Glossary of LCD Terms Active Matrix LCD - A dot matrix display in which 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. Annunciator - A word or special symbol with a dedicated meaning that is driven as a single segment. Array Process - Method of manufacturing whereby displays are arranged in rows and columns on a large laminate, and separated into individual displays after they are filled with LCD fluid. Backplane - The conductive electrode common to all segments. There can be multiple backplanes in a multiplexed display. Bezel - A metal or plastic frame which fits over the LCD and secures it to the PC Board. The bezel usually sandwiches the elastomeric connectors between the LCD and the PC boards.

Standard Character LCD Modules Standard Graphic LCD Modules

Cell Gap - The space between the two pieces of glass that contains the liquid crystal fluid. This gap is different for every fluid, and can be adjusted for optimal viewing angle and contrast.

Chip on Board - A manufacturing technique in which the LCD driver chip is wire-bonded and potted onto a PC board, and connected to the LCD via a flex connector.

Chip on Glass - A manufacturing technique in which the LCD driver chip is attached directly onto the LCD glass substrate.

Chip on Flex - A manufacturing technique in which the LCD driver chip is bonded to a flex connector, which is attached to the contact ledge of the LCD.

Clearing Point - The temperature at which the liquid crystal fluid changes from a nematic into an isotropic state. In practice, a positive image LCD will turn totally black at this temperature and will therefore be unreadable. Because the clearing point is different for every fluid type, ask for design assistance from your supplier if high temperature operation is critical in your application.

Common Plane - See Backplane

C-N Temperature - The temperature at which the liquid crystal fluid changes from a crystalline state to a liquid state. Below this temperature, a cell will be unusable as a display device Because this temperature is different for every fluid type, ask for design assistance from your supplier if low temperature operation is critical in your application.

Contact Ledge - The area along the edge of the display where electrical connections are made.

Contrast Ratio - The ratio of luminance between the dark and light areas of a display.

Delay Time - The interval between the time a drive signal is applied to a segment, and the time it is fully on. Conversely, it can also be the time between when the drive signal is removed from a segment and the time at which it turns fully off. Usually expressed in milliseconds.

Dichroic Display - A type of liquid crystal display where a dye has been added to the fluid. A dichroic display does not require polarizers, which is good; however, they have a number of undesirable traits that make this older technology unattractive.

DIL (Dual in Line) Pins - Two rows of pins attached along parallel sides of a display.

Direct Drive - A method of driving a display whereby individual segments are all driven from separate electrical signals from the driver chip. Direct driving any display is desirable as it results in maximum contrast and viewing angle.

Elastomeric Connector - A flexible thin conductive material used to make connections between an LCD and a PC board.

First Minimum - An LCD construction technique in which the cell geometry is optimized for maximum contrast and viewing angle. The geometry is different for every LCD fluid, so ask for design assistance early in the design process to guarantee a display with optimal viewing and performance characteristics.

Font - The style of a letter or digit.

Ghosting - A condition whereby segments which are in the "off" condition become slightly visible. It is usually caused by an incorrect drive signal being applied to the display. Ghosting is usually worse at higher temperatures, as the threshold voltage of most TN fluids goes down as the temperature rises.

Heat Seal Connector - A thin flexible conductive cable used to connect the LCD to a PC board.

Image Area - The total area bounded by the display characters.

Ink Overlay - The process of applying opaque, colored inks to the display to provide colors or highlight certain aspects of the viewing area.

Isocontrast Plot - Usually a polar plot showing contrast ratio versus viewing angle. Points along the plot represent points of equal contrast.

Liquid Crystal Fluid - An organic material that has both liquid and crystalline properties. The dual nature of these properties is only valid over a limited and well defined temperature range, and is different for every fluid.

Module - An LCD that includes a PCB, driver electronics, bezel, and possibly a backlight.

Multiplex (Mux) - A method of driving a display whereby multiple segments are driven from the same display connection. This is accomplished by time-division multiplexing between the individual segments.

Negative Image - A display that has a dark background and lighter active segments, i.e. light characters on a dark background. Negative image displays must have a backlight for the segments to be visible.

OLED (Organic Light Emitting Diodes) - An OLED is an electronic device made by placing a layer of organic thin film between two conductor plates. When an electrical field is applied to the conductor plates, a bright light is emitted. In practice, an OLED appears similar to an LCD, but since they emit light when put into an electrical field, they do not require backlight. When used to produce displays, OLED technology produces self-luminous displays that do not require backlighting. These properties result in thin, very compact displays. The displays also have a wide viewing angle, up to 160 degrees and require very little power, only 2-10 volts.

Pin Out - Defines the connections along the contact ledges that correspond to the individual segments inside the display.

Pixel - An individual active area within the display. Typically this term applies only to dot-matrix type displays.

Polarizer - An extremely thin stretched polymer that transmits light along one axis. Normally a TN display has polarizers on both the front and back glass surfaces.

Positive Image - A display that has a light background and darker active segments, i.e. black characters on a silver background.

Reflective - A viewing mode that uses ambient or other front lighting to provide the illumination for the display. The reflecting material on the back of the display prevents any backlighting from coming through.

Response Time - The total time between when a drive signal is applied to a segment and when that segment is fully turned on. Usually expressed in milliseconds.

Rise Time - The time necessary for the fluid to turn on. The rise time is usually shown on a graph that shows how the opacity of a segment increases over time after the drive signal is applied. Usually expressed in milliseconds.

Segment - An active area within the display that can be turned on and off. This can be a single segment of a 7-segment character, an annunciator, or a pixel in a dot matrix array.

SIL (Single-In-Line) Pins - A display with connections along a single side.

Static Drive - A method of driving a display whereby individual segments are all driven from separate electrical signal from the driver chip. This term is interchangeable with Direct Drive.

Supertwist (STN) - Any type of display that uses fluids that twist greater than 90o. An STN display has improved viewing angles and contrast at high multiplex rates.

Transflective - A viewing mode that can use both ambient light or a backlight to provide the illumination for the display. This is accomplished by putting a reflector on the back of the display that also allows a small amount of backlight to come through.

Transmissive - A viewing mode that cannot be read using front lighting to provide the illumination for the display, it therefore must use a backlight.

Twisted Nematic (TN) - A type of LCD where the liquid crystal fluid rotates the plane of polarization 90o.

Viewing Area - The area of a display that is visible through a bezel or cut-out in an instrument.

Viewing Angle - The preferred angle for viewing a display, usually described in comparison to a clock face. A 12 o'clock viewing angle means that the preferred viewing direction is above normal to the glass, whereas a 6 o'clock viewing angle means that the preferred viewing direction is below the normal.