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Cell Phone Camera Integrates Xenon Flashlamp

Photonics Spectra
Jan 2005
Hank Hogan

For cell phone manufacturer Kyocera Corp., the solution to its camera problem came in a flash. Kyocera, based in Kyoto, Japan, turned to the Fremont, Calif.-based optoelectronics division of PerkinElmer Inc. to transform the xenon flashlamps found on megapixel digital still cameras into something suitable for a cell phone.

Besides making calls, today's cell phones are pocket organizers, video game consoles, text-messaging tablets and cameras. That last capability presented Kyocera with a challenge. Once content to be able to take a fairly crude picture with a cell phone, consumers now are demanding higher performance. Consequently, companies are responding with cell phone cameras that feature greater and greater pixel counts.

In 2003, most camera phones were 0.3-megapixel devices. By mid-2004, however, manufacturers were producing camera phones -- including Kyocera's A5502K model -- with 1-megapixel resolution or higher.

Megapixel resolutions not only allow for superior image quality, but also demand more from the camera's light source. In an announcement regarding the new phone, Nobuharu Shino, general manager of Kyocera's Yokohama mobile phone division, noted the difficulties that result from the integration of such high-pixel-count cameras with cell phones. Although the CCD camera in the A5502K produces high-resolution photos, to do so it requires a much more powerful illumination source than the LED flash typically found in camera phones, Shino said, and his company thus opted to employ xenon flashlamps.

A xenon flashlamp has a number of advantages over LEDs for this application. The color temperature of a flashlamp, which is between 5500 and 6000 K, is close to that of sunlight, enabling one to capture images that have a natural appearance. In contrast, the standard LED color temperature of approximately 8500 K creates a blue tinge. Xenon flashlamps also produce shorter-duration flashes than an LED and so improve the picture sharpness for moving objects. Finally, the light from a flashlamp can be more evenly distributed over an object than that from a typical LED source.

On the other hand, the flashlamps tend to be larger and consume more power than LEDs. In the cramped confines of a battery-operated cell phone, increasing either volume or power requirements is to be avoided if at all possible.

Capacitor solution

Working closely with the cell phone maker, PerkinElmer's engineering team produced flashlamps in the allowed space that met the power requirements. They did this while creating a lamp that projects light up to four times the distance of current LED technology.

Stephen J. Klibansky, sales manager for lighting products at PerkinElmer Optoelectronics, said that the solution was not so much in the light source as in the capacitors that store the energy to fire the flashlamp. These tend to be the hardest items to fit into the allotted space, and they tend to demand such design tradeoffs as balancing capacitor specifications against flash -- and, hence, picture-taking -- rate.

As for the future, Klibansky said that he expects more xenon flashlamps to be used as camera phone resolutions rise to 2 megapixels and higher. He added that PerkinElmer is working with a vendor to customize capacitors to continue to refine the technology for this application.


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