LCD display.Detailed explanation of LCD display principle. We generally think that an object has three states: solid state, liquid state and gaseous state. In fact, this is only for water. There are some organic compounds that are intermediate between solid state and liquid state.

When the angles of the two polarized fences are perpendicular to each other, the light cannot pass at all.

The liquid crystal display is completed by using the characteristic of the polarizer, which is filled with liquid crystal between the two mutually perpendicular polarizers between the upper and lower fences, and the electric field is used to control the rotation of the liquid crystal branch to change the direction of light, so that different electric field sizes will form different colors, as shown in figure (7).

BMel 1: when there is no electrode, when the incident light passes through the polarizer below, there will be a light wave in one direction, and when it passes through the liquid crystal molecule, because the liquid crystal molecule rotates a total of 90 degrees, so when the light wave reaches the upper polarizer, the polarization direction of the light wave is exactly 90 degrees. The angle difference between the lower polarizer and the upper polarizer is exactly 90 degrees. So the light can pass through smoothly, and if the light hits the red filter, it will be shown in red. The effect is shown in the first two figures in figure (7).

BMur2: when the electrode is added (the largest electrode), the liquid crystal molecules stand under the influence of the electric field, and the light path has not changed, so the light cannot pass through the upper polarizer and cannot be displayed, as shown in figure (7) the liquid crystal under the blue filter.

In order to display any graph, TFT-LCD is displayed by a progressive scan matrix arranged with m × n points. When designing the driving circuit, it is necessary to consider that the liquid crystal electrolysis will deteriorate the liquid crystal material, and the AC drive mode is generally used to ensure the service life. The driving modes that have been formed are: voltage selection mode, ramp mode, DAC mode, simulation mode and so on. Because TFT-LCD is mainly used in notebook computers, the drive circuit is roughly divided into: signal control circuit, power supply circuit, grayscale voltage circuit, common electrode drive circuit, data line drive circuit and address line drive circuit (gate drive IC). The main functions of the above driving circuit are that the signal control circuit supplies the digital signal, the control signal and the clock signal to the digital IC, and the control signal and the clock signal to the grid driving IC; power supply circuit supplies the required power supply voltage to the digital IC and the gate driving IC; grayscale voltage circuit supplies the 10 grayscale voltages generated by the digital driving circuit to the data driver respectively. The common electrode drive circuit supplies the common voltage to the shared electrode relative to the pixel electrode; the data line drive circuit displays the data and clock signal of each six bits of the RGB signal sent by the signal control circuit, sequentially latches the data and continues into the interior, then converts the display data into an analog signal by a 6-bit DA converter, and then converts the output circuit into an impedance to supply the data line of the LCD screen. The gate drive circuit converts the clock signal from the signal control circuit to the ON/OFF voltage through the shift register conversion action, and adds it to the LCD screen in sequence. Finally, the drive circuit is assembled on TAB (automatic welding flexible circuit board) and connected with LCD with ACF (anisotropic conductive film) and TCP (flexible guide tape of drive circuit).

The principle of liquid crystal display is based on the characteristic that the light transmittance of liquid crystal varies with the voltage shown. When the light passes through the upper polarizer, it becomes linearly polarized light, and the polarization direction is consistent with the vibration direction of the polarizer and the arrangement order of liquid crystal molecules on the upper and lower glass substrate. When the light passes through the liquid crystal layer, the linearly polarized light is decomposed into two beams due to the refraction of the liquid crystal. And because the propagation velocity of the two beams is different (the phase is the same), when the two beams of photosynthesis are formed, the vibration direction of the vibrating light is bound to change. The light passing through the liquid crystal layer is gradually distorted. When the light reaches the lower polarizer, the vibration direction of the optical axis is distorted by 90 degrees, which is consistent with the vibration direction of the lower polarizer. In this way, the light passes through the lower polarizer to form a bright field. After the voltage is added, the liquid crystal is oriented under the action of electric field and the distortion disappears. At this time, the linearly polarized light passing through the upper polarizer no longer rotates in the liquid crystal layer and cannot pass through the lower polarizer to form a dark field. The visible liquid crystal itself does not emit light and can only be displayed under the modulation of the external light source. in the whole display process, the liquid crystal acts as a voltage-controlled light valve. The working principle of TFT-LCD can be summarized as follows: when the positive gate voltage is greater than the applied voltage, the drain source electrode is turned on, and when the gate positive voltage is equal to 0 or negative voltage, the drain source electrode is disconnected. The leakage electrode is connected with the ITO pixel electrode, the source electrode is connected with the source line (row electrode), and the gate electrode is connected with the grid line (row electrode). This is how TFT-LCD works simply.