Design of a novel high linearity down conversion mixer for GSM band applications

Abstract

Double balanced Gilbert cell mixer (GCM) is the mostly used kind of mixer as it provides conversion gain and has port to port isolation. This mixer lacks in linearity and noise figure which are to be taken care in designing mixer. Linearity is important for mixer design, to get an undistorted signal at its output. Similarly noise figure of double balanced GCM is more due to more number of components and is to be decreased to add less noise to RF signal. To increase the linearity of mixer, necessary changes are to be done at transconductance stage. The linearity of the mixer proposed is increased, by making use of an additional capacitor in parallel to gate capacitance and derivative superposition method. Derivative superposition method needs more number of transistors at transconductance stage resulting in increase of parasitic capacitance, resulting in an increase of flicker noise from indirect mechanism. This flicker noise due to parasitic capacitance is reduced by placing a tuned inductor in parallel to it