A Common Gate mixer with transconductance nonlinearity cancellation

A highly linear common gate (CG) mixer is designed using transconductance linearization technique combined with elimination of harmonic feedback effect. One of the major contributors of third order nonlinearity in the mixer is the second derivative of transconductor (g_m"). The Multiple Gated Transistor (MGTR) technique is employed in the transconductor of CG mixer to linearize the mixer. Also, an RF current source is used to remove harmonic feedback components which limit IIP3 enhancement. With CG MGTR transconductor, a LC folded cascode current commutating mixer is proposed. The proposed CG mixer for 900 MHz CDMA application is designed with 0.13 ¿m CMOS technology. Simulation result shows that conversion gain of 7 dB NF of 15 dB and IIP3 of 20 dBm while consuming 5.4 mA at 1.2 V supply. Compared with conventional design, the proposed one shows 10 dB IIP3 improvement.