Thread: FAQ: LCD Technologies

more info from that site that contributes to the faq

Precautions for Handling LCD Modules

LCMs have been assembled and adjusted before delivery; therefore, observe the following procedures for handling:

1. Do not subject to excessive shock by dropping the units.
2. Do not modify or adjust the tab of the metal bezel.
3. Do not modify the printed circuit board.
4. Limit the soldering to the printed circuit board to only the I / O terminals.
5. Do not touch the connective rubber ( inter-connector ), or modify its location.

Warning for Static Electricity
LCMs use CMOS LSI. Therefore, measures to protect static electricity have been taken through all the processes from manufacturing to shipping. When handling, take necessary care to prevent static electricity as you would any CMOS IC.

• Do not take LCM from its anti-static bag until it is time to assemble: LCMs are individually packaged in bags treated to resist static electricity. An LCM should not be removed from the bag until it is time to solder the terminals. When storing the LCMs keep them packaged in the anti-static bags, or a container that is resistant to static electricity, or in an electric conductive container.
• Always use a body ground when handing an LCM: Always apply grounding to your body while you are working with an LCM from the time it is taken out of the anti-static bag until it is assembled. When it is necessary to handle the LCM, once it is taken out of the bag, always place it in a electric conductive container. Avoid wearing clothes of chemical fiber. Cotton or conductive treated fiber clothes are recommended.
• Use a no-leak soldering iron: The soldering iron used for soldering the I/ O terminals of the LCM should be insulated at the iron tip or grounded on the iron tip.
• An electrical apparatus is always required for assembly: When the LCM is to be assembled with an electrical apparatus, this assembly should be grounded to avoid transmitting spike noise generated with the motor rotating.
• Make the operation bench equal to the ground When the operation bench is grounded with an aluminum or steel plate, there is always the possibility of an electric shock being generated, when the impedance is too low. It is therefore recommended that an electric conductive (rubber) mat be used.
• Peel off the LCM protective film slowly: To the face of the LCM is a film to protect the display surface from contamination, flaw, adhesion of flux, etc. Peeling off this film too abruptly may cause static electricity to be generated. Thus peel off the tape slowly.
• Attention should be paid to humidity: 50~60%RH is acceptable.

Precautions For Soldering The LCM
The following procedures should be followed when soldering the LCM:

• Solder is to be applied only to the I / O terminals.
• Use a soldering iron with no leakage.

In addition, further attention should be paid to the following.

• Conditions for soldering I / O terminals:
  Temperature at iron tip: 280oC + 10oC
  Soldering time: 3-4 sec. / terminal
  Type of solder: Eutectic solder ( rosin flux filled )
  Avoid using flux, since it may penetrate the LCM and could possibly cause contamination.
  When cleaning is required do not remove the protective film until after soldering the I / O terminals has been completed. This will eliminate contamination with by the dispersion of flux where soldering.
• Removing the wiring:
  When a lead wire or a connector that has been soldered to the I / O terminals of the LCM is to be removed , do so only after the solder at the connection has sufficiently melted. If this wire or connector is forcefully removed, it may cause the terminal to break or peel. It is recommended that a suction-type soldering iron be used. Do not attempt to solder a lead wire or connector for more than 3 times to a given LCM.

Long-Term Storage
When long-term storage of an LCM is necessary, the following procedures should be complied with: If not stored properly, it could cause deterioration of the polarizer and oxidation of the I/O terminals that would make soldering more difficult.

1. Store in original packaging if possible.
2. For individual LCMs, place them in anti-static bags, sealing the opening and storing it where it is not subject to direct sunlight or the light from a fluorescent light.
3. Store in a temperature range of 0oC ~35oC with low humidity. Note, refer to the specific module specification for requirements regarding storage temperature and humidity.

Excess Current Protection
An over current protection circuit is not provided with the LCM. Therefore, it is recommended to use an electrical source which will provide for this current protection.

Precautions for using LCDs
Prevent external shock.
Do not wipe the surface of the LCD with hard materials.
Do not apply excessive force on the surface of the LCD.
Do not apply DC voltage.
Do not expose to direct sunlight or fluorescent light for extended periods.
Avoid storage in high temperature and humidity. (When storage for an extended period at 40oC or higher, R/H should be less than 60%)
The fluid within the LCD is hazardous. Do not permit this liquid to come into contact with the eyes or mouth area.

