A phase-locked loop circuit includes an oscillator, a frequency control device, the frequency control device generating a frequency control signal that controls a frequency of the oscillator, and a bias optimizer that monitors the frequency control device and generates a bias voltage for the oscillator, the oscillator includes a transfer function from bias voltage to frequency that is proportional to a transfer function from a low frequency noise component to frequency, the transfer function from bias voltage to frequency having a convex shape with a local minimum at which a sensitivity of the frequency to changes in the bias voltage is zero, and the bias voltage from the bias optimizer is set to the local minimum.