Lighting Electronics: October 2014 by EEWeb Magazines

July 2014 October

Light at the Museum Upgrading to LEDs

Li-Fi Turns On Internet

Light-Powered Connection

Interview with Jim Bonar CTO & Founder at mLED

mLED

DAZZLES Ultrabright & Ultrasmall LEDs

Join Today

eeweb.com/register

Light shed Lighting Electronics

Trends in Circuit Protection

on Market

The global growth of the outdoor LED market is self-evident as cities around the world including Hong Kong (shown here) adopt LED lighting for everything from parking lots and street lights to building illumination.

CONTENTS

he future of LED lighting technology is certainly bright.

CONTENTS

In spite of fluctuations in the economy and the general

TECH REPORT

lighting industry, LED lighting occupies a significant portion

By Henry Yu Technical Marketing Engineer at Littelfuse

of the overall lighting market. In fact, a 2013 article in Forbes

Light Shed On Market Trends in Circuit Protection

reported that LED lighting holds 18 percent of the $66 billion global lighting market.

Industry analysts predict significant growth over the next decade.

CAPACITIVE SENSING and LED LIGHTING

Li-Fi Exploits LEDs Light-Powered Internet Connection Layout Design In part two, we examined different ways of implementing pulse-width modulation (PWM). In part three, we’ll explore common challenges faced when designing systems with capacitive sensing and LED lighting and how to overcome them.

(Part 3)

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

n this section, we’ll discuss the important layout design rules to be followed in a system with capacitive sensors and any

switching lines such as LEDs and communication. Switching traces running in parallel with capacitive sensor traces couple the switching noise to the sensing system. Since we are trying to

TECH SERIES

reference such as ground running in parallel, but a switching trace changes the reference by rapidly switching between ground and high impedance or VDD thus causing the change of capacitance. Therefore, routing should be done in such a manner that the switching traces and the sensing traces are never run in parallel. Figure 1 shows the recommended layout routing scheme.

Capacititive Sensing and LEDs Layout Design Rules Combining

CAPACITIVE SENSING and LED LIGHTING

July 2014 October

To read the previous article in this series, click on the image to the right.

Upgrading to LEDs

Light-Powered Connection

measure the capacitance in femtofarad resolution, the sensing block is sensitive to the cross talk noise. The sensing system sees a constant capacitance as long as the sensor trace has a fixed

Light at the Museum Li-Fi Turns On Internet

EEWeb FEATURE

Combining

(Part 2)

Pulse Width Modulation (PWM)

n part 1, we explored different LED lighting techniques adopted in capacitive sensing-based UI applications using real-world use cases. Next we’ll learn the different approaches for implementing pulse width modulation (PWM), a key method for LED control applications.

PWM has mainly two properties: Frequency:

Using a PWM signal rapidly switches an LED on and off. As the switching frequency produces LED flickering, the PWM frequency should be >100 Hz to ensure that a human eye doesn’t perceive this effect.

Duty cycle:

PWM controls the brightness of LEDs by changing the duty cycle and keeping the load current constant. The average current seen by the LED depends on the duty cycle. Average current increases as duty cycle increases, in turn increasing the brightness. The duty cycle needs to have as many steps between 0% and 100% as the number of brightness levels required in an application. For example, an application requiring 20 brightness levels from fully off (0%) to fully on (100%) should be able to control the duty cycle in the steps of 5% (total 20 steps, excluding fully off).

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

There are two ways to implement PWM with a microcontroller. Either implement the entire PWM logic in firmware with the help of a simple timer/counter or choose an advanced controller that has integrated hardware PWM capabilities. Combining

CAPACITIVE SENSING and LED LIGHTING (Part 1)

To read the first article in this series, click on the image to the right.

Some applications require more visual effects apart from simply turning on and off an LED. For example, a laptop may blink the power LED with its brightness gradually increasing and then gradually decreasing when the device is in stand-by. This is called the breathing effect. This is one of the many LED effects such as fading and blinking used in devices. These advanced LED effects, when combined with capacitive touch buttons, improve the aesthetics and the user experience of the system. It’s often desirable to implement multiple features using a single System-on-Chip (SoC) to reduce the BOM. In this four-part series, we’ll discuss the different aspects of implementing capacitive sensing and LED lighting using a single SoC, including the following topics. We will briefly describe different LED lighting techniques adopted in capacitive sensing-based UI applications using real-world use cases.

Pulse Width Modulation (PWM) is one of the common techniques used to implement LED effects. We will discuss how to select a suitable SoC by analyzing the different schemes of implementing LED effects using PWM techniques. Combining implementation of multiple features in a single SoC invariably poses challenges. It is very important to overcome those challenges for a robust design. We will discuss some common challenges such as crosstalk between LEDs and capacitive sensors, drive strength capability, and LED load transients that cause noise within the capacitive sensing subsystem and how to avoid them. Power consumption optimization is of high importance for any electronic system. We will discuss design considerations for low power consumption for applications requiring LED effects.

