low-power color tft lcd display for handheld embedded systems free sample

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As an option, you can order this TFT pre-assembled onto a breakout/carrier board. The board allows easy prototyping through its 0.1" headers. You can also include the carrier board in your end product to simplify construction and assembly. The carrier board contains a constant-current switching LED driver. The PCB is sized to fit neatly within the outline of the display.

This display module is a 3 inch diagonal, 240xRGBx400, full color TFT LCD display. It has a wide-screen format and white LED backlight. Its integrated controller gives you a simple, fast, digital interface to the display through your 3v processor"s port pins.

It may be used in either portrait or landscape orientation. In portrait mode, the narrow width of the TFT display works well with portable, handheld, or embedded systems. In landscape mode, the low profile of the TFT LCD display may be used for the user interface of 2U+ rack mount devices, or in bench top laboratory equipment such as power supplies, meters, and signal generators.

Recently, ‘Liquid crystal display (LCD) vs. organic light-emitting diode (OLED) display: who wins?’ has become a topic of heated debate. In this review, we perform a systematic and comparative study of these two flat panel display technologies. First, we review recent advances in LCDs and OLEDs, including material development, device configuration and system integration. Next we analyze and compare their performances by six key display metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility. In this section, we focus on two key parameters: motion picture response time (MPRT) and ambient contrast ratio (ACR), which dramatically affect image quality in practical application scenarios. MPRT determines the image blur of a moving picture, and ACR governs the perceived image contrast under ambient lighting conditions. It is intriguing that LCD can achieve comparable or even slightly better MPRT and ACR than OLED, although its response time and contrast ratio are generally perceived to be much inferior to those of OLED. Finally, three future trends are highlighted, including high dynamic range, virtual reality/augmented reality and smart displays with versatile functions.

Display technology has gradually but profoundly shaped the lifestyle of human beings, which is widely recognized as an indispensable part of the modern world

In this review paper, we present recent progress on LCDs and OLEDs regarding materials, device structures to final panel performances. First, in Section II, we briefly describe the device configurations and operation principles of these two technologies. Then, in Section III, we choose six key metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility, to evaluate LCDs and OLEDs. Their future perspectives are discussed in Section IV, including high dynamic range (HDR), virtual reality/augmented reality (VR/AR) and smart displays with versatile functions.

Liquid crystal (LC) materials do not emit light; therefore, a backlight unit is usually needed (except in reflective displays) to illuminate the display panel. Figure 1 depicts an edge-lit TFT-LCD. The incident LED passes through the light-guide plate and multiple films and is then modulated by the LC layer sandwiched between two crossed polarizers

IPS mode was first proposed in 1973 by SorefFigure 2c). As the voltage increases, the strong in-plane fringing electric fields between the interdigital electrodes reorient the LC directors. Such a unique mechanism makes IPS a favorable candidate for touch panels because no ripple effect occurs upon touching the panel. However, the peak transmittance of IPS is relatively low (~75%) because the LC molecules above the electrodes cannot be effectively reoriented. This low transmittance region is called a dead zone

As summarized in Table 1, these four LCD modes have their own unique features and are used for different applications. For example, TN has the advantages of low cost and high optical efficiency; thus, it is mostly used in wristwatches, signage and laptop computers, for which a wide view is not absolutely necessary. MVA mode is particularly attractive for large TVs because a fast response time, high CR and wide viewing angle are required to display motion pictures. On the other hand, IPS and FFS modes are used in mobile displays, where low power consumption for a long battery life and pressure resistance for touch screens are critical.

Abbreviations: FFS, fringe-field switching; IPS, in-plane switching; LCD, liquid crystal display; MVA, multi-domain vertical alignment; TN, twisted nematic; TV, television.

The basic structure of an OLED display, proposed by Tang and VanSlykeFigure 3a. Electrons and holes are injected from electrodes to organic layers for recombination and light emission; hence, an OLED display is an emissive display, unlike an LCD. Currently, multi-layer structures in OLEDs with different functional materials are commonly used, as shown in Figure 3b. The emitting layer (EML), which is used for light emission, consists of dopant and host materials with high quantum efficiency and high carrier mobility. Hole-transporting layer (HTL) and electron-transporting layer (ETL) between the EML and electrodes bring carriers into the EML for recombination. Hole- and electron-injection layers (HIL and EIL) are inserted between the electrodes and the HTL and ETL interface to facilitate carrier injection from the conductors to the organic layers. When applying voltage to the OLED, electrons and holes supplied from the cathode and anode, respectively, transport to the EML for recombination to give light.

Generally, each layer in an OLED is quite thin, and the total thickness of the whole device is <1 μm (substrates are not included). Thus the OLED is a perfect candidate for flexible displays. For an intrinsic organic material, its carrier mobility (<0.1 cm2 Vs−1) and free carrier concentration (1010 cm−3) are fairly low, limiting the device efficiency. Thus doping technology is commonly used

First, upon electrical excitation, 25% singlets and 75% triplets are formed with higher and lower energy, respectively. In a fluorescent OLED, only singlets decay radiatively through fluorescence with an ~ns exciton lifetime, which sets the theoretical limit of the internal quantum efficiency (IQE) to 25%, as shown in Figure 4a.

Two triplet excitons may fuse to form one singlet exciton through the so-called triplet fusion process, as shown in Figure 4b, and relaxes to the energy from the singlet state, called TTF, which improves the theoretical limit of the IQE to 62.5%.

