LCD TECHNOLOGY OVERVIEW

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LCD TECHNOLOGY OVERVIEW
C O N T E N T S TN STN FSTN DOUBLE STN ECB COLOR
(F)STN MULTI-COLOR TN SURFACE MOUNT
TECHNOLOGY CHIP-ON-BOARD CHIP-ON-GLASS TAPE
AUTOMATED BONDING BACKLIGHTING INTERFACE TEMPERATU
RE RANGES
Tianma Microelectronics (USA) Inc.
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TN
TN Twisted Nematic. A type of liquid crystal
whereas the alignment surface and therefore the
LC molecules are oriented 90 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.
FEATURES Backgrounds Black, White Viewing
Angle 45 degrees (typical) Multiplex Ratio up
to 641 (segments / commons) Most inexpensive
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STN
STN 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 (200 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.
FEATURES Backgrounds Yellow-Green, Gray,
Blue Viewing Angle 75 (typical), 90 (maximum)
degrees Multiplex Ratio up to 4801 (segments
/ commons) Response Time 150 msec (lower than
TN) Suitable for Graphic applications
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FSTN
FSTN 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.
FEATURES Backgrounds Black, White Viewing
Angle 80 degrees (typical) Multiplex Ratio up
to 4801 (segments / commons) Response Time
150 msec (lower than TN)
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DSTN
DSTN, developed by Sharp Corporation, 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. There are only a few
manufacturers that offer this technology Tianma,
Optrex, Hyundai, URT, Varitronix and CFG. Here is
an overview of DSTN technology by different
criteria Contrast better than STN, FSTN offers
automatic contrast compensation with
temperature. Response Time significantly
enhanced. Optical Cast DSTN reduces the tendency
of a screen to be slightly red, green or
blue. Viewing Angle combination of 6 and 12
oclock optimal viewing directions
together Temperature Range -30 to 80 C
operating, -40 to 90 C storage Polarizer Mode
Negative, so DSTN LCDs need backlighting Back
Light CCFL or LED only Resolution up to 122 x
32 dots Suitable Applications Automobiles,
Gasoline Pumps, etc. Always custom designed

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ECB
Electronically Controlled Birefringence (ECB) or
Vertically Aligned Nematic (VAN) is a
electro-optical effect that was first described
in 1971. Through this effect a number of distinct
colors can be displayed in a LCD. The ECB mode
color displays are realized by controlling both
the birefringence of liquid crystals and a pair
of optimizing polarizers with retardation films,
which are brought from operating voltage rate
impressed to liquid crystal layer and inclination
of liquid crystal molecules. Thus, the wavelength
of light exciting a pixel is determined by the
voltage applied to that pixel. Almost every
other LCD manufacturer offers this technology
today.
Features of ECB Color LCD Modules Low power
consumption Under most lighting conditions, no
backlight is required which saves the highest
power-consuming element of the display. Simple
drive electronics The single pixel for all four
colors requires only one set on common and
segment drivers. This also reduces the connector
pitch, the cost, and complexity of the
assembly. No color filters Reflective operation
is possible in most environments. Color filters
add cost and require a backlight to provide
enough illumination to overcome the loss of a
given pixel. Low cost The reduced electronics
and lack of filters make the module significantly
lower in cost comparatively with passive color
STN modules. Response Time about 250 msec
(low) Low Transmission about 1.5 to 20
Applications Gaming, etc. Being very sensitive
to extreme temperatures and responsively slow,
ECB technology is not suitable for the automotive
industry or video applications. Always custom
designed.
TYPES OF ECB PRODUCT
STN multiple colors on green background FSTN
multiple colors on pale background
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MULTI-COLOR TN
The newly developed Selective Multi-Color TN LCD
technology is offered only by Tianma, Optrex, and
Varitronix. 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 be used.

