Electronic Products Defense Spending on the Radar AI, robotics, big data, cybersecurity, and resilience top priorities April 2018
APRIL 2018
DEFENSE SPENDING
on the Also in this issue RADAR
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2 CONTENTS
EDITORIAL STAFF
Contributing Editor Alix Paultre . . . . . . . . . . . . . . . . . . . . . .
SCAN TO DOWNLOAD
Google’s new quantum processor aims to outper- form supercomputers http://bit.ly/2FuOS7U
Battery sensor allows for Li-ion batteries to be charged five times faster http://bit.ly/2FuOAhs
10 tips on how to properly document a design so others can follow http://bit.ly/2FpMJ18
Bolaji Ojo . . . . . . . . . . . . . . . . . Global Editor-in-Chief Richard Quinnell . . . . . . . . . . . . . . . Editor-in-Chief, [email protected] • electronicproducts.com Majeed Ahmad Kamran . . . . .
Contributing Editor Patrick Mannion . . . . . . . . . . . . . . .
Chief Copy Editor Nicole DiGiose . . . . . . . . Technical Content Manager
Contributing Editor Lori O’Toole . . . . . . . . . . . . . . . . . . . . . . . .
Max Teodorescu . . . . . . . . . Digital Content Manager Pam Fuentes . . . . . . . . . . . . . Business Planning Analyst Giulia Fini . . . . . . . . . . . . . . . . . . . . . . . . . . . Graphic Designer Giulia Fini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cover Design Lauren Heller . . . . . . . . . . . . . . . . . .
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Group Publisher Electronics Group Electronic Products Magazine (USPS 539490) (ISSN 0013-4953)— Published monthly by AspenCore, 1225 Franklin Avenue, Suite 400, Garden City, NY 11530. Periodicals postage paid Garden City, NY and additional mailing offices. Electronic Products is distributed at no charge to qualified persons actively engaged in the authorization, recommendation or specification of electronic components, instru- ments, materials, systems and subsystems. The publisher reserves the right to reject any subscription on the basis of information submitted in order to comply with audit regulations. Paid subscriptions avail- able: U.S. subscriber rate $65 per year, 2 years $110. Single issue, $6.00. Information contained herein is subject to change without notice. No responsibility is assumed by the publisher for its accuracy or completeness. Postmaster: Send address changes to Electronic Products, PO Box 489, Skokie, IL 60076-0489. Phone: 847-559-7317 ©2018 by AspenCore. ALL RIGHTS RESERVED Publications Mail Agreement Number 40012807. Return Undeliverable Canadian Addresses to: Station A PO Box 12, Windsor, ON N9A 6J5
Vol. 60, No. 9 April 2018
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4 VIEWPOINT
This synergistic development aspect of electronic design was very appar-
Fluffing the cloud
ent these past weeks at the APEC and he electronic design engineering organic LEDs, wide-bandgap semicon- Embedded World shows as engineers field is a fantastic place to be at ductors, and the digital infrastructure. from around the globe came together any given point and especially so These and other advanced core technol- in San Antonio, Texas, and Nuremberg,
T
in these modern times. The past two ogies enable and empower new solutions Germany, to exchange ideas and look at decades saw the groundwork laid for to serve existing application spaces and the latest in embedded systems. these exciting times in technologies like create and develop new ones. The booths at both events were crammed with the latest solutions avail- able for applications both mature and speculative, and at each (some visitors, including me, bounced between both), there was a buzz of activity as company reps and visitors played with the demon- strations and bounced ideas off of one another. The energy was palpable at each of the venues, and the energy of all of those people dealing with one another in these public marketplaces was palpable.
In this issue, we’ve pulled together some very cool examples of the latest technologies from both shows, and we hope this foments new ideas for new solutions with you. One of the notable aspects of any new technology is that any given group of engineers will tell you sev- eral more applications than you thought of when developing it, and the number and quality of these new technologies are providing the foundation of the remak- ing of society.
The cloud and IoT are shaping society in fundamental ways, and you are the ones shaping the devices in it and the infrastructures supporting it. Every de- vice that you make is a voice in the great chorus of development moving society forward, and these exhibitions are the concert halls. One positive aspect of Em- bedded World, for example, was the fact that most booths contained functional demonstrations of technology and not just displays of components and parts.
