Hantronix, Inc.

TFT LCD Modules
OLED Modules
Graphic Modules
Character Module
Custom Glass LCD Panel


The physical construction of an LCD module varies mostly because of the type of backlight used. An LCD is a passive device and relies on ambient light to be visible. If this is dim or non-existent some means of artificial light must be provided. This is accomplished by using an electro-luminescent (EL) panel, a light emitting diode (LED) array or a cold cathode florescent lamp (CCFL).

EL Backlight, Figure #1 This type of backlight uses a thin panel which, when excited by an AC voltage at about 80 volts at about 400 Hz glows with a soft even light. A DC to AC inverter is used to obtain the AC driving voltage from a 5v or 12v power source. The EL panel is available in a variety of colors with white being the most common. It is the most power efficient of the three types so it is most commonly used with battery operated applications.

LCD's Anatomy

Figure #1

LED Backlight A series of LED's are arranged either along the edges of or behind a diffuser to provide a bright, even back light to the display. LED's are powered from a 5v supply through a series current limiting resistor so they don't require an inverter. LED's are moderately bright and very long lasting and are the most popular back light for small to medium size displays. They consume more power than EL but are brighter. When the cost of the inverter is considered they are also more economical. LED's are available in a variety of colors with yellow-green being the most popular. CCFL Backlight, Figure #2 CCFL can provide moderately bright illumination over a large area and so are the light source of choice for large, flat panel displays. They provide paper white colors so are the only choice for color displays. Florescent lamps require a high voltage, high frequency source of power so they are used with a DC to AC inverter.

LCD's Anatomy

Figure #2

In general, an LCD module consists of a pc board, which supports and connects the surface mount IC's and other electronic components. The LCD glass has metallic contacts applied around the periphery of the bottom surface of the bottom glass. An elostomer connector makes the electrical connection between the glass and gold plated metal contacts on the PCB. A metal bezel is used to hold the glass in contact with the elastomer connector and the PCB. The backlight diffuser, if used, is placed between the PCB and the LCD glass.