• Advantages
• Allows a limited number of colors that are not
  subjected to change
• Less parallax and durability problems compared to
  most conventional designs available on the market
• Resistant to wide range temperatures (-30 to 80
  C operating )
• Inexpensive (TN technology has become
  conventional almost 30 years ago)
• Applications high quality audio and car
  displays, etc.

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IC MOUNTING TECHNOLOGIES
IC COMPARISON
Tianma Microelectronics implements a variety
of integrated circuit mounting methods in designs
of printed circuit boards used with standard and
custom made liquid crystal modules. Tianma has
full production capabilities that incorporate
design requirements for the following IC mounting
technologies Surface Mounting Technology
(SMT) Tape Automated Bonding (TAB) Chip-On-Board
(COB) Chip-On-Glass (COG) During the days of
high demand of integrated circuit components on
the LCD market, Tianma Microelectronics manages
to keep firm control of receiving IC supplies
from contractors. Despite the shortage of
micro-controllers and drivers in the LCD
industry, it is entirely within Tianma
Microelectronics capabilities to provide its
customers with large quantities of high quality
electronic chips supporting the present product
line.
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SURFACE MOUNT TECHNOLOGY (SMT)
QUAD FLAT PACKAGE
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.
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CHIP-ON-BOARD (COB)
BARE DIE

• 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 of Tianmas
  standard Character LCD modules are of the
  Chip-On-Board design.
• Advantages
• Very compact
• Space savings over Surface Mount Technology
  assembly.
• Cost savvy comparatively with SMT, since there
  is no plastic package.

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CHIP-ON-GLASS (COG)
Chip-On-Glass is one of the high-tech mounting
methods that uses Gold Bump or Flip Chip ICs,
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 3
standard C.O.G. LCD modules available at Tianma
with the regular mass production delivery
time. Advantages 1. Very space economical.
Chip-On-Glass LCD modules can be as thin as 2
mm. 2. Cost effective over COB, especially in
graphic LCD modules, because much less IC's are
required. 3. More reliable than TAB because of
the weakness in the bond area of TAB.
Disadvantages 1. COG can only be used at a
certain resolution level where the lines are not
too fine. At very fine pitches COG becomes
difficult to test, and TAB is the preferred
approach. 2. It may be more cost-effective to
use TAB or COB, if a designer has to integrate a
keypad or indicator around the display. 3. The
active area is not centered within the outline
but offset, because of the area where the
circuits are. Since the Chip-On-Glass
integrated circuit has been invented by Epson,
COG technology became very popular due to the
demand for more compact applications. In the near
future we will see this IC mounting method
finding its applications in many other equipment
than cellular phones, PDA's, computer network
servers, satellite receivers, etc. This
year Tianma Microelectronics is going to announce
7 standard Chip-On-Glass LCD modules available
for the regular product lead time.
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TAPE AUTOMATED BONDING (TAB)
TAPE CARRIER PACKAGE

• 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 Tianma.
• Advantages
• Offers compactness (IC and its interfacing
  circuitry can be bent behind the LCD glass
  panel).
• Some times more cost-effective than
  Chip-On-Glass, if a designer has to integrate a
  keypad or indicator around the display.
• The active area is centered (differently from
  COG).
• Can provide interfacing at very fine pitches.
• Disadvantages
• The bonding area is weak. Less reliable than
  COG.
• More expensive than COG. Even though TAB LCD
  modules use the same type of IC as COG, tape
  automated bonding requires a package.

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• LED (Light-Emitting Diode) - Consists of surface
  mount LEDs, which are situated in series along
  the bottom of a shallow plastic tray.
• Features
• Available Colors Yellow-Green (standard), Red,
  Amber, Green, Blue, White
• Life time long, typically 50,000 hours
• Operating temperature range -30 to 70 degrees C
• Requires low voltage DC. No DC/AC inverter
  required
• Simple connection 5 VDC (Anode) and ground
  (Cathode)
• Two methods matrix (array)or edge lighting
• The typical voltage for all standard LED versions
  of LCE modules is 4.2 VDC.

