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A switched resonator concept, which can be used to reduce the size of multiple-band RF systems and which allows better tradeoff between phase noise and power consumption, is demonstrated using a dual-band voltage-controlled oscillator (VCO) in a 0.18-μm CMOS process. To maximize Q of the switched resonator when the switch is on, the mutual inductance between the inductors should be kept low and the switch transistor size should be optimized. The Q factor of switched resonators is ∼30% lower than that of a standalone inductor. The dual-band VCO operates near 900 MHz and 1.8 GHz with phase noise of -125 and -123dBc/Hz at a 600-kHz offset and 16-mW power consumption. Compared to a single-band 1.8-GHz VCO, the dual-band VCO has almost the same phase noise and power consumption, while occupying ∼37% smaller area.