In the area of wireless, one of the trends that we observed was the final filling in, or in the words of the headline, the “fluffing out” of the cloud. There are a lot of wireless devices using wired or sub-gigahertz proprietary wireless systems, for example, and bringing them into the IoT is the true “final mile” of the cloud. Solutions shown ranged from multi-protocol wireless modules and
N
[email protected], or contact your
IM A GE : PIX ABA Y
At ASPENCORE , our editorial mission is to bear witness and to
celebrate human achievement as
manifested through advancement in
technology and engineering ... and
you, the reader, are here to judgeboth the house and our writers on
our respective merits. This is what
editorial independence means to us.
BY W. VICTOR GAO Publisher and Managing Director The ASPENCORE Group
Tribute to an American classic In this month’s perspective, our publisher, Victor Gao, pays tribute to an American classic and delves into our proudly old-fashioned journalistic values
, thank you for your support. ☐
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From all of us at
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favorite
By the time these words go to print, many of our readers will be wheels-up to a productive conference in Münich, Las Vegas, or Shanghai or will have just returned. Here is to safe and pleasant journeys for all on the road. As ever, if you have a comment or want to whis- per us a story tip, you can find me at
EW YORK — American readers of this column are prone to recognize the name E.B. White, a 20th-century author best known for his children’s books such as “Stuart Little” and “Charlotte’s Web.” A resi- dent of this great American city, White was also a prolific columnist for the classic humor, literature, and journal- ism magazine The New Yorker. And in a prose entitled “Unwritten” in April 1930, White observed in his signature self-deprecating style that the work of a writer always represented a choice — the choice of what to write and what not to. Which brings me to the subject of our column this month: Why does a journalist write at all?
While we are on the subject of editorial policy, we expect to share some exciting news soon about how we will extend our remit this year to introduce both more depth and more diversity to the topics covered in our titles. We will give you a snippet of our redesign efforts, with a greater focus on longer, less frequent, but more thought-provoking pieces that delve into an issue without the pressures of a daily publishing cadence. To find out more, please check back in this column next month.
The writers write as they please, and the magazine publishes as it pleases. When the two pleasures coincide, something gets into print. When they don’t, the reader draws a blank. And you, the reader, are here to judge both the house and our writers on our re- spective merits. This is what editorial independence means to us.
, we rather like the good old system at The New Yorker, as de- scribed by White in another column:
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Of course, a great deal of how this mission is achieved is left intentionally undirected and uncoordinated be- tween the house and our writers. As a gentle reader wrote in response to this column last month, today’s publishers face a pivotal task to transform the economics of publishing so the im- portant reporting can be done without fear of loss of funding, which we have seen happen to some of our fellow publishing houses in the industry. And yet as much as
, our editorial mis- sion is to bear witness and to cele- brate human achievement as manifest through advancement in technology and engineering. While every one of our journalists makes their own personal choice as to why and what they write, as a publishing house, we encourage an intention to affirm or, if the writing starts out decrying an inju- ry or injustice on behalf of our readers, that by the end, it arrives at a construc- tive juncture. Sometimes, that takes the form of questioning a dubious claim in a manufacturer’s new product introduction campaign. Other times, it could be the critique of a business trend we believe is over-hyped, a tech- nical achievement that is under-recog- nized, or an important workplace issue that would not have found its voice had it not been for the help of these pages.
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PUBLISHER’S PERSPECTIVE 5
6 OUTLOOK
Their work also suggests a new path to explore for machine learning. “Specifically,” they wrote in their paper, “our experiments elucidate mechanisms for fast learning from noisy data that rely on cascaded net- works, sparsity, and Hebbian plasticity.”
