Design Article
Ultra-low power microcontrollers for compact wireless devices
Scott Hanson
8/1/2011 12:02 PM EDT
A system-level view of the energy-efficient microcontroller
Today’s microcontrollers offer a range of low power features, and the last section showed that next-generation microcontrollers will significantly improve energy efficiency further. However, the microcontroller is only one component in a typical system. Integrating multiple components at the board level has the potential to increase energy significantly without proper attention.
The energy associated with toggling board-level traces and the associated I/O drivers within each component can be very large. More importantly, most board-level components are not designed with the same attention to energy-efficiency as today’s leading low power microcontrollers and can easily dominate an energy budget.
As an example, consider a microcontroller-based system that incorporates energy harvesting functionality at the board level, as shown in figure 5. A solar cell harvests energy from incident light and a boost converter component boosts the solar cell output to charge a battery. A leading commercial microcontroller may have a 500nA functional sleep mode with SRAM retention and a timer running. However, a typical low power boost converter component may draw 10µA or more, effectively dominating the energy budget.
Fig 5: Board-level energy harvesting system.
It will therefore be the job of low power microcontroller providers to incorporate key functionality into next-generation microcontrollers. Single-chip integration also has the important benefit of reducing the bill of materials in a system. Microcontroller vendors are beginning to incorporate wireless communication in their devices (and vice versa), and features like support for energy harvesting will follow shortly. We again use the example of the Archimedes Microcontroller to illustrate the benefit of integration.
As shown in figure 3, Archimedes includes on-board boost converter. By applying many of the low power techniques used elsewhere in the microcontroller, the boost converter consumes only a fraction of the 550pW functional sleep mode power budget. Figure 6 shows Archimedes integrated with a Cymbet 12µAh solid-state battery and an ultra-compact solar cell in a volume of only 8.75mm3. Due to the extreme energy efficiency achieved by Archimedes and its integrated boost converter, a tiny battery and solar cell are capable of delivering power for nearly perpetual operation. This clearly shows that highly integrated microcontrollers have the potential to significantly improve system-level energy efficiency.
Fig 6: Energy harvesting system with Cymbet solid-state battery (bottom layer), Archimedes microcontroller with integrated boost converter (middle layer), and solar cell (top layer).
Energy efficiency is becoming a central concern for the chip industry as chip users seek to develop more compact wireless devices with longer operational lives. Microcontrollers, in particular, are at the heart of these compact wireless devices. In this paper, we reviewed the key sources of power consumption in microcontrollers and considered Archimedes, the world’s most energy-efficient commercial grade microcontroller. Studies of Archimedes revealed some of the techniques used to minimize energy consumption in today’s microcontrollers and provided a snapshot of some new features that will emerge in next-generation microcontrollers. It is this next generation of microcontrollers that will truly drive the growth of compact wireless devices emerging today.
References
1. G. Chen, M. Fojtik, D. Kim, D. Fick, J. Park, M. Seok, M.-T. Chen, Z. Foo, D. Sylvester, D. Blaauw, “Millimeter-Scale Nearly Perpetual Sensor System with Stacked Battery and Solar Cells,” International Solid-State Circuits Conference, pp. 288-289, 2010.
About the author:
Scott Hanson, shanson@ambiqmicro.com, is CEO of Ambiq Micro Inc, Austin, Texas.
This paper was presented at ARM TechCon 2010 - more details of ARM TechCon 2011 in October are available at www.armtechcon.com.
If you found this article to be of interest, visit the Micocontroller Designline where you will find links to relevant technical articles, blogs, new products and news.
You can also get a weekly newsletter highlighting the latest developments in this sector - just Click Here to request this newsletter using the Manage Newsletters tab (if you aren't already a member you'll be asked to register.
Today’s microcontrollers offer a range of low power features, and the last section showed that next-generation microcontrollers will significantly improve energy efficiency further. However, the microcontroller is only one component in a typical system. Integrating multiple components at the board level has the potential to increase energy significantly without proper attention.
The energy associated with toggling board-level traces and the associated I/O drivers within each component can be very large. More importantly, most board-level components are not designed with the same attention to energy-efficiency as today’s leading low power microcontrollers and can easily dominate an energy budget.
As an example, consider a microcontroller-based system that incorporates energy harvesting functionality at the board level, as shown in figure 5. A solar cell harvests energy from incident light and a boost converter component boosts the solar cell output to charge a battery. A leading commercial microcontroller may have a 500nA functional sleep mode with SRAM retention and a timer running. However, a typical low power boost converter component may draw 10µA or more, effectively dominating the energy budget.
