Benefits of LCD screen module

LCD, TFT, IPS, AMOLED, P-OLED, QLED are a partial list of display technologies that can be found in the mainstream consumer electronics market today. But what do they all mean? How does IPS differ from AMOLED, and is such a comparison true? We will tell you how they work, what advantages and disadvantages they have, and whether there is a difference between them from the point of view of the end user.

LCD

Liquid Crystal Display, that is, a liquid crystal display - it was this technology in the late 1990s that made it possible to transform monitors and televisions from comfortable beds for cats with cathode ray tubes inside harmful to humans into thin, elegant devices. She also opened the way to the creation of compact gadgets: laptops, PDAs, smartphones.

Liquid crystals are a substance that is both fluid, like 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: crystals change to another state of aggregation under the influence of temperature

In displays, this property of LCDs is used to regulate 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 the crystals. After that, the light goes through an RGB filter and turns 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 fluxes are connected to each other, 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 backlighting is provided by white LEDs located around the perimeter of the display, and is evenly distributed over the entire area thanks to a special backing. This is where the well-known "diseases" of LCD arise. For example, the light still reaches the pixels that should be black. In old and low-quality displays, "black glow" is easily distinguishable.

It happens that the crystals "get stuck", that is, they do not move even when receiving a signal from the transistor, then a "dead pixel" appears on the display. Due to the specifics of the light source, white flares can be seen at the edges of LCD monitors, and smartphones with LCD cannot be absolutely frameless, although both generations of Xiaomi Mi Mix and Essential Phone strive for this.

Backlight and LCD backing 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 figure out what this means.

TN, or TN + film . In fact, Twisted nematic is a "basic" technology that involves polarizing light and twisting liquid crystals into a spiral. Such displays are inexpensive and relatively easy to manufacture, and at the dawn of their existence on the market they had the lowest response time - 16 ms - but at the same time they were characterized by low contrast and small viewing angles. Today, technologies have stepped forward a lot, and the more advanced IPS has come to replace the TN standard.

IPS (in-plane switching) . Unlike TN, the liquid crystals in the IPS-matrix do not twist into a spiral, but rotate all together in one plane parallel to the display surface. This made it possible to increase the comfortable viewing angles up 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 matrices in the diagram

A clear difference between TN (foreground) and IPS

Initially, IPS matrices had a longer response time and power consumption than TN displays, since the entire crystal array had to be rotated to transmit the signal. But over time, IPS-matrices have lost these shortcomings, in part due to the introduction of thin-film transistors.

TFT LCD. In fact, this is not a separate type of matrix, but rather a subspecies, which is characterized by the use of thin-film-transistors (TFT) as a semiconductor for each subpixel. The size of such a transistor ranges from 0.1 to 0.01 microns, making it possible to create small, high-resolution displays. All modern compact displays have such transistors, and not only in LCD, but also in AMOLED.

LCD advantages:

• inexpensive production;
• slight negative effect on the eyes.

Disadvantages of LCD:

• uneconomical energy distribution;
• "Luminous" black color.

OLED

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 the anode: when exposed to an electric current, emission occurs in them and, as a result, light is emitted.

An OLED matrix consists of many such diodes. In most cases, they are red, green and blue and together make up a pixel (we will omit the subtleties of various combinations of subpixels). But simpler displays can be monochrome and based on diodes of the same color (for example, in smart bracelets).

However, "lights" alone are not enough - a controller is required to display information correctly. And for a long time, the lack of adequate controllers did not allow the production of LED displays in their current form, since it is extremely difficult to correctly control such an array of individual miniature elements.

PMOLED . For this reason, in the first OLED displays, diodes were driven by groups. The controller in PMOLED is the so-called passive matrix (PM). It sends signals to the horizontal and vertical row of diodes, and the point of their intersection is highlighted. Only one pixel can be calculated per clock cycle, so it is impossible to get a complex picture, and even in high resolution. Because of this, manufacturers are also limited in the size of the display: a high-quality image will not come out on a screen with a diagonal of more than three inches.

AMOLED . 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, a sub-pixel) individually, and not in a group. In such a system, called an active matrix (AM), one transistor is responsible for the beginning and end of the signal transmission to the capacitor, and the other for the transmission of the signal from the diode to the screen. Accordingly, if there is no signal, the diode does not light up, and the output is the deepest black color possible, because there is no glow in principle. Due to the fact that the diodes themselves, which lie almost on the surface, glow, the viewing angles of the AMOLED matrix are maximum. But when deviating from the gaze axis, the color can be distorted - go into a red, blue or green tint, or even go in RGB waves.

Such displays are distinguished by high brightness and picture contrast. Previously, this was a real problem: the first AMOLED-screens were almost always "wry-eyed", they could get tired and hurt the eyes. Some displays used pulse width modulation (PWM) to prevent dark images from fading to purple, which also proved painful to the eyes. Due to the organic origin, the diodes sometimes burned out in two to three years, especially with prolonged display of an unchanged picture.