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

INDUSTRY INTERVIEW mLED Dazzles Jim Bonar, CTO and Founder at mLED

Interview with Jim Bonar CTO & Founder at mLED

mLED

DAZZLES Ultrabright & Ultrasmall LEDs

TECH REPORT

FINANCIAL SNAPSHOT Replaced over 8,300 halogen bulbs with LEDs throughout more than 140 galleries, common spaces and office areas

Project

Cost

$ 388,000

Fine Art Glories in Fine Light Museum Upgrades to LED Lighting Xcel Energy rebate

$ 177,000

NEH grant

$ 62,000

Annual energy savings

$ 149,000 or 1.7 million kWh

Payback term

Less than one year

Estimated maintenance hours saved by not changing bulbs

Several added benefits make the change even sweeter. The LEDs use roughly one fifth of the energy that halogens use, reducing energy bills. They emit no ultraviolet (UV) and very little infrared (IR) rays, reducing impact on the art itself. They also burn cooler, helping MIA save on cooling costs. Anecdotally, security guards who spend hours at a time in the galleries say the improved light has improved their moods. On the financial side, two things made the project feasible. First, a $62,000 Sustaining Cultural Heritage grant from the National Endowment for the Humanities helped ease the financial burden.

Second, MIA’s electric utility, Xcel Energy, offered rebates as incentives to help defray the cost of new high efficiency equipment. MIA received $177,000 in Xcel Energy rebates, or about $35 per bulb. Even better, the project will pay for itself in energy savings in less than a year.

SHARING THE LIGHT A few lights still need to be retrofitted in the behind-the-scenes areas at the museum but in many applications there isn’t an LED equivalent yet. McCann continues to work on it. Meantime, they’re providing information to the nation’s other galleries and art communities,

speaking at the Smithsonian and a recent conference of the American Alliance of Museums about the benefits of LEDs and persevering through the trials and tribulations that come with the process. “We’ve gotten calls from all over the country,” explains Shapansky. “We’re happy to share what we’ve learned so that others can reap the same benefits and hopefully complete their projects even faster than we did.”

“The LEDs emit no ultraviolet (UV) and very little infrared (IR) rays, reducing impact on the art.”

2,000 in the first five years

BENEFITS OF LEDS

With over 5,000 lights in it’s 140-plus galleries, the process of changing to the new LED PAR38 and PAR30 lamps took time...pg. 30 •

Use less energy, therefore reducing electric bills

•

Color closely resembles daylight making colors crisp

•

Emit no UV and very little IR rays, reducing impact on the art

•

Cooler, generating less heat, reducing cooling costs

For more about MIA’s new lights and look, visit new.artsmia.org. For more about Xcel Energy’s energy efficiency rebates and programs, visit www.responsiblebynature.com/business.

Lighting Electronics

LED

Light shed

on Market

TECH REPORT

Trends in Circuit Protection

he future of LED lighting technology is certainly bright.

In spite of fluctuations in the economy and the general lighting industry, LED lighting occupies a significant portion

By Henry Yu Technical Marketing Engineer at Littelfuse

of the overall lighting market. In fact, a 2013 article in Forbes reported that LED lighting holds 18 percent of the $66 billion global lighting market. Industry analysts predict significant growth over the next decade.

Lighting Electronics

lectronics engineers and product development managers in the LED lighting segment strive to continue growing right along with the market trends. To succeed in developing LED designs that flourish in the current market, however, they must incorporate reliable circuit protection technologies that deliver a strong return on investment (ROI).

Implementation of surge protection device (SPD) circuit protection, like the LSP05-LSP10 series from Littelfuse, helps outdoor lighting applications deliver their full return on investment.

This up-to-date market overview reveals the current state of the LED market, trends for several LED segments, and forecasts for global growth. While emphasizing the need for industry-leading circuit protection solutions from a reliable manufacturer, it outlines the ideal fuses, varistors, surge protection modules, and transient voltage suppression (TVS) diodes for a variety of LED applications.

Current Market Condition

NEARLY 70 PERCENT OF ALL TRAFFIC LIGHTS IN THE U.S. HAVE BEEN CONVERTED TO LEDS.

Statistical research from the past few years supports the pivotal position of LED technology in the global lighting market. According to IHS Technology, one out of every four dollars spent worldwide on LED drivers was used for lighting applications in 2013. In terms of market share among all end users of LED lighting, a 2014 article from MarketWatch revealed that the commercial segment was the largest and accounted for 52.5 percent of the market in 2012. The same article highlighted that Europe was the largest geographic market segmentâ&#x20AC;&#x201D; accounting for 33.1 percent market share in 2012.

