LCD Alphabet Soup: Understanding Types of LCD Technology

Share this article:

For more LCD Manufacturerinformation, please contact us. We will provide professional answers.

Estimated reading time: 13 minutes

From their discovery in to their first application within displays in the s, liquid crystals have become a mainstream material choice with many impactful applications in the world of electronics.

As the key component behind liquid crystal displays (LCD), these materials change light polarization to create vibrant, high-resolution images on digital screens. The growth of LCD technology has helped propel the larger display panel market enormously, with industry valuation projected to reach $178.20 billion by .

In this post we&#;ll explore the various types of LCD technology currently on the market and some of their distinct applications and advantages.

Types of LCD Technology and Terminology

A prolific variety of LCD types has been developed to best meet their exact use-cases and end-environments. Displays may be optimized for power consumption, contrast ratio, color reproduction, optimal viewing angle, temperature range, cost, and more.

When choosing which type of LCD is best suited for a project, consider the following:

Types of LCDs

PM LCDs: Passive Matrix LCDs

Passive Matrix LCDs are addressed with common and segment electrodes. A pixel or an icon is formed at the intersection where a common and a segment electrode overlap. Common electrodes are addressed one-at-a-time in a sequence. Segment electrodes are addressed simultaneously with the information corresponding to all pixels or icons connected to the current common electrode. This method is referred to as multiplexing.

For multiplexing to work, the liquid crystal structure must have a threshold voltage (below which it does not respond to the applied voltage), and a significant &#;steepness&#; in optical effect as a function of applied voltage once the threshold voltage is exceeded. This optical steepness is directly related to the number of common electrodes which can be addressed. The twisting of the liquid crystal helps create both the threshold voltage and a steep response.

Passive Matrix LCDs offer a cost advantage (both parts and tooling) and are highly customizable. The counterpart to Passive Matrix displays are Active Matrix displays.

AM LCDs: Active-Matrix LCDs

Active-Matrix LCDs were developed to overcome some of the limitations of Passive Matrix LCDs &#; namely resolution, color, and size. Within an Active-Matrix LCD, an &#;active element&#; is added to each pixel location (the intersection between a horizontal row and vertical column electrode). These active elements, which can be diodes or transistors, create a threshold and allow control of the optical response of the liquid crystal structure to the applied voltage. Transistors are used as switches to charge a capacitor, which then provides the voltage to the pixel. Whenever a row is turned on, one at a time, all transistor switches in that row are closed and all pixel capacitors are charged with the appropriate voltage. The capacitor then keeps the voltage applied to the pixel after the row is switched off until the next refresh cycle.

Furthermore, the processes used for manufacturing Active-Matrix LCDs can create much finer details on the electrode structure. This allows splitting each pixel in three sub-pixels with different color. This together with the better voltage control allows full color displays.

TFT: Thin-Film Transistor

The transistor switches used in Active Matrix Displays must not protrude significantly above the surface of the display substrates lest they might interfere with a uniform liquid crystal layer thickness. They must be implemented in thin films of suitable materials. Hence, the name Thin Film Transistors (TFT). While AM and TFT have a different meaning, they are often used interchangeably to indicate a higher performance display.

TFTs can be formed by amorphous silicon (denoted α-Si TFT), by poly-crystalline silicon (LTPS for Low Temperature Poly Silicon), or by semiconducting metal oxides (Ox-TFT or IGZO-TFT for Indium Gallium Zinc Oxide).

Currently the most common Electronics Display Technology on the market is LCD technology and among LCD technologies, TFT display technology is the most widely used across consumer applications (laptops, tablets, TVs, Mobile phones, etc.) as well as many industrial, automotive, and medical applications.

Liquid Crystal Configurations for PM displays

TN: Twisted Nematic

Nematic refers to one of the common phases of liquid crystals (LC). In this phase, rod-like molecules tend to self-align more or less parallel to each other.

As the first commercially successful LCD technology, Passive Matrix Twisted Nematic (TN) LCDs use a 90° twist of the nematic LC fluid between two polarizers to display information. The twist of the LC fluid either blocks light from passing through the LCD cell or allows light to pass, depending on the applied voltage. The applied voltage changes the twisted nematic orientation into an orientation that does not change the polarization of tight. This is called the TN effect.

