A high-sensitive digital photosensor using MOS interface-trap charge pumping

A high-sensitive CMOS photosensor based on a pulse frequency modulation (PFM) scheme is presented. We propose and demonstrate the high-sensitive PFM photosensor, whose output frequency is proportionate to the incident light intensity, that utilizes MOS interface-trap charge pumping (ITCP) as a frequency-controlled ultra-low current. The proposed pixel sensor consists of only 4 transistors: a transistor as an ultra-low current source; a sense amplifier transistor; a selection transistor; and, a reset transistor. The prototype device is fabricated using 0.6-mu m standard CMOS technology. High sensitivity 4.0 x 10(5) Hz/(W . m(-2)), which is larger than two orders of magnitude compared to previous works, was obtained.