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What
is a Liquid Crystal Display?
Why are Liquid Crystal Displays important?
What type of technologies are used to display
letters, numbers and graphics on a LCD?
What are the types of fluids most commonly used in
LCDs?
What is
Twisted Nematics?
What is
Super Twisted Nematics?
What is Film Compensated Super Twisted Nematics?
When referring to LCD technology what is referred to
a viewing angle?
How TN, STN, and FSTN technologies are compare in
contrast ratio, viewing angle, and cost?
What are the three primary Polarization Types in LCD
technology?
Where is Reflective technology found?
Where is Transmissive technology found?
Where is Transflective technology found?
What are the differences between Reflective,
Transflective, and Transmissive displays?
What is
Backlighting?
What is EL (Electroluminescent Lamp)?
What is LED (Light Emitting Diode)?
What is CCFL (Cold Cathode Fluorescent Lamp)?
What are the characteristics of LED, EL, and CCFL
backlight versions?
How are the pixels turned on and off in order to
create an image on the LCD?
What types of techniques are used in LCD technology
to produce color displays?
Do computers use
LCDs?
What is the definition of a Duty Rate?
What is the definition of Bias Ratio?
What types of interfaces are available on a single
chip LCD Controller/Driver IC?
What are the differences between a Driver IC, a
Controller IC and a Controller/Driver IC?
What is
Contrast Ratio?
What is
meant by Chip-On-Board?
What is
meant by Chip-On-Glass?
What is
meant by Chip-On-Flex?
What is the space containing liquid crystal fluid
between two pieces of glass called?
What is used to protect the edges of the glass and
to act as a pressure device, compressing the
elastomeric connector between the PCB and LCD glass?
What is meant by Direct/Static Drives?
What is the most common method of connection for LCD
modules?
What happens when excess DC voltage is applied to an
LCD?
What is meant by DC to AC Inverter?
What is
a Zebra (R) Connector?
What is meant by the "rainbow effect" in LCDs?
Q:
What is a Liquid Crystal Display?
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A: A liquid crystal display consists of an
array of tiny crystals which can be manipulated to
present data, such as, letters, numbers and even
graphics.
Q: Why are Liquid Crystal Displays important?
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A: There are two factors why liquid crystals are
important they are size and weight. A LCD consists
primarily of two glass plates with liquid crystal
material between them. There is no need for bulky
picture tubes in order to display images.
Q: What type of technologies are used to display
letters, numbers and graphics on a LCD?
A: Displaying letters, numbers and graphics are
based on the following three display methods.
Segment system: The display units are arranged to
form a figure "8" to display numbers and letters.
Dot matrix system (Character Display): The display
units are arranged in Rows and Columns to form
characters.
Dot matrix system (Graphic Display): The display
units are arranged in rows and columns to depict
graphics.
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Q: What are the types of fluids most commonly used
in LCDs?
A: There are many types of LCD fluids on the market.
However TN, STN, and FSTN are more commonly used.
TN (Twisted Nematics)
STN (Super Twisted Nematics)
FSTN (Film Compensated Super Twist Nematics)
Q: What is
Twisted Nematics?
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A: Twisted Nematics (TN) was one of the earlier
fluid technology that was implemented in LCDs TN
type displays are primarily used in digital
calculators, digital wristwatches, digital clocks
and in some Caller ID boxes.
Twisted Nematic uses a 90-degree twist to the
molecules between one alignment layer and the other.
A good example of this is fluid being used is in the
meter that displays your cost and gallons pumped at
the gas station. Gas stations screens are clear and
legible from almost any position.
Q:
What is Super Twisted Nematics?
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A: Super twist nematics (STN) has the most options
and features. It offers better viewing angles than
the TN technology. The most common use for this type
of technology can found on vending machines,
portable bar code scanners, hospital equipment, PC
storage devices, etc.
STN is ideal for dot matrix formatted displays, both
character and graphics based. Super Twisted Nematic
displays improve on the more common TN screens by
increasing the rotation of the molecules in their
off state to over 260 degrees. This brings a higher
contrast ratio to larger screens.
Q: What is Film Compensated Super Twisted Nematics?
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A: Film Compensated Super Twisted Neumatic (FSTN) is
the fluid technology that provides the best contrast
ratio, the best viewing angle, and the most
expensive. More companies are now using this type of
fluid for their products.
