Eastman Kodak hopes turning one aspect of chip design on its head will help improve cell phone cameras--or at least help their image quality catch up with their megapixel increases.
"We believe we've created a new camera sensor product that rivals that of real cameras, but it's small enough to be used in a camera phone," said Fas Mosleh, manager of CMOS market work for Kodak's professional and applied imaging group.
There have been nice cameras in high-end mobile phones such as Nokia's N95, but Kodak believes its technology, built into a 5-megapixel sensor product to ship by the end of the year, will help bring better cameras to mainstream mobile phones.
Semiconductor chips currently detect light essentially by counting how many electrons result from light striking a pixel on the image sensor. More intense light means more electrons, and that electronic signal can be converted into digital data.
But Kodak believes it can get some improvements by rewiring the image sensor design to detect the absence of electrons instead--in effect counting "holes" rather than electrons. To do so, some sensor circuitry must be rewired, but Kodak argues that the technology produces less noise than conventional sensors.
The upshot, as promised by Kodak: better picture quality, or the same picture quality when shooting in dim light conditions such as those that prevail in most indoor scenes.
A basic problem with image sensors is the challenge of distinguishing the light's signal--the actual photons striking the sensor--from electronic noise within the sensor. That problem gets worse as pixels get smaller, so more megapixels isn't necessarily progress.
"Image quality has been deteriorating because your image resolution has been going up. Pixelization is better, but your low-light performance is worse," Mosleh said. "If you pick up a camera phone from 2003 or 2004 and compare to one from 2008, that old one will produce nicer pictures."
For product purposes, Kodak is pairing the hole-detector technology with a new color filter array Kodak calls Clear Pixel that's designed to improve low-light performance even more by devoting some pixels to measuring just brightness instead of color.
The 5-megapixel technology package, called the KAC05020, will fit into a small package measuring about .25 inch square and costing between $3 and $6 in large quantities, depending on what associated technology and software is included, Kodak said. It will support capture of 720p high-definition video, too.
Kodak researchers are presenting the sensor technology at the International Solid-State Circuits Conference on Monday in San Francisco.
The hole-detector pMOS technology could apply to larger sensors, but its benefits are clearer on small sensors, Mosleh said.
Kodak will offer KAC05020 samples in the second quarter, with high-volume shipments in the fourth quarter, the company said.
The hole detection, called pMOS in contrast to the usual NMOS sensors, can be built with no changes to semiconductor manufacturing, Mosleh said. However, some changes are necessary. "Pixel designers who have been working with collecting electrons now are collecting the absence. And the circuits coming off the sensor need to be repositioned, so support electronics need to be changed," he said.