85-to-127 GHz CMOS Signal Generation Using a Quadrature VCO With Passive Coupling and Broadband Harmonic Combining for Rotational Spectroscopy

A quadrature LC-VCO incorporating passive coupling and broadband harmonic combining for frequency multiplication by 4, and NMOS switched variable inductors is fabricated in 65 nm bulk CMOS to generate signals at 85 to 127 GHz. The passive quadrature coupling bypasses the need for a broadband on-chip bias-T, while reducing power consumption, phase noise, and the theoretical conversion loss for the 4th order harmonic generation by 3 dB over the linear superposition. The 39% frequency tuning range is at least 4x higher than the other CMOS implementations with center frequency over 90 GHz. At power consumption of 30-45 mW from a 1.5 V power supply, the measured output power varies from - 15 to -23 dBm and phase noise at 10 MHz offset varies from - 108 to -102 dBc/Hz over the output frequency range. These are sufficient for use in millimeter wave rotational spectroscopy.