In accordance with an embodiment, a circuit includes an oscillator having an oscillation frequency dependent on an input signal, a digital accumulator having a first input coupled to an output of the oscillator, a digital-to-analog converter (DAC) coupled to an output of the digital accumulator, an analog loop filter coupled to an output of the digital-to-analog converter, and a comparison circuit having an input coupled to an output of the analog loop filter and an output coupled to a second input of the digital accumulator.