TECH REPORT Some of the most common applications for LED lighting are outdoor, residential, and architectural. Outdoor LED lighting is quickly gaining popularity for tunnels and roadways. In fact, nearly two million LED luminaires were installed in tunnels and roadways in 2012, according to Strategies Unlimited. They are also being used in traffic lights, parking lots, and garages. A recent article from Reuters reported that nearly 70 percent of all traffic lights in the U.S. have been converted to LEDs. The article also stated that the adoption percentage for the European market is currently in the low teens, as of 2010. Residential applications for LED lighting include lighting in kitchens, hallways, and bathrooms. A 2010 characterization report from Navigant Consulting published that the total number of LED lamps installed in U.S. stationary applications grew from just under 7 billion in 2001 to more than 8 billion in 2010. This statistic was especially significant because the majority of the growth occurred in the residential sector. Navigantâ&#x20AC;&#x2122;s report also revealed

LED STREET LIGHT INSTALLATIONS WILL GROW BY 400 PERCENT OVER THE NEXT FIVE YEARS.

that residences account for 71 percent of all lamp installations in the U.S. for a total of 5.8 billion lamps. According to MarketWatch, the architectural segment is the second largest end-user segment for LED lighting. For architectural applications, LEDs are used in both decorative and functional lighting. Decorative LEDs are used to illuminate fountains, pools, gardens and statues. For functional applications, such as building facades and landscaping, LEDs provide visibility and enhance safety on residential and commercial properties.

Lighting Electronics

Future Market Growth Where is the LED market headed? Forbes predicts that growth will continue throughout the next decade, with the global LED market share reaching about 70 percent by 2020. According to McKinsey’s 2012 lighting market report, Asia will occupy about 45 percent of the global general lighting market by 2020. The report indicated that rapid penetration in Japan and China is driving Asia’s market-leading position for transitioning to LEDs in general lighting. In Europe, the current LED value-based market share is approximately 9 percent, McKinsey reported. By 2020, the share is expected to rise to over 70 percent. Outstanding growth is projected across various LED market segments, including the outdoor lighting industry. Strategies Unlimited forecasts that the global outdoor LED lighting market will reach $1.9 billion by 2017. The organization also predicts that LED street light installations will grow by 400 percent over the next five years. According to Semiconductor Today, the market share of LEDs in street lighting worldwide will grow from 53.3 percent in 2014 to 93.8 percent in 2023. LED lighting within residential and architectural industry segments is also expected to grow. Forecasts for LED growth in the residential segment are almost 50 percent for 2016 and over 70 percent for 2020, according to McKinsey. For architectural lighting, MarketWatch revealed that Japan and Europe are the fastest growing regions. McKinsey predicts that architectural lighting will remain the early adopter

for LED lighting, with its market share reaching almost 90 percent by 2020.

Circuit Protection To keep up with the latest trends in LED lighting, electronics engineers and product development managers are continually innovating LED designs. Creating designs for LED lighting applications presents several challenges, including the need to protect the sensitive electronics and circuits within the LEDs against lightning, transient surges, and electrostatic discharge (ESD). These electrical threats may jeopardize the safety of personnel and endanger the consumer’s ROI. If proper safeguards are not used, there could also be compliance issues with regulatory and safety standards related to overvoltage transients. Circuit protection technologies are vital for safeguarding the vulnerable electronics and circuits within LEDs. To prevent LED lighting

FORBES PREDICTS THAT GROWTH WILL CONTINUE THROUGHOUT THE NEXT DECADE, WITH THE GLOBAL LED MARKET SHARE REACHING ABOUT 70 PERCENT BY 2020.

TECH REPORT from experiencing failures within an investment payback period of about five years, high durability and reliability are essential. Before selecting a compatible circuit protection device, it is important to find a manufacturer with knowledge of LED lighting industry standards and the safety issues associated with designing LED retrofit lamps and outdoor luminaires. Littelfuse, the global leader in circuit protection, recommends protection devices for LED driver and power converter circuits and performs testing to ensure compliance with industry standards. The company manufactures a variety of fuses, varistors, surge protection modules (combination of varistors), and TVS diodes for LED lighting applications. The table below indicates the ideal circuit protection device for various applications.

Conclusion As the LED lighting market continues to grow across several application segments, the demand for high-reliability circuit protection technologies will continue to increase. Circuit protection is needed to safeguard sensitive LED electronics and circuits from electrical threats and meet industry standards for safety and reliability. In addition, circuit protection is vital for preventing LED lighting from experiencing failures within an investment payback period of five years. Industry-leading circuit protection solutions like fuses, varistors, surge protection modules, and TVS diodes are designed to protect several LED applications and maximize the lighting investment.

CIRCUIT PROTECTION TECHNOLOGIES ARE VITAL FOR SAFEGUARDING THE VULNERABLE ELECTRONICS AND CIRCUITS WITHIN LEDS.

