Mobiles are getting smarter and that does not just mean they can recognize faces in photos and phone people from a spoken command. They are getting smarter about the way they use energy, meaning you can get more game-playing and social-networking time out of the device before it has to go back on the charger. Here are the top-six reasons that the mobile’s battery life is getting better.
- Better wireless management
In the past it was necessary to shut down WiFi, 3G and GPS to achieve a better battery life from a mobile handset. Now it’s not necessary because software inside the handset manages this in a more efficient way, ensuring that the wireless links are only used when necessary.
Other changes have come to the wireless connectivity. Bluetooth Smart, also known as Bluetooth Low Energy, increases the already impressive energy efficiency of the protocol to the point where a sensor device can run for a year on a lithium button cell. As a result, Bluetooth Smart is key to the design of a growing list of wearables, including step counters and heart-rate monitors that feed a stream of information to smartphones.
- The big.LITTLE Processor architecture
One key to extending battery life in today’s handsets is to ensure that the processor that runs the software is not over-specified for the job at hand. High-performance games and high-definition videos need application processors that can cope with their intensive demands but, much of the time, the phone is running software that does not need the fastest processors available.
The big.LITTLE architecture adopted by many handsets keeps an eye on what software is running. If the high-speed processors are not needed, the code running on them is moved to a leaner core and the others are switched off. Only if the workload gets too intensive do the high-speed, more power-hungry processors get switched on again.
- Sensor hubs
Many phones now have sensor hubs that continually take in data from the many sensors inside the phone. These very low energy, always-on, processors monitor and store accelerometer and other sensor data . The more power-hungry applications processors will then only have to wake for analyzing and displaying the results.
- Fine-tuned voltages
Although intelligent use of processing and wireless operation can result in power savings, when these functions are in use their power consumption can be further minimized by carefully tuning the supply voltage that they need. There is a quadratic relationship between voltage and power in most electronic circuitry. It makes it worth shaving off even 0.1V where you can, because its effect on power is much greater.
This results in a dizzying array of sub–1.5V power rails fed to processors, memory and other peripheral circuitry, these voltage supplies can dynamically move up and down in direct response to how much work the handset needs to do. For example when the handset is idle it is possible to reduce its supply voltage raising the voltage again when performance is needed. The result is a handset that is always looking for the minimum possible voltage for each of its subsystems, all orchestrated by a complex power-management integrated circuit (PMIC).
- A smarter display
The display used to be one of the most power-hungry parts of a mobile device and most of that is due to the backlight. The solution was keeping the backlight as low as possible without compromising visual quality. Handsets do that by measuring ambient light and turning the backlight down if the conditions do not warrant a bright setting. Power-management circuitry ensures that the backlight power can be fine-tuned without causing flicker or other issues, but the main reason the power requirements have dropped is the increased efficiency in WLEDs.
- PMIC optimizations
As well has having to handle many voltage outputs and their changes, the PMIC itself has changed; traditionally, power supplies that convert the battery’s voltage to the many separate supplies needed by the various chips inside the handset, have been mainly optimized for efficiency at high load. Less attention was paid to efficiency when under light load conditions. This traditional approach helped ensure mobile devices do not heat up excessively when performing intensive operations. But in an always-on environment, where data is being processed in the background constantly, broad-spectrum efficiency is now the requirement.
The spread from low to high load can be orders of magnitude, changing from tens of milliamps in a device that is just idling to sudden peaks of over ten Amps as the processor starts up and begins to work through data as quickly as possible, before dropping to a few hundred milliamps for sustained video decoding or a series of Facebook updates. Today’s PMICs now use sophisticated digital techniques to deliver efficiencies of more than 90 per cent from low to high loads across the many voltage rails, helping to keep the handset cool and the battery going for longer between charges – and demonstrated effectively in the latest handsets.