An image sensor, comprising: a pixel circuit including a reset transistor and configured to output a pixel signal; a digital-to-analog converter configured to output a reference signal having a ramp waveform; and a differential comparator connected to the pixel circuit via a signal line for receiving the pixel signal as a pixel input, and connected to the digital-to-analog converter for receiving the reference signal as a reference input, and wherein the differential comparator is configured to receive the pixel signal at the pixel input and the reference signal at the reference input and to output a comparator signal at a comparator output, wherein one of a source or a drain of the reset transistor is connected to the comparator output, wherein: the digital-to-analog converter is configured to initialize to an initial signal level, then the reset transistor is turned on, thereby a current flows from the comparator output through the reset transistor until a balanced state at the differential comparator is achieved, then the reset transistor is turned off, then the digital-to-analog converter outputs the ramp waveform, at which point the differential comparator is configured to perform a P-phase measurement corresponding to a reset level of the pixel circuit, and the digital-to-analog converter is configured to subsequently re-initialize to the initial signal level and then output the ramp waveform, at which point the differential comparator is configured to perform a D-phase measurement corresponding to a data level of the pixel circuit. a pixel circuit including a reset transistor and configured to output a pixel signal; a digital-to-analog converter configured to output a reference signal having a ramp waveform; and a differential comparator connected to the pixel circuit via a signal line for receiving the pixel signal as a pixel input, and connected to the digital-to-analog converter for receiving the reference signal as a reference input, and wherein the differential comparator is configured to receive the pixel signal at the pixel input and the reference signal at the reference input and to output a comparator signal at a comparator output, wherein one of a source or a drain of the reset transistor is connected to the comparator output, wherein: the digital-to-analog converter is configured to initialize to an initial signal level, then the reset transistor is turned on, thereby a current flows from the comparator output through the reset transistor until a balanced state at the differential comparator is achieved, then the reset transistor is turned off, then the digital-to-analog converter outputs the ramp waveform, at which point the differential comparator is configured to perform a P-phase measurement corresponding to a reset level of the pixel circuit, and the digital-to-analog converter is configured to subsequently re-initialize to the initial signal level and then output the ramp waveform, at which point the differential comparator is configured to perform a D-phase measurement corresponding to a data level of the pixel circuit. the digital-to-analog converter is configured to initialize to an initial signal level, then the reset transistor is turned on, thereby a current flows from the comparator output through the reset transistor until a balanced state at the differential comparator is achieved, then the reset transistor is turned off, then the digital-to-analog converter outputs the ramp waveform, at which point the differential comparator is configured to perform a P-phase measurement corresponding to a reset level of the pixel circuit, and the digital-to-analog converter is configured to subsequently re-initialize to the initial signal level and then output the ramp waveform, at which point the differential comparator is configured to perform a D-phase measurement corresponding to a data level of the pixel circuit.