LED LIGHTING APPLICATIONS CIRCUIT-PROTECTION-SOLUTIONS TABLE LED Lighting Applications

Over-Current Solutions

Over-Voltage Solutions (primary front end)

Over-Voltage Solutions (secondary sideadded clamping)

LED Bulb

454 Series Fuse

CH Series Varistor

SMBJ TVS Diode

Complete SMT (surface-mount) OC and OV solutions for lowest cost and manufacturing efficiencies

LED Streetlight (North America)

328 Series Fuse

LSP10277S

1.5KE TVS Diode

Meets ANSI C136.2 and DOE MSSLC for 20kv/10ka high exposure, series indication

LED Streetlight (Europe, Asia)

219 Series Fuse

LSP05277P

P6KE TVS Diode

10kv/5ka, thermally protected surge immunity solution, CE Mark and Class I&II installation support

Area Lighting

209 Series Fuse

LSP05277NP

SMAJ TVS Diode

Lowest cost solution for low-exposure applications

Details

Protect Your Outdoor Lighting Investment LED Lighting SPD Module Design and Installation Guide

Compact, Surge-Tolerant Fuses for Outdoor Lighting 328 and 688 Series Fuses

Open LED Protectors Keep Outdoor LED Strings Shining PLED6M Series

Boost LED String Reliability, Light Engine Efficiency PLEDxSW Open LED Protector

Prevent Damage to Outdoor LED Lighting Fixtures LSP05 & LSP10 SPD Modules

The initial cost of installing outdoor LED lighting can be substantial; payback depends on the system surviving long enough to reap the benefits of the lower wattage demand, lower maintenance cost, and longer lifetime LED lighting offers. This design and installation guide describes example circuits, applicable standards, and recommended circuit protection components. Littelfuse created this resource for electronics designers to guide them in protecting outdoor LED lighting systems from lightning, power faults and other electrical transient threats. Visit the Education Center at www.speed2design.com

Download this guide now

Protecting Protecti ing Technology. Protecting Life.

Lighting Electronics

Li-Fi Exploits

LEDs By Alex Maddalena, Contributing Writer

EEWEB FEATURE

LIGHT-POWERED Internet Connection

“LED bulbs are unique, semiconductor devices.” Back in 2011, Professor Harald Haas

cleverly dubbed “Li-Fi,” overcomes

delivered a groundbreaking TED

many of the challenges currently

(technology, entertainment, design)

posed by traditional RF bandwidth

talk about the untapped potential

limitations. The implications of Li-

of the visible light spectrum. Haas,

Fi in the fifth-generation mobile

chair of Mobile Communications

network are massive; this visible light

at the University of Edinburgh,

communication system can deliver not

demonstrated a way to transmit

one, but thousands of data streams in

data through LEDs via the visible

parallel. In conjunction with lighting

light spectrum as opposed to radio

industry trends leaning towards smart

frequency (RF) bands. This new

LED lighting, a Li-Fi-enabled world

method of data communication,

would be much simpler and efficient.

Lighting Electronics

“Li-Fi transmits data through LEDs via the visible light spectrum.”

“We have to learn to replace these inefficient incandescent light bulbs with LEDs,” Haas stated, explaining a means for establishing visible light communication “networks.” He added that “[LEDs are] a fundamental, basic technology that we exploit with Li-Fi.” The field of visual light communication (VLC) has been studied for a over a decade and is now at a marketable tipping point, which is why Haas cofounded a spinoff company dedicated to commercializing it. The company, pureLiFi, is the culmination of years of research and industry experience with a team dedicated to enabling this groundbreaking, potentially ubiquitous technology.

LED Streaming The enablement of VLC revolves around an LED bulb. When the bulb is illuminated, there is a constant stream of photons emitted, much like other waves in the visible light spectrum, including RF. What makes the LED bulbs unique is the fact that they are semiconductor devices, meaning the light can be modulated at extremely high speeds. With signal processing technology, the light stream from the LED can also contain bits of data that are picked up at a receiver, which are then converted

back into data streams. At this point, the stream is transmitted to the computer as if connected to a wireless network. While this process might seem complicated, upon seeing a demonstration, it seems impossibly simple. During his TED talk, Haas turned on an LED lamp that shined on a flat, unassuming receiver. A video was then projected behind him in conjunction with the lamp turning on. It was only until Haas blocked the LED light with his hand and the video stopped that it became clear that the light had been transmitting the video stream behind him. The result was so surprising, that there were audible gasps from the audience.

