Frequently Asked Questions
[Click Here for Viewing Characteristics]
[Click Here for a Glossary of Terms]
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| What is TCP |
Tape Carrier Package. This is a method of display construction where the row and column drivers are mounted on a tape carrier. |
| What is COG |
Chip on Glass. This is a method of display construction where the row and column drivers are mounted directly to the glass substrate. |
| What is a transmissive display |
A transmissive display is one which requires a backlight for a display image to be seen. The backlight may be implemented using CCFL or LED. |
| What is a transflective display |
A transflective display combines the properties of a transmissive and reflective display. |
| What is a reflective display |
A reflective display uses ambient light in the environment to enable a display image to be seen. No backlight is needed. |
| What type of touchscreens does Hitachi use |
All touchscreens used on Hitachi display modules are 4-wire, analogue resistive type. |
| What is a CCFL |
Cold Cathode Fluorescent Lamp. Used to provide a high brightness, white backlight for transmissive and transflective display. Requires a DC/AC inverter to be used. |
| What is a LED |
Light Emitting Diode. Used to provide a low power, white backlight for transmissive and transflective displays. No inverter is needed. |
| What is an inverter |
An inverter is required to drive a CFL backlight. It requires a DC input voltage and generates a high voltage AC output voltage. |
| What is MTBF |
Mean Time Between Failure is a theoretical measure of the expected reliability of a component or product. |
| What is UL certification |
Underwriters Laboratories Inc. (UL) is an independent, product safety testing and certification organisation. www.ul.com. |
| What is WTR |
Wide Temperature Range typically defines a display module where the operating temperature range is -20 to +70 degrees C. |
| What is the half brightness lifetime of a backlight |
The half brightness lifetime of a CFL or LED backlight is the time taken for the light output of the backlight to reach 50% of it's original output. |
| Are Hitachi LCD modules produced using Pb-free (lead) solder |
Pb-free solder has been used to manufacture all Hitachi display modules since 1st April 2003. |
| What is Pb-free (lead) solder ? |
Pb-free solder contains no lead. |
| What is the 'M' signal |
The ‘M' signal is a square wave of 50% duty which is used by the LCD to switch the polarity of the display driver voltage to ensure there is no DC component applied across the LC cell. Some LCD's generate this internally and some require it to be supplied. |
| What is the FLM signal |
First Line Marker. The signal is required at the start of every display frame. Other names for this signal can be: FRAME, Vertical sync, YD. |
| What is the Doff signal |
Display Off (active low). This signal disables the internal circuitry of the display. This prevents the display being enabled until the controller is initialised and also allows the display to be disabled by software control. |
| What is the CL1 signal |
Data latch signal. Other names for this signal can be: LP, Horizontal sync, Load, Line clock. |
| What is the CL2 signal |
Data shift signal. Other names for this signal can be: Clock, XCK, Shift clock, Pixel clock. |
| 54 Why is the Power On/Off sequence important |
It is important to achieve the correct timing to ensure that the LCD does not become damaged especially when switching ON. The basic requirement is to ensure that the display is not enabled without the supply and timing signals being present. |
| Precautions when using CCFL backlights |
Be careful with the wires from the CCFL tube, ensure that they are not wound around anything or twisted tightly as this can affect the brightness. Do not lengthen the CCFL cable. Be aware of the High voltage danger! |
| What is the difference in driving STN and TFT display modules |
The fundamental difference when driving these displays is the way in which the colours/grey scales are generated. For an STN passive display the pixels are driven by individual bits of the input data. |
| What is a dual scan display |
To improve the contrast on STN passive displays dual scanning is used. This is where the display is effectively split into two with each half being driven simultaneously. This gives a better quality image than single scan but is more expensive. |
| What are bits per pixel (bpp) |
The number of bits per pixel defines the number of colours/grey scales being generated and hence the amount of memory needed to map to the display. For a 320 x 240 monochrome display at 1bpp, 9.6Kbytes of display memory is needed. |
