Innovation powers the 'camera phone'

Innovation powers the 'camera phone'
One of the most amazing trends of recent times in ultraportable applications is convergence: smart phones that blend cell phones with PDAs, digital still cameras (DSCs), music players and global-positioning systems (GPSes); audio video recorders that contain camcorders, DSCs, audio players, voice recorders and movie viewers; and digital paper for paper, displays, printers and copiers. While some of those converged applications will take a while to materialize, others are hitting the market now-and with a vengeance.

One important example happening now combines two very successful ultraportable devices, DSCs and color cell phones, into a single portable device, the camera phone. Let's take a look at the standalone DSC, how one can integrate this function into the camera phone and finally the implications of convergence in terms of power consumption and power sources.

DSCs have enjoyed a brisk growth in the past few years and today more DSCs are sold than notebooks, with one-third of them offering high-resolution (higher than 3 megapixels) capabilities. Top-of-the-line cameras today are capable of resolutions close to 5 megapixels, with as high as 7 on the horizon.

The DSC and its power flow from the source include a number of blocks. The key element in a DSC is its image sensor, which traditionally has been a charge-coupled device (CCD). More recently, that key element is a CMOS integrated circuit that substitutes the film of traditional cameras and typically is powered by a 2.7- to 3.3-volt, 0.5-watt source.

The camera flash in a DSC is produced by a Xeon lamp that is powered for the duration of the light pulse by a boost regulator converting the battery voltage up to 300 V. The lamp is initially excited with a high-voltage (4- to 5-kV) pulse that ionizes the gas mixture within the lamp. The pulse is fired by a strobe unit composed of a high-voltage pulse transformer and an insulated-gate bipolar transistor.

Backlight power drop

The color display backlight can be powered by four white LEDs via an active LED driver, which allows duty cycle modulation of the LED bias current to adjust the luminosity to the ambient light, thereby minimizing the power consumption in the backlight. The focus and shutter motors can be driven by a dual-motor driver and the Li+ battery can be charged by an off-line charger adapter. Finally, the DSP color-correlation unit can be powered by a low-voltage, low-current (1.2-V, 300-milliamp) buck converter.

As an example of the power demands of this application, the peak power dissipated by a palm-sized DSC (1.3 megapixels) during picture taking can be around 2 W and 1.2 W (say, 500 mA at 2.4 V) during viewing. In this case, two rechargeable NiMH cells with 700-mAh capacity in series can then sustain close to one hour of picture taking and viewing.

If DSCs are hot in the marketplace, camera phones are sizzling. It is expected that this year the number of camera phones will surpass the number of DSCs and by 2007 one-fourth of all cell phones produced will have cameras on board.

The Japanese have been leading the demand for high-end camera phones equipped with megapixel, solid-state memory cards and high-resolution color displays. As of this writing, a number of camera phones are being announced in Japan with a resolution of 1 and 1.3 megapixels, which now match the performance of low-end DSCs. Not surprisingly, DSCs are forecast to show a more moderate rate of growth. Cameras for currently produced cell phones are confined inside tiny modules and are generally meeting stringent targets, including 1-cm3 space, 100-mW power, 2.7-V voltage source and $10 cost.

A battle is being waged among the makers of image sensor technology. With cell phone manufacturers willing to allocate 100 mW or less to power dissipation, CCD image sensors come close to that limit, while CMOS sensors typically require half the power. At the lower resolutions, CMOS image sensors seem to have won over CCDs-thanks to their lower power dissipation. At the higher resolutions ( > 1 megapixel) CCDs should still be in the lead.

Today's camera phones have resolutions mostly in the 0.3-megapixel range and basically consume similar peak power levels (below 1.5 W) in call and

picture mode. Extrapolating the DSC example used earlier, a 1.3-megapixel camera phone could exhibit peaks of power consumption in picture mode (2 W) higher than in call mode (1.5 W). Such state-of-the-art camera phones, equipped with a 3.6-V, 1,000-mAh Li+ cell, should warrant around two hours of call and picture mode time. Current camera phones and DSCs come with an 8- to 16-Mbyte memory stick of flash memory for storage. Solid-state memory cards, dubbed Mini SD cards, will go up to 256 Mbytes by the end of the year.

The price of all these features is that it causes a downward spiraling of cell phone talk time-from six hours for regular cell phones to one or two hours for the new camera phones.

Notebook pitfalls

The chipping away at talk time will continue as the pressure for higher numbers of pixels, higher-resolution displays and more features incorporated into the cell phone increases.

With one to two hours of operation, the camera phone is joining the similar power-management pitfalls of its bigger relative, the notebook PC. With both relying on the same liquid-crystal display and battery (Li+) technologies, this is no big surprise.

For the notebook to achieve eight hours of operation, and for the cell phone to go back to its initial talk time, new technologies need to bear fruit. Fuel cells, electrochemical devices converting the energy of a fuellike methanol directly into electricity, have the potential to store 10 times the energy of current batteries. This will be ready for prime time in a couple of years. On the display front, organic LEDs need to take over from current transmissive-LCD technology, thereby eliminating the power-hungry backlight outfits.

RENO ROSSETTI is director of corporate strategy for computing for Fairchild Semiconductor International (San Jose, Calif.).

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