Before the mass adoption of smartphones, when buying phones, we evaluated them mainly by design and only occasionally paid attention to functionality. Times have changed: now all smartphones have approximately the same capabilities, and when looking only at the front panel, one gadget can hardly be distinguished from another. The technical characteristics of devices have come to the fore, and the most important among them for many is the screen. We will tell you what lies behind the terms TFT, TN, IPS, PLS, and help you choose a smartphone with the desired screen characteristics.
Matrix types
Three technologies for the production of matrices are mainly used in modern smartphones: two are based on liquid crystals - TN + film and IPS, and the third - AMOLED - on organic light emitting diodes. But before we start, it is worth talking about the acronym TFT, which is the source of many misconceptions. TFT (thin-film transistor) are thin-film transistors that are used to control the operation of each sub-pixel of modern screens. TFT technology is used in all the types of screens listed above, including AMOLED, so if somewhere it is said about comparing TFT and IPS, then this is a fundamentally wrong question.
Most TFT matrices use amorphous silicon, but TFT on polycrystalline silicon (LTPS-TFT) has recently been introduced into production. The main advantages of the new technology are the reduction of power consumption and the size of transistors, which makes it possible to achieve high pixel densities (more than 500 ppi). OnePlus One became one of the first smartphones with an IPS display and a LTPS-TFT matrix.
Smartphone OnePlus One
Now that we have dealt with TFT, let's go directly to the types of matrices. Despite the wide variety of LCD varieties, they all have the same basic principle of operation: the current applied to the molecules of liquid crystals sets the angle of light polarization (it affects the brightness of the subpixel). The polarized light then passes through a light filter and is colored in the color of the corresponding subpixel. The first to appear in smartphones were the simplest and cheapest TN + film matrices, the name of which is often abbreviated to TN. They have small viewing angles (no more than 60 degrees when deviated from the vertical), and even with small inclinations, the image on screens with such matrices is inverted. Among other disadvantages of TN-matrices are low contrast and low color accuracy. To date, such screens are used only in the cheapest smartphones, and the vast majority of new gadgets have more advanced displays.
The most common technology in mobile gadgets now is IPS technology, sometimes referred to as SFT. IPS-matrices appeared 20 years ago and since then have been produced in various modifications, the number of which is close to two dozen. Nevertheless, it is worth highlighting among them those that are the most technologically advanced and are actively used at the moment: AH-IPS from LG and PLS from Samsung, which are very similar in their properties, which even was the reason for litigation between manufacturers . Modern IPS modifications have wide viewing angles that are close to 180 degrees, realistic color reproduction and provide the ability to create displays with a high pixel density. Unfortunately, gadget manufacturers almost never report the exact type of IPS matrices, although when using a smartphone, the differences will be visible to the naked eye. Cheaper IPS matrices are characterized by fading of the picture when the screen is tilted, as well as low color accuracy: the image can be either too “acidic” or, on the contrary, “faded”.
As for power consumption, in liquid crystal displays it is mostly determined by the power of the backlight elements (smartphones use LEDs for this purpose), so the consumption of TN + film and IPS matrices can be considered approximately the same at the same brightness level.
Matrices created on the basis of organic light-emitting diodes (OLED) are completely different from LCDs. In them, the subpixels themselves, which are subminiature organic light-emitting diodes, serve as a light source. Since there is no need for external illumination, such screens can be made thinner than liquid crystal. Smartphones use a variation of OLED technology, AMOLED, which uses an active TFT matrix to drive sub-pixels. This is what allows AMOLEDs to display colors, while conventional OLED panels can only be monochrome. AMOLED matrices provide the deepest blacks, since it only requires completely turning off the LEDs to “display” it. Compared to LCDs, these matrices have lower power consumption, especially when using dark themes, in which the black areas of the screen do not consume power at all. Another characteristic feature of AMOLED is too saturated colors. At the dawn of their appearance, such matrices really had incredible color reproduction, and although such “childish sores” are long gone, most smartphones with such screens still have a built-in saturation setting that allows you to bring the image on AMOLED closer in perception to IPS screens.
Another limitation of AMOLED screens used to be the unequal lifetime of LEDs of different colors. After a couple of years of using a smartphone, this could lead to sub-pixel burnout and afterimage of some interface elements, primarily on the notification panel. But, as in the case of color reproduction, this problem is long gone, and modern organic LEDs are designed for at least three years of continuous operation.
Let's summarize briefly. The most high-quality and brightest image at the moment is provided by AMOLED matrices: even Apple is rumored to use such displays in one of the next iPhones. But, it should be borne in mind that Samsung, as the main manufacturer of such panels, keeps all the latest developments for itself, and sells “last year's” matrices to other manufacturers. Therefore, when choosing a smartphone not from Samsung, you should look towards high-quality IPS screens. But in no case should you choose gadgets with TN + film displays - today this technology is already considered obsolete.
The perception of the image on the screen can be influenced not only by the technology of the matrix, but also by the pattern of subpixels. However, with LCDs, everything is quite simple: in them, each RGB pixel consists of three elongated subpixels, which, depending on the modification of the technology, can be in the form of a rectangle or a “tick”.
