According to AbbreviationFinder, LCD displays with a small number of sectors, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. A dedicated external circuit supplies an electrical load to control each segment. This structure is difficult to visualize for some display devices.
Small monochrome screens like those found in personal organizers, or old laptop screens have a passive matrix structure where they employ technologies such as super-twisted nematic (STN) or double layer STN (DSTN) (DSTN corrects the problem of STN color shift), and color STN (CSTN) (a technology where color is added using an internal color filter). Each row or column on the screen has a single electrical circuit. Pixels are addressed by row and column directions at the same time. This type of screen is called a passive-directed matrix because the pixel must retain its state between refresh periods without benefiting from a constant electrical charge. As the number of pixels (and consequently columns and rows) increases, this type of display becomes less appropriate. Very slow response times and rather poor contrast are typical for passive matrices aimed at LCD screens.
In high resolution color devices such as modern LCD monitors and televisions use an active matrix structure. An array of thin-film transistors (TFTs) is added to polarization and color filters. Each pixel has its own dedicated transistor, which will allow each line in the column to access one pixel. When a row line is on, all lines in the column are connected to a row of pixels and a correct supply voltage is driven to all lines in the column. When the row line is deactivated, the next row line is activated. All lines in the row are activated sequentially during an update operation. The active matrix is aimed at devices with a higher brightness and size than the passive matrix (aimed at devices of small size, and, in general, that have shorter response times, producing much better images).
Active matrix technologies
Twisted nematic (TN)
Twisted nematic screens contain liquid crystal elements that are unwound and rolled to varying degrees to allow light to pass through. When no voltage is applied to a TN liquid crystal cell, the light is polarized to pass through the cell. In proportion to the applied voltage, LC cells rotate up to 90 degrees changing polarization and blocking the path of light. To properly adjust the tension level of almost any level of gray or transmission that can be achieved.
In-plane switching (IPS)
In-plane switching is an LCD technology that aligns liquid crystal cells in a horizontal direction. In this method, the electric field is applied across each end of the crystal, but this requires two transistors for each pixel instead of one transistor that was necessary for a standard TFT screen. This causes a greater blocking of the transmission area to occur, it also requires a higher background brightness, which will consume more power, making this type of screen less desirable for laptops.
Vertical alignment (VA)
Vertical alignment, VA displays are a form of LCD displays in which the liquid crystal material is in a vertical state eliminating the need for extra transistors (as in IPS). When no voltage is applied, the liquid crystal cell remains perpendicular to the substrate creating a black screen.
Quality control
Some LCD panels have faulty transistors, causing the pixels to turn on or off permanently, commonly referred to as stuck pixels or dead pixels, respectively. Unlike integrated circuits, LCD panels with a few faulty pixels are often still usable. It is also economically prohibitive to scrap a panel, with a few faulty pixels because LCD panels are so much larger than ICs. Manufacturers have different standards for determining an acceptable number of defective pixels. The maximum acceptable number of defective pixels for LCDs varies greatly. Initially, Samsung had a zero tolerance policy for LCD monitors sold in Korea. Currently however, Samsung adheres to the less restrictive ISO 13406-2 standard. Other companies have had policies that tolerated up to 11 dead pixels. Dead pixel policies are a debate in which there are two opposing positions – those of manufacturers and customers. To regulate the acceptance of defectives and to protect the end user, ISO published the ISO 13406-2 standard. However, not all LCD manufacturers conform to this standard and the ISO standard is often interpreted in different ways. To regulate the acceptance of defectives and to protect the end user, ISO published the ISO 13406-2 standard. However, not all LCD manufacturers conform to this standard and the ISO standard is often interpreted in different ways. To regulate the acceptance of defectives and to protect the end user, ISO published the ISO 13406-2 standard. However, not all LCD manufacturers conform to this standard and the ISO standard is often interpreted in different ways.
LCD panels are more likely to be defective than most ICs, due to their larger size. The standard is much more followed now due to fierce competition between manufacturers and better quality control. A defective 4 pixel SVGA LCD panel is generally considered defective and customers can request an exchange for a new one. Some manufacturers, particularly in South Korea, where some of the largest LCD panel manufacturers are located, such as LG, now have a “zero defective pixel warranty” and may be required to have the device replaced with another in case a pixel is defective. Even where those guarantees don’t exist, the location of defective pixels matters. A display with only a few defective pixels may be unacceptable if the defective pixels are close to each other. Manufacturers can also relax their criteria for replacing bad pixels when they are in the center of the display area.
