Making mobile batteries last longer

Research is being done in India to improve the power efficiency of devices.

The demand for premium features on low-cost mobile handsets in the country "" the world's fastest-growing mobile market "" coupled with the poor power supply in rural India, has turned the attention of telecom equipment providers towards improving the energy efficiency of equipment and battery life.

NXP Semiconductors has many initiatives focusing on energy efficiency "" from enhancing the life of battery-operated devices, to increasing the energy efficiency of mains-supplied equipment.

ST Microelectronics and Texas Instruments are doing a lot of work in this regard in India. While Texas Instruments is focusing on portable and plug-in power, LCT and Maxim are handling the transmission and distribution aspects.

The per unit cost of power has been falling by half every two years. This implies that you get twice the computing power for the same cost every two years.

However, "the lithium-ion battery cell capacity has increased 8 per cent year on year for the last 14 years," says Ram Ananth, engineering manager for power management products of Texas Instruments India.

Hence researchers are increasingly concentrating on getting devices to do more and more complex things without using more power and getting batteries to deliver more.

Every mobile handset is powered by a battery, which can last for three hours of talk time after being charged for one hour. If more features like music player and camera are included in the handset, they will consume additional battery power requiring more frequent charging.

As power supply in rural areas is very erratic, telecom players, to expand their markets, need to power handsets with batteries that can get charged more quickly.

The slow progress in improving energy efficiency is attributed to some hurdles in chemistry and physics of batteries. "The more the energy is stored in a small package, the more volatile and dangerous it becomes. The downside of this lithium-ion/polymer technology is manufacturability," Ananth points out.

Recently, more than 120 Nokia mobile handsets exploded in India while being charged. Nokia had to replace thousands of batteries. Such being the risk with batteries, companies are increasingly focusing on the chip-level design to bring down the usage of batteries, that is improving the power efficiency of devices.

"What consumes a lot of power in a mobile device is having a lot of stand-alone, single-function chips, rather than one or two highly integrated 'system on chip' solutions "" commonly referred to as SoCs. We have been designing processor IP with low-power SoCs for the last 15 years to ensure maximum MHz performance per milliwatt of power," said Ian Drew, VP (segment marketing), ARM, which provides developers with intellectual property (IP) solutions in the form of processors, physical IP and SoC designs.

However, even chip designing poses problems. "As chips become more complex, they become harder to control, particularly when it comes to switching between architectures "" internal to an SoC and between one SoC to another. We'll see more demand for chip design tools that enable one to avoid big spikes in power demands on the processor," says Drew.

The energy efficiency of the battery also depends on the duration of its use. Real time response is most desirable in any computing or personal portable electronic device.

To realise the real time response desired, it is necessary that the speed of the devices used is very high. High speed mean high power dissipation.

"High power dissipation means less usable battery time. How do we compromise? The answer lies in using efficient power management products in electronic devices. These devices will maximise the conversion efficiencies (battery power to usable power at maximum efficiencies) and monitoring functions in the personal portable devices that systematically turn parts of the electronics off so as to save power that enhances the battery time," says Ananth.

According to him, the best bet for the future is probably fuel cells. "But it may be more than a decade before they start appearing in mass-market portable devices," he says.