Abstract: A quadrature mixer with a shared transconductor stage is analyzed,including voltage conversion gain,linearity,noise figure,and image rejection.The analysis indicates it has better performance than a conventional Gilbert mixer pair in commutating mode.A quadrature down-conversion mixer based on this topology is designed and optimized for an ultra high frequency RFID reader.Operating in the 915MHz ISM band,the presented quadrature mixer measures a conversion gain of 12.5dB,an IIP3 of 10dBm,an IIP2 of 58dBm,and an SSB noise figure of 17.6dB.The chip was fabricated in a 0.18μm 1P6M RF CMOS process and consumes only 3mA of current from a 1.8V power supply.

Key words: quadrature mixer, shared transconductor stage, RFID reader, CMOS, low power, high linearity