What is TFT LCD Screen

 

TFT LCD (Thin Film Transistor Liquid Crystal Display) is the abbreviation of Thin Film Transistor Liquid Crystal Display. The cross section of the TFT panel is shown in Figure 1.

The structure of LCD is introduced. Polarizer.

The top polarizer can polarize stray light from random polarization in a given polarization direction. Before applying an electric field to the electrodes, the liquid crystals are arranged in a twisted structure. The light in this case changes according to the twisted structure of the liquid crystal. The lower polarizer is oriented perpendicular to the upper polarizer. When the light reaches the bottom polarizer, the two polarizers are aligned with each other. Light can pass through them unhindered, as shown in Figure 2

Glass substrate, TFT substrate, color film substrate

Using high-precision photolithography, the pattern is applied to the glass substrate to gradually transfer the images of multiple LCD electrodes in sequence (Figure 3). TFT glass has as many transistors as there are pixels on the display, and color generation is provided by color filter glass with color filters. The movement of the liquid crystal is caused by the potential difference between the electrodes on the TFT glass and the color filter glass. It is this movement of the liquid crystal that produces the color and determines the brightness of the LCD.

LCD liquid crystal

Liquid crystals are almost transparent substances and exhibit the characteristics of crystals and liquids at the same time. Two glass plates sealed with epoxy resin and with a groove in the left corner allow the introduction of liquid crystals (under vacuum) before the final sealing of the glass plates. The potential difference determines the orientation of the liquid crystal. When polarizers and color filters are used, the difference in the orientation of the liquid crystal causes the difference in transmittance (or reflectance) and the resulting color. Liquid crystals are substances that present different phases (solid, liquid crystal or liquid) at different temperatures

Leveling film

The film is deposited on two glass plates (upper and lower), with a series of parallel grooves, so that the liquid crystal molecules are aligned in the appropriate direction (Figure 5 has a series of parallel grooves, so that the liquid crystal molecules are aligned in the corresponding direction)

LCD development

Liquid crystal was discovered more than 100 years ago. When heated, their external state can change from solid to liquid crystal, and even completely transform into liquid form as the temperature rises further. Over the years, people have made great efforts to improve liquid crystals, and as a result they have been widely used in electronic calculators and digital clocks. At present, the application range of color liquid crystal is wider: mobile phones, personal computers and TVs, which have the characteristics of low thickness, low power consumption, high resolution and brightness. In addition, in the foreseeable future, driven by the rapid spread of flat panel displays, the demand for LCD panels is expected to grow substantially.

How does LCD work

When a voltage is applied to the two LCD electrodes, the stronger the "unfolding" of the liquid crystal molecules, the higher the applied potential (Figure 6). Voltage sensitivity is one of the main characteristics of liquid crystals. Figure 7 shows the normal "white" mode of the LCD. As long as no potential difference is applied, light can pass through the liquid crystal layer, and the liquid crystal molecules will change the orientation of the light plane according to their own angle. However, when a voltage is applied, the liquid crystal molecules will "unfold" and "straighten" the light directed to the upper polarizing filter. Therefore, light will not be able to pass through the active area of the LCD, and this area will be darker than the surrounding area.

LCD control mode

Figure 8 shows the LCD control circuit. In a selected period of time, the switch is closed and an input voltage is applied to the liquid crystal, which will cause the orientation of the liquid crystal molecules to change. When the switch is closed, a certain charge is stored in Clc, and the voltage across Clc decreases with time. Consider adding a storage capacitor Cst in parallel with Clc to expand the storage capacity of the charge.

