A research team at UCLouvain in Belgium is part of a new wave of electronic engineers that design applications to have a positive impact on society. At Louvain, the focus is on creating biomedical innovations that have minimal environmental impact. The team's latest work is SleepRider, an ultra-low power Arm-based SoC that reduces the requirement for potentially harmful batteries.
To find out more, we spoke to postdoctoral researcher at UCLouvain, Rémi Dekimpe. Research in solid-state circuits tends to be end-use agnostic. The aim is to improve performance. Our team, who work on electronic circuits and system design, felt that we were missing something. Specifically, the need to focus on meaningful applications and products that can have a positive socio-ecological impact.
Biomedical applications have been a big thrust for us in using our sensors to measure physiological signals, and then processing them to try to infer the state of the patient. If you detect an abnormality, you can then try to see if there is an underlying problem. For example, we have been working on the detection of epileptic seizures, using signals recorded from the vagus nerve to detect their onset. We have done similar things with encephalogram signals and cardiac signals.
“The power consumption of a chip has a bearing on the batteries you need to power the device, and batteries can have a significant environmental impact.”
But as well as trying to implement positive applications, we are actively working to reduce the impact of the electronics themselves. The power consumption of a chip has a bearing on the batteries you need to power the device, and batteries can have a significant environmental impact. By reducing the power consumption of the SoC, you can reduce the size of the batteries required. And you will not need to replace them as frequently.
Our team has been working on ultra-low power microcontrollers for over 10 years. First, we had SleepWalker; then SleepRunner; and now SleepRider. The name reflects the fact that the chip can perform tasks with a power consumption that's so low it’s as if the chip was sleeping.
There are obvious challenges here. When you try to operate chips at low power by reducing the supply voltage, it becomes difficult to get as much performance. When you want to run complex computing tasks, it can be a struggle. For example, when you have classification or detection algorithms to detect seizures.
You also get problems with variability issues, known as process voltage and temperature variations. These make the chip less robust and reduce the yield of the chips that you manufacture. Typically, when the temperature or voltage changes, or when the type of fabrication process changes slightly, you can end up with circuits that do not function properly.
There are several ways to tackle the issue. People have previously used techniques such as adaptive voltage scaling, adaptive frequency scaling, and adaptive back-biasing. The latter involves using a specific characteristic of Fully Depleted Silicon on Insulator Technology (FDSOI). Transistors have a back-gate, which are used to tune their threshold voltage. In turn, that allows you to modulate the performance level of the circuit. This effect is present in most transistor technologies, but it is much stronger in FDSOI, which makes it particularly efficient. We have pioneered a new approach that combines regulation of frequency and back-bias. And it allows us to compensate for changes in both delays and leakage in the digital circuits.
“We have kept working with Arm cores, mainly due to the ecosystem Arm offers.”
SleepWalker, SleepRunner and SleepRider have been designed using several generations of Arm microcontroller. We first used Arm IP on an academic project. We wanted our students to work on actual applications for practical circuit design. It then made sense to use Arm cores for our microcontroller research too. They deliver the right characteristics, in terms of the core size, compute, and power consumption, which offer a good trade-off compared to the alternatives.
We have kept working with Arm cores, mainly due to the ecosystem Arm offers. The different cores, IP, and tools make it easy to set up a new system at our level in the academic research group. And when we need something, it's not usually long before we can get it. The process is extremely simple and swift, and the Arm team is responsive when we ask for something new.
“Look at the numbers, and you’ll see how electronics, and specifically information and communication technologies, have a clear, significant impact on the world. And it is growing fast.”
We are still working on new generations of ultra-low-power microcontrollers. But we have since changed the name of the SoC. It’s now called ICare (IC for Integrated Circuit). The chip has been designed and fabricated, and we are now publishing the first results. We’re still measuring other areas of its performance, the results of which we hope to publish later.
We can no longer think of electronics in general as just the process of digitalization, where most of the impact it has on the world tends to be hidden from people. Look at the numbers, and you will see how electronics, and specifically information and communication technologies, have a clear, significant impact on the world. And it’s growing fast, especially with the advent of the Internet of Things, and the widespread deployment of all these different electronic systems in our environment.
Our university has launched several spinouts based on the work we have done here. They include a start-up called e-peas, which works on energy harvesting and processing solutions for longer battery life, and increased robustness in all Internet of Things applications. That all started with some of the microcontrollers that were designed in our lab. That’s really satisfying to see.
Rémi Dekimpe is a postdoctoral researcher in the Electronic Circuits and Systems research group at UC Louvain
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