Free Internet? One of the biggest benefits of pureLiFi’s Li-Fi model is that it simplifies the users’ monthly utility bill. Most Americans spend upwards of $50 per month on average and unreliable Internet service, but LiFi offers faster and more dependable speeds—and all by simply turning on the light. This would mean that the Internet would come for free with the electric bill. While a LED needs to be turned on in order for a Li-Fi connection to be established, it can also

EEWEB FEATURE be dimmed to a nearly “off” position and still transmit data. In a statement earlier this year, Haas confirmed that while nearly off, Li-Fi still maintains nearly 100 percent of its data transmission capabilities. This can lead to an “always-on” state that still won’t make a dent in an energy bill. The benefits that Li-Fi possess would mean the elimination of bulky, ineffective base stations that emit potentially hazardous frequencies—not to mention the amount of energy it takes to power and cool them. As a result, the potential applications for Li-Fi are, at the moment, boundless. Imagine being able to employ new electronic medical devices in hospitals where RF devices were previously deemed harmful to use, all powered through preexisting light. Li-Fi can also be enabled through streetlights and car headlights, offering the potential to communicate between vehicles to prevent harmful or deadly accidents on the road. Even a flashlight in a smartphone device can be turned into a data transmission method. Haas summed up the huge scope of Li-Fi by stating, “Wherever we have light, there is the potential to transmit data.” With over 14 billion functioning light bulbs in the world, it won’t be long before that vision becomes a reality.

“Li-Fi can be enabled through streetlights and car headlights.”

Click the image below to view the TED TALK video.

Lighting Electronics

Combining

CAPACITIVE SENSING and LED LIGHTING (Part 3)

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

TECH SERIES

In part two, we examined different ways of implementing pulse-width modulation (PWM). In part three, we’ll explore common challenges faced when designing systems with capacitive sensing and LED lighting and how to overcome them.

Layout Design

n this section, we’ll discuss the important layout design rules to be followed in a system with capacitive sensors and any switching lines such as LEDs and communication. Switching traces running in parallel with capacitive sensor traces couple the switching noise to the sensing system. Since we are trying to measure the capacitance in femtofarad resolution, the sensing block is sensitive to the cross talk noise. The sensing system sees a constant capacitance as long as the sensor trace has a fixed reference such as ground running in parallel, but a switching trace changes the reference by rapidly switching between ground and high impedance or VDD thus causing the change of capacitance. Therefore, routing should be done in such a manner that the switching traces and the sensing traces are never run in parallel. Figure 1 shows the recommended layout routing scheme.

Combining

CAPACITIVE SENSING and LED LIGHTING

To read the previous article in this series, click on the image to the right.

(Part 2)

Pulse Width Modulation (PWM)

PWM has mainly two properties: Frequency:

Duty cycle:

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

CAPACITIVE SENSING and LED LIGHTING (Part 1)

To read the first article in this series, click on the image to the right.

apacitive touch sensing is the very popular technology used to implement intuitive user interfaces (UI) in many electronics applications including smart phones, tablets, LCD/LED TVs, and many others. Touch buttons are fast replacing traditional mechanical buttons. However, unlike mechanical buttons which provide tactile feedback to users by their nature, touch buttons need additional components to provide feedback. LEDs are widely used to provide visual feedback and backlight illumination in touch-based UIs. Some applications require more visual effects apart from simply turning on and off an LED. For example, a laptop may blink the power LED with its brightness gradually increasing and then gradually decreasing when the device is in stand-by. This is called the breathing effect. This is one of the many LED effects such as fading and blinking used in devices. These advanced LED effects, when combined with capacitive touch buttons, improve the aesthetics and the user experience of the system. It’s often desirable to implement multiple features using a single System-on-Chip (SoC) to reduce the BOM. In this four-part series, we’ll discuss the different aspects of implementing capacitive sensing and LED lighting using a single SoC, including the following topics. We will briefly describe different LED lighting techniques adopted in capacitive sensing-based UI applications using real-world use cases.

By Vairamuthu Ramasamy and Shruti Hanumanthaiah

Lighting Electronics

Figure 1. Recommended routing scheme. We should be able to route sensor traces in parallel to prevent increasing routing complexity further. Let’s look at an issue associated with routing two sensor lines in parallel. Assume that when one line is scanned, the other line is floating. Now touching the floating line will cause a change of capacitance with the other line. This can be resolved by grounding all the sensor pins that are not scanned. This is possible since controllers usually have one capacitive-sensing, blockmultiplexing sensor pin. However, if the device supports simultaneous scanning of multiple scan lines, then the pins that require simultaneous scanning should not be routed in parallel. For example, Cypress’ PSoC devices support simultaneous dual-channel scanning.

Isolation of switching pins and sensing pins during schematic design (see figure 2) helps to avoid parallel routing during layout design. Note that the advantage of choosing any pin for PWM drive in a firmware-based implementation allows for more convenient pin assignment. Considering the fact that electronic systems are becoming increasingly complex, it may not be always possible to completely avoid parallel routing. In such cases, cross talk can be limited by reducing the slew rate on the LED line using a capacitor as shown in figure 3. The value of the capacitor is typically 0.1 µF.

“CYPRESS’ PSOC DEVICES SUPPORT SIMULTANEOUS DUAL-CHANNEL SCANNING.”

