Terahertz 4th-Order Downconversion Mixer Using Symmetric MOS Varactors

A 4th-order subharmonic downconversion mixer with a radio frequency (RF) of 480 GHz and intermediate frequency (IF) of 20 GHz that employs MOS symmetric varactors (SVARs) is demonstrated in 65-nm CMOS. The mixer achieves the minimum conversion loss of 25 dB at 20 GHz, VG = 0.5 V and VNW = 1 V. The return loss of the output port can reach nearly 30 dB, achieving a good matching effect, and can operate at a LO power of 9 dBm. The 4-GHz IF bandwidth spans between 18 and 22 GHz.