Integrated circuits with phase-locked loops are provided. A phase-locked loop may include voltage-controlled-oscillator (VCO) circuitry. The VCO circuitry may include multiple VCO circuits that receive power supply signals from a positive power supply terminal and a ground power supply terminal. Low-pass filters may be connected to the positive and ground power supply terminals to suppress high frequency noise that may be injected through the power supply terminals. The VCO circuitry may be operable in multiple modes. In a given mode, a selected one of the multiple VCO circuits is enabled while disabling the remaining VCO circuits. Switch circuits formed from transmission gates with pull-down transistors may be used to select which VCO circuit is active.