With the introduction of heavy metal atoms (such as Ir and Pt) into the emitters, strong spin-orbital coupling greatly reduces the triplet lifetime to ~μs, which results in efficient phosphorescent emission. The singlet exciton experiences intersystem crossing to the triplet state for light emission, achieving a 100% IQE, as shown in Figure 4c. Owing to the long radiative lifetime (~μs) in a phosphorescent OLED, the triplet may interact with another triplet and polaron (triplet-triplet annihilation and triplet-polaron annihilation, respectively), which results in efficiency roll-off under high current driving

The energy between the singlet and triplet can be reduced (<0.1 eV) by minimizing the exchange energyFigure 4d. Achieving a 100% IQE is possible for TADF emission without a heavy atom in the organic material, which reduces the material cost and is more flexible for organic molecular design.

In practical applications, red and green phosphorescent emitters are the mainstream for active matrix (AM) OLEDs due to their high IQE. While, for blue emitters, TTF is mostly used because of its longer operation lifetime

To evaluate the performance of display devices, several metrics are commonly used, such as response time, CR, color gamut, panel flexibility, viewing angle, resolution density, peak brightness, lifetime, among others. Here we compare LCD and OLED devices based on these metrics one by one.

A fast response time helps to mitigate motion image blur and boost the optical efficiency, but this statement is only qualitatively correct. When quantifying the visual performance of a moving object, motion picture response time (MPRT) is more representative, and the following equation should be used

where Tf is the frame time (e.g., Tf=16.67 ms for 60 fps). Using this equation, we can easily obtain an MPRT as long as the LC response time and TFT frame rate are known. The results are plotted in Figure 5.

From Figure 5, we can gain several important physical insights: (1) Increasing the frame rate is a simple approach to suppress image motion blur, but its improvement gradually saturates. For example, if the LC response time is 10 ms, then increasing the frame rate from 30 to 60 fps would significantly reduce the MPRT. However, as the TFT frame rate continues to increase to 120 and 240 fps, then the improvement gradually saturates. (2) At a given frame rate, say 120 fps, as the LC response time decreases, the MPRT decreases almost linearly and then saturates. This means that the MPRT is mainly determined by the TFT frame rate once the LC response time is fast enough, i.e., τ≪Tf. Under such conditions, Equation (1) is reduced to MPRT≈0.8Tf. (3) When the LC response is <2 ms, its MPRT is comparable to that of an OLED at the same frame rate, e.g., 120 fps. Here we assume the OLED’s response time is 0.

The last finding is somehow counter to the intuition that a LCD should have a more severe motion picture image blur, as its response time is approximately 1000 × slower than that of an OLED (ms vs. μs). To validate this prediction, Chen et al.

If we want to further suppress image blur to an unnoticeable level (MPRT<2 ms), decreasing the duty ratio (for LCDs, this is the on-time ratio of the backlight, called scanning backlight or blinking backlight) is mostly adopted

High CR is a critical requirement for achieving supreme image quality. OLEDs are emissive, so, in theory, their CR could approach infinity to one. However, this is true only under dark ambient conditions. In most cases, ambient light is inevitable. Therefore, for practical applications, a more meaningful parameter, called the ACR, should be considered

As Figure 6 depicts, there are two types of surface reflections. The first one is from a direct light source, i.e., the sun or a light bulb, denoted as A1. Its reflection is fairly specular, and in practice, we can avoid this reflection (i.e., strong glare from direct sun) by simply adjusting the display position or viewing direction. However, the second reflection, denoted as A2, is quite difficult to avoid. It comes from an extended background light source, such as a clear sky or scattered ceiling light. In our analysis, we mainly focus on the second reflection (A2).

To investigate the ACR, we have to clarify the reflectance first. A large TV is often operated by remote control, so touchscreen functionality is not required. As a result, an anti-reflection coating is commonly adopted. Let us assume that the reflectance is 1.2% for both LCD and OLED TVs. For the peak brightness and CR, different TV makers have their own specifications. Here, without losing generality, let us use the following brands as examples for comparison: LCD peak brightness=1200 nits, LCD CR=5000:1 (Sony 75″ X940E LCD TV); OLED peak brightness=600 nits, and OLED CR=infinity (Sony 77″ A1E OLED TV). The obtained ACR for both LCD and OLED TVs is plotted in Figure 7a. As expected, OLEDs have a much higher ACR in the low illuminance region (dark room) but drop sharply as ambient light gets brighter. At 63 lux, OLEDs have the same ACR as LCDs. Beyond 63 lux, LCDs take over. In many countries, 60 lux is the typical lighting condition in a family living room. This implies that LCDs have a higher ACR when the ambient light is brighter than 60 lux, such as in office lighting (320–500 lux) and a living room with the window shades or curtain open. Please note that, in our simulation, we used the real peak brightness of LCDs (1200 nits) and OLEDs (600 nits). In most cases, the displayed contents could vary from black to white. If we consider a typical 50% average picture level (i.e., 600 nits for LCDs vs. 300 nits for OLEDs), then the crossover point drops to 31 lux (not shown here), and LCDs are even more favorable. This is because the on-state brightness plays an important role to the ACR, as Equation (2) shows.

Calculated ACR as a function of different ambient light conditions for LCD and OLED TVs. Here we assume that the LCD peak brightness is 1200 nits and OLED peak brightness is 600 nits, with a surface reflectance of 1.2% for both the LCD and OLED. (a) LCD CR: 5000:1, OLED CR: infinity; (b) LCD CR: 20 000:1, OLED CR: infinity.