This site has a nice graphic describing the differences

Transmissive type TFT LCD contains a backlight where light travels from the backlight through color filter and LC then appears on the panel. The main advantage of this type of display is it's high brightness. However the brighter the light the higher the electric load consumed. Reflective type TFT LCD contains a reflective mirror, utilizing the external light for image display. The main advantage of this type of display includes it's power saving, and light-weight (without backlight) characteristics. However this type of display is more ideal for viewing with external light sources

and this one has a nice graphic showing how most backlights work these days using phlatlight

PhlatLight technology, combined with GLT's patented MicroLens light guides, enable large-size LCD panels to be edge-lit, as opposed to direct backlighting. The result is dramatically reduced LED count, and simplified color and thermal management compared to conventional LED-based backlighting solutions

And this post wouldn't be complete without a link to wikipedia...hopefully they get more info on the subjects

LCD
TFT LCD
Transflective
Anti-reflective

The last thing I found tonight was a nice little flash of how they are made:
http://www.auo.com/auoDEV/content/te...s_popup_en.htm

http://www.stealthcomputer.com/faq_lcd_technology.htm

The four most common touch screen technologies include resistive, infrared, capacitive and SAW (surface acoustic wave). Each technology offers its own unique advantages and disadvantages as described below. Resistive and capacitive touch screen technologies are the most popular for industrial applications. They are both very reliable. If the application requires that operators can wear gloves when using the touch screen, then we generally recommend the resistive technology (capacitive doesn't support). Otherwise the capacitive technology (better optical characteristics) is more often recommended.

Resistive
A resistive touch screen typically uses a display overlay consisting of layers, each with a conductive coating on the inner surface. The conductive inner layers are separated by special separator dots, evenly distributed across the active area. Finger pressure causes internal electrical contact at the point of touch, supplying the electronic interface (touch screen controller) with vertical and horizontal analog voltages for digitization. For CRT applications, resistive touch screens are generally spherical (curved) to match the CRT and minimize parallax. The nature of the material used for curved (spherical) applications limits light throughput such that two options are offered: Polished (clear) or antiglare. The polished choice offers clarity but includes some glare. The antiglare choice will minimize glare, but will also slightly diffuse the light throughput (image). Either choice will demonstrate either more glare (polished) or more light diffusion (antiglare) than associated with typical non-touch screen displays. Despite the tradeoffs, the resistive touch screen technology remains a popular choice, often because it can be operated while wearing gloves (unlike capacitive technology). Note that resistive touch screen materials used for flat panel touch screens are different and demonstrate much better optical clarity (even with antiglare). The resistive technology is far more common for flat panel applications.

Capacitive
A capacitive touch screen includes an overlay made of glass with a coating of capacitive (charge storing) material deposited electrically over its surface. Oscillator circuits located at corners of the glass overlay will each measure the capacitance of a person touching the overlay. Each oscillator will vary in frequency according to where a person touches the overlay. A touch screen controller measures the frequency changes to determine the X and Y coordinates of the touch. Because the capacitive coating is even harder than the glass it is applied to, it is very resistant to scratches from (SIC) sharp objects. It can even resist damage from sparks. A capacitive touch screen cannot be activated while wearing most types of gloves (non-conductive).

Infrared
An infrared touch screen surrounds the face of the display with a bezel of light emitting-diodes (LEDs) and diametrically opposing phototransistor detectors. The controller circuitry directs a sequence of pulses to the LED's, scanning the screen with an invisible lattice of infrared light beams just in front of the surface. The controller circuitry then detects input at the location where the light beams become obstructed by any solid object. The infrared frame housing the transmitters can impose design constraints on operator interface products.

SAW (Surface Acoustic Wave)
A SAW touch screen uses a solid glass display overlay for the touch sensor. Two surface acoustic (sound) waves, inaudible to the human ear, are transmitted across the surface of the glass sensor, one for vertical detection and one for horizontal detection. Each wave is spread across the screen by bouncing off reflector arrays along the edges of the overlay. Two receivers detect the waves, one for each axis. Since the velocity of the acoustic wave through glass is known and the size of the overlay is fixed, the arrival time of the waves at the respective receivers is known. When the user touches the glass surface, the water content of the user's finger absorbs some of the energy of the acoustic wave, weakening it. The controller circuitry measures the time at which the received amplitude dips to determine the X and Y coordinates of the touch location. In addition to the X and Y coordinates, SAW technology can also provide Z axis (depth) information. The harder the user presses against the screen, the more energy the finger will absorb, and the greater will be the dip in signal strength. The signal strength is then measured by the controller to provide the Z axis information. Today, few software applications are designed to make use of this feature.

