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. But what do they all mean? What is the difference between IPS and AMOLED, and is this comparison true? We will explain how they work, what advantages and disadvantages they have, and whether there is a difference between them from the end user's point of view.
Table of Contents
Liquid Crystal Display
That is liquid crystal display - this technology in the late 1990s allowed to turn monitors and TVs from comfortable beds for cats with harmful to humans cathode-ray tubes inside into thin elegant devices. It also opened the way to the creation of compact gadgets: laptops, PDAs, smartphones.
Liquid crystals are a substance that is both fluid as a liquid and anisotropic as a crystal. The latter quality means that optical, electrical, and other properties change at different orientations of liquid crystal molecules.
Crystal, liquid crystal, liquid: crystals change to another aggregate state under the influence of temperature
In displays, this property is used to regulate the LCD light conductivity: depending on the signal from the transistor crystals are oriented in a certain way. Before them is a polarizer, "collecting" light waves in the plane of crystals. After them, the light passes through the RGB filter and turns red, green or blue, respectively. Then, if it is not blocked by the front polarizer, and emerges on the screen in the form of the subpixels. Several of these light streams are connected to each other, and on the display, we see the pixel of the expected color, and its combination with neighboring pixels is able to give the gamma of the sRGB spectrum.
Diagram of an LCD pixel
When the display is on, the illumination is carried out by white LEDs located on the perimeter of the display and is evenly distributed over the entire area thanks to a special substrate. This gives rise to the famous "disease" LCD. For example, up to the pixels that should be black, the light still comes. In old and low-quality displays can easily be seen "black glow".
It happens that the crystals "get stuck", that is, do not move even when receiving a signal from the transistor, then"broken pixel" appears on the display. Because of the specifics of the light source on the edges of LCD monitors are visible white highlights, and smartphones with LCD can not be completely frameless, although both generations of Xiaomi Mi Mix and Essential Phone to this aim.
The backlight of the LCD substrate and the Apple iPod Touch
However, in the specifications of devices, we are used to seeing not LCD, but mysterious TN, TFT, IPS, or even Retina. Let's see what it means.
TN, or TN+film
In fact, Twisted nematic, the "basic" technology, which involves the polarization of light and the twisting of liquid crystals in a spiral. These displays are inexpensive and relatively easy to produce, and at the dawn of their presence on the market, they had the lowest response time - 16 MS - but characterized by low contrast and low viewing angles. Today, technology has taken a big step forward, and the TN standard has been replaced by more advanced IPS.
IPS (in-plane switching)
Unlike TN, liquid crystals in IPS-matrix do not twist into a spiral but turn all together in one plane parallel to the display surface. This made it possible to increase the comfortable viewing angles to 178° (that is, in fact, to the maximum), significantly increase the contrast of the image, make the black color much deeper, while maintaining comparative safety for the eyes.
The difference between TN and IPS in the diagram
Visual difference between TN (foreground) and IPS
Initially, IPS-matrices had a longer response time and power consumption than displays with TN technology, since it was necessary to rotate the entire array of crystals to transmit a signal. But over time, IPS-matrix lost these shortcomings, partly — 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 is from 0.1 to 0.01 microns, making it possible to create small displays with high resolution. In all modern compact displays, there are such transistors, not only in LCD but also in AMOLED.
Advantages of LCD:
- low-cost production;
- weak negative impact on the eyes.
Disadvantages of LCD:
- wasteful distribution of energy;
- "glowing" black color.
Organic light-emitting diode, or organic led
Roughly speaking is a semiconductor that emits light in the visible spectrum if it receives a quantum of energy. It has two organic layers enclosed in a cathode and an anode: under the influence of an electric current, emission occurs in them and, as a consequence, light radiation.
An OLED matrix consists of a set of such diodes. In most cases, they are red, green, and blue and together make up a pixel (the subtleties of different combinations of sub-pixels are omitted). But simpler displays can be monochrome and have diodes of the same color (for example, in smart bracelets).
However, some "light bulbs" are not enough - for the correct display of information requires a controller. And for a long time, the lack of adequate controllers did not allow to produce 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, diodes were controlled by groups. The controller in PMOLED is the so-called passive matrix (PM). It gives signals to the horizontal and vertical row of diodes, and the point of their intersection is highlighted. Only one pixel can be calculated in one measure, so it is impossible to get a complex picture and even in high resolution. Because of this, manufacturers are limited in the size of the display: on the screen with a diagonal of more than three inches of high-quality images 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 market of led displays occurred when it became possible to use thin-film transistors and capacitors to control each pixel (or rather sub-pixel) separately, rather than a group. In such a system, which is called the active matrix (AM), one transistor is responsible for the beginning and end of the signal to the capacitor, and the second - for the transmission of the signal 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 there is no glow in principle. Due to the fact that the diodes themselves Shine, lying almost on the surface, the viewing angles of the AMOLED matrix are maximum. But if you deviate from the axis of view can be distorted color - go-to red, blue or green, or even go RGB-waves.