TECH SERIES DRIVE-CURRENT STRENGTH It is important to choose a controller that meets the current drive requirement of an application in order to reduce the bill of materials (BOM). Usually the port pins have a high sinking capability and low sourcing capability. LEDs requiring high current should be connected in a sinking configuration. The drive mode of these pins should be configurable in open-drain mode so that writing 0 drives the pin to a high impedance state to turn the LED off and writing 1 drives the pin to low to turn the LED on. When combined with capacitive sensing, current sinking may produce an unwanted effect, which limits the maximum current a device can sink. We’ll look more at this in part 4. CSx – Sensing Pins LEDx – LED Pins COMx – Communication or other switching lines

Figure 2. Isolated pin assignment of sensors and switching lines.

Sourcing capability is important if the LEDs are connected in a multiplexed configuration. Applications requiring higher drive current will have to use external metal-oxide-semiconductor field-effect transistor (MOSFET) switches to drive the LEDs.

LOAD TRANSIENT NOISE Systems on a chip (SoCs), which can do capacitive sensing as well as drive LEDs are mixed-signal integrated circuits (ICs) which have both analog and digital blocks. The analog and digital circuitry must be separated as much as possible to prevent digital noise from degrading the performance of the capacitive sensing system. The common challenge is that the sensing system picks up the noise on ground when the output pins tied to LEDs in sinking mode switch between logic high and logic low. Figure 3. Cross talk solution.

Lighting Electronics

Figure 4 . Ground-bonding scheme.

Figure 5. Shift in raw count due to LED sinking.

TECH SERIES In order to reduce pin count, some mixedsignal ICs have the analog ground pad and the digital ground pad of the die bonded out to a common ground pin on the package. This bond-wire resistance is usually a few tens of milliohms. This arrangement is shown in figure 4.

Some of the common techniques to overcome this problem are:

Now consider the case where the LEDs are configured in sinking mode. The output pin sinks the LED current to the IC ground when it starts driving low to turn on the LED. This current sink results in an IR drop due to the bond wire resistance, thus shifting the IC ground potential with respect to the board ground. Though this shift is only a few millivolts, the sensing system could be very sensitive as it is trying to measure capacitance in the range of femtofarads. Note that this could be an issue specific to some sensing methods which are sensitive to the ground shift.

• Reduce the parasitic IR drop by reducing the resistance between the board ground and the IC ground by following proper layout guidelines.

This problem becomes severe when multiple output pins sink current simultaneously. This could result in high shifts in the sensor raw count equaling a finger touch, thus causing a false trigger. Figure 5 shows the shift in raw counts due to LED switching.

• For ICs in which the analog and digital grounds are bonded out as separate pins, keep them separate and short them at the power supply end.

• Reduce the parasitic IR drop by reducing the sinking current on the output pins tied to the LEDs. • During schematic design, ensure that the pin assignment is done such that the LEDs are assigned to pins that are far away from the ground pin of the IC and the sensors are assigned to the pins which are close to the ground pin. This way, the parasitic IR drop is minimized. In this part, we explored how to overcome common challenges faced when designing systems with capacitive sensing and LED lighting. In part 4, we’ll address low-power design considerations for such applications.

“ELECTRONIC SYSTEMS ARE BECOMING INCREASINGLY COMPLEX, SO IT MAY NOT BE ALWAYS POSSIBLE TO COMPLETELY AVOID PARALLEL ROUTING.”

Your Circuit Starts Here. Sign up to design, share, and collaborate on your next projectâ&#x20AC;&#x201D;big or small.

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INDUSTRY INTERVIEW

mLED

DAZZLES

Ultrabright & Ultrasmall LEDs Interview with Jim Bonar, CTO & Founder at mLED Ultrahigh brightness, micro-LED solutions developed by mLED signify a new generation of LED technology. With this technology, the company addresses consumer and industrial applications that include head-mounted displays, scopes, smart eyewear, headup displays, rugged computing, digital printing, and lithography. Based in Scotland, mLED is currently active on three continents, delivering innovation through leading edge technology. EEWeb spoke with Jim Bonar, CTO and founder of mLED, about the contrast between micro-LEDs and OLEDs, applications for micro-LED technology, and the surging wearables market. Bonar also discussed the manufacturing process for micro-LEDs, the advantages of high-brightness display, and how the companyâ&#x20AC;&#x2122;s LEDs provide superior resolution.

Lighting Electronics

What led you to start exploring the world of micro-LEDs?

“mLEDs’ niche is definitely with microdisplay applications.”

After more than a decade of being involved with photonic start-ups, I was drawn to the opportunities in III-V solar cell technologies; this was around 2007. However, I became more interested in the idea of light being generated rather than harvested. This is why I started looking at LED technology and novel means to both form and use the structures. It is fair to say that at the time, LEDs were facing similar challenges to those of solar cells. The LED market was still a demanding unique technology that needed further development. This is why I got involved with micro-LED technology. In 2010, I cofounded the company mLED, which was to be the commercialization vehicle for the micro-LED technology developed at the University of Strathclyde since 2001. From there, we have grown the business considerably, and I am now the CTO of the company.

