LCD Computer Monitor, LCD Television Frame.

About LCD Screen :

A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices.

Each pixel of an LCD consists of a layer of liquid crystal molecules aligned between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. With no liquid crystal between the polarizing filters, light passing through one filter would be blocked by the other.

The surfaces of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using a cloth.
In a twisted nematic device, the surface alignment directions at the two electrodes are perpendicular, and so the molecules arrange themselves in a helical structure, or twist. Because the liquid crystal material is birefringent, light passing through one polarizing filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to pass through the second polarized filter. Half of the light is absorbed by the first polarizing filter, but otherwise the entire assembly is transparent.
When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure. This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules are completely untwisted and the polarization of the incident light is not rotated at all as it passes through the liquid crystal layer.
With a twisted nematic liquid crystal device it is usual to operate the device between crossed polarizers, such that it appears bright with no applied voltage. With this setup, the dark voltage-on state is uniform. The device can be operated between parallel polarizers,

Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided by applying either an alternating current, or by reversing the polarity of the electric field as the device is addressed .

When a large number of pixels is required in a display, it is not feasible to drive each directly since then each pixel would require independent electrodes. Instead, the display is multiplexed. In a multiplexed display, electrodes on one side of the display are grouped and wired together, and each group gets its own voltage source. On the other side, the electrodes are also grouped, with each group getting a voltage sink. The groups are designed so each pixel has a unique, unshared combination of source and sink. The electronics, or the software driving the electronics then turns on sinks in sequence, and drives sources for the pixels of each sink.
Important factors to consider when evaluating an LCD monitor include resolution, viewable size, response time, matrix type (passive or active), viewing angle, color support, brightness and contrast ratio, aspect ratio, and input ports (e.g. DVI or VGA).

Display Technology :

3LCD is a video projection system that uses three LCD microdisplay panels to produce an image. It was adopted in 1995 by numerous front projector manufacturers and in 2002 by rear projection TV manufacturers for its compactness and image quality.

3LCD is an active-matrix, HTPS (high-temperature polysilicon) LCD projection technology. It inherits sharp images, brightness and excellent color reproduction from its active matrix technology.

In-plane switching is an LCD technology which aligns the liquid crystal cells in a horizontal direction. In this method, the electrical field is applied through each end of the crystal, but this requires two transistors for each pixel instead of the one needed for a standard thin-film transistor (TFT) display. This results in blocking more transmission area requiring brighter backlights, which consume more power making this type of display undesirable for notebook computers.

Important Internet Resources

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