TN จC Twisted Nematic. A type of liquid crystal whereas the alignment surface and therefore the LC molecules are oriented 90กใ from each surface of glass. Produces images in
two modes: Positive and Negative. Positive Mode provides white background with black segments. Negative Mode provides black background and white segments.
When two polarizing filters are arranged along perpendicular axes, as in the first illustration, light passes through the lead filter and follows the helix arrangement of the liquid
crystal molecules. The light is twisted 90 degrees, thus allowing it to pass through the lower filter. When voltage is applied, however, the liquid crystal molecules straighten out
of their helix pattern. Light is blocked by lower filter and the screen appears black because of there being no twisting effect. The multiplex rate is equal to the number of rows
that can be displayed simultaneously. For example, a display with a multiplex rate of 16 can display 16 rows of information simultaneously.
HTN (High Twisted Nematic) displays are based on a higher molecular twist (usually 110กใ) than TN (90กใ) and therefore offer wider viewing angles and improved contrast. In fact,
these HTN products offer viewing characteristics close to those of STN technology. As low operating voltage as 2.5V and marginal extra cost over TN means that the products
are well suited to hand-held applications.
STN จC Super Twisted Nematic. A high information content LCD that uses adjustable interference of two optical modes to achieve a large number of multiplexed lines, higher
contrast and higher level of gray scale. It results in the birefringence mode. An improved twisted nematic fluid (200กใ twist or greater) which has better contrast and optimum
viewing range than standard twisted nematic. The graph shows a comparison of a voltage versus transmitted light curve of a typical TN and a supertwist nematic (STN) display.
(Generally, a greater twist angle equates to higher multiplexibility.) The V90 and V10 points on the graph indicate the voltages that yield 90 percent and 10 percent light
transmission, respectively. As the figure shows, STN displays have a steeper curve than TN displays, which allows higher multiplex levels for STN displays. (STNs were
developed primarily to overcome the difficulties encountered in multiplexing TN displays.) The multiplex rate is equal to the number of rows that can be displayed simultaneously.
For example, a display with a multiplex rate of 400 can display 400 rows of information simultaneously.
FSTN จC Film Compensation Super Twisted Nematic. LCD with an extra film added to the outside of the cell to compensate the color shift of blue on green to black on white.
The film is made of a polymer with double refraction to remove the interference of colors. It results in retardation compensation. The film (the top layer in the figure) is placed in
the display, either under or over the top polarizer. Some film compensation systems use two films, one on the rear that serves as a collimator, and one on the front that serves
as a dispersion film to broaden the viewing cone. Film compensation improves the viewing angle, but does not affect switching time. FSTN is all standard STN displays with a
polymer film applied to the glass as a compensation layer instead of the second cell as in the case of the DSTN. This simpler and more importantly cost effective method
provides the preferred black on white image for this display technology.
DSTN was the first commercial black and white conversion of the STN display and refers to Double Super Twisted Nematic. DSTN displays are actually two distinct STN filled
glass cells glued together. The first is a LCD display, the second is a glass cell without electrodes or polarizers filled with LC material for use as a compensator which increases
contrast and gives the black on white appearance.
Multi-Color TN display is based on the negative mode. The color coatings and the black matrix (mask) are inside the LCD cell. The black mask allows the light go through
characters and icons only, not the background. The total number of colors ranges from one to three in addition to the black matrix. Customers can select the color for each
segment. No bleaching of colors is observed even when operating at 80 C, ideal for automotive and other outdoor applications. Displays from static to 1/8 multiplex are available.
Black mask is used to mask off non- switching areas in alpha-numeric segment displays. The purpose is to improve contrast and readability. This way, a stronger backlight can
SURFACE MOUNT TECHNOLOGY (SMT)
Surface Mounting Technology (SMT) using quad flat packages on printed circuit boards was the most popular at the early years of liquid crystal display industry, and is still
available for mass production. Plastic Quad Flat Package (QFP) represents itself as a flat rectangular integrated circuit package with its leads projecting from all four sides of
the package without radius. Used with surface mounting method. Made of black epoxy resin. Very moisture absorbent.
Chip-on-Board (COB) is a popular IC mounting method that provides wire bonding as the direct attachment of bare die to laminated printed circuit boards. The LCD driver is
formatted into an area on the PCB. Electrical connections are made by micro diameter gold wires. The entire area is then covered with epoxy. All standard Character LCD
modules are of the Chip-On-Board design.
Chip-On-Glass จC is one of the high-tech mounting methods that uses Gold Bump or Flip Chip ICกฏs, and implemented in most compact applications. Chip-On-Glass integrated
circuits were first introduced by Epson. In flip-chip mounting, the IC chip is not packaged but is mounted directly onto the PCB as a bare chip. Because there is no package,
the mounted footprint of the IC can be minimized, along with the required size of the PCB. This technology reduces a mounting area and is better suited to handling high-speed
or high-frequency signals. Currently, there are 12 standard C.O.G. LCD modules available with the regular mass production delivery time.
mounting method finding its applications in many other equipment than cellular phones, PDA's, computer network servers, satellite receivers, etc.
TAPE AUTOMATED BONDING (TAB)
Tape Automated Bonding (TAB) LCD driver or controller electronics are encapsulated in a thin, hard bubble package, of which the drive leads extend from the bubble package
on a thin plastic substrate. The adhesive along the edges is used to attach the TAB to the LCD glass and/or PCB.
Tape Automated Bonding IC mounting method uses the same type of integrated circuits as Chip-On-Glass technology - Gold Bumped Flip Chips. After this type IC chip has
been produced, we a gold bump is placed on the IC chip and then sealed onto the polymide board. (This procedure is called ILB or Inner Lead Bonding) and is how the TCP
IC is produced. TAB LCD modules are always custom made from us.