The application of liquid crystal display modules is very extensive, and the technologies involved have different categories according to different occasions.
You can customize the LCD module as you need creative and innovative electronic projects.
LCD Driver Placement Classification of LCD module
SMT-Surface Mount Technology
SMT surface mount technology is a technology for mounting four-sided flat package components on PCB boards. This technology was very commonly used in the early liquid crystal display industry, and it is still used in mass production. The components it uses generally have relatively short metal feet (or terminals), which are connected to the corresponding PCB board through solder (silver) or gold-plated copper pads.
COB-chip onboard packaging technology
COB is a very popular IC packaging method. It connects the bare chip to the PCB board through metal leads, and the LCD driver is placed in this area on the PCB. The electrical connection is achieved through very thin gold wires, and this area is finally covered with epoxy resin for protection.
Almost all character LCD display modules of our company are designed and produced through this technology.
COG-Chip on Glass Bonding Technology
COG is a high-tech connection method that uses gold bumps or flip-chip ICs to achieve a very compact application.
COG integrated circuits were first introduced by EPSON. When using this technology, the IC chip is not packaged but is directly placed on the glass as a bare chip. Because there is no package, the connection part of the IC can be minimized with the size of the glass. This technology reduces the assembly area and is more suitable for processing high-speed or high-frequency signals.
TAB Automatic Bonding Technology
The TAB LCD drive/control circuit is sealed in a thin rigid bubble package, and the drive pins extend from the rigid bubble package to a thin plastic substrate. The adhesive along the edges is used to attach the TAB to the LCD glass or PCB board.
The TAB IC assembly method uses the same integrated circuit as the COG technology —gold bump or flip-chip IC. After the IC chip is produced, the gold bumps are placed on the IC and then sealed to the plastic substrate (this process is called ILB or internal lead bonding). TAB LCD modules are generally customized.
TFT display (TN type) LCD module
TFT (Thin Film Transistor) is an active-matrix liquid crystal display that supports a full-color display. This display is characterized by high brightness, bright colors, and supports the display of fast animation, complex graphics, and various custom fonts. TFT is a perfect display product that can provide rich customer interfaces.
It is usually used in consumer electronic products, such as DVD players or handheld devices. It is also very suitable for various industrial applications.
The TFT display screen contains very tiny switching transistors and capacitive devices. These tiny switching transistors control every pixel in the display screen, and only need a small amount of energy to control the rotation direction of the liquid crystal. This will allow faster control of each red, green, and blue base point, resulting in clear, fast-moving color graphics.
The transistors in the TFT are arranged in a matrix on the substrate glass, and each pixel on the display screen will remain closed until the addressing command requires the state of the transistor to be changed.
Different from the traditional passive matrix display, in order to activate a specific pixel, the corresponding row will be opened first, and then the modified command will be sent to the appropriate column, where only the capacitor in each specific pixel receives the opened Command until the next refresh cycle.
Essentially, each transistor acts as an active switch. By adding an active switch, the number of scan lines can be limited and the crossover effect problem can be eliminated.
The main problem of the TN type TFT display is the small viewing angle, especially in the vertical direction.
If you look from the bottom to the top, you will clearly see that the picture will become very dark, even if it moves slightly, the contrast And the change of the color tone will also be clearly observed, which may be the main shortcoming of the current mainstream TN display. In recent years, some TN-type displays have better viewing angles than other products, but they still have a big gap with other display technologies.
The MVA-Multi-quadrant vertical alignment method
MVA (Multi-Quadrant Vertical Alignment Method) display technology can provide a wider viewing angle, better black depth, faster response time and better color performance.
Each pixel in the MVA display screen contains three sub-pixels (red, green, and blue), and each sub-pixel is further divided into 2 or more sub-pixels. Due to the ridge polarizer, the liquid crystal is in these areas Randomly arranged within. When a command is applied to the transistor, the liquid crystal will flip. As these liquid crystals are placed randomly, it will allow the backlight to maintain the desired color saturation in all different directions and provide a viewing angle of 150 degrees.
How it works:
1. The light is generated from the backlight (usually LED). Light generates a spectrum close to white
2. The driver IC will determine whether the pixel is turned on or off through logic control
»Inactive LCD pixels will prevent light from passing
»The activated LCD pixels will open with the direction of the light and let the light pass-through
3. Add a circular polarizer on the top to increase contrast
4. The color is displayed on all sub-pixels (red, green, blue) through color filters
IPS-lateral electric field effect display technology
The development of the IPS TFT display is to improve the problem of poor viewing angle and insufficient color expression of ordinary TN display. The movement of the liquid crystal molecules is parallel to the glass substrate, not perpendicular. This change can reduce the scattering of light in the pixel matrix, and provide a wider viewing angle and better color expression.
Due to its wider viewing angle and more accurate color expression (almost no color difference), IPS displays are widely used in high-end monitors for professional graphics processing.
