Abstract: An active pixel sensor is disposed on a semiconductor substrate of a first conductivity type, and comprises a plurality of semiconductor regions disposed in the substrate, each successive one of the semiconductor regions being enclosed entirely within another enclosing one of the semiconductor regions. The plurality of semiconductor regions alternates between the first conductivity type and a second conductivity type opposite to that of the first conductivity type. A first enclosing one of the semiconductor regions containing all other ones of the semiconductor regions is of the second conductivity type, such that a plurality of series-connected photodiodes is formed between the substrate and an innermost enclosed one of the semiconductor regions. A plurality of reset switches each has a first terminal coupled to a different one of the alternating semiconductor regions, and a second terminal switchably coupled to a reset potential.