Relaxation-type monolithic silicon bipolar voltage-controlled oscillators (VCO's) with center frequencies ranging from 1.5 to 5 GHz are described. The maximum oscillating frequency achieved is 7.4 GHz. The VCO's dissipate about 70 mW from a 3.6-V supply, including the output buffer and voltage-to-current converter stages. Two types of on-chip timing capacitor structures and various configurations used in achieving these results are described. A wide tuning range has been achieved which is sufficient to cover the normal process tolerances and supply variations expected in a practical environment. The circuits are fabricated in an advanced 0.8-µm double-poly self-aligned bipolar technology.