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This paper presents a novel dual-band SiGe HBT differential VCO using a control voltage for both band-switching and frequency-tuning. It uses a dual-band resonator comprised of a HPF connected in parallel with a series LC circuit and back-to-back varactor diodes. A dual-band switching is achieved by feeding a forward or reverse bias for the varactor diodes. In addition, a frequency-tuning is realized by varying a control voltage for the varactor diodes. A miniaturized size and high performance are expected since no additional VCOs, resonators, matching elements, control voltages or currents are required for a dual-band switching. The implemented 0.35-μm SiGe HBT differential VCO has presented a low-band oscillation from 0.65 to 0.93 GHz with a control voltage from 5.1 to 16 V and a high-band oscillation from 1.49 to 1.56 GHz with a control voltage from 0 to 5 V. A supply voltage keeps constant with 5 V. The phase noise at 100 kHz offset shows less than -104 dBc/Hz for the low-band oscillation and less than -102 dBc/Hz for the high-band oscillation. This is the first report on the dual-band differential VCO using a control voltage for both band-switching and frequency-tuning.