E-Paper Displays Mature

How innovative solutions are taking E-paper displays from niche to mainstream IoT applications.

Adding to the existing strengths of Electronic Paper Displays (EPDs)—ultra-low power consumption, superb readability, and compact size—are several breakthrough enhancements, including new colors, faster display updating, even lower power usage, and a much wider operating temperature range.

Integrating these next generation EPDs into IoT devices can undoubtedly improve the functionality and lower the cost of current IoT systems. But more exciting still, these new EPDs also have the potential to enable fresh IoT applications that will give early adopters in the development community an opportunity to pioneer entirely new markets.

Why Electronic Paper is Already Ideal for IoT Applications
To understand why EPDs are poised to revolutionize IoT devices and make possible wholly new IoT applications, it is helpful to first understand current generation EPD technology’s key advantages over older flat panel display technologies, such as LCDs and OLEDs.

As the name suggests, an Electronic Paper Display displays images and text that are easily readable in natural light, just like printed ink on a sheet of paper. In this, an EPD is fundamentally unlike other display technologies, which all require their own internal luminance source—one that is power hungry, bulky, complex to design and manufacture, usually impractical to maintain, and prone to defects including uneven brightness, burn in, gradual dimming, and failure.

The EPD technology used by Pervasive Displays creates images from hundreds of minute charged ink particles within each of the tiny capsules that form each pixel. By varying the electrical field across the capsule, ink particles of the desired color are moved to the top surface of the paper, instantly changing the pixel’s color. As the particles are solid ink-like pigments, they create a clear and sharp image that looks like ink on paper. Users find the EPD graphics and text are not only more quickly read and understood, but are also more visually pleasing, and reduce eye strain, because they so precisely mimic the appearance of traditional printing and writing technologies that have been used for thousands of years.

For the IoT, a slim, compact, high-contrast EPD which is clearly visible in natural light is a huge boon. Such a display requires far less power than other technologies and is visible in a wide range of lighting conditions, from dim interior lighting, to bright sunlight that makes other displays painful or impossible to read. In addition, EPDs provide a very wide viewing angle and they help users to read and comprehend critical information without delay.

Figure 1: A 2.71-inch e-paper display showing bidet/washlet information

An EPD shares another similarity with ink on paper: it is bi-stable. Energy is only consumed when the image is being changed. On the other hand, display technologies that are not bi-stable constantly drain power to refresh and illuminate the image, whether it changes or not. For IoT applications, which often display static images and text for hours on end, and may rely solely on battery or environmental power, this is yet another huge energy saver, adding to the power saved by not requiring a constant internal light source. EPDs are such frugal energy users that some can provide an updating display that is driven and maintained simply by the residual energy available when a battery-free RFID tag is scanned.

The zero-power static display capability of electronic paper also frees users from the inconvenience of having to switch on a battery-powered display every time they need to briefly check the device status. Instead, the device condition is always instantly readable at a glance, minimizing unnecessary energy drain. For a typical IoT device with a 2-inch display that may only be updated a few times per day, a traditional LCD will consume well over 250 times more power than an EPD module. By slashing the energy consumption of the display—one of the most power-hungry components—to a minimum, IoT devices can operate in the field, perhaps with zero maintenance, for years. In the same situation, a constant LCD display could deplete its battery in a matter of days.

However, while the EPD’s crystal-clear display, ultra-low energy use and slim size seem almost tailor-made for the IoT—certain limitations have, until recently, frustratingly prevented full use of EPDs in some of the most promising IoT markets. Today, however, several new EPD technologies are set to sweep those barriers aside.

EPDs are already ideal for a wide range of IoT applications, but the latest electronic paper technology enhancements and innovations are about to expand EPD reach and usability much further—bringing the IoT to new environments and new markets.

Wider Temperature Range Extends Global Markets and Creates New Applications
Many IoT applications require devices to be usable in the field, often outdoors, and in extreme temperature conditions. Early generations of EPD technology had a narrow operational temperature range. This limited their deployment in some IoT applications or required additional hardware to stabilize the temperature.

Fortunately, recent innovations have dramatically extended EPD operating temperature range. Today, EPD modules can operate from -20 °C to +40 °C. This much wider temperature range makes an unmodified EPD-equipped IoT device usable in far more global climate environments, all-year round, and also in high- and low-temperature facilities. The temperature range extension has been achieved largely by improving the sequence and timing of the display’s driving waveforms.

