An analog-to-digital converter may convert an analog signal into digital codes representative of the changing level of the analog signal. An analog high pass filter may receive and continuously differentiate the analog signal. A voltage controlled oscillator may receive the differentiated analog signal and continuously generates an output that is an integral of the differentiated analog signal in the phase domain. A time-to-digital converter may sample the output of the voltage controlled oscillator and convert each sample into a digital code representative of the current phase of the sampled output of the voltage controlled oscillator.