Innovations impacting products, technology, and applications
IM A GE : WIKIMEDIA C OMMONS
Physicists to build laser so powerful it could rip apart fabric of space
These researchers propose to pulse
between electrons and their anti-matter counterparts, positrons. According to theory, any vacuum is filled with such electron-positron pairs. These pairs would be undetectable because they wouldn’t interact with anything — with the possible exception of the beam from a 100-petawatt laser. Which is one of the reasons why Chinese researchers are about to begin building a 100-PW laser.
balance. That balance would be
vacuum might not be empty at all; it might only seem empty on
Brian Santo A
The key to smarter, faster AI likely found by modeling moth brains R
esearchers at the Univer- sity of Wash- ington have devel- oped a relatively simple neural network that mimics biological neural systems. The performance of the new neural-network model points to the possibility of building AIs that are less complex yet far more effi- cient at learning because of it. At the same time, the research, published in the arXiv repository, yielded new insight into how living creatures learn — or at least how some creatures learn some things.
The UW researchers built a mathemat- ical model that mimics all of this, and their neural models of moths learned quickly with minimal simulated odor inputs. Their results are similar to the behavior that they observe in the moths, strongly suggesting that they have an accurate model.
The process does not work at all without octopamine, described as a neu- romodulator. Release of the chemical is triggered by a reward — for example, the moth finding sugar to consume. When a moth finds a reward, the octopamine that is released stimulates enhanced activity in the AL and MB. The practical effect of this enhanced activity is to strengthen the connections between correlated neurons in the moth’s neurological system. The mechanism is called Hebbian learning; the extent to which the strength of neuro- nal connections can be changed is called Hebbian plasticity.
Signals from the AL are forwarded to a structure called the mushroom body (MB). The MB contains roughly 4,000 cells (Kenyon cells) associated with forming memories. Signals go through two more ancillary structures (each numbering in the tens of cells), the function of which is believed to be to read out the signals from the MB. These sparser structures act as noise filters, the researchers wrote. Noise isn’t eliminated but is sufficiently reduced for the purpose of effective learning.
AL contains roughly 60 isolated clusters of cells (called glomeruli — it pays to enhance your word power!), each of which focuses on a single odor stimuli feature. The AL, the researchers say, is inherently noisy. The researchers liken the AL to a pre-amplifier, “providing gain control and sharpening of odor representations.”
Biological systems rarely do anything like this. Instead, they are commonly organized as feed-forward cascades. The beginning of the cascade in hawk moths is a set of about 30,000 chemical receptor neurons (RNs), which feed signals into an antennal lobe (AL). The
Most neural networks operate on the principle of backpropagation. With this technique, the weights between neurons (essentially the strength of the connection between them) are constantly recalculated through a process of feeding outputs back into the system so that inputs and outputs can be compared and adjusted against each other.
The University of Washington has been analyzing insect biology for decades; this research team chose moths because UW labs have already thoroughly mapped their neurological systems. They already knew that moths can learn smells after experi- encing them only a few times. Despite the relative simplicity, however, it remained unclear precisely how moths’ neurological systems worked when learning.
Starting with these observations, UW researchers resolved to devise a relatively simple neural-network model that mimics the relatively uncomplicated structure of a moth’s neurological system.
The most common path to emulate the effectiveness of biological neural systems has been to create increasingly complex artificial intelligences with increasingly complicated machine-learning capabilities. Biological systems that outperform AIs sometimes aren’t all that complex, however, and living creatures often learn far more quickly than AIs using significantly fewer experiences to learn than AIs require data sets.
If so, that will have ramifications both for biology and for neural networks. That the behavior of the model was so similar to that of actual biological systems encouraged the researchers to expect that they might now have a clearer understanding of the mechanisms at work in living creatures. The olfactory/neuro- logical systems of moths are structurally similar to those of many other creatures, the researchers noted.
OUTLOOK 7
an incredibly powerful beam for a few trillionths of a second through a vacuum with the expectation that it will induce elec- tron-positron pairs to break apart. Positrons are ephemeral, but the electrons would remain. It would look like producing some- thing out of nothing. The proposed process is being described as “breaking the vacuum.” 2 The formula E=MC suggested two things. One is that mass can be turned into extraordinary amounts of energy. Scientists followed that lead in a number of directions, including the devel- opment of the atomic energy. The formula also suggests that it’s possible to translate energy into mass, though doing so is consid- ered significantly harder. Breaking the vacuum would be a rare instance of it.