Recently, an LCD panel with an in-cell polarizer was proposed to decouple the depolarization effect of the LC layer and color filtersFigure 7b. Now, the crossover point takes place at 16 lux, which continues to favor LCDs.

For mobile displays, such as smartphones, touch functionality is required. Thus the outer surface is often subject to fingerprints, grease and other contaminants. Therefore, only a simple grade AR coating is used, and the total surface reflectance amounts to ~4.4%. Let us use the FFS LCD as an example for comparison with an OLED. The following parameters are used in our simulations: the LCD peak brightness is 600 nits and CR is 2000:1, while the OLED peak brightness is 500 nits and CR is infinity. Figure 8a depicts the calculated results, where the intersection occurs at 107 lux, which corresponds to a very dark overcast day. If the newly proposed structure with an in-cell polarizer is used, the FFS LCD could attain a 3000:1 CRFigure 8b), corresponding to an office building hallway or restroom lighting. For reference, a typical office light is in the range of 320–500 luxFigure 8 depicts, OLEDs have a superior ACR under dark ambient conditions, but this advantage gradually diminishes as the ambient light increases. This was indeed experimentally confirmed by LG Display

Calculated ACR as a function of different ambient light conditions for LCD and OLED smartphones. Reflectance is assumed to be 4.4% for both LCD and OLED. (a) LCD CR: 2000:1, OLED CR: infinity; (b) LCD CR: 3000:1, OLED CR: infinity. (LCD peak brightness: 600 nits; OLED peak brightness: 500 nits).

For conventional LCDs employing a WLED backlight, the yellow spectrum generated by YAG (yttrium aluminum garnet) phosphor is too broad to become highly saturated RGB primary colors, as shown in Figure 9aTable 2. The first choice is the RG-phosphor-converted WLEDFigure 9b, the red and green emission spectra are well separated; still, the green spectrum (generated by β-sialon:Eu2+ phosphor) is fairly broad and red spectrum (generated by K2SiF6:Mn4+ (potassium silicofluoride, KSF) phosphor) is not deep enough, leading to 70%–80% Rec. 2020, depending on the color filters used.

Transmission spectra of color filters and emission spectra of (a) YAG WLED, (b) KSF WLED, (c) QDEF and (d) Vivid Color LED. KSF, potassium silicofluoride; QDEF, quantum dot enhancement film; WLED, white light-emitting diode; YAG, yttrium aluminum garnet.

aHere we only consider Cd-based quantum-dots (QDs). For heavy-metal-free QDs, e.g., InP QD, the FWHM is broader (40–50 nm) and color gamut is 70–80%. Their optical efficiency is slightly lower than that of Cd-based QDs.

A QD-enhanced backlight (e.g., quantum dot enhancement film, QDEF) offers another option for a wide color gamutFigure 9c), so that high purity RGB colors can be realized and a color gamut of ~90% Rec. 2020 can be achieved. One safety concern is that some high-performance QDs contain the heavy metal Cd. To be compatible with the restriction of hazardous substances, the maximum cadmium content should be under 100 ppm in any consumer electronic product

Recently, a new LED technology, called the Vivid Color LED, was demonstratedFigure 9d), which leads to an unprecedented color gamut (~98% Rec. 2020) together with specially designed color filters. Such a color gamut is comparable to that of laser-lit displays but without laser speckles. Moreover, the Vivid Color LED is heavy-metal free and shows good thermal stability. If the efficiency and cost can be further improved, it would be a perfect candidate for an LCD backlight.

A color filter array is another effective approach to enhance the color gamut of an OLED. For example, in 2017, AUO demonstrated a 5-inch top-emission OLED panel with 95% Rec. 2020. In this design, so-called symmetric panel stacking with a color filter is employed to generate purer RGB primary colors

As mentioned earlier, TFT LCDs are a fairly mature technology. They can be operated for >10 years without noticeable performance degradation. However, OLEDs are more sensitive to moisture and oxygen than LCDs. Thus their lifetime, especially for blue OLEDs, is still an issue. For mobile displays, this is not a critical issue because the expected usage of a smartphone is approximately 2–3 years. However, for large TVs, a lifetime of >30 000 h (>10 years) has become the normal expectation for consumers.

Here we focus on two types of lifetime: storage and operational. To enable a 10-year storage lifetime, according to the analysis−6 g (m2-day)−1 and 1 × 10−5 cm3 (m2-day)−1, respectively. To achieve these values, organic and/or inorganic thin films have been developed to effectively protect the OLED and lengthen its storage lifetime. Meanwhile, it is compatible to flexible substrates and favors a thinner display profile

Power consumption is equally important as other metrics. For LCDs, power consumption consists of two parts: the backlight and driving electronics. The ratio between these two depends on the display size and resolution density. For a 55″ 4K LCD TV, the backlight occupies approximately 90% of the total power consumption. To make full use of the backlight, a dual brightness enhancement film is commonly embedded to recycle mismatched polarized light

The power efficiency of an OLED is generally limited by the extraction efficiency (ηext~20%). To improve the power efficiency, multiple approaches can be used, such as a microlens array, a corrugated structure with a high refractive index substrateFigure 11 shows the power efficiencies of white, green, red and blue phosphorescent as well as blue fluorescent/TTF OLEDs over time. For OLEDs with fluorescent emitters in the 1980s and 1990s, the power efficiency was limited by the IQE, typically <10 lm W−1(Refs. 41, 114, 115, 116, 117, 118). With the incorporation of phosphorescent emitters in the ~2000 s, the power efficiency was significantly improved owing to the materials and device engineering−1 was demonstrated in 2011 (Ref. 127), which showed a >100 × improvement compared with that of the basic two-layer device proposed in 1987 (1.5 lm W−1 in Ref. 41). A white OLED with a power efficiency >100 lm W−1 was also demonstrated, which was comparable to the power efficiency of a LCD backlight. For red and blue OLEDs, their power efficiencies are generally lower than that of the green OLED due to their lower photopic sensitivity function, and there is a tradeoff between color saturation and power efficiency. Note, we separated the performances of blue phosphorescent and fluorescent/TTF OLEDs. For the blue phosphorescent OLEDs, although the power efficiency can be as high as ~80 lm W−1, the operation lifetime is short and color is sky-blue. For display applications, the blue TTF OLED is the favored choice, with an acceptable lifetime and color but a much lower power efficiency (16 lm W−1) than its phosphorescent counterpartFigure 11 shows.