Example of a Segmented TN Display

TN displays can be normally white (NW) when they use two orthogonal liner polarizers or normally black (NB) when parallel linear polarizers are used. &#;Normally&#; refers to what happens when no voltage is applied.

Initially, Passive TN LCDs were used in segmented, icon, or character displays where an image element was turned &#;on&#; and &#;off&#; depending on how the fluid was driven. Improvements were made along the way to address the limited viewing angle of TN technology, which can suffer from contrast loss or even inversion at shallow angles.  

The TN effect is also used in some Active Matrix liquid crystal displays (AM-LCDs).

HTN: Hyper Twisted Nematic

It can be advantageous to twist the director of the nematic phase a bit more than 90 degrees, but less than 180 degrees. Displays like this are a subset of TN displays and are sometimes caller Hyper Twisted Nematic Displays.

STN: Super Twisted Nematic

The numbers of rows or icons that can be addressed in a TN display without Active Matrix addressing is very limited. This is related to how strongly the liquid crystal responds to the applied voltage. Twisting the LC nematic fluid more than 180 degrees (typically between 210 and 270 degrees) causes the display to require a much smaller voltage difference between on and off pixels. This in turn allows addressing of many more rows without an active matrix. Displays with a twist between 210 and 270 degrees are called Super Twisted Nematic displays.

The higher display resolution of STN displays comes at a price. The optical effect is no longer neutrally black and white as in a TN display. Rather these displays are naturally yellow and black or blue and white. The color can be somewhat compensated with colored polarizers, but that comes at the expense of brightness and contrast.

FSTN: Film Compensated Super Twisted Nematic

The color in STN displays is caused by birefringence. Adding the same birefringence in the opposite direction can compensate for the effect. Initially this was done by stacking two STN displays on top of each other. This is referred to as Double STN or DSTN, but this is of course thicker and more expensive.

Example of a FSTN display

The birefringence of an STN display can be approximated with a stretched transparent plastic film. Adding such a film to an STN display instead of the 2nd STN display is a lot more attractive and has almost the same performance. This is referred to as a Film Compensated STN display (FSTN, or sometimes if two films are used as FFSTN).   

FSTN displays are used commonly in consumer, medical and industrial display applications that require low cost and do not need high resolution images or full color.

WVTN: Wide View Twisted Nematic

Another development to the TN display was to use the same concept as in FSTN displays on TN displays. However, the film cannot just be a stretched polymer. Instead, a twisted liquid crystal structure is made and polymerized into a film that is used as a compensation film for TN displays. As this method mostly improves the display characteristics at shallow viewing angles while preserving the excellent performance in straight on viewing, this technology is called  Wide View Twisted Nematic (WVTN).

VA or VAN: Vertically Aligned Nematic liquid crystal displays

Examples of Passive Matrix VA (PMVA) Displays

The above display technologies have liquid crystal molecules that are aligned nearly parallel to the display surface with more or less twisting when going from one substrate to the other. In VA (also called VAN) displays, the liquid crystal molecules are aligned vertically with respect to the display surface. Applying a voltage causes the molecules to lay flat, with or without twist.

The advantage of this arrangement is a very dark black state with very little light leakage. This allows making displays with a black mask and colored icons or symbols. These displays look like color displays with brilliant colors, however each image element or icon can only have its assigned color or black.

Sometimes these displays are referred to as PMVA displays to distinguish them from VA displays using an active matrix.

Liquid Crystal Configurations for AM displays

Example of a TFT LCD

Due to the ability in AM displays to address one row while the other rows are isolated, the demands on the electro-optical performance of the Liquid Crystal Configuration are less stringent. In principle, all the above mentioned configurations can be used in AM displays. In practice, TN, and WVTN are frequently used as well as some versions of VA technology described below. (MVA, AIFF-MVA, PVA, ASV).

IPS: In-Plane Switching and FFS: Fringe Field Switching

In-Plane Switching (IPS) and Fringe Field Switching (FFS) are technologies that apply the electric stimulus between electrodes on only one substrate unlike all other technologies described here where the electric stimulus is applied between electrodes on both substrates.

