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Startups target subthreshold to solve IoT power consumption challenge

The need for IoT power has stymied the market. Learn how three startups are trying to tackle the problem with subthreshold.

While the internet of things has the potential to place intelligent sensors on our bodies, in our homes, within our distribution centers and at our stores, one problem remains: how to power IoT. To date, wireless sensors have been energy hogs, consuming a few volts of electricity and needing to be recharged after several hours.

Startup suppliers are beginning to tackle this issue and design products that require little to no power. Their work is in the early stages of development, but the outlook for subthreshold to satisfy IoT power consumption is favorable.

"Energy has been an issue for IoT device suppliers, and these new subthreshold systems hold a great deal of promise," said Rob Lineback, senior market research analyst at IC Insights Inc., a semiconductor market research company.

Challenge: How to solve the IoT power consumption problem?

As vendors dabble with smaller IoT device form factors, power emerges as a key gating factor. Suppliers want to push more intelligence out to the network edge, but that goal means that, somehow, energy needs to be available to support the device's processing.

Energy has been an issue for IoT device suppliers, and these new subthreshold systems hold a great deal of promise.
Rob Linebacksenior market research analyst, IC Insights

At the heart of IoT devices are logic circuits inside silicon chips. These circuits are built primarily from that fundamental bit of electronics, the transistor. What makes the transistor remarkable is that it functions as a gate, either letting electrical current pass through or not, based on the input of another part of the circuit. It works, in the post-vacuum-tube era, by dint of a bit of "semiconductive" material in the middle. One can control whether a semiconductor is conductive (think "ones") or not (think "zeros"), and the whole miraculous operations only requires a handful of volts to power.

But it does, nevertheless, require some power. And the dirty little secret about semiconductor transistors is that they "leak" a small amount of electrical current across the gate even when they are switched off. There's a threshold, above which the system sees a one and below which the system sees a zero, even though there's still a bit of current passing through -- a "subthreshold" current. The trick to subthreshold computing, then, is using the leaking current below the normal threshold for your ones (and less still as your zeros). If this were easy, of course, it would have been how semiconductor chips worked from the beginning. So, the commercial viability of the approach is still being determined in practice.

For product designers, meeting IoT power consumption needs requires a series of tradeoffs. Typically, IoT devices require a few volts to run and rely on batteries that periodically must be recharged or replaced. However many IoT use cases -- from emerging product niches such as wearables to sensors in dispersed or remote locations -- are being placed in areas where recharging and replacing can be challenging.

Solution: Subthreshold IoT power to the rescue

In response, three silicon startups, Ambiq Micro Inc., PsiKick Inc. and Minima Processor Ltd., are rolling out subthreshold systems. The vendors are building microprocessors that consume drastically less power, as low as 0.1% of the energy consumed by traditional chips.

Ambiq's work stems from research done at the University of Michigan. The company, which was founded in 2010, developed a patented Subthreshold Power Optimized Technology (SPOT) platform designed to reduce the amount of power consumed by semiconductors. A few potential areas of interest are smart credit cards, medical devices and wearables, said Scott Hanson, Ambiq CTO and founder.

The firm's subthreshold CMOS 32-bit offering, called the Apollo family, is based on ARM processors and integrated circuits from Taiwan Semiconductor Manufacturing Co. Ltd. The new ARM CPUs are fabricated with proprietary optimizations of standard CMOS processes that allow transistor operation at subthreshold voltages (less than 0.5 V), rather than using transistors that are turned all the way on at 1.8 V. Ambiq claims the SPOT platform optimizes active and sleep-mode power states, so microcontrollers consume five to 10 times less energy than comparable products.

PsiKick's co-founders David Wentzloff and Benton Calhoun began their quest in MIT's Energy-Efficient Circuits and Systems laboratory. The two went on to become professors at the University of Michigan and the University of Virginia, respectively, and formed PsiKick in 2012. The company focuses on the networking portion of the subthreshold market and developed a wireless sensor, which it claims consumes between 100 and 1,000 times less energy than chips operating above threshold voltages.

VTT Technical Research Centre of Finland Ltd., Aalto University and the University of Turku developed technology to make an IoT system as much as 20 times more energy efficient than current products. To commercialize the technology, Minima Processor was founded in April 2016 and raised a total of €5.5 million ($6.3 million) in seed funding. "Always-on audio is one IoT area that interests us," said Toni Soini, CEO at Minima Processor.

The trouble with subthreshold IoT power

The startups faced a number of challenges, the first hurdle being the technology issue. Historically, if voltage was reduced below the nominal threshold voltage for a transistor, a large amount of energy was lost through problems such as leakage, logic swings, noise, temperature sensitivity and process drift. Manufacture of these chips takes more precision than ever and longer-term reliability could still be an issue.

Next, the companies need to find a niche for their products. "Not every IoT device vendor wants a subthreshold system," admitted Ambiq's Hanson. Suppliers can build products with 8-bit and 16-bit chips, which offer relatively limited processing capabilities but use little power. If device suppliers opt for more powerful 32-bit systems, however, they would need subthreshold systems.

New subthreshold markets emerge

Ambiq has started to ship products; its Apollo Platform is finding a home in smartwatches, a growing market segment where IC Insights projected $8.6 billion in revenue in 2016. Fossil Group Inc., Skagen Denmark Ltd. and Misfit Inc. have licensed Ambiq technology for use in their smartwatches.

The first timepiece with Ambiq-supplied circuitry is expected to be the PowerWatch, which Matrix Industries Inc. expects to ship in October 2017; it runs off of a person's body heat and includes a power meter that tells users how much electricity their body heat produces. Akram Boukai, co-founder and CEO of Matrix Industries and another person with a connection to the University of Michigan laboratory, called the firm an energy-harvesting device supplier and said he expects to branch out into other consumer and commercial IoT niches.

As subthreshold begins to widely solve IoT power consumption issues and subthreshold systems start to ship in volume, the new vendors will have to build ecosystems capable of supporting the microprocessors: integrated chipsets, management tools, APIs and intellectual property agreements. The firms are small: Ambiq has 60 employees and Minima Processor has 11. Currently, they all plan to grow the business, add employees and become established organizations. However, the reigning chip vendors are also eyeing this space and could develop alternatives to better power IoT -- or swoop in and acquire these startups as they get their feet off the ground.

Next Steps

Learn about IoT power consumption challenges in precision farming applications

Explore more about designing IoT experiences and interfaces

This was last published in July 2017

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Do you think subthreshold will solve the IoT power issue? Why or why not?
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Your article is outdated...we have already achieved a SOC for IOT complete with CPU, MEM, connections to senors and full Bluetooth LE 4,2 compliance operating at 0.9V peak voltage, 2.5mW. Yes, we belief that this will solve the IoT power issues and will either extend the life of battery or operate without battery by using small portable energy harvesters depending on the system and ergonomic design of the IOT device.
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