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Direct conversion architectures have the advantage of no image frequencies, fewer components and lower cost. However, local oscillator (LO) leakage reduces receiver sensitivity, causes LO pulling, and is a challenging problem for direct conversion transceiver design. Proposed is a mixer using the second-order harmonic of the LO. The proposed subharmonic mixer is based on a switching common-gate structure. This mixer, built using 65 nm CMOS technology, achieves measured voltage conversion gain better than 3 dB for frequencies between 5 to 75 GHz with a current consumption of 2 mA at 1.5 V power supply. In the 57 to 66 GHz frequency band, the LO to RF port isolation is better than 38 dB and the noise figure is 14.8 dB when driven with a 30 GHz quadrature LO input.