Energy storage capacitor

In fact, the control of the liquid crystal must be carried out by AC voltage. To activate the LCD, voltage is applied only when the switch is turned on, and then the switch is turned off immediately. In some cases, the voltage across the liquid crystal drops due to leakage. To prevent this, we can use a parallel capacitor to compensate for the leakage voltage. As the capacitance Cst increases, the shape of the voltage across it is close to a zigzag

The working principle of TFT LCD

The TFT acts as a switch. The gate of the TFT is connected to the scan line, the source is connected to the data line, and the drain is connected to Clc and Cst. When the shutter is activated (selected on the scan line), the TFT channel is opened, and the image data will be written into Clc and Cst. When the shutter is not selected, the TFT channel is closed

The basic structure of TFT LCD

The core of TFT-LCD structure includes liquid crystal, two polarizers and glass plate: upper color film substrate and lower TFT array substrate. Inject liquid crystal material between the two glass plates

Luminous flux adjustment

By controlling the magnitude of the input voltage applied to the liquid crystal, the arrangement, orientation and direction of the molecules can be changed, which will cause the volume of the luminous flux through the liquid crystal to change accordingly

Color formation

When the light flux passes through the color filter integrated in the top colored glass, each pixel of the image is formed by mixing basic RGB color elements (R-red, G-green, and B-cyan). If the red, green, and blue pixel elements are selected in equal proportions, white light will be produced. By adjusting the ratio of these three elements, the required number of different colors is obtained

 

AMOLED, OLED, IPS, TFT, etc.: What are the differences between these types of displays and which one is better

If a person "is famous for his clothes and his heart is his heart", then TVs, computer monitors, smartphones and tablets will appear on the display. They also often see off. When buying such a device, it is not always possible to personally evaluate the aesthetics and other characteristics of its screen, because many transactions are conducted over the Internet. However, if you know the meaning of the 3 letters, it is easy to understand the display effect of the device even if you do not see it.

For example, LED, LCD, IPS, TFT, OLED, QLED, AMOLED. All of these are screen manufacturing technologies that determine its characteristics. Let's talk about LED, AMOLED, QLED, OLED displays and their differences with IPS, TFT, LCD, etc.

Content

LCD and LED LCD, TFT, LED, AMOLED and other "ice" are just abbreviations, the difference between them is worlds apart. In addition, some of these concepts are unparalleled. So, no one will tell you which TV is best: LCD or LED, because LCD (large iquid ç rystal d isplay) is a liquid crystal display or just LCD, and LED (large mitting d IODE) is one of the types Its backlight (LED). In other words, the TV can be LCD and LED at the same time

The structure diagram of the LED backlight LCD screen is shown in the figure below:

TFT and LCD "How about TFT TV? Is it better or worse than liquid crystal?" Not because TFT is a type of liquid crystal display in active matrix LCD. Active matrix is a display color management system in which each pixel is controlled by its own set of thin film micro transistors

The LCD screens of all modern TVs, monitors, smartphones, and tablets have an active matrix, so it is not appropriate to compare these devices with LCDs and TFTs. TFT and IPS. IPS properties and version "But IPS screens are definitely better than TFTs. It's not useless to write this on the forum!?" Again, those who write in this way did not guess. IPS is a type of TFT. Same as TN, PLS, VA, MVA, PVA, etc. TFT screens are sometimes erroneously called TN displays, which really do not serve the picture quality-of all TFT choices, they have the worst color rendering, the lowest brightness and contrast, and a very limited viewing angle. On the other hand, TN screens are known for their low cost, fast response and high refresh rate.

The next step is the development of active matrix technology, which eliminates the main shortcomings of TN. Change the position of the crystal and the voltage point on the battery to make the black become true black. When looking at the screen from the side, the color is the same as when looking at the front. In addition, the IPS screen has significantly improved color reproduction and increased overall brightness and contrast, but compared with TN, the response speed has decreased. Today, IPS is being developed in parallel by three companies-Panasonic (which took over the "baton" from Hitachi, the developer of the first version), NEC and LG. Each version and generation of the technology has its own characteristics and names. The product lineup of Hitachi and Panasonic includes: IPS (Super TFT), S-IPS (Super-IPS), AS-IPS (Advanced super-IPS), IPS-Pro (IPS-provectus, IPS alpha, IPS alpha next gen). The development of NEC is named: SFT (Super Fine TFT), A-SFT (Advanced SFT), SA-SFT (Super-advanced SFT), UA-SFT (Ultra-advanced SFT). The names of LG products are: S-IPS (Super-IPS), AS-IPS (Advanced super-IPS), H-IPS (Horizontal IPS), E-IPS (Enhanced IPS), P-IPS (Professional IPS) ), AH-IPS (Advanced High Performance IPS).