Figure 2: A 1.6-inch e-paper display with weather information

With an extended operating temperature, the sheer quantity of potential new applications now fully opening up to EPD-equipped IoT products is too numerous to mention. It includes industrial, logistics, transportation, and automotive—and to give more specific examples: cold-chain logistics temperature logging, and RFID tags, as well as many similar applications in outdoor and harsh environments.

Faster Refresh Rates for More Timely, Dynamic Information
Older EPDs had relatively slow update times of a second or more, possibly delaying operator response to new information. This made the screens less practical when rapid display changes were required, for example in sensing and monitoring applications, for fast-changing data, and for animation.

This limitation existed mainly because the entire screen had to be cleared and redrawn to make even a small change. However, by only updating the section of the display that has been changed, the latest EPDs can now update important data with almost no significant delay. These partial updates can achieve refresh speeds of 300-600 ms—a four-fold improvement. In addition, these partial updates use even less power than a full screen refresh, further reducing the EPD’s already very low energy consumption.

Figure 3: The partial update process only updates the information on the screen which needs to change, such as the room temperature and energy usage information.

In brief, partial updates are performed by comparing the previous image and the new image to get a delta image. This delta image is then input into the EPD. Because of the physical characteristics of the EPD’s ink particles, the waveform used to program the delta image into the display is adjusted based on ambient temperature. There is no limit to the size of screen that partial updates can work on, although larger sizes of screen updates will require more RAM and faster CPU speeds to drive the waveforms properly.

Partial updates do have some limitations. Numerous partial updates without performing a full screen refresh can result in ghosting artifacts, especially for black to white pixel transitions. This can be mitigated by minimizing these black to white transitions. For three color screens, partial updates work on all three colors. However, as the third color (red or yellow) updates relatively slowly, taking a few seconds, partial updates generally only make sense to be done on the black and white pixels in the image.

Moreover, unlike earlier versions of partial update technology, the latest EPD modules do not require additional dedicated electronics for partial updating, thereby providing potential for more reductions in display module cost, complexity, size, and power consumption.

In general, just like the other recent innovations discussed here, partial update technology opens up new applications and markets for EPDs. Partial update technology combines all the power consumption and readability advantages of an EPD with a responsive, rapidly updated display.

More Colors: Attractive, Informative, Safer
Moving beyond early EPDs that only offered monochrome black and white displays, the latest EPDs from Pervasive Displays provide three colors: black, white and red, and most recently, black, white and yellow. For retail applications, these additional vivid eye-catching colors greatly enhance the attention-grabbing power of pricing, signage, and product displays. This allows retailers to draw customers’ attention to special offers, and deals, or special conditions—improving stock throughput, saving staff and customers’ time, and increasing customer satisfaction.

Figure 4: E-paper displays from Pervasive Displays are now available in black, white and yellow as well as black white and red.

For industrial and monitoring applications, bright colors are perfect for instantly bringing attention to critical data—such as warnings or sensor measurements that are outside of nominal range. Simply adding color hints can greatly enhance efficiency and safety, as well as reducing operator fatigue.

In addition, with EPDs providing sharp display resolutions of up to 200+ DPI, these additional colors provide more options for dithering (displaying alternate adjacent pixels in different colors) to generate new shades beyond the standard three, a strong tool for creating attractive retail displays.

Rethinking the EPD: A New Generation of Display
Adding all these improvements in refresh rate, power consumption, operating temperature, and color to EPDs demands a rethink of the EPD’s role in the IoT. In a sense, these EPDs are almost a new class of display technology. The new EPD can now replace LCDs and OLEDs in applications that require features like responsive display updates and color highlighting, and it can be used across a huge area of the globe, from the arctic to the equator, and in environments from the heat of a desert oil well or an iron foundry to the chill of a medical sample storage area or a refrigerated goods truck.

And EPDs can achieve all this without compromising their unbeatable natural light visibility, and with power consumption lower than 0.5 percent of an equivalent LCD screen—offering the potential for five to seven years of battery life on a coin cell battery and practical operation driven by solar and other environmental power sources.

HD Lee is Founder, CTO and President, Pervasive Displays. Lee has over 17 years’ experience in research and development for advanced displays, specializing in TFT-LCD, OLED and e-paper. Lee was a co-founder of Jemitek, a mobile LCD design house, which was acquired by Innolux in 2006. In 2011 he co-founded Pervasive Displays Inc., a world-leading low power display company that focuses on industrial applications and has sold more than 10 million e-paper displays. The company was acquired by SES-imagotag in 2016. Privately, Lee holds 43 granted patents with more patents pending. He has an MS and BS in Electronic Engineering from the National Taiwan University.



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