SiGe subharmonic mixer for direct conversion receivers

A second harmonic mixer appropriate for direct conversion receivers is realized in 0.18 μm SiGe technology. The realized topology offers a unique mechanism to prevent LO to RF leakage, thus, suppress the DC Offset voltage due to LO self mixing. The constant current consumption of the topology provides a proper isolation of the noise mixing operation from the supply lines. Large signal analysis of the topology is presented and the dependence of the conversion gain on the biasing conditions is investigated. Measurements are acquired to verify the conversion gain gathered from the analysis and the simulation results. According to measurement results, the conversion gain of the circuit is 35 dB and the second harmonic of LO to RF leakage is less than 70 dB.