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A low power and robust class-C voltage-controlled oscillator (VCO) is presented in this letter. It features 1) an automatic startup loop to achieve the optimal point and address the inherent risk of startup failure and 2) a digital amplitude control loop to stabilize amplitude and enhance the PVT (process, voltage and temperature) tolerance. The design is implemented in a 0.18 μm CMOS process. Measurement demonstrates the VCO has a 20% tuning range and phase noise of -123.0 dBc/Hz at 1 MHz offset from a 3.1 GHz carrier while consuming 1.57-mW power from a 1 V supply, yielding a Figure-of-Merit (FoM) of 191.1. While operating under the minimum power of 560 μW, it produces -111.3 dBc/Hz phase noise at 1 MHz offset from a 3.1 GHz carrier showing a 183.8 FoM.