LCD panels also have defects known as mura, which has a small crack that causes small changes in brightness or color.
Zero current display (bistable)
The zenithal bistable device (ZBD), developed by QinetiQ (formerly DERA), can maintain an image without power. Crystals can exist in one of two stable orientations (black and white) and the current is only needed to change the image. ZBD Displays is a spin-off of QinetiQ which manufactures both grayscale and color ZBD devices.
A French company, Nemoptic, has developed another ‘ zero-power paper ‘, just as LCD technology has been mass produced since July 2003. This technology is intended for use in applications such as Electronic Shelf Labels, E-books (electronic books), E-documents (electronic documents), E-newspapers (electronic newspapers), E-dictionaries (electronic dictionaries), industrial sensors, Ultra Mobile PC , etc. Zero-power LCD displays are a category of electronic paper.
Kent Displays has also developed a “non-current” display that is used in Polymer Stabilized Cholesteric Liquid Crystals or Stabilized Polymer of Cholesteric Liquid Crystals (ChLCD). The main drawback to the ChLCD is its slow refresh rate, especially in low temperatures.
In 2004 researchers at the University of Oxford also demonstrated two new types of bistable zero-power LCD displays based on Zenithal’s bistable techniques.
Several flip-flop technologies, such as the 360 ° BTN and cholesteric flip-flop, rely primarily on most of the liquid crystal (LC) properties and the use of the strong anchor standard, with film alignment and LC similarly mixing the traditional monostable materials. Other bistable technologies (eg Binem Technology ) are primarily based on surface properties and require specific measurements of the weakness of the anchoring materials.
Drawbacks
LCD technology still has some drawbacks compared to other display technologies:
Resolution
Although CRTs are capable of displaying multiple video resolutions without introducing artifacts, LCD displays produce sharp images only at their ‘native resolution’, and sometimes at fractions of the original resolution. When attempting to run LCD panels at non-native resolutions the panel typically results in image scaling, introduces image blurring or hang-ups, and is generally susceptible to various types of HDTV blurring. Many LCD screens are not capable of displaying low resolution screen modes (eg 320×200) due to these scaling limitations.
Contrast
Although LCD displays typically have more vibrant images and better “real world” contrast (the ability to maintain contrast and color variation in bright environments) than CRTs, they have lower contrast than CRTs in terms of black depth.. Contrast is the difference between full power on (white) and pixel off (black), and LCD screens can have “backlight bleed” where light (usually viewed from the corners of the screen) screen) leaks out and black leaks turn to gray. As of December 2007, the best LCD screens may come close to the contrast of plasma screens in terms of delivering depth of black, but most LCDs still lag behind.
Response time
- LCD screens tend to have slower response times than their plasma and CRT counterparts, especially older screens, creating ghost images when images loaded quickly. For example, when scrolling the mouse quickly on an LCD screen, multiple cursors can be seen.
- Some LCD screens have significant lag contributions. If the lag is large enough, that screen may be unsuitable for fast and accurate mouse operations (CAD, FPS gaming) compared to small CRT or LCD monitors with negligible amounts of input lag. Short delays are sometimes highlighted in marketing.
Vision angle
LCD panels tend to have a limited viewing angle relative to CRTs and plasma displays. This reduces the number of people who can comfortably view the same image – laptop screens are an excellent example. Thus, this lack of radiation is what gives LCD screens their reduced power consumption compared to plasma screens and CRTs. While viewing angles have improved to the point where it is rare for colors to be totally off the mark in normal use, at typical computer use distances LCD screens still allow for small, and even different, changes in user posture. positions between your eyes produce noticeable color distortion, even for the best LCD screens on the market.
Durability
LCD monitors tend to be more fragile than their corresponding CRTs. The screen can be especially vulnerable due to the lack of thick protective glass like CRT monitors. Its durability depends on its frequency of use. The manufacturers provide in the user manual a durability time of the screen, regularly expressed in hours of use. But this time can be extended by lowering the brightness levels of the image (still under study).