Right now, OLEDs are getting a considerable amount of attention in the market. Where do OLEDs fall short, and what advantages do mLEDs have over OLEDs? The advancements made in OLED technology have been outstanding over the last 10 years, and there has been a lot of development “under the hood” to progress the technology. OLEDs definitely have a place in the market and

are becoming a technology of choice for displays. They have advantages compared to technologies, such as liquid crystal or MEMS, because OLED technology, like our LED technology, is based on direct emission. There is no need for an external pattern generator. It’s also advantageous as companies scale up the capability to secure the supply chain so it can be used in smartphones and TVs. However, mLED’s solution has an advantage because with an inorganic LED, you can have orders of magnitude higher brightness displays than OLED, while not encountering the reliability issues of typical OLEDs themselves. It’s also not possible to drive up OLEDs to high-current density without degrading the structure and shortening the lifetime, especially if emitting in the blue wavelength region. This is important because if you want higher luminance from your display, then you have to consider the current, and the power has to be dissipated in that display. That leads to two issues: one is the reliability issue and the other is the power consumption. This also means that mLED can reduce the brightness of the displays and with that reduce the power consumption by five to seven times depending on the application. We are looking for structures that are going to be no more than 2 inches diagonal because mLEDs’ niche is definitely with microdisplay applications.

INDUSTRY INTERVIEW

“We can make microdisplays that would be more rugged, more reliable, and more luminous.” What specific applications are you targeting with micro-LED technology?

What is the capability of microdisplays in terms of brightness and resolution?

If you were to think of a mobile or wearable device, the biggest inconvenience to the person using it is battery life. Getting a device with both extended battery life and improved image resolution requires a microdisplay technology that not only provides the luminance needed, but also saves power. This is where we really see the advantages of micro-LED technology— the ability to have micropixelated LEDs with spatial, spectral, and temporal control of the LEDs at the microlevel. With these advantages we can make microdisplays that would be more rugged, more reliable, and more luminous in additon to having extended battery life.

As discussed, we have major luminance advantages with this technology that provide unparalleled performance. Unlike OLEDs, one of our challenges is that we have to hybridize the display with a control backplane. What’s required there is the ability to form a complementary metal-oxide semiconductor control backplane and to ‘flip-chip’ on the LED pixelated array. This is important because a challenge is to reduce the bond pitch of subpixel to subpixel for a high-resolution display. With our unique process, we can make robust LEDs down to the dimensions of 3 microns while maintaining extremely high brightness. We are now progressing

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this to LED pixels with dimensions of 1 micron. To put our size into context, traditional LEDs usually measure in around 200 microns by 200 microns, or for solid state lighting, 1 mm by 1 mm. The challenge here comes with the ability to go to fine-pitch bonding. Today, we are aiming for 10-micron bond pitches. We are working on our roadmap to achieve that exact pitch with an ultimate goal of achieving 5-micron pitch. Our aim at the moment is to achieve a display resolution of 720p, with subpixel pitch of 10 microns.

Could you talk about the manufacturing process involved in micro-LEDs? Our manufacturing process is based on simplifying the process flow and having the ability to routinely fabricate LED micropixelated arrays in a robust manner, utilizing standard, parallel semiconductor processes. This is of extreme importance to me. With regard to performance, you actually see light generated from pixels

at tens of nanoamps. When we start to run these monochrome devices (operational wavelength of 520 nm) at roughly 700 nanoamps, the pixel brightness is around one million nits. To put that into context, if you were to look at an iPhone display, the brightness level at maximum performance is 400 nits. We are talking about orders of magnitude in brightness levels. Smaller pixels within LEDs offer an extremely high-power density and the ability to sustain those power densities at a range of current densities. mLED has a technique that enables our micropixelated LEDs to operate at current densities of ~10,000 A/cm2. This highlights the robustness of our LED structures. However, our strategy is to not require high current densities but to operate at low-current densities (<10 A/ cm2) while still maintaining brightness so we donâ&#x20AC;&#x2122;t have issues with thermal management or reliability. Micro-LEDs can compartmentalize into one part of an overall structure. You then have this silicon doing the control, and very importantly, you have to look at how to bond those two together. We are working with people to develop techniques that reduce bond pitch.

INDUSTRY INTERVIEW

You mentioned that the mLED displays are at the order of 1 million nits while the iPhone display comes in around 400 nits. What are the advantages of such a high brightness display? One advantage of mLED displays comes in situations where the user struggles to see a screen in a bright, sunlit area. The second aspect is that with the capability of a high brightness level, a user can adjust the brightness down to 1000 nits or 5000 nits, which means the power consumption for the device goes down as well. The ability to reduce the power consumption down to an order of magnitude is where the benefits start to become apparent for the applications we are targeting.

different approach; we are starting to have discussions with various people in the wearable market and finding opportunities where we will be able to implement our micro-LED capabilities. We have been warmly received and have a few supply agreements on the table.

