A 90-96 GHz CMOS Down-Conversion Mixer with High Conversion Gain and Excellent LO-RF Isolation

A 90-96 GHz down-conversion mixer for 94 GHz image radar sensors using standard 90 nm CMOS technology is reported. RF negative resistance compensation (NRC) technique, i.e. NMOS LC-oscillator-based RF transconductance (GM) stage load, is used to increase the output impedance and suppress the feedback capacitance C-gd of RF GM stage. Hence, conversion gain (CG), noise figure (NF) and LO-RF isolation of the mixer can be enhanced. The mixer consumes 15 mW and achieves excellent RF-port input reflection coefficient of -10 similar to -36.4 dB for frequencies of 85 similar to 105 GHz. The corresponding -10 dB input matching bandwidth is 20 GHz. In addition, for frequencies of 90 similar to 96 GHz, the mixer achieves CG of 6.3 similar to 9 dB (the corresponding 3-dB CG bandwidth is greater than 6 GHz) and LO-RF isolation of 40 similar to 45.1 dB, one of the best CG and LO-RF isolation 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 (IIP3) of 1 dBm at 94 GHz. These results demonstrate the proposed down-conversion mixer architecture is very promising for 94 GHz image radar sensors.