This paper presents the design of a novel SiGe HBT voltage controlled oscillator (VCO) that uses a lumped-element transformer as the feedback network. The VCO design employs a filter-type transformer, as opposed to an inductive transformer, to improve both the power consumption and tuning range. Unlike for the conventional cross-coupled differential oscillator and the coupled-Colpitt's oscillator, the transformer isolates the frequency selecting passive components from the parasitics of the biasing circuitry, enabling a linear tuning range of over 1 GHz (12 %) at 10 GHz. The isolation also improves the resonator loaded Q, thereby reducing the power consumption of the VCO. The measured phase noise varied between -108 dBc/Hz to -104 dBc/Hz @ 1 MHz offset over the entire tuning range of 1.04 GHz. The oscillator provides an output power of -7.5 dBm without any buffering, at 4.75 mW of power consumption from a 2 V power supply.