Fig 5: Board-level energy harvesting system.
It will therefore be the job of low power microcontroller providers to incorporate key functionality into next-generation microcontrollers. Single-chip integration also has the important benefit of reducing the bill of materials in a system. Microcontroller vendors are beginning to incorporate wireless communication in their devices (and vice versa), and features like support for energy harvesting will follow shortly. We again use the example of the Archimedes Microcontroller to illustrate the benefit of integration.
As shown in figure 3, Archimedes includes on-board boost converter. By applying many of the low power techniques used elsewhere in the microcontroller, the boost converter consumes only a fraction of the 550pW functional sleep mode power budget. Figure 6 shows Archimedes integrated with a Cymbet 12µAh solid-state battery and an ultra-compact solar cell in a volume of only 8.75mm3. Due to the extreme energy efficiency achieved by Archimedes and its integrated boost converter, a tiny battery and solar cell are capable of delivering power for nearly perpetual operation. This clearly shows that highly integrated microcontrollers have the potential to significantly improve system-level energy efficiency.
Fig 6: Energy harvesting system with Cymbet solid-state battery (bottom layer), Archimedes microcontroller with integrated boost converter (middle layer), and solar cell (top layer).
Energy efficiency is becoming a central concern for the chip industry as chip users seek to develop more compact wireless devices with longer operational lives. Microcontrollers, in particular, are at the heart of these compact wireless devices. In this paper, we reviewed the key sources of power consumption in microcontrollers and considered Archimedes, the world’s most energy-efficient commercial grade microcontroller. Studies of Archimedes revealed some of the techniques used to minimize energy consumption in today’s microcontrollers and provided a snapshot of some new features that will emerge in next-generation microcontrollers. It is this next generation of microcontrollers that will truly drive the growth of compact wireless devices emerging today.
References
1. G. Chen, M. Fojtik, D. Kim, D. Fick, J. Park, M. Seok, M.-T. Chen, Z. Foo, D. Sylvester, D. Blaauw, “Millimeter-Scale Nearly Perpetual Sensor System with Stacked Battery and Solar Cells,” International Solid-State Circuits Conference, pp. 288-289, 2010.
About the author:
Scott Hanson, shanson@ambiqmicro.com, is CEO of Ambiq Micro Inc, Austin, Texas.
This paper was presented at ARM TechCon 2010 - more details of ARM TechCon 2011 in October are available at www.armtechcon.com.If you found this article to be of interest, visit the Micocontroller Designline where you will find links to relevant technical articles, blogs, new products and news.
You can also get a weekly newsletter highlighting the latest developments in this sector - just Click Here to request this newsletter using the Manage Newsletters tab (if you aren't already a member you'll be asked to register.
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Jerry.Brittingham
8/2/2011 2:34 AM EDT
Where do I get a RF device that only takes micro amps?
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Les_Slater
8/3/2011 3:03 AM EDT
The biggest take home message I get out of this article is the extent we have to reset our brains.
Common sense might tell us that minimizing active time so that we can spend most of the time sleeping is the path to lowest energy consumption. However, looking at figure 4 reveals this is not necessarily so. Time constraints permitting it would be best to run this architecture at 73 KHz to realize the approximately 25pJ per instruction.
Running at the lowest energy expenditure per instruction renders the lowest total energy for a given computational task. Even if the active time involved is a substantial portion of the cycle it still uses the lowest total energy.
Looking at power or current can be quite misleading.
Les Slater
Chicago
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Ray Keefe
8/3/2011 5:04 PM EDT
Hi Les,
agreed. Iusually think of there being 4 components to ultra-low power. And a balance between them has to be obtained:
- energy per instruction
- instructions per task
- energy per sleep interval
- time to wake
I consider the wake/sleep transition to be an area not usually looked at closely enough so my congratualtions to the author for bringing this up..
This is where a device like the MSP430 did so well for so long. The fast start from sleep using the DCO, quick execution at low energy per instruction, and fast return to sleep worked well in its favour.
Ray Keefe
Successful Endeavours
www.successful.com.au
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Les_Slater
8/4/2011 7:06 AM EDT
Ray,
I started looking at this issue in 1988 when I was a Principal Engineer at DEC. There I proposed looking at power consumption based on cumulative energy dissipated by node transitions derived from simulation traces. This was to be then added to static power. Nobody paid any attention to that proposal.
Les
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