To compare the power consumption of LCDs and OLEDs with the same resolution density, the displayed contents should be considered as well. In general, OLEDs are more efficient than LCDs for displaying dark images because black pixels consume little power for an emissive display, while LCDs are more efficient than OLEDs at displaying bright images. Currently, a ~65% average picture level is the intersection point between RGB OLEDs and LCDs

Flexible displays have a long history and have been attempted by many companies, but this technology has only recently begun to see commercial implementations for consumer electronics

In addition to the aforementioned six display metrics, other parameters are equally important. For example, high-resolution density has become a standard for all high-end display devices. Currently, LCD is taking the lead in consumer electronic products. Eight-hundred ppi or even >1000 ppi LCDs have already been demonstrated and commercialized, such as in the Sony 5.5″ 4k Smartphone Xperia Z5 Premium. The resolution of RGB OLEDs is limited by the physical dimension of the fine-pitch shadow mask. To compete with LCDs, most OLED displays use the PenTile RGB subpixel matrix scheme

The viewing angle is another important property that defines the viewing experience at large oblique angles, which is quite critical for multi-viewer applications. OLEDs are self-emissive and have an angular distribution that is much broader than that of LCDs. For instance, at a 30° viewing angle, the OLED brightness only decreases by 30%, whereas the LCD brightness decrease exceeds 50%. To widen an LCD’s viewing angle, three options can be used. (1) Remove the brightness-enhancement film in the backlight system. The tradeoff is decreased on-axis brightness

In addition to brightness, color, grayscale and the CR also vary with the viewing angle, known as color shift and gamma shift. In these aspects, LCDs and OLEDs have different mechanisms. For LCDs, they are induced by the anisotropic property of the LC material, which could be compensated for with uniaxial or biaxial films

Cost is another key factor for consumers. LCDs have been the topic of extensive investigation and investment, whereas OLED technology is emerging and its fabrication yield and capability are still far behind LCDs. As a result, the price of OLEDs is about twice as high as that of LCDs, especially for large displays. As more investment is made in OLEDs and more advanced fabrication technology is developed, such as ink-jet printing

Currently, both LCDs and OLEDs are commercialized and compete with each other in almost every display segment. They are basically two different technologies (non-emissive vs. emissive), but as a display, they share quite similar perspectives in the near future. Here we will focus on three aspects: HDR, VR/AR and smart displays with versatile functions.

Both LCD and OLED are HDR-compatible. Currently, the best HDR LCDs can produce brighter highlights than OLEDs, but OLEDs have better overall CRs thanks to their superior black level. To enhance an LCD’s CR, a local dimming backlight is commonly used, but its dimming accuracy is limited by the number of LED segmentations

Also worth mentioning here is ultra-high brightness. Mostly, people pay more attention to the required high CR (CR>100 000:1) of HDR but fail to notice that CR is jointly determined by the dark state and peak brightness. For example, a 12-bit Perceptual Quantizer curve is generated for a range up to 10 000 nits, which is far beyond what current displays can provide

The peak brightness of LCDs could be boosted to 2000 nits or even higher by simply using a high-power backlight. OLEDs are self-emissive, so their peak brightness would trade with lifetime. As a result, more advanced OLED materials and novel structural designs are highly desirable in the future. Another reason to boost peak brightness is to increase sunlight readability. Especially for some outdoor applications, such as public displays, peak brightness is critical to ensure good readability under strong ambient light. As discussed in the section of ‘CR and ACR’, high brightness leads to a high ACR, except that the power consumption will increase.

Immersive VR/AR are two emerging wearable display technologies with great potential in entertainment, education, training, design, advertisement and medical diagnostics. However, new opportunities arise along with new challenges. VR head-mounted displays require a resolution density as high as >2000 ppi to eliminate the so-called screen door effect and generate more realistic immersive experiences.

An LCD’s resolution density is determined by the TFTs and color filter arrays. In SID 2017, Samsung demonstrated an LCD panel with a resolution of 2250 ppi for VR applications. The pitches of the sub-pixel and pixel are 3.76 and 11.28 μm, respectively. Meanwhile, field sequential color provides another promising option to triple the LCD resolution density

As for AR applications, lightweight, low power and high brightness are mainly determined by the display components. LC on silicon can generate high brightness

Currently, displays are no longer limited to traditional usages, such as TVs, pads or smartphones. Instead, they have become more diversified and are used in smart windows, smart mirrors, smart fridges, smart vending machines and so on. They have entered all aspects of our daily lives.