An example of AMOLED display burnout

However, today technologies have gone far ahead, and the listed problems have for the most part already been resolved. AMOLED displays are capable of producing natural colors without heavy eye strain, while IPS displays, on the contrary, tightened up in the area of ​​richness and contrast. In terms of energy 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 no longer as high as in the late 2000s.

Nevertheless, AMOLED is undeniably gaining in popularity in the areas that are gaining popularity. We are talking about frameless gadgets, where LEDs are much easier to place than side-backlit liquid crystals, and curved (and, in the future, bending) displays, for which LCD technology is unsuitable in principle. But this is where a new type of OLED comes into play.

P-OLED . In fact, there is some trickery in separating these displays into a separate category. Indeed, in fact, the fundamental difference between P-OLED (or POLED, not to be confused with PMOLED) from AMOLED is one thing - the use of a plastic (plastic, P) substrate, which allows the display to bend, instead of glass. But it is more difficult and more expensive to manufacture than standard glass. By the way, AMOLED displays are much thinner than LCD due to the smaller number of "layers", and P-OLED, in turn, is thinner than AMOLED.

All smartphones with a curved display (mainly Samsung and LG) use P-OLED. Even in the flagships of Samsung in 2017, where, according to the manufacturer, there is both Super AMOLED and Infinity Display at once. The fact is that these are marketing names that have practically nothing to do with actual production technologies. From this point of view, OLED displays are installed there, which are controlled by an active matrix of thin-film transistors and lie on a plastic substrate - that is, the same AMOLED, or P-OLED. By the way, although the display in LG V30 does not bend, it still lies on a plastic substrate.

OLED advantages:

• high contrast and brightness;
• deep and not energy-consuming black color;
• the ability to use in new form factors.

Disadvantages of OLED:

• strong effect on the eyes;
• expensive and complex production.

Marketing moves

Retina and Super Retina . Translated from English, this word means "retina", and Steve Jobs chose him for a reason. During the presentation of the iPhone 4 in 2010, he said that the human eye is not able to distinguish between 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 has been called Super Retina, although it will have an AMOLED display, and not IPS, as in the rest of the company's smartphones. In other words, the name also has nothing to do with the screen manufacturing technology.

Super AMOLED . This trademark belongs to Samsung, which produces displays both for itself and for 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 layer of the screen, that is, combined them into a single display element. As a result, when deviating from the gaze axis, the picture ceased to delaminate. Very soon the technology reached almost all smartphones, and today it is not entirely clear why "super" is better than "regular" AMOLEDs produced by the same company.

Infinity Display . Everything is quite simple here: "infinite display" means just an almost complete absence of side frames and the presence of minimal frames at the top and bottom. On the other hand, you can't imagine some ordinary frameless smartphone at the presentation - you have to name it beautifully.

Advanced technologies

Micro-LED or ILED . This technology is a logical alternative to OLEDs: it is based on inorganic (Inorganic, I) gallium nitride of a very small size. According to the assessment of experts, micro-LED will be able to compete with the usual OLED in all key parameters: the higher the contrast, the best stock of brightness, faster response time, durability, smaller size and lower power consumption in half. But, alas, such diodes are very difficult to mass produce, so the technology will not yet be able to compete with conventional solutions on the market.

However, this did not stop Sony from showing a 55-inch TV with a matrix of inorganic LEDs at CES-2012. Apple bought LuxVue, a research and development company in this area , in 2014 . And although the iPhone X uses classic AMOLED, future models may already have micro-LED matrices, which, we are assured , will increase the pixel density to 1500 ppi.

A prototype Sony micro-LED TV called Crystal LED

Quantum Dots, or QD-LED, or QLED... This promising technology has taken a bit of everything from those already on the market. She got an internal backlight from LCD displays, but it does not "hit" into liquid crystals, but into very small crystals with a glow effect, deposited directly on the screen - quantum particles. The size of each dot depends on what color it will shine, the range is from two to six nanometers (for comparison: the thickness of a human hair is 100,000 nanometers). The result is vibrant, rich yet natural colors. TVs with such displays were first released by Sony in 2013. There are several models from Samsung on the market now. The quantum dots in them are used in the illumination layer. So far, this is a very expensive technology to manufacture: the average cost of QLED TVs is about $ 2500-3000.

Quantum dots are produced as a microscopic powder and then sprayed onto a screen

conclusions

In practice, modern LCD and AMOLED displays are becoming less and less different 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 time and are kept on the market only due to their cheapness and ease of production, although high image quality is also present. Due to their structure, LCD displays are thicker than LED ones and are unpromising in terms of new curvature and bezelless trends. So their withdrawal from the market is already on the horizon, while LED technologies are confidently developing in several directions at once and, as they say, are waiting in the wings.