All developers are improving technology in the same direction. This is the reduction of response time, the increase of contrast, color depth and naturalness, the improvement of viewing angle, the elimination of color distortion, the reduction of power consumption, and most importantly-the reduction of matrix production costs. In recent years, IPS screen computer monitors have "followed TN" in response speed, and can be used not only for professional graphics cards, but also for dynamic games. Most users, except perhaps professionals in the field of graphics and design, will not notice the difference in pictures on IPS monitors of different brands, but there are also considerable differences between their budget and the high-end version. LG's P-IPS and AH-IPS matrix reproduce the highest image quality. They are the most expensive. VA / MVA / PVA Matrix VA, MVA and PVA occupy the middle position between TN and IPS in terms of image quality and price. Compared with TN, they have a wider viewing angle, more accurately convey the depth and naturalness of colors, and they are cheaper than IPS. However, these types of screens are not widely used. They are used to produce monitors for personal computers and budget TV series. There are several types of LED LCD backlight technology. They differ in color, the position of the LEDs on the LCD panel, and the way they dim. A backlight with only white LEDs is called WLED. Its structure is relatively simple, but its color gamut is limited. RGB LED backlights based on red, green and blue LEDs cover a wider range of colors than WLEDs, but are prone to degradation (different color diodes decay at different rates), are heavy and expensive. GB-R LED is the next step in the development of LCD, in which green + blue combination LEDs covered with red phosphors (self-luminous pigments) are used instead of white LEDs. This solution allows us to cover 99% of the RGB palette and get rid of the shortcomings of RGB LEDs. GB-R LED technology is used in AH-IPS and PLS matrix. The RB-G LED is a variation of the previous type of backlight. It is not a blue-green LED, but a red-blue LED covered with green phosphor.

According to the position of the light-emitting elements on the LCD panel, LED backlights are divided into the following types: Edge LED-LEDs are arranged linearly around the periphery of the screen. This is economical, but does not provide uniform illumination and acceptable contrast levels. Direct LED-LED array is distributed throughout the display area. This technology provides a more realistic picture, but this type of panels consumes a lot of energy and is thick, which makes them difficult to install on ultra-thin TVs. Side lighting-Diodes are located only at the edges of the screen, and light guides connected to them provide illumination. This type of backlight is considered the best because it provides uniformity comparable to that of direct LEDs without its disadvantages. The three types of backlights are divided into two types-support local dimming (Local Dimming) and dynamic contrast (DCR), or not. Local dimming and DCR screens look more realistic. OLED and AMOLED Although the concept of OLED is the same as that of LED, it actually has nothing in common with LED. OLED (ø rganic large flying e mitting d IODE)-an element capable of emitting light through electric current-this shows the manufacturing technology based on the performance of organic semiconductors. Each sub-pixel on an OLED screen is a separate organic light-emitting diode (OLED). Unlike LCDs, OLED panels do not require backlighting because they will light up with each point. Other characteristics and characteristics of OLED and LED: Due to the small number of layers, the thickness is small and the weight is light. Unlimited viewing angle. Even lighting. The fastest response time. flexibility. Significantly improve brightness, contrast and color saturation. Low sensitivity to external temperature, but high sensitivity to moisture. The service life is short and there is a tendency for degradation: the burn-out speed of blue diodes is 3 times faster than that of red, and almost 10 times faster than that of green. The dependence of resource consumption on screen brightness-the higher it is, the faster the fading will occur. Sensitivity to mechanical damage. A small defect can cause the screen to fail completely. Flicker is achieved by applying PWM (Pulse Width Modulation) to brightness control. The OLED screen uses PWM as an option. High price.