The Shanghai Institute of Optics and Fine Mechanics in China currently holds the record for the most powerful laser. In 2016, the Shanghai Superintense Ultrafast Laser Facility (SULF) achieved a burst of 5.3 PW. The institute is currently preparing to nearly double its record by using SULF to emit a 10-PW pulse by the end of this year.
It is also planning to build a 100-PW laser called the Station of Extreme Light (SEL), which could come online as early as 2023. Photon energy from the device could reach 15 keV.
European researchers were thinking about building a 200- PW laser but have held off even planning such a beast until they turn on a 1-PW laser in Prague this year and then build two more facilities that would take intermediate steps toward 100 PW or more, reported Science.
Russia is building the infrastructure to support a proposed 180-PW laser called the Exawatt Center for Extreme Light Studies (XCELS). Japanese researchers, who held the record with a 2-PW pulse before the Chinese eclipsed them, have proposals for a 30-PW device, according to Science.
Breaking the vacuum would be spectacular, but high-en- ergy lasers could be useful in other applications as well. They have been used for particle acceleration, inertial confinement fusion, radiation therapy, and for secondary-source generation
OCK
of X-rays, electrons, protons, neutrons, and ions, according to physicists at Cambridge University. A paper that they wrote in
TERST
2015 explains the different types of high-energy lasers. China’s
: SHUT SEL would be an OPCPA laser. GE A
Brian Santo
IM
Embedded systems for use on semi- and fully autonomous unmanned platforms, whether on the ground, in the air, or at sea, will require the development of low-power, ultra-small form-factor (USFF) processing, networking, full-motion video, and data-storage solutions. It’s estimated, for example, that a fully autonomous car will require 50 to 100 times the com- pute power needed to support today’s advanced driver-assistance systems.
The new technologies will provide
new capabilities upon which the warfighter will surely become dependent. As such, they mustalso feature the defenses needed
to ensure that their network and computing environments areprotected against adversaries and
so remain operationally effective.
BY MIKE MACPHERSON Vice President, Strategic Planning, Curtiss-Wright Defense Solutions www.curtisswright.com
Defense spending opens door to system
technology innovations- New investments in cyber-defense and the continued integration of cyber-ca- pabilities into the full spectrum of military operations
- Investments in C4ISR to develop resil- ient, survivable, federated networks and information ecosystems
- Advanced autonomous systems, AI, and machine learning.
An example of an advanced tech- nology upon which the warfighter has become dependent is GPS. When intro- duced as part of the DoD’s Second Offset strategy in the mid-1970s, GPS provided a significant advantage in the battlefield thanks to its ability to deliver accurate
The new technologies will provide new capabilities upon which the warfighter will surely become dependent. As such, they must also feature the defenses needed to ensure that their network and computing environments are protected against adversaries and so remain opera- tionally effective.
Ensuring operational effectiveness in the field: GPS
The overarching investment strategy described in the DNS is to bring these advanced technologies to the battlefield in order to provide a force multiplier that gives warfighters a strategic and tacti- cal advantage over the adversary. That said, it’s not enough to just deploy new technologies, it’s also necessary to ensure that those technologies are brought into the battlefield in a way that protects and secures them with the resiliency that they need to survive enemy attempts to dis- able or disrupt their intended operation.
Investments in AI and ML will provide capabilities that disrupt battle- field applications such as intelligence, surveillance, reconnaissance (ISR), and electronic warfare (EW). Support- ing these new capabilities will require advances in heterogeneous high-perfor- mance embedded computing (HPEC) technologies.
T
New spending on advanced com- puting will result in improvements for leveraging big data analytics, enabling the warfighter immediate access to all of their critical information. Such access will require the use of cloud-computing technologies to enable data access by any device, wherever the soldier is located, at any time it’s desired. More than that, to bring the power of machine learning (ML) for AI to the network edge will require far greater local processing capa- bility in order to deliver real-time data and solve the cloud’s inherent latency and bandwidth limitations.
However, advanced technology by itself isn’t enough. It also needs to be affordable, reliable, and sustainable. The warfighters’ lives depend on the tech- nology, and history has proven that if a soldier can’t trust their technology, they will abandon it.
