This brief presents a 46 μW 0.8-2 GHz tunable oscillator with built-in self-calibrated process, supply voltage, and temperature compensation for applications in low-power radios. With single-point current calibration at room temperature, the proposed voltage-controlled oscillator (VCO) achieves 2.24% frequency accuracy against process variation, 1.6% frequency shift over 0.85- to 1.15-V supply voltage, and 167-ppm/°C temperature sensitivity between -7°C and 76°C. The sub-135-pJ on-chip self-calibration is based on a successive approximation scheme. Our design shows 3.4× improved process variation tolerance, 45× improved supply sensitivity, and 5.2× improved temperature sensitivity, as compared with the free-running VCO without self-calibration. Measurements are taken from 94 chips fabricated in two different lots in Taiwan Semiconductor Manufacturing Company 65-nm CMOS process.