Types of phone displays. What are the screens.
Recently, there are many abbreviations for designating the types of displays of mobile devices, which in turn often complicates the task of choosing the type of display when buying a mobile phone. In this article, we will try to figure out what types of screens are for mobile devices, in order to help determine the choice of phone screen.
Currently, only two of the most common technologies can be distinguished: these are screens based on LCD (LCD displays) and OLED (displays on organic semiconductors). The main difference from the LCD is that there are no backlight lamps; directly on the surface, elements of the surface glow in OLED displays.
So, we will consider displays of each technology separately.
LCD (liquid cristal display), i.e. displays based on liquid crystals (LCD). Liquid crystals, like solid ones, have a strictly defined crystal lattice structure and are transparent to light. But, unlike other crystals, liquid can change the structure under external influence (electric current or temperature), twist, becoming opaque. By controlling the current, you can create inscriptions or pictures on the screen. But it is worth noting that LCD displays are not able to work from reflected light, so the backlight is their mandatory attribute. Due to the reduction in size, the lamp is usually located on its side, and in front of it is a mirror, so most LCD matrices in the center have a brightness higher than at the edges.
LCD displays are also divided into two types: active and passive. Passive matrices include STN (Super Twisted Nematic), a technology of twisted crystals. This type of matrix is called passive, because it is not able to quickly display information due to the large electric capacity of the cells, the voltage on them cannot change fast enough, so the picture is updated slowly. Typically, STN displays have a lower resolution and display a significantly lower number of colors. Also, from the disadvantages of these matrices, a small viewing angle of the screen and poor visibility in bright sunlight can be noted. And of the advantages of this type of display can be noted quite low power consumption and low cost, so they are actively used in low-cost phones.
CSTN (Color Super Twist Nematic) is a more advanced STN technology. The first CSTN displays had a long response time. At present, displays with CSTN-matrices provide shorter response times, wide viewing angles and high-quality colors, which are almost not inferior to TFT screens.
FSTN (Film Super Twisted Nematic) is also a more advanced STN technology, it differs only in that the FSTN matrices have a special film on the outside that allows you to compensate for color shifts, i.e. this is a film-compensated matrix that improves the viewing angle, but the response time is still great.
DSTN (Dual Super Twisted Nematic) – Advanced STN technology. In such a matrix, one bilayer cell consists of 2 STN cells, whose molecules rotate in opposite directions during operation. Light passing through such a structure in a “locked” state loses a significant part of its energy. The contrast and resolution of DSTN matrices is quite high.
Passive matrices also include Samsung UFB’s own technology (Ultra Fine and Bright). Displays created using this technology have increased brightness and contrast (capable of displaying 262 thousand colors), while the power consumption is reduced compared to traditional LCDs, and the cost of their production is not large.
Active matrices include TFT (Thin Film Transistors) – a type of LCD display whose active matrix uses thin-film transparent transistors. that is, under the surface of the screen is a layer of thin-film transistors, each of which controls a single point on the screen. Thus, in the color display of the phone, their number can reach several tens, or even hundreds of thousands.
The principle of operation of the TFT matrix is to control the intensity of the light flux using its polarization. The change in the polarization vector is carried out by liquid crystals depending on the electric field applied to them. For each pixel there are three transistors, each of which corresponds to one of three RGB colors and a capacitor that supports the required voltage.
TFT matrices accelerated the display, but there were still problems, such as color reproduction, viewing angles, and also dead pixels – when the transistor fails. To combat color distortion when changing the vertical view, two methods were developed: MVA (Multi Domain Alignment) – i.e. in this method, the working cell was divided into two zones that are controlled simultaneously, but the LCDs in each of them are oriented differently. But the problem wasn’t completely solved, the method of rotating the LCD in one IPS plane (In-Plane Switching) turned out to be more successful in terms of overall color reproduction and, in particular, in displaying dark tones.