The advantage of these technologies is a much wider and more symmetrical viewing angle along with the elimination of the contrast inversion (or color shift) seen in TN TFT LCDs when viewed from various angles. IPS and FFS displays also are less sensitive to pressure, which is a big advantage in touchscreen displays.

Throughout the development of these technologies, there were the initial type, super, advanced, pro, etc. versions, which led to a lot of acronyms like (S-IPS, AS-IPS, H-IPS, FFS-Pro)

MVA and PVA: (Patterned) Multidomain Vertically Aligned

PVA and MVA are active-matrix equivalents to the VA or VAN technology described above.

Here, each color sub-pixel is further divided into zones (called domains) having a different direction of the molecular movement when voltage is applied. Again, the purpose is a much wider and more symmetric viewing performance and the elimination of color shifts and contrast inversion at shallow angles. MVA technology achieves that with carefully designed protrusions on the inside surfaces of the display, while PVA uses fine patterning of the electrodes on both substrates.

Note: PMVA is reserved for passive matrix vertically aligned and does not mean patterned multidomain vertically aligned.

ASV: Axially Symmetric Vertically Aligned aka Advanced Super View

ASV is a version of MVA where instead of two or four domains per pixel the liquid crystal switches in radial directions all around the center of the pixel. This technology was developed and used exclusively by Sharp and is no longer in production.

AIFF MVA: Amplified Intrinsic Fringe-Field Multidomain Vertically Aligned

Even more exotic, AIFF-MVA is a technology attempting to combine the benefits of VA type displays with fringe field switching.

LCD Periphery

IC: Integrated Circuit

The integrated circuit is a patterned piece of silicon or other type of semiconducting material. A modern IC contains millions or even billions of tiny transistors. Their tiny size allows for the fabrication of smaller, faster, more efficient, and less expensive electronic circuits. The driver chips addressing electronics displays are ICs.

PCBA: Printed Circuit Board Assembly

Legacy LCDs normally have the driver ICs (integrated circuit) mounted on a printed circuit board (PCBA) which consists of a flat sheet of insulating material used to mount and connect the driver IC and electronic periphery to the LCD. PCBs can be a single-sided, double-sided or multi-layer.

FPC: Flexible Printed Circuit

Often PCBAs are connected to the display with flexible printed circuits. It&#;s also possible to mount all necessary components on FPCs without the need of a PCBA in the display module.

Display driver IC&#;s are often mounted directly onto the display glass. This is done with an anisotropic conductive film (ACF) adhesive.

LVDS: Low Voltage Differential Signaling

Low Voltage Differential Signaling (LVDS) is an interface to the display, not a display technology itself. This technology is not specific to displays, as it&#;s used in many other applications as well. It&#;s a high-speed signal that provides some noise immunity for the display. It also allows for longer distances compared to parallel interfaces.

As display resolutions increase, data transmission rates must increase as well. At high frequencies, single-ended signaling circuits can begin to act as antennas to radiate and receive radiated noise. Low Voltage Differential Signaling (LVDS) addresses many of these shortcomings by using differential signaling at low voltages to transmit display data at high speeds.

MIPI®: Mobile Industry Processor Interface

Mobile Industry Processor Interface (MIPI®) is a high-speed Display Serial Interface (DSI) between the host processor and the display module. It has a low pin count, high bandwidth, and low Electro Magnetic Interference (EMI), and is commonly used in cameras, cell phones and tablets.

New Vision Display&#;s LCD capabilities

New Vision Display (NVD) has decades of experience designing and manufacturing custom display and touch panel assemblies for some of the world&#;s largest original equipment manufacturers (OEMs) in the automotive, medical, industrial, and consumer markets.

NVD&#;s state-of-the-art factories are equipped to build solutions using a wide range of display and touch technologies. To view our extensive portfolio, visit our Products Page.

With industry-leading certifications and expert engineers on staff, NVD can handle your design needs, even for the most rigorous and complex end environments. To learn more about what makes us the display manufacturer for your needs, contact us today.

Many intelligent terminals use the TFT LCD module as the human-machine interface (HMI) given its high performance in display quality, cost efficiency, and custom flexibility, for instance, a typical computer monitor, television screen, and mobile.

