Embodiments of the present disclosure provide ADCs particularly suitable for PDAF image sensors, which ADCs may have an increased speed and/or reduced design complexity and power consumption compared to conventional implementations. An example ADC for a PDAF image sensor is configured to implement modified SAR techniques which reduce the number of bit trials required for conversion, and enable increased number of samples in a row-conversion time period of the image sensor. The ADC may implement the modified SAR techniques in combination with CMS in pixel readout signal chain, which may reduce noise without a proportionate increase in ADC sample rate.