A voltage control signal at a voltage control signal input terminal is used to adjust an output frequency of an oscillator circuit. The voltage level of the voltage control signal is converted in a one-bit analog-to-digital converter (ADC) to a digital output indicative of the voltage level. Successive digital representations of the voltage level of the voltage control signal are upsampled to generate upsampled blocks of data. A dither circuit inserts a digital dither in the upsampled blocks of data to generate dithered upsampled data, which is used to generate a control signal for a feedback divider of a phase-locked loop circuit and thereby adjust the output frequency.