The disclosure relates to a square wave RC oscillator circuit, example embodiments of which include an oscillator circuit for generating an output square wave signal (OUT) having first and second voltage output levels (L, H), the oscillator circuit comprising: a comparator having an output and first and second inputs; a switching circuit configured to provide an oscillatory waveform at the first input of the comparator; and a feedback circuit arranged to sample the first input of the comparator each time the output square wave signal (OUT) switches between the first and second voltage output levels (L, H) and to compare this sampled voltage with first and second reference voltages (VA, VB) to adjust a voltage provided to the second input of the comparator.