What is a NIT?
A NIT is a measurement of light in candelas per meter square (Cd/m2)
For an LCD monitor it is brightness out of the front panel of the display. A NIT is a good basic reference when comparing brightness from monitor to monitor. Most desktop LCD's or Notebook LCD's have a brightness of 200 to 250 Nits. These standard LCD's are not readable in direct or even indirect sunlight as they become washed out.

How do I know how many NIT's I require for my application?
Applications will vary depending on the location of the LCD and how much ambient light is available that could cause the display to become washed out or unreadable. As a rule of thumb; notebooks and desktop LCD's which are generally used in office light conditions are in the 200-250 nit range. For indoor use with uncontrolled or indirect sunlight it is recommended that a display of 500 - 900 nits be used. If the application is outdoors or in direct sunlight then at least 1000 nits and up should be considered.

What is considered a true sunlight readable or outdoor readable LCD?
First, the display screen on a sunlight readable/outdoor readable LCD should be bright enough so that the display is visible in direct or strong sunlight. Second, the display contrast ratio must be maintained at 5 to 1 or higher.

Although a display with less than 500 nits screen brightness and a mere 2 to 1 contrast ratio can be read in outdoor environments, the quality of the display will be dreadfully poor and not get the desired information across effectivley. A true sunlight readable display is normally considered to be an LCD with at least 1000 nits of screen brightness and a contrast ratio greater than 5 to 1. In outdoor environments under the shade, such a display can provide an excellent image quality.

What is Luminance?
Luminance is the scientific term for "Photopic Brightness" which specifies the visual brightness of an object. In layman's terms, it is commonly referred to as "brightness". Luminance is specified in candelas per square meter (Cd/m2) or nits. In the US, the British unit Foot-lamberts (fL) is also frequently used. To convert from fL to nits, multiply the number in fL by 3.426 (i.e. 1 fL = 3.426 nits).

Luminance is an influential factor of perceived picture quality in an LCD. The importance of luminance is enhanced by the fact that humans will react more positively to a brightly illuminated screen. In indoor environments, a standard active-matrix LCD with a screen luminance of around 250 nits will look good. In the same scenario an LCD with a luminance of 1,000 nits or more will look utterly captivating.

What is Contrast Ratio (CR)?
Contrast ratio (CR) is the ratio of luminance between the brightest "white" and the darkest "black" that can be produced on a display. CR is another influence of perceived picture quality. If a picture has high CR, you will consider it to be sharper and crisper than a picture with lower CR. For example, a typical newspaper picture has a CR of about 5 to 7, whereas a high quality magazine picture has a CR that is greater than 15. Therefore, the magazine picture will look better even if the resolution is the same as that of the newspaper picture.

A typical AMLCD exhibits a CR of approximately 300 to 700 when measured in a dark room. The CR on the same unit measured under ambient illumination is drastically lowered due to surface reflection (glare). For example, a standard 200 nit LCD measured in a dark room has a 300 CR, but will have less than a 2.0 CR under intense direct sunlight. This is due to the fact that surface glare increases the luminance by over 200 nits both on the "white" and the "black" that are produced on the display screen. The result is the luminance of the white is slightly over 400 nits, and the luminance of the black is over 200 nits. The CR ratio then becomes less than 2 and the picture quality is drastically reduce and not acceptable.

What is a Viewing Angle and why does it matter?
The viewing angle is the angle at which the image quality of an LCD degrades and becomes unacceptable for the intended application. Viewing angles are usually quoted in horizontal and vertical degrees with importance dependent on the specific application. As the observer physically moves to the sides of the LCD, the images will degrade in three ways. First, the luminance drops. Second, the contrast ratio usually drops off at large angles. Third, the colors may shift. Most modern LCD's have acceptable viewing angles even for viewing from the sides.

