An image sensor is described. The image sensor includes a pixel array having a unit cell that includes visible light photodiodes and an infra-red photodiode. The visible light photodiodes and the infra-red photodiode are coupled to a particular column of the pixel array. The unit cell has a first capacitor coupled to the visible light photodiodes to store charge from each of the visible light photodiodes. The unit cell having a readout circuit to provide the first capacitor's voltage on the particular column. The unit cell having a second capacitor that is coupled to the infra-red photodiode through a transfer gate transistor to receive charge from the infra-red photodiode during a time-of-flight exposure. The unit cell has a back-drain transistor coupled to the infra-red photodiode.