For developers of military embed- ded COTS electronics solutions, this additional spending promises increased support for technologies that address resilience, lethality, and readiness. Designers of defense and aerospace systems and platforms desire to contin- uously introduce advanced technology that provides the warfighter with an indisputable advantage in the battlefield. These technologies range from sensors, computing, and networking to electro- mechanical systems.
The technological priorities called out in the NDS will drive a significant increase in R&D spending to close technology gaps in advanced computing, artificial intelligence (AI), and autonomy and robotics. Among the priorities for mod- ernizing key defense capabilities cited in the NDS that commercial off-the-shelf (COTS) vendors are well-positioned to support are:
AI, big data, and robotics critical but need to be affordable
This article will lay out some of the areas where that budget will be spent and what areas may present opportunities for designers to innovate to close current and future technology gaps.
he U.S. Department of Defense’s (DoD’s) 2018 National Defense Strategy (NDS) said it clearly: “Our backlog of deferred readiness, procure- ment, and modernization requirements has grown in the last decade and a half and can no longer be ignored. We will make targeted, disciplined increases in personnel and platforms to meet key capability and capacity needs.” With that in mind, Congress increased the FY 2018 defense budget to $700 billion — an increase of $108 billion.
Mil/Aero Electronics
position, navigation, and timing (PNT) data. This technology was essential for applications such as precision-guided weapons like the Tomahawk missile. Over the years, it’s become clear that our dependence on GPS also makes it a vul- nerability. In environments in which GPS is denied or disabled, all of the weapons that depend on it are made ineffective. To counter that vulnerability and threat, an assured PNT (A-PNT) solution must be available that is able to operate even in a GPS-denied environment. New cost-ef- fective and accurate COTS-based A-PNT technologies will enable the deployment of cost-effective, rugged solutions for GPS-denied environments.
Making AI and autonomous vehicles resilient
The development of new technologies based on AI will enable man-to-machine teaming solutions that deliver a significant advantage in the battlefield. Leveraging AI, autonomy, and robotics will result in machines that can operate independently, whether as an individual entity, paired with other machines in applications (such as a swarm configuration of drones), or in a soldier-machine interface in which the machine has its own autonomous capabil- ity augmenting the warfighter.
An example of the latter is an auton- omous ground combat “mule” able to relieve the warfighter’s personal burden of carrying batteries, chargers, ammuni- tion, etc. By reducing the weight in the warfighter’s backpack, these small auton- omous vehicles will significantly increase the soldier’s ability to fight.
Likewise, the use of autonomous aerial vehicles to deliver logistics equipment or to locate
IEDs will reduce the warfighter’s exposure to risk and improve their lethality. On the other hand, as these new solutions become common, adver- saries will strive to find ways to attack and disable them. For example, one strategy for countering a learning machine is to spoof it with false information, forcing it to produce an incorrect answer.
Improving resilience, another key goal of the DNS, will ensure that de- ployed systems have the ruggedness and reliability to survive harsh environments and the security to protect against enemy attempts to exploit their vulnerabilities.
Autonomous vehicles, such as mine detectors, can keep the warfighter out of harm’s way, but that autonomy needs to be trusted. For this, the system requires the resilience, or self-resilience, that ensures that it’s reliable and can’t be easily disabled.
A machine can be manual, semi-au- tonomous, or fully autonomous. In each of these states, the higher the level of autonomy, the more the machine needs self-resilience. When a machine is fully manual, the warfighter provides the resil- ience. In the case of a semi-autonomous system, resilience is shared between the operator and the machine. In a fully autonomous system, resiliency depends completely on the expert systems built into that machine.
Autonomous systems need resilience and security
To be able to confidently depend on fully autonomous systems will require invest- ments in technologies that provide both resilience and security.
An example of resiliency is found in safety-certifiable avionics systems for manned or unmanned military aircraft. To operate safely over do- mestic airspace, these platforms are increasingly required to meet DO-254 hardware and DO-178 software certi- fication for specific Design Assurance Levels (DALs) recognized by aviation authorities around the world, such as the FAA in the U.S., the Canadian Transport Board, and EASA in Europe and the U.K. While safety certification is handled at the platform level, the electronic modules used to build out avionics subsystems must be supported with comprehensive data artifacts. His- torically, modules for safety-certifiable subsystems were costly custom designs that took years to design and millions of dollars to develop.