As these new applications are emerging, LCDs and OLEDs have new opportunities as well as new challenges. Let us take a vehicle display as an example: high brightness, good sunlight readability, and a wide working temperature range are required

We have briefly reviewed the recent progress of LCD and OLED technologies. Each technology has its own pros and cons. For example, LCDs are leading in lifetime, cost, resolution density and peak brightness; are comparable to OLEDs in ACR, viewing angle, power consumption and color gamut (with QD-based backlights); and are inferior to OLED in black state, panel flexibility and response time. Two concepts are elucidated in detail: the motion picture response time and ACR. It has been demonstrated that LCDs can achieve comparable image motion blur to OLEDs, although their response time is 1000 × slower than that of OLEDs (ms vs. μs). In terms of the ACR, our study shows that LCDs have a comparable or even better ACR than OLEDs if the ambient illuminance is >50 lux, even if its static CR is only 5000:1. The main reason is the higher brightness of LCDs. New trends for LCDs and OLEDs are also highlighted, including ultra-high peak brightness for HDR, ultra-high-resolution density for VR, ultra-low power consumption for AR and ultra-versatile functionality for vehicle display, transparent display and mirror display applications. The competition between LCDs and OLEDs is still ongoing. We believe these two TFT-based display technologies will coexist for a long time.

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The liquid crystal research of the 1960s was characterized by the discovery of and experiments on the properties of the liquid crystals. George H. Heilmeier of the RCA based his research on that of Williams, diving into the electro-optical nature of the crystals. After many attempts to use the liquid crystals to display different colors, he created the first working LCD using something called a dynamic scattering mode (DSM) that, when voltage is applied, turns the clear liquid crystal layer into a more translucent state. Heilmeier was thus deemed the inventor of the LCD.

In the late 1960s, the United Kingdom Royal Radar Establishment (RRE) discovered the cyanobiphenyl liquid crystal, a type that was fitting for LCD usage in terms of stability and temperature. In 1968, Bernard Lechner of RCA created the idea of a TFT-based LCD, and in that same year, he and several others brought that idea into reality using Heilmeier’s DSM LCD.

After the LCD’s entrance into the field of display technology, the 1970s were full of expansive research into improving the LCD and making it appropriate for a greater variety of applications. In 1970, the twisted nematic field effect was patented in Switzerland with credited inventors being Wolfgang Helfrich and Martin Schadt. This twisted nematic (TN) effect soon conjoined with products that entered the international markets like Japan’s electronic industry. In the US, the same patent was filed by James Fergason in 1971. His company, ILIXCO, known today as LXD Incorporated, manufactured TN-effect LCDs which grew to overshadow the DSM models. TN LCDs offered better features like lower operating voltages and power consumption.

From this, the first digital clock, or more specifically an electronic quartz wristwatch, using a TN-LCD and consisting of four digits was patented in the US and released to consumers in 1972. Japan’s Sharp Corporation, in 1975, began mass production of digital watch and pocket calculator TN LCDs, and eventually, other Japanese corporations began to rise in the market for wristwatch displays. Seiko, as an example, developed the first six-digit TN-based LCD quartz watch, an upgrade from the original four-digit watch.

Nevertheless, the DSM LCD was not rendered completely useless. A 1972 development by the North American Rockwell Microelectronics Corp integrated the DSM LCD into calculators marketed by Lloyds Electronics. These required a form of internal light to show the display, and so backlightswere also incorporated into these calculators. Shortly after, in 1973, Sharp Corporation brought DSM LCD pocket-sized calculators into the picture. A polymer called polyimide was used as the orientation layer of liquid crystal molecules.

In the 1980s, there was rapid progress made in creating usable products with this new LCD research. Color LCD television screens were first developed in Japan during this decade. Because of the limit in response times due to large display size (correlated with a large number of pixels), the first TVs were handheld/pocket TVs. Seiko Epson, or Epson, created the first LCD TV, releasing it to the public in 1982, which was soon followed by their first fully colored display pocket LCD TV in 1984. Also in 1984 was the first commercial TFT LCD display: Citizen Watch’s 2.7 inch color LCD TV. Shortly after, in 1988, Sharp Corporation created a 14 inch full-color TFT LCD that used an active matrix and had full-motion properties. Large-size LCDs now made LCD integration into large flat-panel displays like LCD screens and LCD monitors possible. LCD projection technology, first created by Epson, became readily available to consumers in compact and fully colored modes in 1989.

The LCD growth in the 1990s focused more on the optical properties of these new displays in attempts to advance their quality and abilities. Hitachi engineers were integral to the analysis of the LCD industry, previously centered in Japan, began expanding and moving towards South Korea, Taiwan, and later China as well.

As we entered the new century, the prominence of LCDs boomed. They surpassed the previously popular cathode-ray tube (CRT) displays in both image quality and sales across the world in 2007. Other developments continued to be made, such as the manufacturing of even larger displays, adoption of transparent and flexible materials for LCD hardware, and creation of more methods to

As of today, as LCD displays have developed quite a bit, but have remained consistent in structure. Illuminated by a backlight, the display consists of, from outermost to innermost two polarizers, two substrates (typically glass), electrodes, and the liquid crystal layer. Closer to the surface is sometimes a color filter as well, using an RGB scheme. As light passes through the polarizer closest to the backlight, it enters the liquid crystal layer. Now, depending on whether an electric field directed by the electrodes is present, the liquid crystal will behave differently. Whether using a TN, IPS, or MVS LCD, the electrode electric field will alter the orientation of the liquid crystal molecules to then affect the polarization of the passing light. If the light is polarized properly, it will pass completely through the color filter and surface polarizer, displaying a certain color. If partially polarized correctly, it will display a medium level of light, or a less bright color. If not polarized properly, the light will not pass the surface, and no color will be displayed.

