94 GHz down-conversion mixer with gain enhanced Gilbert cell in 90 nm CMOS

A 94 GHz down-conversion mixer for image radar sensors using standard 90 nm CMOS technology is reported. The down-conversion mixer comprises a double-balanced Gilbert cell with an LC-tank-oscillator-based RF transconductance stage load for conversion gain (CG) enhancement and noise figure (NF) suppression, two miniature planar baluns for converting the single RF and LO input signals to differential signals, and an IF amplifier. The mixer consumes 9.5 mW and achieves excellent RF-port input reflection coefficient (S-11) of -27.2 dB at 94 GHz, and S-11 smaller than -10 dB for frequencies of 83.6-110 GHz. That is, RF-port -10 dB input matching bandwidth is greater than 26.4 GHz. In addition, for frequencies of 75-100 GHz, the mixer achieves CG of 4.9-7.9 dB (the corresponding 3-dB CG bandwidth is greater than 25 GHz), LO-RF isolation of 38.5-44.7 dB and NF of 15.4-21.2 dB, one of the best CG, LO-RF isolation and NF results ever reported for a down-conversion mixer with operation frequency around 94 GHz. Furthermore, the mixer achieves an excellent input third-order intercept point of 2.6 dBm at 94 GHz. These results demonstrate the proposed down-conversion mixer architecture is promising for 94 GHz image radar sensors.