The Future of Mobile Power
It is difficult to summarize the impact of the myriad of mobile devices that are carried around in the pockets of modern society, but for sure they have made us more connected, informed and interesting. What we do know is that these devices require power to operate and for the foreseeable future will continue to do so. The question is how much energy and from what sources will future mobile devices draw their power.
If we attempt to break down the family of existing pocket sized mobile devices we can identify two major categories, those used for communication and those used for entertainment. In reality that line has vanished and many devices now provide both functions adding additional power requirements beyond simple “talk time”. Looking forward, that requirement will continue as features such as mobile two-way video and IPTV will become ubiquitous requiring improvements in both efficiency and battery technology.
It is widely accepted that battery technology has not yet caught up with modern electronics. Engineers and scientists continue to look for higher energy density storage solutions. There are a few on the horizon and one which leaps off the pages of a science fiction novel is carbon nano-tube super capacitors. By growing fields of tiny carbon nano-tubes on the plates, extremely large charge densities can be achieved. Super capacitors lack the chemical processes that limit the life span of batteries and since these storage devices are capacitors, they can provide very fast charge times as well.
Beyond improving the energy storage of mobile devices, there is the potential for power generation through various harvesting methods. Since these devices are often “mobile”, energy can be scavenged from light and vibration and stored. These supplemental energy sources will dramatically extend the run time of mobile devices. By placing photovoltaic cells on the back of a PMD, a user could simply lay the device on a surface upside down and recharge it anywhere there’s light. While in your pocket, the vibration of everyday use could also provide additional energy.
In addition to harvesting, wireless charging will finally cut the last wires tethered to your PMD. Technologies such as Vertical Fountain Flux charging can directly charge a mobile device without damaging nearby magnetic sensitive materials (e.g. credit card magnetic strips, etc.). All that a user needs to do is lay the PMD on the charger pad… and that’s all. Other wireless power technologies are being developed and someday may be standardized and ubiquitous allowing your PMD to operate without ever being connected to wires.
So we know these devices need power and those technologies are improving, but what about the consumption part of the equation. The features and functionality of PMDs is constantly increasing while manufacturers continue to provide improve run times. This can only mean that the energy efficiency of the functionality is improving. One of the biggest consumers of energy (besides the RF components) is the display. Devices are using larger displays as touch technology becomes increasingly popular. The larger LCD displays require higher power back-lights, so any improvement here goes a long way to improving power consumption.
There are several promising display technologies that can improve the power consumption. One is Sequential Frame LCD which removes the color filters from the display which absorb up to 85% of the back-light energy. These displays use red, green and blue LEDs as the back light and special frame sequencing to quickly switch between each primary color frame forming a complete color image. This can reduce the back-light requirements to only 20% of that of conventional LCDs dramatically reducing power.
Another display technology is Organic LEDs or OLEDs. Not only does this technology dramatically reduce power, but it also allows for some very creative displays. Since the technology can be “printed” on plastic, it can be flexible allowing displays to role-up or bend allowing for even larger displays in PMDs.
Finally, the power converters themselves are evolving. It will soon be possible using Micro Electro-Mechanical Systems technology or MEMS to build power transformers and high density capacitors right on the die of integrated circuits allowing a complete power supply in a chip. Currently, integrated buck switching regulators contain everything except the output filter comprised of an inductor and capacitor. By integrating those last two large components onto the die and moving the switching frequencies higher, high efficiency converters can be built on a chip again shrinking the PMD even smaller or providing more room for energy storage.
There is no doubt that we are increasing our use of mobile devices and users expect each generation to provide a richer user experience as well as improved run time between charges. Ultimately, we may rely completely on these devices and rarely sit in front of a “computer”. The lines have already blurred in many cases and with the emergence of new technologies, next generation PMDs will continue to amaze us.
National Semiconductor Corporation
This article first appeared in the January, 2009 issue of Portable Design. Reprinted with permission.
Santa Clara, CA