1927: Vsevolod Frederiks in Russian devised the electrically switched light valve, called the Fréedericksz transition, the essential effect of all LCD technology.

1967: Bernard Lechner, Frank Marlowe, Edward Nester and Juri Tults built the first LCD to operate at television rates using discrete MOS transistors wired to the device.

1968: A research group at RCA laboratories in the US, headed by George Heilmeier, developed the first LCDs based on DSM (dynamic scattering mode) and the first bistable LCD using a mixture of cholesteric and nematic liquid crystals. The result sparked a worldwide effort to further develop LCDs. George H. Heilmeier was inducted in the National Inventors Hall of Fame and credited with the invention of LCDs. Heilmeier’s work is an IEEE Milestone.

1979, Peter Le Comber and Walter Spear at University of Dundee discovered that hydrogenated amorphous silicon (Alpha-Si:H) thin film transistors were suitable to drive LCDs. This is the major breakthrough that led to LCD television and computer displays.

1972: Tadashi Sasaki and Tomio Wada at Sharp Corporation built a prototype desktop calculator with a dynamic scattering LCD and started a program to build the first truly portable handheld calculator.

Let us start with the basics first; refresh the knowledge about TN and LCD displays in general, later we will talk about TFTs (Thin Film Transistors), how they differ from regular monochrome LCD displays. Then we will go on to the ghosting effect, so we will not only discuss the technology behind the construction of the TFT, but also some phenomena, like the ghosting effect, or grayscale inversion, that are important to understand when using an LCD TFT display.

Next, we will look at different technologies of the TFT LCD displays like TN, IPS, VA, and of course about transmissive and transflective LCD displays, because TFT displays also can be transmissive and transflective. In the last part we will talk about backlight.

Let us start with a short review of the most basic liquid crystal cell, which is the TN (twisted nematic) display. On the picture above, we can see that the light can be transmit through the cell or blocked by the liquid crystal cell using voltage. If you want to learn more about monochrome LCD displays and the basics of LCD displays, follow this link.

What is a TFT LCD display and how it is different from a monochrome LCD display? TFT is called an active display. Active, means we have one or more transistors in every cell, in every pixel and in every subpixel. TFT stands for Thin Film Transistor, transistors that are very small and very thin and are built into the pixel, so they are not somewhere outside in a controller, but they are in the pixel itself. For example, in a 55-inch TV set, the TFT display contains millions of transistors in the pixels. We do not see them, because they are very small and hidden, if we zoom in, however, we can see them in every corner of each pixel, like on the picture below.

On the picture above we can see subpixels, that are basic RGB (Red, Green, Blue) colors and a black part, with the transistors and electronic circuits. We just need to know that we have pixels, and subpixels, and each subpixel has transistors. This makes the display active, and thus is called  the TFT display. TFT displays are usually color displays, but there are also monochrome TFT displays, that are active, and have transistors, but have no colors. The colors in the TFT LCD display are typically added by color filters on each subpixel. Usually the filters are RGB, but we also have RGBW (Red, Green, Blue, White) LCD displays with added subpixels without the filter (White) to make the display brighter.

Going a little bit deeper, into the TFT cell, there is a part inside well known to us from the monochrome LCD display Riverdi University lecture. We have a cell, liquid crystal, polarizers, an ITO (Indium Tin Oxide) layer for the electrodes, and additionally an electronic circuit. Usually, the electronic circuit consists of one transistor and some capacitors to sustain the pixel state when we switch the pixel OFF and ON. In a TFT LCD display the pixels are much more complicated because apart from building the liquid crystal part, we also need to build an electronic part.

That is why TFT LCD display technologies are very expensive to manufacture. If you are familiar with electronics, you know that the transistor is a kind of switch, and it allows us to switch the pixel ON and OFF. Because it is built into the pixel itself, it can be done very quickly and be very well controlled. We can control the exact state of every pixel not only the ON and OFF states, but also all the states in between. We can switch the light of the cells ON and OFF in several steps. Usually for TFT LCD displays it will be 8-bit steps per color, so we have 256 steps of brightness for every color, and every subpixel. Because we have three subpixels, we have a 24-bit color range, that means over 16 million combinations, we can, at least theoretically, show on our TFT LCD display over 16 million distinct colors using RGB pixels.

Now that we know how the TFT LCD display works, we can now learn some practical things one of which is LCD TFT ghosting. We know how the image is created, but what happens when we have the image on the screen for a prolonged time, and how to prevent it. In LCD displays we have something called LCD ghosting. We do not see it very often, but in some displays this phenomenon still exists.

If some elements of the picture i.e., your company logo is in the same place of the screen for a long period of time, for couple of weeks, months or a year, the crystals will memorize the state and later, when we change the image, we may see some ghosting of those elements. It really depends on many conditions like temperature and even the screen image that we display on the screen for longer periods of time. When you build your application, you can use some techniques to avoid it, like very rapid contrast change and of course to avoid the positioning the same image in the same position for a longer time.

You may have seen this phenomenon already as it is common in every display technology, and even companies like Apple put information on their websites, that users may encounter this phenomenon and how to fix it. It is called image ghosting or image persistence, and even Retina displays are not free of it.

Another issue present in TFT displays, especially TN LCD displays, is grayscale inversion. This is a phenomenon that changes the colors of the screen according to the viewing angle, and it is only one-sided. When buying a TFT LCD display, first we need to check what kind of technology it is. If it is an IPS display, like the Riverdi IPS display line, then we do not need to worry about the grayscale inversion because all the viewing angles will be the same and all of them will be very high, like 80, 85, or 89 degrees. But if you buy a more common or older display technology type, like the TN (twisted nematic) display, you need to think where it will be used, because one viewing angle will be out. It may be sometimes confusing, and you need to be careful as most factories define viewing direction of the screen and mistake this with the greyscale inversion side.

