CMOS monolithic wideband image rejection mixer with polyphase filters

The image rejection ratio in double balanced mixers is strongly dependent on the balance between its branches. The influence of mismatches is analysed and conclusions on the key aspects of the design to increase the image rejection are discussed. A practical circuit implementation is described: a 1.9 GHz downconversion image rejection mixer is fabricated in 0.6 /spl mu/m CMOS standard technology. Measurements on the prototype showed a 34 dB image rejection and an overall conversion gain of 16 dB.