Two EETAsia Articles

EETAsia published two good image sensor articles today. One comes from Kodak application engineer and explains operation of 4T pixel, which Kodak calls Pixelux.
The second aricle talks about camera-phone image sensors:

Compared with standalone DSCs, "camera phones have 20 times less space to work with, and they need to cost 20 times less," said Jess Lee, VP for the mainstream-products business at OmniVision Technologies Inc. Those realities have some vendors questioning whether turning a camera phone into a high-end DSC is worth an effort.

Studies have found that "90 percent of camera-phone users never print pictures taken with their camera phones," said Philippe Quinio, marketing director of the imaging division at STMicroelectronics (ST).

More specifically, 7 billion images captured by handsets have never been uploaded or printed, said Rutie Adar, product marketing director at TransChip Inc.

Kodak draws a distinction between the two products by calling camera phones "a photo-capable device" and DSCs "a photo-taking device." If current trends continue, "camera phones will become a niche product," said Nancy Carr, VP of marketing for strategic relationships at Kodak's Consumer Digital Group.

"The reduction in pixel size to 2.2μm and eventually to sub-2μm obviously presents challenges in terms of reduced low-light sensitivity, and an associated increase in noise and decrease in overall image quality," said Tony Henning, editor of Future Image Inc.'s Mobile Imaging Report.

At the heart of the issue lies the system-level design that manages the imaging flow. "Pixel technology, image-sensor processor algorithms that can compensate for bad optics and optimized specs for optics are the three fundamentals you need to own," said ST's Quinio. "Missing one of the three could be a problem."

"Autofocus based on a very simple voice-coil system is too big and bulky for a thin camera phone," said OmniVision's Lee, and "its cost adder is about $4." The technology's ability to clear the stringent drop test—as high as 1.5m—required for camera phones is another concern. The drop test for DSCs isn't as rigorous.

Liquid lenses such as those from Varioptic are now reaching the market; microlenses from Microalign show great promise; and prism lenses from Olympus—along with piezo-driven actuators from Johnson Electric, 1 Ltd and New Scale Technologies—promise small, light, rugged, power-efficient motors to drive autofocus and optical zoom, Henning said. All of these advances will produce "improvements in camera phones" and will become "major differentiators for the manufacturers who deploy them first," he said.

Another design factor that separates the image quality of DSCs from that of camera phones is the availability of image memory. In a DSC, a raw image is first grabbed and stored to memory and is then postprocessed to JPEG, ST's Quinio said. In camera phones with no frame memory, raw images are grabbed and processed on the fly, typically using a small line buffer.

Micron Technology believes it's just a matter of time before frame-level memory is integrated into system-on-chip sensors. "Multiple image frames are essential for enabling video functions in camera phones," said Gove.