The major reason why this fluid has a better
contrast ratio than the STN, is its ability to offer
a much lighter color background and darker pixels
than the STN fluid.
Q: When referring to LCD technology what is referred
to a viewing angle?
A: A viewing angle is the direction in which the
display will look its best. Viewing directions are
specified in terms of a clock position, see below:
East 3 O'clock
South 6 O'clock
West 9 O'clock
North 12 O'clock
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Q: How are TN, STN, and FSTN technologies compare in
contrast ratio, viewing angle, and cost?
A: Note:
A = Best and most expensive
B = Good and medium expensive
C = Worst and least expensive
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Q: What are the three primary Polarization Types in
LCD technology?
A: The three primary types of display polarization
technologies are:
Reflective
Transmissive
Transflective
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to top
Q:
Where is Reflective technology found?
A: Reflective technology is most commonly found on
calculators and some inexpensive digital
wristwatches. Since Liquid Crystal Displays are
non-emissive type of displays this means that they
do not generate their own light source, they rely on
an external light source. The light source might be
using the sun, a current ambient light in order to
see the characters on the display.
So, when a display is "Reflective" it means that is
needs to have a light source in front of the display
in order for you to read the display.
Q: Where is Transmissive technology found?
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A: Transmissive technology is the opposite of the
Reflective technology. Transmissive technology can
be found in Medical devices, test and measurement
instruments, automotive audio, laptop computers etc.
This technology requires a backlight in order to see
the characters. In addition, most transmissive
displays are negative mode, meaning that the text
will be a light color and the background of the
display is dark colored.
With this technology, the light source must be
behind the LCD panel, so that the light shines
through the display and the pixels that are
activated, this will allow the light to pass.
Q: Where is Transflective technology found?
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A: Transflective technology is probably the most
commonly used polarization types in LCDs. Most
cellular phones, PDA, GPS, etc. use this type of
polarization.
Transflective is a type of backing, bonded to the
rear polarizer, which enables light to pass through
the back as well as reflecting light from the front.
Q: What are the differences between Reflective,
Transflective, and Transmissive displays?
A: Reflective displays include a diffuser, this
layer reflects the light that enters the front of
the display. Reflective displays require ambient
light for the light source since there is no
backlight.
Transflective displays have a type of backlighting
which is bonded to the rear polarizer. This enables
light to pass through the back, as well as
reflecting light from the front.
Transmissive displays do not have reflectors or
transflectors laminated to the rear polarizer. A
backlight must be used with this type of LCD
configuration.
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to top
Q: What is
Backlighting?
A: Backlighting is a technique used to make LCD
easier to read. A backlit display is illuminated so
that the foreground appears sharper in contrast with
the background.
There are three common backlight technologies for
the LCD:
EL (Electroluminiscent Lamp)
LED (Light Emitting Diode)
CCFL (Cold Cathode Fluorescent Lamp)
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to top
Q:
What is EL (Electroluminiscent Lamp)?
A: The EL (Electroluminiscent Lamp) backlight is
very thin and offers a uniform light source. EL is
popular due to its relative low cost, as compared to
the other backlight sources
Although the EL has some great benefits, there are
some drawbacks to its technology. The EL does not
perform very well under high humidity conditions.
When the display is subject to high humidity, the EL
begins to delaminate and starts to malfunction.
Another problems with the EL include the need to
have a DC to AC converter also known as an inverter.
Q: What is LED (Light Emitting Diode)?
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A: LED (Light Emitting Diode) is the most commonly
used backlight for Cellular phones. The LED
backlight offers some benefits over the EL
backlight. To start, the LED backlight does not
require an inverter, just a DC source of
+3VDC~+5VDC. Secondly, depending on the backlight
configuration, the brightness can very bright, and
thirdly, the life of the LED exceeds 50K hours.
Q: What is CCFL (Cold Cathode Fluorescent Lamp)?
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A: This type of light source is most common in
graphics and color displays. It provides a uniform
and bright white light. A common application that
would use a CCFL backlight is a Laptop computer.
Some other applications that use this type of
backlight include, gas pumps, medical instruments,
industrial PCs, etc.
The CCFL has a drawback that is similar to the EL
backlight it also needs a DC-AC Inverter. Though not
the same type as the EL, the CCFL inverter needs to
generate more voltage than those used for the EL. A
typical EL inverter outputs 120VAC @400Hz, whereas
the CCFL Inverter needs to output 1000VAC @
30kHz~40kHz.
