SANTA CLARA, Calif.—Flashlights are fantastic tools until they die and you find yourself in the dark, fumbling around for replacement batteries. That type of dynamic will constrain the growth of Internet of Things applications and devices unless we resolve the power problem.
That was the message from Prithi Ramakrishnan and Charles Dittmer (pictured nearby) at a Bluetooth World presentation March 15 at Levi’s Stadium here.
"How do we get to billions of devices," Ramakrishnan, ARM wireless product manager, said. "Will we achieve these volumes if we have to change billions of batteries every year? Perhaps not. But billions of devices need not mean billions of batteries."
She and Dittmer, ARM wireless technical marketing manager, walked their Bluetooth World audience through elements of low-power design best practices, highlighting how the industry moves toward optimizing power-constrained devices and effective use of energy-harvesting systems.
The latter is still in its formative stages, but the former — systems using 1V and sub-volt designs — is within our grasp today, Dittmer said. In some cases, with a sub-volt design, battery life improvements of 60% on existing 1.2V alkaline batteries are possible.
The road to IoT ubiquity begins with a good wireless protocol, as well as a well-considered IP and systems design, such as low peak and sleep currents and low voltages.
As an example, Dittmer showed a picture of an oscilloscope image of ARM Cordio wireless IP, noting the Tx (transmit) current was roughly 7 mA.
"You say, ‘gosh, 7 milliamps is not that bad,’ but others are doing 5-6 mA," Dittmer said. "But you … really have to compare apples to apples and talk about milliwatts."
Those solutions pulling 5-7 mA are at 3V, which, according to Dittmer equates roughly to 15-21 mW in Tx mode. ARM radio IP runs at 950mV (sub-volt). Rounding up to 1V, 7 mA equates to 7mW, he said. And the technology goes to sleep at 800nW, he added.
"This enables true 1V solutions to take advantage of different 1-volt battery-size topologies," Dittmer said. "If you’re powering your radio and your SoC at 1V, you’re extending your battery life because as the battery decay curve goes down, you’re still operating at 1V." (see slide left).
Dittmer called out as an example an ARM Cordio BT4 Bluetooth Smart test chip that uses a Zinc/Air hearing aid battery. Running at 1V, the micro-beacon has a battery life of more than two years.
If 1V and sub-volt power unlocks system-design creativity, then hearables are becoming the new wearables, Dittmer noted. The Bragi Dash wireless smart earphones, which can serve as a small MP3 player, just might be the poster child for hearables, he noted.
"Beyond audio and hearing, the ear is also a great place for biometrics. This is enabled by moving to 1V technology and the associated small batteries," Dittmer said.
If optimizing low-voltage battery-backed designs is possible today, designing systems that really take advantage of energy harvesting is very close.
1V and sub-volt technologies mean that pulling in energy from mechanical, thermal, vibrating, RF, natural and other sources is much more realistic.
Solar-powered devices deployed by Fraunhofer, between panes of glass, can enable alarm and temperature-sensing systems, storing enough solar energy to run overnight.
Dittmer closed with a call to action, noting that there are some sticking points within this ecosystem.
The processor and radio technologies are at 1V but "a big problem for IoT nodes is many of these are sensors which typically run at 3.5V, 2 and 1.8V today," he said. "Any sensor people in here? We need 1V sensors! That's my call to action. Other pieces of ecosystem have to follow this low-power low-voltage trend."
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