For LCD's used in outdoor applications, defining the viewing angle based on CR alone is not adequate. Under very bright ambient light conditions the display is hardly visible when the screen luminance drops below 200 nits. Therefore, the viewing angles are defined based on both the CR and the Luminance.

some info cut from source to fit post limit

a very good site for lcd info is here

they have an awesome table that shows the differences of the following types of lcds in an easy to read format

• TN (Twisted Nematic): Without Overdrive, this type of panel offers the fastest pixel response time. This does however come at the expensive of viewing angles and color fidelity. Out of all TFT-LCD panels, the TN type has the lowest contrast. It is also a 6-bit color depth panel, meaning dithering or frame rate control (FRC) must be employed to reach close to a full 8-bit depth. Pixels in their active state on a TN are black, while in their inactive, white.
• (P-)MVA ({Premium} Multidomain Vertical Alignment): The liquid crystal (LC) cells on MVA panels are in their active state white, and in inactive black and are separated into four domains. This slightly improves viewing angle over TN-type displays (MVAs provide ~45 degrees). MVA panels also provide a high contrast ratio. Grayscale inversion is minimal on these displays. Response time is the second slowest in the industry without ODCs. MVAs and all derivatives hide details at a perpendicular viewing angle due to their multidomain nature. Cells are never perfectly vertical or horizontal in an MVA, but they can be very close.
• PVA (Patterned-ITO Vertical Alignment): Developed by Samsung, PVA is very similar to MVA. Viewing angles are very similar and inversion is minimal at wide viewing angles. Samsung is not clear on the true color depth of these panels. These panels deliver the slowest response time. Cells are vertical when light is blocked, and horizontal when light is let through.
• S-PVA (Super Patterned-ITO Vertical Alignment): These types of panels deliver a full 8-bit color depth and have a structure split into eight domains. At wide viewing angles, they have less color shift and a lower black level than MVAs. According to Samsung, they have a higher contrast ratio and better response time than MVAs as well.
• S-MVA (Super Multidomain Vertical Alignment): Likely similar to P-MVA from AU Optronics, Chi Mei Optoelectronics has developed the S-MVA type of panel. These also include multidomain, vertically-aligned liquid crystals so that the cells stay in the same shape at different positions, increasing brightness at wide viewing angles. According to CMO, S-MVA improves viewing angles from conventional MVA types to 80 degrees in all angles. Like other types of panels, response time has gradually improved on these as well.
• IPS (In-Plane Switching): The IPS panel was pioneered by Hitachi to fix the problems that plague the VA and TN types. Like TN, most IPSes contain only a single domain, although DD-IPS (dual domain IPS) does exist. This technology sports the least distortion at wide viewing angles. Two transistors per each pixel are needed, so brighter backlighting is crucial and power consumption is higher than competing technologies, but response time benefits greatly from this. Color depth varies. One disadvantage is that a purple-black is now introduced in black colors at different viewing angles.
• S-IPS (Super In-Plane Switching): LG Philips LCD improved on IPS with their S-IPS technology. These offer a lower black level, higher contrast ratio, lower response time, and a wider viewing angle than traditional IPS technology. Color depth on S-IPS panels is 8-bit. The purple-black tinting still applies to wide viewing angles, but orange and red hues are greatly reduced versus other technologies at wider viewing angles.
• AS-IPS (Advanced/Enhanced Super In-Plane Switching): These type of panels are LG Philips LCD's third generation of IPS technology. This is mainly just a wieldy moniker for improvements in the front-end driving electronics, including ODC to reduce response time, and a dynamic contrast ratio technology, raising contrast up to 1600:1. The diagonal viewing angle is also increased to 178 degrees, from 170 on S-IPS panels. AS-IPS panels very often include much brighter backlights than S-IPS types.
• A-MVA (Advanced Multidomain Vertical Alignment): This is a new panel from AU Optronics promising contrast ratio and viewing angle performance comparable to Samsung's 8-domain S-PVA panels. These should be capable of true 8-bit color. Still, it is unknown if ODC will force them to dither.

Common Problems

• High gamma/washout effect.
• Vertical line? here's an account: Blue line going vertically down screen
• backlight leaking. Backlight usually forms X shape or along one edge
• DVI port problems (booting to POST does not show up on some people's PCs).
• Bad gradient banding or fuzzy screens
• Oversaturation, fading or dim picture