On the picture above, you can see further explanation of the grayscale inversion from Wikipedia. It says that some early panels and also nowadays TN displays, have grayscale inversion not necessary up-down, but it can be any angle, you need to check in the datasheet. The reason technologies like IPS (In-Plane Switching), used in the latest Riverdi displays, or VA, were developed, was to avoid this phenomenon. Also, we do not want to brag, but the Wikipedia definition references our website.

We know already that TN (twisted nematic) displays, suffer from grayscale inversion, which means the display has one viewing side, where the image color suddenly changes. It is tricky, and you need to be careful. On the picture above there is a part of the LCD TFT specification of a TN (twisted nematic) display, that has grayscale inversion, and if we go to this table, we can see the viewing angles. They are defined at 70, 70, 60 and 70 degrees, that is the maximum viewing angle, at which the user can see the image. Normally we may think that 70 degrees is better, so we will choose left and right side to be 70 degrees, and then up and down, and if we do not know the grayscale inversion phenomena, we may put our user on the bottom side which is also 70 degrees. The viewing direction will be then like a 6 o’clock direction, so we call it a 6 o’clock display. But you need to be careful! Looking at the specification, we can see that this display was defined as a 12 o’clock display, so it is best for it to be seen from a 12 o’clock direction. But we can find that the 12 o’clock has a lower viewing angle – 60 degrees. What does it mean? It means that on this side there will be no grayscale inversion. If we go to 40, 50, 60 degrees and even a little bit more, probably we will still see the image properly. Maybe with lower contrast, but the colors will not change. If we go from the bottom, from a 6 o’clock direction where we have the grayscale inversion, after 70 degrees or lower we will see a sudden color change, and of course this is something we want to avoid.

To summarize, when you buy older technology like TN and displays, which are still very popular, and Riverdi is selling them as well, you need to be careful where you put your display. If it is a handheld device, you will see the display from the bottom, but if you put it on a wall, you will see the display from the top, so you need to define it during the design phase, because later it is usually impossible or expensive to change the direction.

We will talk now about the other TFT technologies, that allow us to have wider viewing angles and more vivid colors. The most basic technology for monochrome and TFT LCD displays is twisted nematic (TN). As we already know, this kind of displays have a problem with grayscale inversion. On one side we have a higher retardation and will not get a clear image. That is why we have other technologies like VA (Vertical Alignment), where the liquid crystal is differently organized, and another variation of the TFT technology – IPS which is In-Plane Switching. The VA and IPS LCD displays do not have a problem with the viewing angles, you can see a clear image from all sides.

Nowadays all TV sets, tablets and of course mobile phones are IPS or VA. You can turn them around and see the image clear from all sides. But, for monitor applications the TN technology is still widely used, because the monitor usually is in front of you and most of the time you look directly at it, from top, left or right side, but very rarely from the bottom, so the grayscale inversion viewing angle can be placed there. This technology still is very practical because it is affordable and has some advantages for gamers because it is very fast.

Apart from the different organization of the liquid crystals, we also organize subpixels a little bit differently in a VA and IPS LCD displays. When we look closer at the TN display, we will just see the subpixels with color filters. If we look at the VA or IPS display they will have subpixels of subpixels. The subpixels are divided into smaller parts. In this way we can achieve even wider viewing angles and better colors for the user, but of course, it is more complicated and more expensive to do.

The picture above presents the TN display and grayscale inversion. For IPS or VA technology there is no such effect. The picture will be the same from all the sides we look so these technologies are popular where we need wide viewing angles, and TN is popular where we don’t need that, like in monitors. Other advantages of IPS LCD displays are they give accurate colors, and wide viewing angles. What is also important in practice, in our projects, is that the IPS LCD displays are less susceptible to mechanical force. When we apply mechanical force to the screen, and have an optically bonded touch screen, we push the display as well as squeeze the cells. When we have a TN display, every push on the cell changes the image suddenly, with the IPS LCD displays with in-plane switching, different liquid crystals organization, this effect is lesser. It is not completely removed but it is much less distinct. That is another reason IPS displays are very popular for smartphones, tablets, when we have the touchscreens usually optically bonded.

If we wanted to talk about disadvantages, there is a question mark over it, as some of them may be true, some of them do not rely on real cases, what kind of display, what kind of technology is it. Sometimes the IPS displays can have higher power consumption than others, in many cases however, not. They can be more expensive, but not necessarily. The new IPS panels can cost like TN panels, but IPS panels definitely have a longer response time. Again, it is not a rule, you can make IPS panels that are very fast, faster than TN panels, but if you want the fastest possible display, probably the TN panel will be the fastest. That is why the TN technology is still popular on the gaming market. Of course, you can find a lot of discussions on the internet, which technology is better, but it really depends on what you want to achieve.

