A Startup Robust Feedback Class-C VCO With Constant Amplitude Control in 0.18 $\mu$m CMOS

A feedback class-C VCO with constant amplitude control is presented in this letter. Its dual-loop topology helps to stabilize amplitude and ensure startup robustness over process, voltage and temperature (PVT) variations. Besides, this VCO facilitates a direct amplitude calibration method to find optimal point for different applications. A prototype VCO is implemented in a 0.18 μm CMOS process. Measurement shows the VCO has a 4.55-5.16 GHz frequency tuning range and a phase noise of -123.3 dBc/Hz at 1 MHz offset from a 5 GHz carrier with a 2.78 mW power consumption. The FOM is -192.8 dBc/Hz.