Design of CMOS Super Low Intermediate-frequency Downmixer

Because of good image-reject performance and easy to integrate the configrution of super-low-intermediate frequency is widely used in design of transceiver.As an important part of receiver,mixer is used to change the frequency.Its preformance has great effect on receiver.a super-low-intermediate frequency CMOS mixer applied in GSM is presented.A circuit to decrease the current in the input and a circuit called commonmode feedback to fix the voltage level of ouput.This mixer is applied in GSM of 869~894 MHz and with the output intermidiate frequency at 100 kHz.Its gain is 17 dB,IIP3 is 9.6 dB and noise figure is 17.5 dB.