Now, let us look at the backlight types. As we see here, on the picture above, we have four distinct types of backlight possible. The most common, 95 or 99 per cent of the TFT LCD displays on the market are the transmissive LCD display type, where we need the backlight from the back. If you remember from our Monochrome LCD Displays lecture, for transmissive LCD displays you need the backlight to be always on. If you switch the backlight off, you will not see anything. The same as for monochrome LCD displays, but less popular for TFT displays, we have the transflective LCD display type. They are not popular because usually for transflective TFT displays, the colors lack in brightness, and the displays are not very practical to use. You can see the screen, but the application is limited. Some transflective LCD displays are used by military, in applications where power consumption is paramount; where you can switch the backlight off and you agree to have lower image quality but still see the image. Power consumption and saving energy is most important in some kind of applications and you can use transflective LCD displays there. The reflective type of LCD displays are almost never used in TFT. There is one technology called Low Power Reflective Displays (LPRD) that is used in TFT but it is not popular. Lastly, we have a variation of reflective displays with frontlight, where we add frontlight to the reflective display and have the image even without external light.

Just a few words about Low Power Reflective Displays (LPRD). This kind of display uses environmental light, ambient light to reflect, and produce some colors. The colors are not perfect, not perfectly clear, but this technology is becoming increasingly popular because it allows to have color displays in battery powered applications. For example, a smartwatch would be a case for that technology, or an electrical bike or scooter, where we can not only have a standard monochrome LCD display but also a TFT LCD color display without the backlight; we can see the image even in

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strong sunlight and not need backlight at all. So, this kind of TFL LCD display technology is getting more and more popular when we have outdoor LCD displays and need a low power consumption.

On the picture above, we have some examples of how transmissive and reflective LCD displays work in the sunlight. If we have a simple image, like a black and white pattern, then on a transmissive LCD display, even with 1000 candela brightness, the image probably will be lower quality than for a reflective LCD display; if we have sunlight, we have very strong light reflections on the surface of the screen. We have talked about contrast in more detail in the lecture Sunlight Readable Displays. So, reflective LCD displays are a better solution for outdoor applications than transmissive LCD displays, where you need a really strong backlight, 1000 candela or more, to be really seen outdoors.

To show you how the backlight of LCD displays is built, we took the picture above. You can see the edge backlight there, where we have LEDs here on the small PCB on the edge, and we have a diffuser that distributes the light to the whole surface of LCD screen.

In addition to the backlight, we have something that is called a frontlight. It is similar to backlight, it also uses the LEDs to put the light into it, but the frontlight needs to be transparent as we have the display behind. On the example on the picture above we can see an e-paper display. The e-paper display is also a TFT display variation, but it is not LCD (liquid crystal), it is a different technology, but the back of the display is the same and it is reflective. The example you see is the Kindle 4 eBook reader. It uses an e-paper display and a frontlight as well, so you can read eBooks even during the night.

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An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system.embedded as part of a complete device often including electrical or electronic hardware and mechanical parts.

Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use today.

Modern embedded systems are often based on microcontrollers (i.e. microprocessors with integrated memory and peripheral interfaces), but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also common, especially in more complex systems. In either case, the processor(s) used may be types ranging from general purpose to those specialized in a certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP).

Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase its reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.

Embedded systems range in size from portable personal devices such as digital watches and MP3 players to bigger machines like home appliances, industrial assembly lines, robots, transport vehicles, traffic light controllers, and medical imaging systems. Often they constitute subsystems of other machines like avionics in aircraft and astrionics in spacecraft. Large installations like factories, pipelines and electrical grids rely on multiple embedded systems networked together. Generalized through software customization, embedded systems such as programmable logic controllers frequently comprise their functional units.

Embedded systems range from those low in complexity, with a single microcontroller chip, to very high with multiple units, peripherals and networks, which may reside in equipment racks or across large geographical areas connected via long-distance communications lines.

The origins of the microprocessor and the microcontroller can be traced back to the MOS integrated circuit, which is an integrated circuit chip fabricated from MOSFETs (metal–oxide–semiconductor field-effect transistors) and was developed in the early 1960s. By 1964, MOS chips had reached higher transistor density and lower manufacturing costs than bipolar chips. MOS chips further increased in complexity at a rate predicted by Moore"s law, leading to large-scale integration (LSI) with hundreds of transistors on a single MOS chip by the late 1960s. The application of MOS LSI chips to computing was the basis for the first microprocessors, as engineers began recognizing that a complete computer processor system could be contained on several MOS LSI chips.

The first multi-chip microprocessors, the Four-Phase Systems AL1 in 1969 and the Garrett AiResearch MP944 in 1970, were developed with multiple MOS LSI chips. The first single-chip microprocessor was the Intel 4004, released in 1971. It was developed by Federico Faggin, using his silicon-gate MOS technology, along with Intel engineers Marcian Hoff and Stan Mazor, and Busicom engineer Masatoshi Shima.

One of the first recognizably modern embedded systems was the Apollo Guidance Computer,Charles Stark Draper at the MIT Instrumentation Laboratory. At the project"s inception, the Apollo guidance computer was considered the riskiest item in the Apollo project as it employed the then newly developed monolithic integrated circuits to reduce the computer"s size and weight.

An early mass-produced embedded system was the Autonetics D-17 guidance computer for the Minuteman missile, released in 1961. When the Minuteman II went into production in 1966, the D-17 was replaced with a new computer that represented the first high-volume use of integrated circuits.

Since these early applications in the 1960s, embedded systems have come down in price and there has been a dramatic rise in processing power and functionality. An early microprocessor, the Intel 4004 (released in 1971), was designed for calculators and other small systems but still required external memory and support chips. By the early 1980s, memory, input and output system components had been integrated into the same chip as the processor forming a microcontroller. Microcontrollers find applications where a general-purpose computer would be too costly. As the cost of microprocessors and microcontrollers fell, the prevalence of embedded systems increased.

Today, a comparatively low-cost microcontroller may be programmed to fulfill the same role as a large