High linearity up-conversion mixer

Mixer is a fundamental block of the transmitter path exerting great influence on the transmitter linearity level. This article is concerned with a method to enhance the linearity of the Gilbert cell mixer using several parallel-connected differential pairs in an attempt to reduce a variation in incremental transconductance with respect to an input signal amplitude. As part of the study, a Gilbert cell with two parallel-connected differential pairs and a Gilbert cell with three parallel-connected differential pairs were designed and simulated. Both concepts demonstrate an increase in OIP3 value in comparison with a classical Gilbert cell. We used a Si-Ge component library with a design rule of 130 nm. The simulations were conducted in the CAD Advanced Design System.