caused by g’ m of the input transistors, with an equal magnitude and opposite phase related to the intrinsic IM2 current of the stage, and cancels the total IM2 current. Spectre-RF simulation results show that the proposed techniques simultaneously improve the third-order input intercept point and second-order input intercept point by $\sim 14.1$ and 16.4 dB, respectively, compared with the conventional active mixer, while 1.66-mA extra current is drawn from a single 1.2 V power supply.