In recent years, a new class of cost-ef- fective DO-254-certifiable COTS boards has become available, greatly speeding and lowering the cost of inte-
Fig. 1: The VPX3-1703 is an example of an Arm-based 3U OpenVPX single-board computer designed for DO-254 safety-certifiable avionics applications.
Fig. 2: Security in the field is critical, so the DTS1 NAS supports cost-effective two-layer encryption.
Mil/Aero Electronics grating safety-certifiable applications. The preferred processor architecture for these COTS modules has been the Power Architecture family of devices being that Intel processors only support DO-254 up to the DAL C level.
As NXP shifts its focus from devel- opment of new Power Architecture pro- cessors toward Arm-based processors, designers of safety-certifiable systems are increasingly turning to Arm-based solutions. Arm processors support D0-254 up to the most stringent and critical level, DAL A, and also provide the additional benefit of very low power dissipation. The VPX3-1703 3U Open-
VPX is a good example of an Arm-based single-board computer (SBC) (Fig. 1). It is designed for DO-254 safety-certifiable avionics applications.
The concepts of resilience and trusted systems refer not only to safety but also to data and hardware security. Great strides are being made today to enable COTS systems with anti-tamper technol- ogies, cybersecurity, and protection of data-at-rest and data-in-motion.
For example, the Data Transport System (DTS1) network attached storage (NAS) device supports cost-effective two-layer encryption (Fig. 2). The DTS1 is also easily integrated into net- work-centric systems.
Design for tech-savvy warfighters
The soldiers now using this equipment are digital natives — almost born with modern technologies in their hands. Along with this technological adept- ness comes a high level of assumption and expectation.
Today’s warfighter expects and de- pends on access to technologies as good as or better than what they have at home, such as an iPhone X, and social net- working services to enable information sharing in real time in the battlefield. All of today’s internet resources, whether searching on Google or asking questions of Siri or Alexa, are only years away from being available to the warfighter. As we increasingly bring reliable networked desktop computing, mobile platform, and social media capabilities to the warfighter to enable “network-centric warfare,” the network itself has become a key component of our ability to operate.
This technological adeptness can also be leveraged to address readiness, an area of military spending that has been relatively underfunded in recent years. Advanced computing can be brought to bear for training and mis- sion-planning and exploiting technolo- gies developed for the gaming industry to provide sophisticated, realistic scenarios and experiences.
By having training embedded in the actual deployed platform, warfighters will be able to train while they operate without requiring a dedicated training location. Realistic simulation can be done virtually, providing, for example, the ability to train for a specific mis- sion while en route.
Contain costs with open systems
Many of the technologies discussed
Mil/Aero Electronics above will benefit from the use of open systems, which reduce design risk and greatly speed time to deployment. The use of open systems also delivers significant cost reductions. Affordability results from competition and provides an alternative to expensive proprietary solutions.
Another key benefit of open systems is seen in technology insertions. Open systems enable the rapid insertion of new technology by defining an inter- face between different entities whose advancements progress at different rates. An open-systems interface, such as the OpenVPX system architecture, functions as a differential that enables the use of technologies that evolve out of synchrony.
For example, the fire control com- puter algorithms used in a main battle tank to handle ballistic solutions tend to evolve at a very slow relative rate with very little change from one year to the next. In comparison, the underlying processing technology used to run those algorithms progresses much faster. On the flip side, with EW as the example, the very sophisticated algorithms used to help identify a specific signal of interest in the noise of the electromagnetic spec- trum have developed at a much faster rate than the processors that are used to run them in deployed systems.
The result is that the most advanced EW algorithms wait for processor bandwidths to catch up in order for them to be put to use. The use of open-standard interfaces enables the processing technology and the algo- rithms used on deployed platforms to advance at different rates.
Innovation opens door to vulnerabilities
For every new opportunity and tech- nological leap forward, there is likely to be an associated vulnerability that emerges. While investing in the tech- nologies sought by the DoD in order to enable new capabilities and increase force lethality, technology providers must also invest in mitigating against those vulnerabilities.
