All types of smartphone screens
LCD, TFT, IPS, AMOLED, P-OLED, QLED - this is an incomplete list of display technologies that can be found today in the mass market of consumer electronics. When you go to buy another gadget, you constantly come across this and scold yourself that you have not figured it out in time.
So here it is a chance. Read about the specifics of each and how they differ ...
Liquid Crystal Display, that is, liquid crystal display - this technology in the late 1990s made it possible to transform monitors and televisions from comfortable stools for cats with harmful cathode-ray tubes inside to thin elegant devices. She also opened the way to the creation of compact gadgets: laptops, PDAs, smartphones.
Liquid crystals - a substance that is both fluid, as a liquid, and anisotropic, like a crystal. The latter quality means that with different orientations of liquid crystal molecules, optical, electrical, and other properties change.
Crystalline, liquid crystal, liquid: the crystals are transferred to another state of aggregation under the influence of temperature
In displays, this LCD property is used to control the light conductivity: depending on the signal from the transistor, the crystals are oriented in a certain way. In front of them is a polarizer that “collects” light waves into the plane of crystals. After them, the light passes through the RGB filter and becomes red, green or blue, respectively. Then, if not blocked by the front polarizer, it appears on the screen as a subpixel. Several of these light streams are interconnected, and on the display we see a pixel of the expected color, and its combination with neighboring pixels is capable of producing a gamut of the sRGB spectrum.
LCD pixel circuit
When the display is turned on, the backlight is carried out by white LEDs located around the perimeter of the display, and is evenly distributed over the entire area thanks to a special substrate. This is where the well-known LCD diseases come from. For example, to the pixels, which should be black, the light still comes. In the old and low-quality displays, the "black glow" is easily discernible.
It happens that the crystals "get stuck", that is, they do not move even when receiving a signal from the transistor, then a "broken pixel" appears on the display.Due to the specifics of the light source, white light can be seen at the edges of LCD monitors, and LCD smartphones cannot be absolutely frameless, although both generations of Xiaomi Mi Mix and Essential Phone are striving for this.
TN, or TN + film.
In fact, Twisted nematic is a “basic” technology that implies the polarization of light and the twisting of liquid crystals into a spiral. Such displays are inexpensive and relatively easy to manufacture, and at the dawn of their presence on the market they had the lowest response time - 16 ms - but they were characterized by low contrast and low viewing angles. Today, technology has made great strides forward, and the TN standard has been replaced by the more advanced IPS.
IPS (in-plane switching).
Unlike TN, the liquid crystals in the IPS matrix do not twist into a spiral, but turn all together in the same plane parallel to the display surface. This made it possible to increase comfortable viewing angles to 178 ° (that is, in fact, to a maximum), to significantly increase the image contrast, to make the black color much deeper, while maintaining comparative eye safety.
Apple iPod Touch LCD Backlight
Clear difference between TN (foreground) and IPS
Initially, IPS-matrix had a greater response time and power consumption than displays with technology TN,since the signal transmission required to rotate the entire array of crystals. But over time, the IPS-matrix lost these shortcomings, in part - due to the introduction of thin-film transistors.
In fact, this is not a separate type of matrix, but rather a subspecies, which is characterized by the use of thin-film transistors (thin-film-transistor, TFT) as a semiconductor for each subpixel. The size of this transistor ranges from 0.1 to 0.01 microns, making it possible to create small displays with high resolution. All modern compact displays are such transistors, and not only in the LCD, but also in AMOLED.
slight negative effect on the eyes.
Disadvantages of LCD:
uneconomic energy distribution;
"Glowing" black color.
Organic light-emitting diode, or organic light-emitting diode - roughly speaking, it is a semiconductor that emits light in the visible spectrum if it receives a quantum of energy. It has two organic layers enclosed in the cathode and anode: when exposed to an electric current, they emit and, as a result, emit light.
The OLED-matrix consists of many such diodes.In most cases, they are red, green and blue and together constitute a pixel (we will omit the subtleties of various combinations of subpixels). But simpler displays can be monochrome and basically have diodes of the same color (for example, in smart bracelets).
However, some “light bulbs” are few — a controller is required to display the information correctly. And for a long time, the lack of adequate controllers did not allow producing LED displays in their current form, since it is extremely difficult to correctly manage such an array of individual miniature elements.
For this reason, in the first OLED displays, the diodes were controlled in groups. The controller in PMOLED is the so-called passive matrix (PM). It sends signals to the horizontal and vertical rows of diodes, and their point of intersection is highlighted. In one clock cycle, you can calculate only one pixel, so it is impossible to get a complex picture, and even in high resolution. Because of this, the manufacturers are limited in the size of the display: on a screen with a diagonal of more than three inches, a quality image will not work.
Previously, PMOLED displays were placed in such MP3 players, now they are used in the same smart bracelets
A breakthrough in the LED display market occurred when it became possible to use thin-film transistors and capacitors to control each pixel (more precisely, subpixel) separately, and not a group. In such a system, which is called an active matrix (active matrix, AM), one transistor is responsible for the beginning and end of the signal transmission to the capacitor, and the second for the signal transmission from the diode to the screen. Accordingly, if there is no signal, the diode does not glow, and the output is the deepest black color, because the glow is absent in principle. Due to the fact that the diodes themselves, which lie practically on the surface, shine, the viewing angles of the AMOLED matrix are maximum. But if you deviate from the axis of view, the color may be distorted - go to red, blue or green, or go at all in RGB waves.