| What is the benefit of an on-board DC/DC converter |
An on board DC/DC converter is used to generate the Vlcd or Vo voltage (the contrast control voltage). The contrast of the display can therefore be controlled by a low level DC voltage or an external potentiometer. |
| Why are temperature compensation circuits sometimes required |
Liquid crystal material is sensitive to temperature variation. Temperature compensation is sometimes necessary in environments where the operating temperature of the display module may vary significantly. |
| What is a display controller |
A display controller acts as the interface between the system CPU and the display row and column drivers. The controller may have on-chip display memory or require external memory. |
| What is the thickness of the LCD glass |
LCD glass is produced in three thickness': 0.5mm, 0.7mm and 1.1mm. |
| How do LCDs work |
LCDs contain rod shaped molecules, initially all pointing in the same direction, that can change their orientation in response to small amounts of electricity. |
| What is Liquid Crystal |
Liquid crystal is a substance that is neither liquid nor solid but exists somewhere in between the two. Liquid crystal materials are formed by blending certain base materials with other materials to obtain various desired properties. |
| How many types of viewing modes are used in LCD glass |
Three. Reflective, Transmissive and Transflective. |
| What is ZIF |
Zero Insertion Force refers to a particular type of connector which might be used to connect the display to other parts of the system. The displays FPC might be connected to the rest of the system via a ZIF connector. |
| What is a FPC |
Flexible Printed Circuit is a popular mechanical interface to connect the display to other parts of the system. The FPC carries all the necessary interface signals needed by the display. |
| What is Negative Mode |
This is when the controlled pixels are light / transparent in colour against a dark background. |
| What is Positive Mode |
This is when the controlled pixels are dark in colour against a light background. |
| How is the viewing direction defined |
The preferred angle of viewing a display, usually described in comparison to a clock face, i.e. 12 o'clock for above the normal, or 6 o'clock for below the normal. |
| How is contrast defined |
The ratio of the luminance between the dark and light areas of the display. The higher the number the better the display performance. |
| What is the difference between series and parallel LED backlight circuits |
LEDs in parallel circuits can be driven using low level DC voltages such as 3.3 or 5v. The overall current drawn by the circuit is the sum of the LED driving currents. |
| What is the Viewing Area |
The area of a display which is visible through a bezel. This area is made up of the "Active Area" and the boarder around the active area. |
| What is the Active Area |
The area (L x H) of the display that has active segments/pixels. |
| What is LCD |
Liquid Crystal Display. |
| What is Liquid Crystal Fluid |
An organic material which, over a specified temperature range, exhibits characteristics of both liquid and crystalline properties. |
| What is an LCD module |
Liquid Crystal Display Module is an LCD which includes a PCB, driver electronics, bezel, and possibly a backlight. |
| What is a Polariser |
A stretched polymer which transmits light in only one axis. A typical display has polarisers on the front and back. |
| What is Dithering |
The method of mixing up neighbouring pixels or consecutive frames of pixel information in a random fashion to create the effect of many intermediate levels of colour or grey scale. |
| What is the Refresh Rate |
The number of times the screen image is "displayed" or refreshed per second, expressed in Hz. |
| What is the Resolution |
Number of dots or pixels per unit of area (L x H). The greater the pixels per unit area the higher the resolution, giving more detail. |
| What is the Response Time |
The reaction time for a pixel to turn on and off. An active-matrix LCD panel's response time is fast enough to display full-motion video and rapid mouse cursor movements. |
| What is Vlcd |
The DC voltage required by the LCD controller/driver to power the LCD. This is also known as contrast adjustment. |
| What is an Active Matrix LCD |
A dot matrix display where every pixel of the display is controlled by a thin film transistor that is deposited directly onto the glass substrate. Every pixel is driven in a static mode, resulting in very high contrast and viewing angle. |
| What is Saturation Voltage |
RMS voltage required to turn fluid to 90% (on). |
| What is Threshold Voltage |
RMS voltage required to turn fluid to 10% (on). |
