An active pixel image sensor is formed on a P-type epitaxial layer on a P-type substrate. An active pixel array is in the P-type epitaxial layer. Each pixel includes an N-well functioning as a collection node, and a P-well adjacent the N-well. The P-well includes only NMOS transistors functioning as active elements. The in-pixel transistors cooperate with off-pixel PMOS transistors to form A-D converters.