A Low-Power Class-C Voltage-Controlled Oscillator With Robust Start-Up and Compact High-Q Capacitor Array

This brief presents a class-C voltage-controlled oscillator (VCO) that ensures a robust start-up with low phase noise and high power efficiency. The proposed start-up scheme, which uses a voltage converter that operates according to the output state, relieves the start-up difficulty by supplying a time-varying bias voltage to the core transistors and allows the VCO to operate in an optimal state. The start-up circuitry is enabled only during initial operation, so power efficiency is improved without phase noise degradation. Furthermore, a capacitor array with a high quality factor is implemented by a direct capacitor connection that exhibits low series resistance. Fabricated with a 65-nm CMOS, the VCO demonstrates a frequency tuning range of 13.1% from 19.3 to 22.0 GHz. The measured minimum phase noise at a 1-MHz offset is −106.33 dBc/Hz at an oscillation frequency of 19.7 GHz, while dissipating 3.8-mW of power from a 1.0-V supply. The VCO occupies an active area of 0.064 mm 2 . It reveals a figure-of-merit and figure-of-merit with area of −186.4 and −198.3 dBc/Hz, respectively.