A CMOS image sensor implementing a low noise active reset operation uses control circuitry outside a pixel sensor array and transistors in a pixel sensor as parts of an amplifier that charges a photodiode node. In one configuration, a reference transistor in the control circuit controls a current mirrored to a column line, and each pixel sensor in the corresponding column contains a transistor that acts as half of a differential pair when the row containing the pixel sensor is selected. A 4-transistor pixel sensor can be implemented using only NMOS transistors with PMOS transistors in the control circuitry used to complete an amplifier circuit.