A Low Conversion Loss 120 GHz Passive IQ Down-Conversion Subharmonic Mixer with Multiphase LO Distribution in 28 nm CMOS

This paper presents a passive IQ down-conversion subharmonic mixer (SHM) operating around 120GHz realized in a 28nm CMOS process. The use of a subharmonic mixer enables the local oscillator (LO) signal distribution at a lower frequency, in this case at f
O
/2 of 60GHz, and hence lower DC power consumption. However, the conversion loss of a passive subharmonic mixer is typically much higher than that of a passive fundamental mixer. In this work we enhance the SHM multiphase concept by a shunt resonant inductance attached between two cascaded mixer cores. This enables the mixer conversion loss reduction concept, reported so far typically only below 30GHz, to be applied here at frequencies around 120GHz. We achieve a very low voltage conversion loss of 3.8dB for a single SHM channel, without integrating any amplifiers in the RF or IF path. The multiphase LO distribution for both I and Q channels dissipates only 39.6mW in total. With the high measured 2LO-RF isolation above 66.8dB over the entire RF bandwidth of 17GHz, the LO self-mixing is highly suppressed, resulting in a minimized DC-offset voltage.