Structure, working principle and classification of LCD

LCD itself does not emit light but is a passive display device that realizes display by irradiating liquid crystal material with external light. The basic structure of the LCD is shown in the figure.

The basic structure of LCD is shown in Fig. 10-1. The liquid crystal material is encapsulated between two conductive glass electrodes, the upper (front) and lower (back). The liquid crystal molecules are arranged vertically and twisted 90° at the top and bottom. External incident light passes through the upper polarizer to form polarized light, which is rotated by 90° through the parallel-arranged liquid crystal material, and then reflected by the reflector through the lower polarizer that is perpendicular to the upper polarizer, and is transparent. If the upper and lower electrodes plus a certain voltage, under the action of the electric field forced to add in the electrode part of the liquid crystal molecules into a vertical arrangement, the role of its spinning disappears resulting in the polarized light incident from the upper polarizer is not rotated, the light can not be returned to the lower polarizer, was black. When the voltage is removed, the liquid crystal molecules resume their twisted structure. Therefore, the electrodes can be made into various shapes according to the need to display a variety of words, numbers, and graphics.

There are many ways to categorize LCDs

1) Classification by electro-optical effect electro-optical effect refers to the role of electricity, the initial arrangement of liquid crystal molecules changed to other arrangements, so that the optical properties of the liquid crystal box change, that is, electricity through the liquid crystal molecules of light modulation.

LCD liquid crystal displays according to the different electro-optical effects can be divided into electric field effect class, current effect class, and electro-thermal effect class 3 kinds. Electric field effect can be divided into twisted nematic effect TN (Twisted Nematic) type, GH type, and super-twisted effect STN (SuperTwisted) type, etc.

Currently, TN-type and STN-type LCDs are widely used in microcontroller applications.

2) Classification according to display content LCD can be divided into 3 types according to its display content: field type (also known as stroke type), dot-matrix character type, and dot-matrix diagram.

Field-type LCDs are liquid crystal displays composed of long, brushstroke-like display pixels.

The dot matrix character type has 192 built-in characters, including numbers, letters, and common punctuation marks. In addition, users can customize 5x7 dot matrix characters or other dot matrix characters. Depending on the LCD model, the number of lines per screen can be 1, 2, or 4, and each line can display 8, 16, 20, 24, 32, or 40 characters.

Dot-matrix form of LCD liquid crystal display in addition to displaying characters, but also can display a variety of graphic information, Chinese characters, and so on.

3) Classification according to the way of lighting LCD liquid crystal displays according to the different ways of lighting, can be divided into two categories with backlight and without backlight.

LCD without backlight is to rely on the reflective film on the back of the display to reflect the incoming natural light from below. Most devices with LCDs use natural light as the light source and can be used without backlighting.

If the product operates in low light or dark conditions, choose an LCD monitor with a backlight.