Terahertz Even-Order Subharmonic Mixer Using Symmetric MOS Varactors

A 560-GHz radio frequency (RF) front-end employing an accumulation mode MOS symmetric varactor (SVAR) subharmonic mixer achieves a minimum single sideband (SSB) noise figure (NF) of 35 dB in the fourth-order subharmonic mixing (SHM) mode which is 5 dB lower than that of SiGe HBT mixers. The front-end fabricated in 65-nm CMOS also achieves 45-dB SSB NF for sixth-order SHM at RF=810 GHz and 60-dB SSB NF for tenth-order SHM at RF=1.2 THz. Use of SVARs in a mixer is the first and the 1.2-THz RF is the highest for mixers in silicon technologies. The measurement results are explained using the parametric amplification theory.