Flat-panel displays

Liquid-crystal displays are helping manufacturers meet consumer demand for smaller, more portable products. LCDs draw less current and run on lower voltage than comparable displays of light-emitting diodes. The also are more difficult to drive because they rely on complex chemical properties. LCDs consist of liquid crystal sandwiched between polarizing glass plates. Liquid-crystal molecules are elongated in shape and align themselves to external electric fields. Molecular orientation determines how the material reflects light. Display segments are made visible or translucent by electrically aligning localized molecules to the polarizing plates. Voltage is applied across electrodes on the front and back planes of the assembly. LCDs are available as either graphic, pixel-addressable devices or as alphanumeric character displays. Alphanumeric devices are frequently used in equipment such as handheld terminals and various kinds of industrial control panels. Typical configurations are eight lines by 40 characters. Most such panels are packaged with optional fluorescent or electroluminescent back lighting. Graphic displays are available that range from full-screen laptop computer size to 640 X 200-pixel half-screen sizes. As with CRTs, LCDs can be packaged with touchscreens to provide integrated operator panels. Full-color LCDs are employed in applications where they can help operators distinguish intensity levels. Typical formats include units having 8.7 and 10.7-in. diagonals that provide a VGA-compatible display. One way microcontrollers drive LCDs is through a multiplexed interface. This method is suited for displays comprising a large number of segments in matrix arrangement. However, it requires a complex circuit that generates several intermediate voltages to safely control display segments. Commercial LCD drivers for medium to large displays commonly provide this function. If the display has only a few characters, an easier way to control it is with a static drive. This method involves individual connections to each display segment, and it eliminates the need for an interface IC. Static drive is similar to the control method used for seven-segment cathode displays. It employs a common backplane driver and individual segment drivers for the electrodes on the