The origin of the name IPS is because the liquid crystal molecules in the IPS glass are parallel to the glass substrate, and always parallel to the glass substrate (if the interference of the electrodes is not considered).
When voltage is applied to the glass, the liquid crystal molecules in the cell all rotate 90 degrees. By the way, IPS glass will let light pass through in the active state, and block light in the passive state (that is, when there is no pressure), so if a thin film transistor is broken, then the corresponding pixel keeps the black state all the time, which is different from ordinary TN glass.
IPS can provide stable and accurate color performance from all viewing angles without blurring or grayscale inversion. It can also display clear images in a very fast response time. When touching the screen, there will be no halo effect. Each pixel in the IPS display contains three sub-pixels (red, green, and blue), and each sub-pixel has a pair of electrodes to control the inversion of the liquid crystal.
Unlike ordinary TN-type TFTs, the electrodes are only located on the upper and lower substrates. On the glass, the electrode in the IPS is only located on a glass substrate. When a voltage is applied to the electrode, all the liquid crystal molecules are aligned parallel to the substrate and allow light to pass through the polarizer and color filter.
In fact, the TN type display forces the liquid crystal molecules to be perpendicular to the glass so as to block the passage of light at a wider viewing angle, while the liquid crystal molecules of the IPS display are always arranged in a straight line, which allows light to pass through all viewing angles.
LTPS- low-temperature polysilicon technology
Low-temperature polysilicon (LTPS) means that polysilicon is synthesized at a relatively low temperature (~650°C and lower) compared to traditional methods (above 900°C). Because large glass panels are easily deformed when exposed to high temperatures, LTPS technology is very important for the display industry. More importantly, the use of polysilicon in LTPS is used in large-scale electronic equipment (such as flat-screen displays or image sensors). ) There is great potential in production.
Polysilicon is a pure electrical conductor composed of many crystals or highly ordered lattice products. In 1984, research showed that amorphous silicon is a perfect material to form polysilicon with a stable structure and low surface roughness. The silicon film is formed by low-pressure chemical vapor deposition (LPCVD) to minimize its surface roughness.
First, amorphous silicon is deposited at 560-640°C and then recrystallized at 900-1000°C. Starting from an amorphous film, rather than directly depositing crystals, is to produce a better structure and better smoothness. In 1988, researchers discovered that the use of lower temperatures in the heat treatment stage, along with advanced plasma-enhanced chemical vapor deposition, can promote higher levels of conductivity.
These technological achievements have deeply affected the microelectronics field, the optoelectronic field, and the display enhancement industry.
The following applications require the support of LTPS technology:
1. The circuit is made of a glass-integrated driver, scanner and multiplexer-to reduce the use of additional ICs and glass connectors
2. Smaller display screen-high aperture ratio-mobile application
3. In the case of high current load (OLED needs current drive), it has better stability than amorphous silicon
Transflective mode-semi-reflective transflective
Semi-reflective LCD combines some of the characteristics of transmissive and reflective. The ambient light passes through the LCD and reaches the semi-reflective layer. Most of the light is reflected back, but some light will not be reflected back and lost. Correspondingly, if the ambient light is relatively weak, the backlight can be used to provide the light source required for the display.
The light from the backlight can illuminate the LCD display after passing through the semi-reflective layer. However, like the ambient light, some light cannot pass through the semi-reflective layer. Layer and lost.
The transflective LCD is mainly used in equipment that needs to work under complex light conditions (from a completely dark environment to a strong light environment). Under weaker light conditions, the transflective LCD can provide a similar transmissive display effect, and under strong light conditions, they can provide a display effect similar to the reflective type.
However, this is a compromise effect after all, because the transflective LCD will lose some light so the display reflection/transmission efficiency is low.
The picture below shows a simple transflective display. We can see that there are two areas, T and R. The box thickness in these two areas is different. The box thickness in the T area is the R area. Twice, that is, dT= 2*DR, this is to maintain the reflection and transmission intensity of the phase circumference in these two areas, and provide the same color expression because, in the T zone, light only needs to pass through the liquid crystal layer, And in the R zone, the light needs to pass twice.
On the basis of the existing transmissive TFT products, a reflective film is added to achieve a semi-reflective and semi-transparent display effect.
Features: simple operation, strong applicability, wide coverage of sizes and models
Full viewing angle
By adding a dedicated full viewing angle polarizer, ordinary TFT products can obtain a wider viewing angle.
Features: simple operation, strong applicability, wide coverage of sizes and models
Sunlight readability-readability under the sun
1. Use semi-reflective and semi-transparent glass panels to achieve a readable effect in the sun
2. By using ultra-bright backlight (usually 1000nits and above) on the transmissive TFT, to achieve the effect of being readable in sunlight
A liquid crystal product based on surface alignment. The liquid crystal molecules are oriented at 90 degrees on each glass surface. Images are produced in the following two modes: positive and negative. The positive mode provides a white background and black pen segments. The negative mode provides black background and white strokes.
