Abstract: Aiming at the problem that image interference signal is difficult to filter, a broadband IQ up-conversion mixer applied to 5G millimeter wave communication is designed based on 65 nm CMOS process. In the core of the circuit, an improved Gilbert mixer structure is used to achieve high conversion gain through current multiplexing transconductance stage and negative resistance technology. At the output end of mixer, a signal synthesis circuit with small area and simple structure is designed based on the transformer balun. At the same time, a differential orthogonal coupler is used to generate four orthogonal LO signals. Simulation results show that the IQ up-conversion mixer circuit achieves a maximum conversion gain of 4.53 dB. The OP1 dB is 3.25 dBm, the image reject ratio is above 20 dB, and the LO to RF isolation is greater than 27 dB. The miniaturization of the passive circuit makes the total area of the chip only 0.327 mm². The power consumption of the chip is only 28.6 mW from a 1.2 V supply.