Active-matrix liquid crystal display


Active-matrix liquid crystal display

An active matrix liquid crystal display (AMLCD) is a type of flat panel display, currently the overwhelming choice of notebook computer manufacturers, due to light weight, very good image quality, wide color gamut, and response time. The term was first used in 1975 by Dr T. Peter Brody to describe a method of switching individual elements of a flat panel display, using a CdSe TFT for each pixel. [Brody's company for developing active matrix is mentioned [http://www.rogerfidler.com/about/autobio.asp by Rogerfidler.com] ]

Introduction

The most common example of an active matrix display contains, besides the polarising sheets and cells of liquid crystal, a matrix of thin-film transistors (TFTs) to make a TFT LCD. These devices store the electrical state of each pixel on the display while all the other pixels are being updated. This method provides a much brighter, sharper display than a passive matrix of the same size. An important specification for these displays is their viewing-angle.

Thin film transistors are usually used for constructing an active matrix so that the two terms are often interchanged, even though a thin film transistor is just one component in an active matrix and some designs have used other active components such as diodes. Whereas a passive matrix display uses a simple conductive grid to deliver current to the liquid crystals in the target area, an active matrix display uses a grid of transistors and capacitors (which are called the thin film transistors) with the ability to hold a charge for a limited period of time. Because of the switching action of transistors, only the desired pixel receives a charge, and the pixel acts as a capacitor to hold the charge until the next refresh cycle, improving image quality over a passive matrix.

Resolution

There are many different active matrix displays on the market. Each display is associated with a specific physical display resolution. The display resolution signifies the number of dots (pixels) on the entire screen. The higher the resolution, the more dots or pixels on your display device. The total number of pixels in an active matrix display is fixed. For example, a VGA display has a very low resolution at 640 x 480.

See also

* Liquid crystal display
* Active matrix addressing
* OLED

References

* [http://www.eduard-rhein-stiftung.de/html/Preistraeger_e.html Eduard Rhein Stiftung 1988 Technology Award Dr. T. Peter Brody: Basic development of TFT liquid crystal display]


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