Such displays are distinguished by high brightness and contrast of the picture. Previously, this was a real problem: the first AMOLED screens were almost always “out of sight”, their eyes could get tired and sore. In some displays, pulse-width modulation (PWM) was used so that the dark image does not “go away” into a purple hue, which also turned out to be painful for the eyes.Because of their organic origin, the diodes sometimes burn out within two to three years, especially when displaying a constant picture for a long time.
Burnout example AMOLED display
However, today technologies have gone far ahead, and the problems listed for the most part have already been solved. AMOLED-displays are capable of producing natural colors without a strong eye strain, while IPS-displays, on the contrary, are enhanced in the area of rich colors and contrast. In terms of power consumption, AMOLED technology was initially about one and a half times more efficient than LCD, but according to tests of various devices, we can say that today this figure has almost leveled off.
Even five years ago, the difference was not as high as in the late 2000s.
Nevertheless, AMOLED undoubtedly wins in the increasingly popular areas. We are talking about frameless gadgets, where to place LEDs is much easier than liquid crystals with side illumination, and curved (and in the future - bending) displays, for which LCD technology is unsuitable in principle. But here comes the new type of OLED-matrix.
In fact, there is a share of slyness in distinguishing these displays into a separate category.Indeed, in essence, the fundamental difference between P-OLED (or POLED, not to be confused with PMOLED) from AMOLED is the use of a plastic (plastic, P) substrate, which allows the display to be bent instead of glass. But it is harder and more expensive to manufacture than standard glass. By the way, AMOLED displays, due to a smaller number of “layers,” are much thinner than LCD, and P-OLED, in turn, is thinner than AMOLED.
In all smartphones with a curved display (mainly Samsung and LG) it is P-OLED that is used. Even in the flagships of Samsung 2017, where, according to the manufacturer, is immediately and Super AMOLED, and Infinity Display. The fact is that these are marketing names, having practically no relation to actual production technologies. From this point of view, there are installed displays of organic LEDs, which are controlled by the active matrix of thin-film transistors and lie on a plastic substrate - that is, the same AMOLED, or P-OLED. By the way, in LG V30 the display, though not bent, but still lies on a plastic substrate.
Advantages of OLED:
high contrast and brightness;
deep and energy-efficient black color;
possibility of use in new form factors.
strong effect on the eyes;
expensive and complicated production.
Retina and Super Retina.
Translated from English, this word means "retina", and Steve Jobs chose it for a reason. During the presentation of the iPhone 4 in 2010, he said that the human eye is not able to distinguish pixels if the ppi display indicator exceeds 300. Strictly speaking, any appropriate display may be called Retina, but for obvious reasons no one except Apple uses this term. The display of the future iPhone X was named Super Retina, although it will be installed AMOLED-display, not IPS, as in the rest of the company's smartphones. In other words, the name also has nothing to do with screen manufacturing technology.
iPhone 4 - the first smartphone with a Retina display
The iPhone X is the first and only smartphone with a Super Retina display.
This trademark is owned by Samsung, which produces displays for both itself and its competitors, including Apple. Initially, the main difference between Super AMOLED and just AMOLED was that the company removed the air gap between the matrix and the touch screen layer, that is, combined them into a single display element. As a result, when deviating from the axis of view, the picture ceased to stratify. Very soon, the technology reached almost all smartphones, and today it is not quite clear what the “super” is better than the “ordinary” AMOLED produced by the same company.
It's all quite simple: "endless display" means only the almost complete absence of side frames and the presence of minimal frames above and below. On the other hand, not to present the usual frameless smartphone at the presentation - it should be called beautifully.
Micro-LED or ILED.
This technology is a logical alternative to organic LEDs: it is based on inorganic (Inorganic, I) from gallium nitride, a very small size. According to experts, micro-LED will be able to compete with the usual OLED in all key parameters: higher contrast, better brightness, faster response time, durability, smaller size and half the power consumption. But, alas, such diodes are very difficult in mass production, therefore, so far the technology will not be able to compete in the market with the usual solutions.
However, this did not prevent Sony from showing at the CES-2012 55-inch TV with a matrix of inorganic LEDs. In 2014, Apple bought LuxVue, a company specializing in research in this area. And although the iPhone X uses the classic AMOLED, matrices with micro-LEDs can already be installed in future models, which, we are assured, will increase the pixel density to 1500 ppi.
Prototype Sony TV with a micro-LED matrix called Crystal LED
Quantum Dots, or QD-LED, or QLED.
This promising technology from Samsung took a bit of everything already existing on the market. She got the internal illumination from the LCD displays, only she “hits” it not into liquid crystals, but into very small crystals with a luminescence effect, sprayed directly onto the screen - quantum particles. The size of each point depends on what color it will shine, the range is from two to six nanometers (for comparison: the thickness of a human hair is 100000 nanometers). As a result, bright, saturated and at the same time natural colors are obtained. But while it is very expensive in the production of technology: the average cost of QLED TVs is about $ 2500-3000. In mobile electronics, such displays are not used, and whether or when they will be is unknown.
Quantum dots are produced in the form of a microscopic powder and then sprayed onto the screen.
Quantum dots are produced in the form of a microscopic powder and then sprayed onto the screen.
In practice, modern LCD and AMOLED displays are less and less different in image quality and energy efficiency.But the future - for LED technology in one form or another. Liquid crystals have become obsolete and are held on the market only due to their low cost and ease of production, although the high quality of the picture is also present. LCD displays, due to their structure, are thicker than LED displays, and are unpromising from the point of view of new trends in curvature and framelessness. So their withdrawal from the market is already visible on the horizon, while LED-technologies are confidently developing in several directions at once and, as they say, are waiting in the wings.