Balanced and differential voltage controlled oscillators (VCOs) are investigated with analytic noise models. Fully integrated VCOs in K u-band are implemented on an InGaP-GaAs heterojunction bipolar transistor technology. The balanced VCO has higher output power and lower phase-noise performance, while drawing lower current than the differential VCO. This coincides with the analytical expectation. The shot noise of collector current contributes less to the phase noise in the balanced VCO (B-VCO) than in the differential VCO. The B-VCO shows 2-3 dB lower phase-noise performances of 90.5, -113.8 dBc/Hz at the offset frequencies 100 kHz, and 1-MHz offset at 13.5 GHz than the differential VCO, and figures of merit of 180.7 and -177.6 dBc/Hz are achieved, respectively.