A voltage-controlled oscillator (VCO) comprises a supply voltage node, configured to receive a supply voltage, a VCO output capacitor, configured to provide an oscillating output voltage across the capacitor, a discharge switch configured to discharge the capacitor according to an oscillation frequency of the oscillating output voltage, and a comparator circuit configured to provide, to a control terminal of the discharge switch, a control signal that is determined based on a comparison of the output voltage and a specified threshold voltage. The oscillating output voltage includes a pulse having a ramp slope that is determined as a function of a magnitude of the supply voltage, and is capable of being adjusted independently of the oscillation frequency.