A 13.1% tuning range 115GHz frequency generator based on an injection-locked frequency doubler in 65nm CMOS

Ultra-scaled CMOS devices offer the possibility of operation beyond 100GHz where new applications are envisioned in the near future, including imaging and spectroscopy systems for scientific, medical, space, and industrial applications at low cost, light weight and easy assembly [1]. However, a long path toward complete systems of any commercial interest is required, even though simple building blocks have already been presented [2–6]. One of the challenges of such high-frequency transceivers is the on-chip reference generation. Adoption of a voltage-controlled oscillator (VCO) at fundamental frequency sets an increasingly severe trade-off between high spectral purity and frequency tuning due to a dramatic reduction of resonator quality factor and large parasitics introduced by active devices and buffers, operating close to the transition frequency. As an example, state-of-the-art varactor-tuned VCOs beyond 100GHz in standard CMOS technology display a tuning range of less than 3%, not enough to cover process spreads [3–5]. An alternative solution relies on frequency multiplication of a lower frequency reference, with the potential advantage of a higher tuning range and lower phase noise set by the lower frequency VCO enslaving the multiplier.