When two polarizers are arranged along the vertical axis, as shown in the left picture below, light passes through the guide layer and travels along with the spiral arrangement of liquid crystal molecules. The light is distorted 90 degrees so that it passes through the underlying filter. When a voltage is applied, the liquid crystal molecules will change their spiral pattern, and the light will be blocked by the underlying filter. Since there is no distortion, this part of the display will appear black.
The multiplexing rate is the number of lines that can be displayed at the same time. For example, the multiplexing rate is 16, which means that 16 lines of information can be displayed at the same time.
ETN Contrast-enhanced Twisted Nematic
Low-cost LCD technology, containing dyes in the LCD fluid, used to improve the background color effect in the negative mode to increase the display contrast, like ordinary TN-type products, only suitable for 1 to 1/4 low-cost The application of the empty ratio can support a maximum duty ratio of 1/8, which is suitable for wide temperature products.
ETN type products are ideal solutions for electronic products that require high readability (such as audio, air conditioning controllers, etc.).
HTN-high twist nematic
A liquid crystal product based on surface alignment, the liquid crystal molecules are oriented 110 degrees on each glass surface.
Images are generated in the following two modes:
(1) Positive and negative. The positive mode provides a white background and black pen segments.
(2) Negative mode provides black background and white strokes.
When two polarizers are arranged along the vertical axis, as shown in the left picture below, light passes through the guide layer and travels along with the spiral arrangement of liquid crystal molecules. The light is distorted 110 degrees so that it passes through the underlying filter. When a voltage is applied, the liquid crystal molecules will change their spiral pattern, and the light will be blocked by the underlying filter. Since there is no distortion, this part of the display will appear black.
STN-Super Twisted Nematic
A kind of LCD display technology that can drive more channels and contain more information content by using the adjustability in two optical modes. It uses birefringence mode, which is better than ordinary TN and can achieve higher Improved twisted nematic fluid for contrast and wider viewing angle.
The following figure shows a typical comparison between the voltage and transmitted light curves of ordinary TN and STN (usually, a larger twist angle means a stronger multi-channel drive capability). V90 and V10 on the graph represent the voltage change when the light transmittance drops from 90% to 10%.
As shown in the figure below, the STN display has a steeper curve than the TN display, which will bring the higher multi-channel driving capability to the STN display. (In fact, the development of STN is mainly to overcome the difficulties encountered by TN display in multi-channel driving).
The multiplexing rate is the number of lines that can be displayed at the same time. For example, the multiplexing rate is 400, which means that 400 lines of information can be displayed at the same time.
ESTN-Enhanced Super Twisted Nematic
The enhanced super twisted nematic display technology is used to enhance the display performance of STN. It is cheaper than Double STN and Film STN, but can have almost the same performance as the above two display technologies under wide temperature working conditions.
ESTN is mainly used for negative display, and can obtain higher contrast by optimizing the color of the backlight. For some vehicle-mounted and high-end industrial applications that have harsher operating temperature requirements, this display technology is an ideal solution.
1. Transmissive negative mode
2. Wide operating temperature range
3. Ultra-wide viewing angle
4. High brightness, high contrast
5. Duty cycle: 1/8 ~1/136
FSTN-Super Twisted Nematic with Compensation Film
An LCD display technology that additionally adds a film material outside the box to compensate for the color shift from blue/green to black under a white background. This kind of film is composed of a polymer with birefringence ability, used to remove color interference to achieve defect compensation.
The film is placed on the display screen, generally under or above the upper polarizer. Some other compensation systems use two films, one at the back for alignment, and the other at the front as a dispersion film to widen the viewing cone. The compensation of the membrane material increases the viewing angle but does not affect the conversion time.
FSTN is based on an ordinary STN display, adding a layer of the polymer film as a glass compensation layer on the glass, instead of the second layer box based on DSTN. This simpler and more cost-effective display technology provides a better display in black on a white background.
ASTN-Enhanced Super Twisted Nematic
An LCD display technology that additionally adds a special TEP (temperature-following elliptical polarizer) compensation film outside the box. As compensation, TEP film can increase the display contrast and provide a better display effect in black on a white background.
1. The product is lighter and thinner
2. Easy to make thin slices
3. To achieve higher brightness by reducing reflection
4. Need temperature compensation drive — to improve the conversion time at low temperatures
5. Cost advantage
BM STN-Super twisted nematic with black mask
With the technology of adding a black mask in the box, the light leakage between the electrode gaps will be effectively blocked by the BM layer. This BM layer can absorb/block more than 99% of light waves to significantly increase contrast. The BM STN series with character display is an ideal solution for display products that require high readability.
In addition, it can also be used with different colors of the backlight to meet different needs, such as red, white, amber, and green, And blue. BM STN display screens are widely used in medical equipment (blood pressure monitors) and household appliances (coffee machines, stereos, etc.).