Lighting Tradeoffs in Low-cost Handset Design
By Adolfo Garcia, Advanced Analogic Technologies, Inc.
Despite the industry’s relentless focus on many exciting new features and capabilities available in today’s high performance smart phones, the largest untapped segment of the handset market lies at the opposite end of the product line.
Adolfo Garcia, Advanced Analogic Technologies, Inc.
By Adolfo Garcia, Advanced Analogic Technologies, Inc.
Despite the industry’s relentless focus on many exciting new features and capabilities available in today’s high performance smart phones, the largest untapped segment of the handset market lies at the opposite end of the product line. Emerging markets in China, India, Africa, Russia and South America offer tens and possibly hundreds of millions of potential new customers. Unlike established handset markets in South Korea, Taiwan, Western Europe, Japan and North America that are largely saturated, these under-developed regions often provide little or no existing telecommunications infrastructure and a built in demand for the benefits of wireless connectivity.
To address this need, a number of leading handset manufacturers has begun designing a new breed of extremely low cost cell phones. But manufacturing handsets for a user base with little disposal income offers an entirely new set of challenges. How does the designer deliver basic connectivity to a user base at minimal cost? And what types of tradeoffs does the designer face to achieve that goal?
Take a quick look at any new high performance smart phone today and it’s obvious that many of the new bells and whistles are based on recent advances in display and lighting technology. Many handsets now offer camera and video playback functionality, Internet access and mobile broadcast TV via a large 2.5-to-3 inch diagonal main display as well as date and time information via a sub panel. Fashion, keypad and status lighting are common features as well.
Each display requires multiple White LEDs and drivers for backlighting the main and subpanels and RGB LEDs and drivers for fashion lighting or status indicators. To help designers minimize the footprint of their handsets, power semiconductor manufacturers over the last several years have developed a variety of vertically-integrated power management ICs which combine charge pumps, multiple outputs for White and Flash LEDs and, in some cases, even LDOs to support these functions.
Clearly customers in these new emerging markets cannot afford these highly attractive, but in many ways ancillary features. They need basic connectivity at an extremely affordable price. One way handset manufacturers will address this cost limitation is by moving to smaller, lower cost monochrome TFT panels in place of the larger, more expensive color screens used in most handsets in the industrialized world. However, these lower-cost, highly opaque monochrome displays still require relatively high levels of backlighting to make them readable. So how does the designer meet this need for reasonable backlight performance while also meeting the stringent cost requirements of this new class of phones?
One way is by moving to smaller 2- and 3-channel charge-pump-based white LED (WLED) drivers that offer part-to-part current accuracy and channel-to-channel current matching comparable to leading edge drivers at a small sacrifice in power efficiency. Devices that drive 2 or 3 LEDs at up to 30 mA each and offer part-to-part current accuracy at better than 10 percent and channel-to-channel current matching at better than 3 percent can support the illumination of lower cost, monochrome TFT-LCD panels. As an example, AnalogicTech has recently introduced a family of devices of this type that is available in an extremely compact 2×2-mm package. For details, see white LED drivers.
Moreover, by moving from a fractional charge pump to devices that automatically switch between 1x and 2x mode, designers can reduce the number of external components and associated cost. A WLED driver of this type will only require a small 1 µF capacitor for the charge pump and a single external resistor to set the full-scale LED current.
Developing handsets for users in emerging markets, particularly in poorer rural areas, will clearly require innovative thinking. But by making the right tradeoffs in functionality and taking advantage of the latest advances in power semiconductor design, handset manufacturers can develop the ideal products for these users’ needs.
Adolfo A. Garcia is Product Line Director for Lighting & Display Products at Advanced Analogic Technologies, Inc., in Sunnyvale, CA. www.analogictech.com/ He manages all product development, product definition, marketing, and business development activities for his product line. Adolfo has held design, applications, and marketing management positions at Analog Devices, Linear Technology, and Micrel.
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