A charge-injection method for Gilbert cell biasing

A CMOS Gilbert cell mixer biasing topology is presented. The new biasing technique offers several key advantages over the traditional biasing arrangement. First, the new topology allows the designer to easily adjust the bias current present in the Gilbert cell input transistors, while maintaining bias currents in other portions of the circuit. Second, the mixer linearity can be improved using this biasing method by accurate adjustment of the input MOSFET operating point. Third, the biasing method reduces the “voltage headroom” difficulties inherent to the Gilbert cell, which uses a stacked arrangement of transistors. The importance of these adjustments with regard to the mixer conversion gain and IP3 is examined