Q: How are the pixels turned on and off in order to
create an image on the LCD?
A: Addressing is the process by which pixels are
turned on and off in order to create an image. There
are two main types of display addressing:
Direct Addressing
Multiplex Addressing
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Q: What types of techniques are used in LCD
technology to produce color displays?
A: Color LCD use two basic techniques for producing
color. The technologies are Passive Matrix and Thin
Film Transistors (TFT) often referred as Active
Matrix. Passive Matrix is the less expensive of the
two technologies. TFT or Active Matrix produces
color images that are as sharp as traditional CRT
displays, but the technology is expensive.
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to top
Q: Do
computers use LCDs?
A: Yes, computers use two main types of LCDs; they
are Passive and Active Matrix often referred as thin
Film Transistors (TFT).
Q: What is the definition of a Duty Rate?
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A: A Duty Rate is also known as multiplex rate, this
is the fraction of the total frame time that each
row of the LCD is addressed.
Q:
What is the definition of Bias Ratio?
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A: Bias Ratio of an LCD is also known as the Voltage
margin and is defined as the ratio of V on (voltage
on pixels that are currently addressed to the
ON-state) divided by V off (voltage on pixels that
are not currently addressed).
Q: What types of interfaces are available on a
single chip LCD Controller/Driver IC?
A: Almost all LCD single-chip controllers can be
interfaced by an 8-bit, 4-bit, or 1-bit interface.
Q: What are the differences between a Driver IC, a
Controller IC and a Controller/Driver IC?
A: There are two types of Driver IC's, Common
Drivers and Segment Drivers. Common Drivers output
signals to create the rows or numbers of lines. The
Segment Drivers output the necessary signals to
create the characters or columns.
The Controller IC receives data written in ASCII or
JIS code from the MPU and stores this data in RAM.
This data is then converted into serial character
patterns and transferred to the LCD driver IC.
Drive/Controller IC is probably the most commonly
found in a graphics module. This IC receives data
from the MPU and stores it in RAM. Also, it accepts
commands directly from the MPU for both the common
and segment drivers.
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to top
Q: What is
Contrast Ratio?
A: Contrast Ratio is the ratio of brightness or
luminance of the pixel to the background.
Q:
What is meant by Chip-On-Board?
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A: Chip-On-Board is when the LCD driver wafer is
mounted on the PCB with gold wires to connect it to
other circuits. Also, it is covered with epoxy.
Q:
What is meant by Chip-On-Glass?
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A: Chip-On-Glass is a new technology that mounts the
LCD driver to the contact edge of the LCD glass.
Q:
What is meant by Chip-On-Flex?
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top
A: Chip-On-Flex is when the contact edge of the LCD
glass is mounted to a flex connector that
incorporates an LCD driver.
Q: What is the space containing liquid crystal fluid
between two pieces of glass called?
A: It is the Cell Gap.
Q:
What is used to protect the edges of the glass and
to act as a pressure device, compressing the
elastomer connector between the PCB and LCD glass?
A: A Bezel which is a frame of plastic metal.
Q: What is meant by Direct/Static Drives?
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A: It is the method in which each conductive lead on
the contact edge connects to one segment or
annunciator (a word, phrase, or symbol; an active
element)
Q: What is the most common method of connection for
LCD modules?
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A: The most common method of connection for LCD is
the Elastomer Connector, which is a silicone rubber
strip made up of sequentially spaced conductive and
non-conductive material.
Q: What happens when excess DC voltage is applied to
an LCD?
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A: A dead short is created. Conductive particles
from one piece of glass are transferred through the
liquid crystal fluid and deposited on the conductive
surface of the opposite piece of glass.
Q: What is meant by DC to AC Inverter?
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A: This type of Inverter converts DC to AC at a high
frequency, and powers electroluminescent lamps.
Q:
What is a Zebra (R) Connector?
->back to top
A: Same as a elastomeric connector.
Q: What is meant by the "rainbow effect" in LCDs?
->back to top
A: The term "rainbow effect" refers to a red and
green circle or rainbow on the LCD glass. The LCD
panel under uneven pressure causes this problem from
the bezel. This problem is very common in LCD
modules and normally it will not affect the
performance or the appearance of the display when
operational. |
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LCD Module
Character
LCD Module
Graphic LCD Module
TFT-LCD Module |
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