eetimes.com
Philips CCD rivals 35-mm quality
By Peter Clarke
EE Times
(12/09/99, 12:07 p.m. EDT)
WASHINGTON ? Digital still cameras could rival the image quality of
35-mm film photography within a couple of years due to a charge
coupled device (CCD) image sensor with over six million pixels
developed by Philips Semiconductors (Eindhoven, Netherlands).
Herman Peek, a senior scientist at the company, presented a paper on
the prototype device at this week's International Electron Devices
Meeting. "This is the largest number of pixels and the smallest pixel
size for a digital still camera ever published in the world," Peek said
during the presentation of his paper.
Although the prototype sensor is monochrome, and the use of red,
green and blue filters would reduce resolution to 2 million tricolor
pixels, Peek said the small size of individual light sensing elements,
3-micron x 3-micron, would allow such a sensor to rival small format
film photography.
"We are approaching the grain size of film, which is about 2 microns
diameter, but image quality is also determined by the quality of the
lens. The same thing effects CCD."
Images produced using the sensor and displayed by Peek, albeit
through an overhead projector system, were indistinguishable from
images obtained from film. Individual hairs could been seen on the
heads of head-and-shoulder portraits, which prompted congratulations
from the audience.
Peek said he expects to see a similar high-resolution CCD sensor in
production within about two years, although it might include fewer
pixels. "I don't think we will go to more pixels," he said. "We are
already asking, 'Is six million too much and are we adding cost
unnecessarily?' Perhaps five million or four million is the right amount."
For a 2/3-inch format, Peck showed that the pixel size was on the
limit of lens resolution, although the device could also be used for
lens-less applications.
The Philips CCD is built using a 0.5-micron CCD process operating at
14 volts and has an active area of 2,048 active lines and 3,072 active
measuring 9.11 mm x 6.07 mm. The sensor has a dark current of 800
picoamperes/centimeter2 and a dynamic range of 63 dB. In his paper,
Peek also discussed how novel techniques had been used to overcome
problems with dark current suppression.
The development of a high-resolution sensor using CCD technology
represents a fight back by the technology against a challenge it faces
from lower cost CMOS image sensors, which also allow the possibility
of including signal processing and logic circuits on the same die.
"CCD will always be expensive in comparison with CMOS image
sensors," Peek said. "CCD can't compete with CMOS on price but it
can on quality, and image quality is very important to consumers." |
