Robustness Enhancement of a Class-C Quadrature Oscillator Using Capacitive Source Degeneration Coupling

This brief presents a low-phase-noise Class-C-type quadrature voltage-controlled oscillator (QVCO) with a robust start-up. The chip was implemented using the 0.18-μm CMOS technology. A source degeneration coupling technique is used to generate quadrature signals and enables the elimination of bimodal oscillation. Capacitive degeneration coupling also provides negative impedance to compensate for losses in the LC tank, resulting in less power consumption in the core circuit to sustain oscillation. The proposed 2.4-GHz QVCO design achieves a 13.46% tuning range and a phase noise of -128.65 dBc/Hz at a 1-MHz offset while only consuming 2.67 mW from a 1.8-V supply. The oscillator demonstrated robust operation from -25 °C to 85 °C with phase noise lower than -122 dBc/Hz at a 1-MHz offset. The proposed QVCO achieves a remarkable figure of merit of -192 dBc/Hz.