Lampex Electronics Limited


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LCD FAQs

Q.How do I know what type of LCD to use for our product?

A. That will really depends on a number of factors including multiplex driving scheme, temperature, voltage/power, artwork design, contrast requirements and cost budget.

	Pros:	Cons:
TN	Economic to build, low tooling cost Excellent choice for icons/segment drive. True black and white operation Fast response time when properly design Good for Low MUX: direct drive to 1/16 (really max out at 1/4) Well established technology, little surprise and has very high yield Good for negative mode display	Not good for high multiplex application, i.e. 1/16 can be the limit Limited viewing cone (the higher the multiplex scheme, the narrower the cone)
HTN	Much better contrast and also wide viewing cone Good for medium multiplex application (<1/64 Mux scheme) Very cheap to build and also with good tooling cost Material cost is close to that of TN display	Tinted green or yellowish background give old feel Sluggish response The multiplex level range is very narrow for most application (<1/64 Mux scheme)
STN	Extremely wide viewing cone, in most cases, for less than 1/64th multiplex scheme, a viewing cone independent display is possible to build. Good for high multiplex level (excellent for as high as 1/240 multiplex scheme meaning that it is possible to build QVGA display Also well established this day Possible to get black and white display through use of compensation film For most people, the light yellow/green background color is pleasant.	Expensive to build Specification by non-professional is difficult Almost necessary to use standard driver for driving display, meaning that the design (i.e. multiplex scheme) would need to match closely to one of standard multiplex scheme available on the market. Optimization of electronic circuitry is as important as that of LCD, in some cases, it is difficult for engineer with little LCD background to fully comprehend what is needed for good looking display Slower response due to very high frequency Color shift with temperature (e.g. Auto application) limits its application (depends on materials and configuration) Darker background as compare with TN displays

Q.What is life time of LCD and backlight?

A. Very long, in most cases, providing the operating condition is stable, the LCD may operate for years. Just for reference, below is typical life time for displays:

	LCD	LED	EL	CCFL
Current consumptions	N/A	High (7.5mA per die)	Low (0.12 mA/cm2)	Low
Service Life	>80,000 hrs	Long >30,000 hrs	Short (typical 5,000 hrs)	Long (typical 30,000 hrs)
Driving Characteristics	AC	DC	AC	AC
Brightness	N/A	Low to medium	Low to Medium	High

Q.What is thickness of LCD and glasses?

A.Thickness of LCD depends on stacking height. Typical standard structure of LCD consists of:

Layer	Description
1	Top Polarizer with thickness of approximately 0.08mm~0.15mm
2	Top Glass with thickness between 0.5mm and 1.1mm typical
3	Liquid crystal cell with thickness negligible (4 to 9 micron)
4	Bottom Glass with thickness between 0.5mm and 1.1 mm typical
5	Bottom polarizer with or without reflector

Q. What is a TFT-LCD?

A. TFT-LCD, which stands for thin-film-transistor liquid crystal display, consists of glass substrates on the bottom, a color filter substrate on the top and liquid crystal in between. The special properties of the liquid crystal are manipulated to create images. These technology intensive products represent the next generation in displays. They are flat and thin, easy to carry around and consume less power. Refer to the Technology section for details.

Q. What is the future outlook for TFT-LCDs?

A.TFT-LCDs solve the problems of portability, bulkiness and electro-magnetic emissions that CRT displays present. The current brightness and response time problems with TFT-LCDs are being addressed with technology advancements. The main applications for TFT-LCD was notebook PCs and desktop monitors, where they replace CRT`s thick tubes. Importantly, industrial applications and value-added niche markets such as medical equipment and instrument panels are growing fast. In the future, TFT-LCDs will be found in most every facet of life.

Q.What are the common types of LCDs used in the market?

A.There are two types of LCDs commonly used in the market. One is TN (twisted nematic); this type of LCD has a narrow viewing angle. The other is STN (super-twisted Nematic); this has a wider viewing angle.

Q. How many types of display methods are available?

A.Basically there are three types of display methods:

Segment type (7segments, 14, segments, 16 segments)
Dot Matrix type.
Graphical type.

Q. What types of connectors are used in LCDs?

A.The connectors used for LCDs are elastomeric (rubber connector), pin and flexible cable.

Q. How many types of viewing modes are used in LCD glass?

A.There are three types of basic modes:
"Reflective", "Trans-missive", and "Trans-flective". " Tran-missive" and "Trans-flective" are used with an LED, EL, or CCFL backlight.

Q. Is temperature a matter of concern in LCDs?

Yes, since the LCDs are widely used, some of the applications will be in extreme weather conditions where a wide temperature range is required. Normally the wide temperature range for a TN type LCD is -30 ~ 75C (operation Temp.) and -30 ~ 70C (storage temp.)

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