New technique in design of active rf cmos mixers for low flicker noise and high conversion gain

Flicker noise of the switches in a Gilbert type RF mixer is one of the main challenges in design of CMOS active mixer in zero IF receivers. In this paper a new technique is proposed for reduction of the flicker noise in active mixers while the mixer has high conversion gain. In this technique the gate-source voltage of the switches is biased in sub-threshold region, leading to low dc current flows through the switches for the weak RF input signals. Thus; little amount of switches flicker noise transfers to the output, moreover high resistor loads can be used for having appropriate conversion gain. For proof of the idea a prototype mixer is designed in 0.18µm CMOS technology to work in the 5-6 GHz frequency band. The simulation results show 10 dB double side band thermal noise figure, 150 kHz flicker noise corner frequency, 9dB conversion gain, 62.2dBm IIP2, and 1.8dBm IIP3 for the designed mixer, while the circuit draws 6.7mA from the 1.8V power supply.