We present an analytical model, design, and measurement results on fundamental, harmonic, and subharmonic down conversion mixing approaches in 65-nm CMOS around and above the transistor cutoff frequency fmax, targeting submillimeter-wave operation. Analytical expressions for the mixing approaches are derived and compared with the simulation and measurement results. To investigate how to improve the performance of a passive mixer around and beyond fmax, the relation between local oscillator (LO) harmonics (including both the harmonic amplitude and phase), mixer gate bias, and conversion gain is studied.

To demonstrate mixing approaches, we present integrated 160- and 280-GHz down-converters with integrated LO manufactured in 65-nm CMOS process with fmax= 210 GHz. The LO in both down-converters is based on exploiting higher harmonics of a differential Colpitts topology voltage-controlled oscillator (VCO). Passive conversion losses of 22 and 25.5 dB are obtained over the 150-180-GHz and the 230-290-GHz frequency range, respectively. Two additional versions of the down converter at 170 and 280 GHz, respectively, without integrated VCO are also presented to examine the mixer performance in the 110-325-GHz range.

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