[OPTICAL REVIEW Vol. 11, No. 3 (2004) 176-181]
© 2004 The Optical Society of Japan
Building a Simple Model of a Pulse-Frequency-Modulation Photosensor and Demonstration of a 128× 128-pixel Pulse-Frequency-Modulation Image Sensor Fabricated in a Standard 0.35-μm Complementary Metal-Oxide Semiconductor Technology
Keiichiro KAGAWA*, Norikatsu YOSHIDA1, Takashi TOKUDA, Jun OHTA and Masahiro NUNOSHITA
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan
1Matsushita Electric., 1006 Kadoma, Kadoma City, Osaka 571-8501, Japan
(Received December 10, 2003; Accepted February 19, 2004)
We present a simple model of the pulse-frequency-modulation (PFM) photosensor that provides explicit relationships between circuit parameters and output characteristics. The model treats the PFM photosensor with a feedback loop as an open loop circuit. Several characteristics such as output pulse frequency for light intensity and photosensitivity are expressed by device parameters of a photodiode, reset transistor, and chain of inverters. The relationships derived from the proposed model help us to comprehend the results by simulation program with integrated circuit emphasis (SPICE) or experiments. We design and fabricate a 128× 128-pixel PFM image sensor with photosensitivity of 0.15 Hz/lux. As a demonstration, a figure of a dinosaur is captured using the fabricated image sensor to discuss its operation. Characteristics of a normal pixel and white and black defect pixels are measured and discussed based on the results of formulations.
Key words: pulse-frequency-modulation photosensor, CMOS image sensor, vision chip
*E-mail address: kagawa@ms.naist.jp