As product managers of the terminals, or only enthusiasts who are interested in intelligent products, you should know the basic manufacturing knowledge and product concepts of LCD for making the right decision.

It also can help you to communicate with your suppliers, give ideas of what can be tailored in the interface, and make the selection.

TFT LCD manufacturing processes

From a product perspective, we can divide the TFT LCD module into three layers, from bottom to top: backlight unit, electrical system, and light-and-color control system. 

learn more about TFT-LCD: &#;What are active matrix LCD and TFT-LCD?&#;

From the manufacturing process perspective,  it starts from the light-and-color control system and then assembles all three parts.

Therefore, there are three main processes, the TFT array process, cell layer process, and LCD module assembly. 

The first two processes are about the production of the light-and-color control system, including TFT substrate, CF substrate, and LC (liquid crystal), collectively referred to as LCD panel. 

The last step is the integration and assembly of the LCD panel, electrical system, and backlight unit.

TFT array process

This process is to produce usable thin-film transistors (TFT) substrate and color filter(CF) substrate.

The TFT array process is similar to making the semiconductor. 

To get qualified products, it needs to repeat the processes of cleaning, coating, increasing photoresist, exposure, development, etching, removing the photoresist, etc. Generally, it needs to repeat 5 to 7 times.

Figure1: Step 1- TFT array process

Cell Layer process

This process takes the output from the previous process as the top and bottom substrates, drips liquid crystal in between, and then bonds them together as a whole. 

The combined glass made in this process is called an LCD panel. 

In the LCD industry, these two processes, TFT-array and cell layer, are finished by the same LCD manufacturer. In another word, those LCD factories supply LCD panels. 

After that, the big &#;glass&#; can be cut into pieces as needed in different sizes.

Figure2: Step 2- Cell Layer process

LCD module (LCM) assembly

Using the cut-size LCD panel as the basic materials, LCM manufacturers proceed with the bonding of the backlight unit, and electrical components (like driver IC, FPC, etc.) onto the &#;glass&#; panel, then assemble it with the outer frames (or bezel) for protection.

In the TFT display, it is common to do the custom in the LCM stage.  

The size of the screen, the backlight unit, and the electrical system provide choices to cope with the requirement of the main system of the terminals.

Figure3: Step 3- LCD module (LCM) assembly

Now you have known how the LCD and LCD module is produced in a factory in different steps.

Moreover, you still should understand some basic concepts and features of LCD, which are related to the display quality and the setting with your devices. 

Actually, in the communication and development for a display, display manufacturers will provide specifications of the LCD as a baisc for further discussion. 

Here are the key concepts in the specification:

8 Key Concepts of LCD and TFT-LCD

Size of Screen

Figure4: The common size of each monitor

Display size uses the diagonal length of the actual visible area, the unit is an inch (1 inch =2.54 cm) in common.

Aspect Ratio

The aspect ratio is the proportional relationship and ratio of the width to the height of the visible area of the LCD, also called the screen ratio. 

The aspect ratio of LCD is mainly 4:3, 5:4, 16:10, and 16:9, the ratio of 16:9 is closer to the golden section ratio, which is more comfortable for human eyes to watch. 

In the design of the TFT LCD module, H (horizontal) is usually used to represent the length, and V (vertical) represents the width.

Figure5: Aspect Ratio sample

Contact us to discuss your requirements of 24.6 inch TFT LCD Modules Price. Our experienced sales team can help you identify the options that best suit your needs.

Additional resources:
How to make "Hello World" on Oled 128x64 SPI - Displays
Where to find
4 Tips to Select a TFT Meter Display
Ultimate 3D Printer Upgrade Purchase Guide
Top TFT LCD Display Modules for Your Projects
54-Inch PM OLED vs. Alternatives: Which is Best for You?
What Are the Benefits of 12864 LCD Screen?

Active Area (AA)

Figure6: Active Area(AA) sample

The active area is the total area of the TFT LCD screen that can be displayed. 

But in common, factories mark only the length and width of the area on the draw for easy understanding.

Through the display size (diagonal length) and aspect ratio of the LCD screen, the specific length and width of the effective display area can be calculated by using the Pythagorean theorem.

Pixel

Pixel, one of the small dots that make up a screen display, is used as a unit of resolution.