Everything is more interesting in AMOLED screens. Since in such matrices the subpixels themselves are the light sources, and the human eye is more sensitive to pure green light than to pure red or blue, using the same pattern in AMOLED as in IPS would degrade color reproduction and make the picture unrealistic. An attempt to solve this problem was the first version of the PenTile technology, which used two types of pixels: RG (red-green) and BG (blue-green), consisting of two subpixels of the corresponding colors. Moreover, if the red and blue subpixels had a shape close to squares, then the green ones looked more like strongly elongated rectangles. The disadvantages of this pattern were "dirty" white color, jagged edges at the junction of different colors, and at low ppi - a clearly visible grid of the subpixel substrate, which appears due to too much distance between them. In addition, the resolution indicated in the characteristics of such devices was “dishonest”: if an IPS HD matrix has 2764800 subpixels, then an AMOLED HD matrix has only 1843200, which led to a visible difference in the clarity of IPS and AMOLED matrices with the naked eye, seemingly the same pixel density. The latest flagship smartphone with such an AMOLED matrix was the Samsung Galaxy S III.
In the Galaxy Note II smartpad, the South Korean company made an attempt to abandon PenTile: the device's screen had full-fledged RBG pixels, albeit with an unusual arrangement of subpixels. However, for unclear reasons, Samsung subsequently abandoned such a pattern - perhaps the manufacturer faced the problem of further increasing ppi.
Samsung has returned to RG-BG pixels in its modern screens with a new type of pattern called Diamond PenTile. The new technology made it possible to make the white color more natural, and as for the jagged edges (for example, individual red sub-pixels were clearly visible around a white object on a black background), this problem was solved even easier - by increasing the ppi to such an extent that the bumps were no longer noticeable . Diamond PenTile has been used in all Samsung flagships since the Galaxy S4.
At the end of this section, it is worth mentioning another picture of AMOLED matrices - PenTile RGBW, which is obtained by adding a fourth, white, to the three main subpixels. Before the advent of Diamond PenTile, such a pattern was the only recipe for pure white, but it never became widespread - one of the latest mobile gadgets with PenTile RGBW was the Galaxy Note 10.1 2014 tablet. Now AMOLED matrices with RGBW pixels are used in TVs, because they do not require a high ppi. To be fair, we also mention that RGBW pixels can also be used in LCDs, but we are not aware of examples of the use of such matrices in smartphones.
Unlike AMOLED, high-quality IPS matrices have never experienced quality problems associated with sub-pixel patterns. However, Diamond PenTile technology, together with high pixel density, allowed AMOLED to catch up and overtake IPS. Therefore, if you are picky about gadgets, you should not buy a smartphone with an AMOLED screen, which has a pixel density of less than 300 ppi. At a higher density, no defects will be noticeable.
Design features
The variety of displays of modern mobile gadgets does not end with imaging technologies alone. One of the first things that manufacturers took up was the air gap between the projection-capacitive sensor and the display itself. This is how the OGS technology appeared, combining the sensor and the matrix in one glass package in the form of a sandwich. This gave a significant breakthrough in image quality: the maximum brightness and viewing angles increased, color reproduction was improved. Of course, the thickness of the entire package has also been reduced, allowing for thinner smartphones. Alas, the technology also has drawbacks: now, if you break the glass, it is almost impossible to change it separately from the display. But the quality advantages still turned out to be more important, and now non-OGS screens can only be found in the cheapest devices.
Recently, experiments with the shape of glass have also become popular. And they began not recently, but at least in 2011: HTC Sensation had a glass concave in the center, which, according to the manufacturer, was supposed to protect the screen from scratches. But such glasses reached a qualitatively new level with the advent of “2.5D screens” with glass curved at the edges, which creates the feeling of an “infinite” screen and makes the edges of smartphones smoother. Such glasses are actively used by Apple in their gadgets, and recently they have become more and more popular.
A logical step in the same direction was the bending of not only the glass, but also the display itself, which was made possible by using polymer substrates instead of glass ones. Here the palm, of course, belongs to Samsung with its Galaxy Note Edge smartphone, in which one of the side edges of the screen was curved.
Another way was proposed by LG, which managed to bend not only the display, but the entire smartphone along its short side. However, LG G Flex and its successor did not gain popularity, after which the manufacturer abandoned the further production of such devices.
Also, some companies are trying to improve human interaction with the screen, working on its touch part. For example, some devices are equipped with sensors with increased sensitivity that allow you to work with them even with gloves, while other screens receive an inductive substrate to support styluses. The first technology is actively used by Samsung and Microsoft (formerly Nokia), and the second by Samsung, Microsoft and Apple.
The future of screens
Do not think that modern displays in smartphones have reached the highest point of their development: technology still has room to grow. One of the most promising are quantum dot displays (QLED). A quantum dot is a microscopic piece of a semiconductor in which quantum effects begin to play a significant role. Simplified, the process of radiation looks like this: the impact of a weak electric current causes the electrons of quantum dots to change energy, while emitting light. The frequency of the emitted light depends on the size and material of the dots, so that almost any color in the visible range can be achieved. Scientists promise that QLED matrices will have better color reproduction, contrast, higher brightness and lower power consumption. Partially, quantum dot screen technology is used in Sony TV screens, and prototypes are available from LG and Philips, but there is no talk about the mass use of such displays in TVs or smartphones.
It is also highly likely that in the near future we will see in smartphones not just curved, but also fully flexible displays. Moreover, almost ready for mass production prototypes of such AMOLED matrices have been around for a couple of years. The limitation is the electronics of the smartphone, which is still impossible to make flexible. On the other hand, large companies can change the very concept of a smartphone by releasing something like the gadget shown in the photo below - we just have to wait, because the development of technology is happening right before our eyes.