When should we expect to see micro-LED technology on the market? Definitely in the first two quarters of next year. We have been making great strides with our customers, and we are embarking on an ambitious roadmap for our wearable applications, and we plan to deliver.

How has the customer reception and implementation been with micro-LED technology? Our demo systems have been seeding the market. In fact, we have already moved with one of our European customers into a volume supply agreement, and we are working on a similar agreement with a North American customer.

â&#x20AC;&#x153;Our company, mLED, has been warmly received and has a few supply agreements on the table.â&#x20AC;?

Traditionally, start-up companies develop a technology, and it can take up to several years before that hits the market in volume. We have taken a

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FINE ART GLORIES IN FINE LIGHT Minneapolis Institute of Arts upgrades to LED lighting By Xcel Energy

GETTING THE LIGHT RIGHT There are few places where lighting is as important as in a gallery or museum. The art has to look great or people wonâ&#x20AC;&#x2122;t come to see it. So when the staff at the Minneapolis Institute of Arts starting wondering if it were time to consider LED lighting to replace the halogens in the galleries, it caused a stir.

TECH REPORT

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“Some of our colleagues were reluctant about using LEDs at their desks, so you can imagine how skeptical they were about using them in the galleries,” says Shawn McCann, MIA’s mechanical maintenance and utility specialist. “But we knew from using LEDs in our exit signs and elsewhere that we could be saving money with more efficient bulbs, so we wanted to explore it.” “At the time, LED lighting was still developing so it was hard to guide them toward a good solution,” says Sara Terrell, Xcel Energy account manager. “You hate to tell people to wait on their efficiency plans, but that’s what we decided to do until a better solution came along.” The process was a long one but was well worth their time and energy. “Now that we’re saving $149,000 a year in electric bills, it’s easy to say we did the right thing,” says Karl Shapansky, MIA lighting designer and technician. “But at the time it was hard to go through the process of testing various bulbs in several applications and locations.”

Packages would come one at a time with the promise of a solution. “Our method wasn’t very scientific,” says Shapansky. “We’d plug them in and ask people their opinions.” The museum had several things to consider, including the cost of the bulbs, retrofitting them into the existing fixtures, the various types of bulbs they would need, the need to stock extras for specific artist requests as new exhibits came through, and the impact on the art itself. Over the course of several years, the lighting market changed, the options grew and finally, a solution presented itself. The staff at MIA was ready to make the lighting leap.

NEW LIGHTS, NEW LOOK

FINDING THE RIGHT SOLUTION

Before making the purchase, the lights were tested in a few galleries. The new light made the art look fantastic, but that’s when they noticed the paint problem. The light gave the walls a yellow and purple cast. The installation was halted while the search for a new paint began. “It added to the length of the project but we had to fix it,” says Shapansky.

No stranger to conservation and sustainability efforts, MIA’s Green Team led the charge to upgrade to more efficient lighting. They started the process in 2007 and started receiving samples from all over the country.

With over 5,000 lights in its 140-plus galleries, the process of changing to the new LED PAR38 and PAR30 lamps took a long time. The team would remove the art from one gallery, install the lights,

“The new lights improve the depth of the artwork, making it look crisp and detailed.”

TECH REPORT paint the walls, and replace the art. After two major phases spanning almost two years, it was done. “The new lights improve the depth of the artwork, making it look crisp and detailed, especially bringing out greens, blues and purples,” says Charles Walbridge, MIA photographer and Green Team leader. “The lights combined with the neutral, warm, gray paint really make the art stand out.”

The museum itself is now a standout. The Minneapolis Institute of Arts is the first museum of its size to have 100 percent LED lighting in its galleries.

REACTION AND DISCOVERIES “People either love it or have no idea we made the change,” says Shapansky. “I love it because the art looks great, but also because I can spend more time designing and less time up on the lift changing bulbs.” Shapansky used to replace 35 to 40 bulbs a week. The new LEDs should last five to eight years, or 22 times longer than halogens.

“We’re saving $149,000 a year in electric bills.”

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TECH REPORT

FINANCIAL SNAPSHOT Project

Replaced over 8,300 halogen bulbs with LEDs throughout more than 140 galleries, common spaces and office areas

Cost

$ 388,000

Xcel Energy rebate

$ 177,000

NEH grant

$ 62,000

Annual energy savings

$ 149,000 or 1.7 million kWh

Payback term

Less than one year

Estimated maintenance hours saved by not changing bulbs

“The LEDs emit no ultraviolet (UV) and very little infrared (IR) rays, reducing impact on the art.”

2,000 in the first five years

BENEFITS OF LEDS •

Use less energy, therefore reducing electric bills

•

Color closely resembles daylight making colors crisp

•

Emit no UV and very little IR rays, reducing impact on the art

•

Cooler, generating less heat, reducing cooling costs

For more about MIA’s new lights and look, visit new.artsmia.org. For more about Xcel Energy’s energy efficiency rebates and programs, visit www.responsiblebynature.com/business.

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