Pixel Pitch

PPI is the pixel density of a display, the number of pixels per inch size. 

The display providing clearer images has a high PPI value.

(X: the number of pixels in length,

Y: the number of pixels in width,

Z: the size of the screen)

Figure7: PPI calculation formula

Resolution

Resolution is a measure of the image display, which depends on the size of the dots that make up the image. 

Usually, it is measured by the number of horizontal and vertical pixels, in the form of &#;horizontal pixels × vertical pixels&#;.

For instance, a display with a resolution of *768 pixels means it has pixels in the horizontal direction on the effective display area, while 768 pixels in the vertical direction. 

In a fixed plane, the higher the resolution, the more details a monitor can display.

Figure8: The common resolution size corresponding to LCD

Power Consumption

Since about 90% of the power consumption of TFT LCD is from the backlight, to adjust the power consumption of the LCD module it needs to start from the backlight. 

In theory, to achieve the same brightness, the big-size LCD consumes more power than the smaller one. In practice, it still ways to regulate.

Lifespan

How long does an LCD last? 

The lifespan of the LCD module mainly depends on its illuminance (LED strips in the backlight). When the performance of the light source drops dramatically, the display is useless.  

The industry uses Hour to value the lifespan of an LCD. And in normal, LCD and TFT LCD can last for tens of thousands of hours.

That is to say, if the LCD is used for 5 hours a day, it can last more than 10 years.

8 Key Optical Parameters of TFT LCD

Viewing Angle 

The viewing is determined for the horizontal or 3, 9 o&#;clock direction and the vertical or 6, 12 o&#;clock direction concerning the optical axis which is normal to the LCD surface.

The viewing angle is the angle from the normal to the four directions of up, down, left, and right, which is sequentially defined as U, D, L, R. 

Generally, the viewing angle of the horizontal direction L, R is larger than that of the vertical direction U, D. 

For the small and medium-sized LCD, the general viewing angle can be 30 degrees, the wide viewing can achieve 45 degrees, and the full viewing angle means it is almost close to 90 degrees.

BM-7A professional equipment measurement

Aperture Ratio

Figure10: Aperture Ratio

It is the calculated result of the effective area of each pixel that can transmit light divided by the total area of the pixel. 

The higher the aperture ratio, the screen has higher light transmittance and a brighter display.

Response Time

The response time measures the response speed of the LCD screen to the input signal, that is, the response time of the LCD from dark to bright or from bright to dark.

The unit is ms (milliseconds). 

When the screen is switched, the faster the response, the smoother the switching is.

Luminance (Brightness)

People also refer to it as brightness (even though both concepts are not the same).

It is the luminous intensity, projected on a given area and direction. 

Its unit is candela per square meter (cd/m2), which can be measured by BM-7/A. The test method is shown in the following figure.

Figure11: Luminance measurement by BM-7A

Uniformity of luminance variation is important. The higher the uniformity, the display quality of the LCD screen is more consistent.

Luminance Uniformity

Generally, in small and medium-sized LCMs, we measure the brightness of 9 points, then divide the measured minimum value by the maximum value to obtain the uniformity of the LCD. 

Figure12&#;Calculation method of luminance uniformity

Contrast Ratio (CR)

Figure13:Calculation formula of CR

Optically, the contrast is the ratio of brightness between complete white to complete black. 

With a higher contrast ratio, in theory, the display should produce deeper blacks with increased grayscale detail.

Color Gamut

Color gamut is the range of colors within the visible color space, for example, all the colors visible to the human eye.

The range of color gamut of an LCD is represented by the triangular area formed by the connection of R, G, and B. 

The wider the area of the triangle indicates the device can express richer in color and vice versa.

Figure14: Color gamut- visible colour spectrum vs RGB display & printing

Color Depth

Color depth indicates the number of colors that a pixel can display. The unit is &#;bit&#;.

When an LCD has more color depth (number of bits),  its intensity level (grayscale) between the brightest and the darkest is larger, it can display more numbers in a color. It means the LCD can display images very fine. 

Above are the basic knowledge and general concepts of LCD, explore more you can read below articles or contact us for any query:

For more information, please visit 24.6 inch TFT LCDs Module For Sale.