A 219-to-238-GHz Coupled Standing-Wave VCO with 3.4-dBm Peak Output Power in 65nm CMOS

In this paper, we present a 0.23-THz harmonic VCO based on coupled standing wave oscillators. The transistors with drain inductances (realized by transmission lines) provide the necessary loss compensation for oscillation. At the same time, the drain transmission lines direct the output second harmonic power to the pad, thus minimizing the routing losses for the high frequency output power. Furthermore, they couple the neighboring oscillators, forcing them to oscillate out-of-phase, canceling the large fundamental frequency as well as other odd harmonics while generating in-phase second harmonics. This makes for a compact structure that minimizes the losses of the passive network by avoiding extra coupling and routing elements. The standing wave nature of the oscillators allows us to use bias as frequency tuning control and employ the transistors to play a double role as active varactors as well. We therefore avoid the undesired varactor loss and achieve a wide bandwidth of operation with reasonable variation in the output power. The chip was fabricated in a 65nm CMOS process and provides 219-to-238 GHz frequency (8.35% tuning range) with 3.4 dBm maximum output power and -105.8 dBc/Hz phase noise (at 10-MHz offset) while consuming 195 mW from a 1.5-V supply.