The use of COTS-based open sys- tems provides a cost-effective approach to bringing these capabilities to the warfighter quickly and with the least risk. To bring the powerful benefits of advanced computing, AI, auton- omy, and robotics to the warfighter, COTS solutions must be designed and packaged to meet the environ- mental and usage requirements of the battlefield. The equipment must be dependable and operate while exposed to extreme environmental conditions. The technology must also be designed and packaged to ensure safe and secure operation. Care must be taken to en- sure safe operation without requiring burdensome safety precautions. System designers need to design and package next-generation COTS solutions to eliminate vulnerabilities to adversarial access or attack, including cybersecu- rity and protection against reverse-en- gineering to prevent physical access intended to disrupt operation.
It’s essential that these new technol- ogies assure the security of the defense systems and critical information during development and operation.
Another area of great importance is testing, which must be done to ensure that deployed COTS solutions are reliable and deliver error-free operation throughout their useful life.
Conclusion
The DoD and warfighters depend on trusted and proven sources of supply, and Congress has made available the funds to make this happen. Now it’s up to designers and other innovators to realize the full promise of new technol- ogies outlined here, just as examples. For sure, the COTS approach provides a proven alternative to costly, closed proprietary system architectures, speeds deployment, and ensures that critical technologies remain readily available over the lifecycle of their use. How tech- nologists build upon and apply it for next-generation battlefield deployments with more tech-savvy warfighters will be interesting to watch. ☐
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Discrete Semiconductors System integration considerations for heart rate sensing designs When it comes to optical
Subdermal Tissue HRM designs, developers have a choice of doing it all or purchasing it all
BY MORRIE ALTMEJD
Skin
Senior Staff Systems Engineer, Silicon Labs www.silabs.com Excitation signal
Attenuated Typically green and pulse (525 nm ), 100 µs
esigning an optical heart rate
modulated long pulses light
monitoring (HRM) system, also repeated at 25 Hz known as photoplethysmography
D Sensor
(PPG), is a complex and multidisciplinary
Green LED
Photodiodeundertaking. Design factors include human ergonomics, signal processing and
Optical blocking is critical to prevent
filtering, optical and mechanical design, the unmodulated excitation signal from
overwhelming the desired signal
low-noise signal receiving circuits, and low-noise current pulse creation.
Fig. 1: Principles of operation for optical heart rate monitoring.
Wearable manufacturers are increas- ingly adding HRM capabilities to their into highly integrated modules. These effectively served the health and fitness health and fitness products, which is modules enable a simpler implementa- market for years, HRM is now migrating to helping to drive down the cost of sensors tion that reduces the cost and complexity wrist-based wearables. Advances in optical used in HRM applications. Many HRM of adding HRM to wearable products. sensing technology and high-performance, sensors now combine discrete compo- Wearable form factors are steadily low-power processors have enabled the nents such as photodetectors and LEDs changing as well. While chest straps have wrist-based form factor to be viable for Fig. 2: The basic electronics required to capture optical heart rate.
Discrete Semiconductors
ated by the travel through the skin and is picked up by a photodiode and sent to the electronic subsystem for processing. The amplitude modulation due to the pulse is detected, analyzed, and displayed.
A fundamental approach to HRM sys- tem design uses a custom-programmed, off-the-shelf MCU that controls the puls- ing of external LED drivers and simul- taneously reads the current output of a discrete photodiode. Note that the current output of the photodiode must be con- verted to voltage to drive analog-to-digital (A/D) blocks. The schematic in Fig. 2 shows the outline of such a system.
Here, it’s worth noting that the I-to-V converter creates a voltage equal to V REF Fig. 3: An integrated heart rate sensor requires only external LEDs. at 0 photodiode current, and the voltage decreases with increasing current.
HRM building blocks
The current pulses generally used in heart rate systems are between 2 mA and 300 mA, depending on the color of the subject’s skin and the intensity of sunlight with which the desired signal needs to compete. The infrared (IR) radiation in sunlight passes through skin tissue with little attenuation, unlike the desired green LED light, and can swamp the desired signal unless the green light is very strong or unless an expensive IR blocking filter is added.