• EL ( Electro Luminescent) - A thin membrane
  consisting of two coated electrode plates with an
  aluminum reflector. When AC voltage is applied to
  the electrodes, the electrons collide with the
  light emission core. The energy given off is
  light. Inverter (DC to AC) is used to power
  electro luminescent lamps.
• Features
• Available Colors White (standard), Blue,
  Yellow-Green
• Service Life 4000 hours (driven with inverter,
  20 C temp, and 70 humidity) and 1500 hours
  (driven with a fixed power supply and frequency
  generator, 20 C temp, and 70 humidity)
• Operating temperature range -20 to 50 degrees C

TYPES OF LCD BACK LIGHT

• CCFL (Cold Cathode Fluorescent Lamp) - A
  miniature high voltage cold cathode (field
  emission) lamp made of lead-glass with mercury
  inside that provides fluorescent back lighting or
  edge lighting . Uses a diffusing light guide.
  High brightness, high efficiency and
  vibration-proof.
• Features
• Available Colors White (standard)
• Life time 15,000 20,000 hours
• Operating temperature range -20 to 50 degrees C
• Low power consumption and excellent lighting
  characteristics
• Easy intensity control
• Low heat generation and thin diameter lamps

• FIBER OPTIC - Fiber optics are flattened and
  then sandwiched between two pieces of pliable
  plastic. The top piece is used as the diffuser.
  The opposite ends are tied into a coupler, which
  is connected to an LED or Halogen light source.
• Features
• Available Colors White, Green, Blue, Amber and
  Red
• Life time long, remote light source offers
  10,000 to 100,000 hours life and easy
  replacement.
• Operating temperature range (optical fibers) -40
  to 85 degrees C
• Low power consumption. Sources require less power
  than EL, CCFL, or LED Array and no inverter. As
  low as 10-20mA at 2vdc
• Compact, panels are thin and sources are smaller
  than EL or CCFL inverters
• Heat free, adds no heat or EMI to interfere with
  switch operation
• Very durable. Optical Fibers are not affected by
  extremes in humidity (0 to 100) and temperature
  

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FFC (Flexible Flat Cable) - cable with two smooth
or corrugated, but essentially flat, surfaces.
Attached to the PCB by soldering or plugging into
a zero insertion force connector. Very reliable.
FPC (Flexible Print Circuit) is a circuit
substrate of patterning Cu electrode with
Polyimide film as a base. Usually offers more
flexibility than Flexible Flat Cables.
Heat Seal - consists of microscopic metal
particles within the Hot Melt Adhesive covering
the entire area. Very flexible and eligible for
connecting a large number of terminals
simultaneously by single sealing operation.
TYPES OF CONNECTORS
Pins - allow self-aligning connection to printed
circuit boards via plug in strip sockets. Work
well in harsh environments. Two conventional
methods DIL (Dual-In-Line) and SIL
(Single-In-Line).
Zebra Strips or Elastomeric - strips of
silicone rubber made up of sequentially spaced
conductive and non-conductive material. This is
the most common connection method for complete
LCD modules. Resistant to shock and vibration.
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TEMPERATURE CHARACTERISTICS
TN MODULES
STN MODULES
OPERATING
OPERATING
STORAGE
STORAGE
NORMAL RANGE
NORMAL RANGE
0 50
0 50
-20 60
-20 60
WIDE RANGE
WIDE RANGE
-20 70
-20 70
-30 80
-30 80
STN PANELS
TN PANELS
OPERATING
OPERATING
STORAGE
STORAGE
NORMAL RANGE
NORMAL RANGE
0 50
-20 60
0 50
-20 60
-20 70
-10 60
-20 70
-30 80
WIDE RANGE
WIDE RANGE
-20 70
-30 80
-30 85
-40 90
-30 80
-40 90
The above numbers are in C.