A W-band CMOS down-conversion mixer using CMOS-inverter-based RF GM stage for conversion gain and linearity enhancement

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A W-band (75–110 GHz) down-conversion mixer with CMOS-inverter-based RF transconductance (GM) stage for 94 GHz image radar sensors in 90 nm CMOS is reported. Due to the current bleeding and GM contribution of the upper PMOS transistors of the RF GM stage, a larger load resistance can be adopted and a larger GM can be obtained while keeps the same linearity. This leads to a conversion gain (CG) enhancement. In addition, the second-order term GM (g2) and third-order term GM (g3) of the main NMOS transistors of the RF GM stage can be cancelled by those of the upper PMOS transistors and the auxiliary NMOS transistors of the RF GM stage. This leads to a better linearity. The mixer consumes 8.56 mW and achieves an excellent RF-port input reflection coefficient of − 10 to − 18 dB for frequencies of 88.4–103.4 GHz. In addition, for frequencies of 70–100 GHz, the mixer achieves CG of 13.9–17.5 dB and LO-RF isolation of 40.6–43.5 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 prominent NF of 16.4 dB and output third-order intercept point of 14.1 dBm at 94 GHz. These results demonstrate that the proposed down-conversion mixer architecture is very promising for 94 GHz image radar sensors.