Generally speaking, the intensity of the green LED light, where it enters the skin, is between 0.1 and three times the intensity of sunlight. Due to heavy
Fig. 4: A highly integrated HRM sensor module incorporating all essential components.
attenuation by the tissue, the signal that arrives at the photodiode is quite weak many designs. The HRM algorithms have to deal with many skin types, motion and generates just enough current to al- also reached a level of sophistication to be rejection, development time, and physical low for a reasonable signal-to-noise ratio acceptable in wrist form factors. size. These design considerations impact (SNR) — 70 to 100 dB — due to shot
Other new wearable sensing form fac- system integration choices: whether to use noise even in the presence of perfect, tors and locations are emerging — such highly integrated modules or architectures noise-free op-amps and A/D converters. as headbands, sport and fitness clothing, incorporating more discrete components. The shot noise is due to the finite and earbuds. However, the majority of Fig. 1 shows the fundamentals of mea- number of electrons received for every wearable biometric sensing will be done suring heart rate signals, which depend reading that occurs at 25 Hz. The on the wrist. on the heart rate pressure wave being photodiode sizes used in the design are 2 2 optically extracted from tissue. It displays between 0.1 mm and 7 mm . Howev-
HRM design fundamentals the travel path of the light entering the er, above 1 mm, there are diminishing No two HRM applications are alike. skin. The expansion and contraction of returns due to the effect of sunlight.
System developers must consider many the capillaries — caused by the heart rate The difficult and costly function design tradeoffs: end-user comfort, pressure wave — modulate the light signal blocks to implement in an optical heart sensing accuracy, system cost, power injected into the tissue by the green LEDs. rate system design, as shown in Fig. 2, are consumption, sunlight rejection, how The received signal is greatly attenu- the fast, high-current V-to-I converters that drive the LED, a current-to-volt- age converter for the photodiode, and a reliable algorithm in the MCU that sequences the pulses under host control. A low-noise LED driver — featuring 300 mA and 75–100 dB SNR — that can be set to very low currents down to 2 mA while still creating very narrow light pulses down to 10 µs is an expensive block to achieve with discrete op-amps.
The narrow pulses of light down to 10 µs, shown in Fig. 2, allow the system to tolerate motion and sunlight. Typically, two light measurements are made for each 25-Hz sample. One measurement is taken with LEDs turned off and one with LEDs turned on. The calculated differ- ence removes the effect of ambient light and gives the desired raw optical signal measurement that is insensitive to the flickering background light.
The short duration of the optical pulses both allows and requires a rela- tively strong light pulse. It is essential to stay brighter than the sunlight signal, which may be present and not allow the PPG signal carrier to be dwarfed by the sunlight signal.
If the sunlight signal is larger than the PPG carrier, then although it may be removed by subtraction, the signal can be so large that external modulation such as swinging an arm in and out of shadow can create difficult-to-remove artifacts. As a result, systems that use low-current LED drivers and large photodiodes can suffer severely from motion artifacts in bright-light situations.
Discrete vs. integrated design
Much of the desired HRM sensing func- tionality is available pre-designed and integrated into a single device. Packing most of this functionality into one piece of silicon results in a relatively small 3 x 3-mm package that can even integrate the photodiode itself.
Fig. 3 shows an example of a sche-
matic with an optical sensor. This HRM design is relatively easy to implement. You just need to focus on the optical por- tion of the design, which includes optical blocking between the parts on the board and coupling the system to the skin.
While the approach shown in Fig. 3 results in a high-performance HRM solu- tion, it’s not as small or power-efficient as some designers would like. To achieve an even smaller solution, the LED die and the control silicon must be integrated into a single package that incorporates all essential functions, including the optical blocking and the lenses that improve the LED output. Fig. 4 illustrates this more integrated approach, based on a Silicon Labs Si117x optical sensor.
No external LEDs are required for this HRM design. The LEDs and photodiode are all internal to the module, which can be installed right below the optical ports at the back of a wearable product such as a smartwatch. This approach enables a shorter distance between the LEDs and photodiode than is possible with a dis- crete design. The reduced distance allows operation at extremely low power due to lower optical losses traversing the skin.