380-GHz Third Harmonic Signal Generation Using Differentially Pumped Varactors in a CMOS Voltage Controlled Oscillator

An LC-VCO incorporating differentially pumped varactors for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^{\mathrm {rd}}$ </tex-math></inline-formula> order harmonic generation is demonstrated in a 65-nm bulk CMOS process with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{max}$ </tex-math></inline-formula> of ~250 GHz. The differentially pumped N-type Accumulation mode MOS varactor pair acting as a symmetric varactor serves as a frequency tuning element, as well as the non-linear reactive elements for harmonic generation. The measurements show that the circuit has a peak radiated power of -15.2 dBm with a frequency tuning range between 361.4 to 383.3 GHz or 5.9 %, and a peak DC-THz efficiency of 0.102 %. Among the CMOS oscillator signal generators with an on-chip antenna and output frequency greater than 300 GHz, the circuit exhibits the state-of-the-art DC-THz efficiency.