Principle of Monochrome LCD

- Aug 26, 2020-

LCD technology is to pour liquid crystal between two planes lined with fine grooves. The slots on the two planes are perpendicular to each other (intersect at 90 degrees). In other words, if the molecules on one plane are aligned north-south, the molecules on the other plane are aligned east-west, and the molecules between the two planes are forced into a 90-degree twisted state. Because the light travels along the direction of the molecular arrangement, the light is also twisted 90 degrees when passing through the liquid crystal. When a voltage is applied to the liquid crystal, the liquid crystal molecules will rotate, changing the light transmittance, so as to realize multi-gray scale display.

LCD relies on polarization filters (plates) and light itself. Natural light diverges randomly in all directions. The polarization filter is actually a series of increasingly thinner parallel lines. These lines form a net, blocking all light that is not parallel to these lines. The line of the polarization filter is exactly perpendicular to the first one, so it can completely block the polarized light. Only when the lines of the two filters are completely parallel, or the light itself has been twisted to match the second polarized filter, the light can penetrate.

LCD is composed of two polarized filters that are perpendicular to each other, so under normal circumstances, all light that attempts to penetrate should be blocked. However, because the two filters are filled with twisted liquid crystals, after the light passes through the first filter, it will be twisted 90 degrees by the liquid crystal molecules, and finally pass through the second filter.

From the perspective of the structure of the liquid crystal display, whether it is a notebook computer or a desktop system, the LCD display used is a layered structure composed of different parts. The LCD is composed of two glass plates with thickness specifications of 0.7mm, 0.63mm, 0.5mm (it can also be made thinner by physical or chemical thinning), between which is a uniform 3~5μm containing liquid crystal (LC) material Spaced apart. Because the liquid crystal material itself does not emit light, it is necessary to configure additional light sources for the display screen. There is a light guide plate (or uniform light plate) and reflective film on the back of the liquid crystal display screen. The main function of the light guide plate is to convert the line light source or the point light source. It is a surface light source perpendicular to the display plane. The light emitted by the backlight enters the liquid crystal layer after passing through the first polarizing filter layer. The crystal droplets in the liquid crystal layer are all contained in a small cell structure, and one or more cells constitute a pixel on the screen. There are transparent electrodes between the glass plate and the liquid crystal material. The electrodes are divided into rows and columns. At the intersection of the rows and columns, the optical rotation state of the liquid crystal is changed by changing the voltage. The liquid crystal material acts like a small light valve. Around the liquid crystal material are the control circuit part and the drive circuit part. When the electrodes in the LCD generate an electric field, the liquid crystal molecules will be twisted, so that the light passing through it will be refracted regularly, and then displayed on the second screen.