Such displays are characterized by high brightness and contrast of the picture. Previously it was a real problem: the first AMOLED screens have almost always been "spread", they could be tired and hurt your eyes. Some displays used pulse width modulation (PWM) to ensure that the dark image does not "go" in purple, which also turned out to be painful for the eyes. Because of the organic origin of the diodes sometimes burned for two or three years, especially with the long-term display of the unchanged image.
An example of a burn-in of AMOLED display
However, today the technology has gone far ahead, and these problems, for the most part, have already been solved. AMOLED displays are capable of delivering natural colors without severe eye strain, and IPS displays are, in contrast, tightened in the area of the richness of color and contrast. In terms of power consumption, AMOLED-technology was originally about one and a half times more efficient than LCD, but according to the tests of different devices, we can say that today this figure is almost leveled.
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 LEDs are much easier to place than liquid crystals with side lighting, and curved (and in the future - bending) displays, for which LCD technology is not suitable in principle. But then a new type of OLED matrices comes into play.
In fact, there is a bit of guile in highlighting these displays in a separate category. In fact, the fundamental difference between P-OLED (or POLED, not to be confused with PMOLED) and AMOLED is the use of a plastic (plastic, P) substrate that allows bending the display instead of a glass one. But it is more complex and expensive to produce than standard glass. By the way, AMOLED-displays due to fewer "layers" are much thinner than LCD, and P-OLED, in turn, thinner than AMOLED.
All smartphones with curved display (mainly Samsung and LG) use P-OLED. Even in the flagship Samsung 2017, where, according to the manufacturer, is immediately and Super AMOLED, and Infinity Display. The fact is that these are marketing names that have virtually nothing to do with actual production technologies. From this point of view, there are displays of organic LEDs that 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, the LG V30 display though not bent, but still lies on a plastic substrate.
Advantages of OLED:
- high contrast and brightness;
- deep and non-energy-consuming black;
- ability to use in new form factors.
Disadvantages of OLED:
- strong effect on eyes;
- expensive and complex production.
Retina and Super Retina
Translated from English, the 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 display PPI exceeds 300. Strictly speaking, any corresponding display can 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 have AMOLED-display, not IPS, as in other smartphones of the company. In other words, the name has nothing to do with the technology of manufacturing the screen.
This brand is owned by Samsung, which produces displays for itself and for its competitors, including Apple. Initially, the main difference between Super AMOLED and simply 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, the deviation from the axis of view of the picture ceased to delaminate. Very soon the technology reached almost all smartphones, and today it is not clear what "super" is better than "conventional" AMOLED produced by the same company.
Here everything is quite simple: "infinite display" means only the almost complete absence of side frames and the presence of a minimum of top and bottom frames. On the other hand, do not present the same at the presentation of some ordinary frameless smartphone-should be called beautiful.
Micro-LED, or ILED
This technology is a logical alternative to organic LEDs: it is based on inorganic (Inorganic, I) gallium nitride, which is very small in size. According to experts, micro-LED will be able to compete with the usual OLED on all key parameters: higher contrast, better brightness, less response time, durability, smaller size, and half the power consumption. But, alas, such diodes are very complex in mass production, so while the technology will not be able to compete in the market with the usual solutions.
However, this did not prevent Sony to show at 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, future models may already be installed matrix with micro-LED, which, as we are assured, will increase the pixel density to 1500 PPI.
A prototype of the Sony TV with an array of micro-LED called Crystal LED
Quantum Dots or QD LED or QLED
This promising technology has taken a little bit of everything from the existing ones on the market. From LCD displays she got the internal illumination, that's just "beats" it is not in liquid crystals, and very small crystals with a glow effect, sprayed directly on the screen — quantum particles. From 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 — 100000 nanometers). The result is bright, rich and at the same time natural colors. TVs with such displays were first released by Sony in 2013. Now there are several Samsung models on the market. Quantum dots are used in the illumination layer. While this is a very expensive technology in production: the average cost of QLED-TVs is about $2500-3000. In mobile electronics, such displays are not used, and whether and when — is unknown.
Quantum dots are produced as a microscopic powder and then sprayed onto the screen
In practice, modern LCD and AMOLED displays differ less from each other in image quality and energy efficiency. But the future belongs to led technologies in one form or another. Liquid crystals have already outlived their age and are kept on the market only due to the cheapness and simplicity of production, although the high quality of the picture is also present. Due to its structure, LCD displays are thicker than led displays and have no prospects in terms of new trends in curvature and framelessness. So their withdrawal from the market is already visible on the horizon, while LED technologies are steadily developing in several directions and, as they say, are waiting in the wings.