The LCD display is due to the electric field applied on the display pixel, and the electric field is generated by the synthesis of the potential signal on the two electrodes before and after the display pixel, it is very easy to establish a direct current electric field on the display pixel, but the direct current electric field will lead to the chemical reaction of the liquid crystal material and the aging of the electrode, thereby rapidly reducing the display life of the liquid crystal. Therefore, it is necessary to establish an AC driving electric field, and the DC component of this AC electric field is required to be as small as possible, and the DC component is usually required to be less than 50mV. In practical application, because of the use of digital circuit drive, the AC electric field is established by pulsed voltage signal. The strength of the AC electric field on the display pixel is expressed by the RMS value of the AC voltage. When the RMS value is greater than the threshold voltage of the liquid crystal, the pixel will show the display state. When the RMS value is less than the threshold voltage, the pixel does not produce electro-optical effect. When the RMS value is near the threshold voltage, the liquid crystal will show a weak electro-optical effect, which will affect the contrast of the liquid crystal display device. The driver of the liquid crystal display is used to adjust the phase, peak value, frequency, etc. of the potential signal applied on the electrode of the liquid crystal display device, and establish the driving electric field to achieve the display effect of the liquid crystal display device. There are many kinds of driving methods for liquid crystal display, the commonly used driving methods are: static driving method and dynamic driving method. For TN and STN-LCD, static drive or multi-channel drive is generally used. Both methods have advantages and disadvantages. The static drive response speed is fast, the power consumption is low, the drive power is low, but the drive electrode degree must be the same as the number of display pen segments, so the use is not as wide as the multi-way drive.
1. Static drive method Static drive method is the most basic method to obtain the best display quality. It is suitable for driving pen segment liquid crystal display devices. Table 1 shows the electrode structure of such a liquid crystal display device. When multiple digits are combined, the back electrode BP is connected together. The pulse signal of the oscillator is directly applied to the back electrode BP of the liquid crystal display device after frequency division, and the pulse signal of the segment electrode is generated by the display selection signal A and the timing pulse through the logic XOR synthesis. When A display pixel is displayed and selected, A = 1, the pulse voltage phase difference of the two electrodes on the display pixel is 180. A 2V voltage pulse sequence is generated on the display pixel to make the display pixel display characteristics; When A certain display pixel is non-display selection, A = 0, the pulse voltage phase of the two electrodes on the display pixel is the same, and the resultant voltage pulse on the display pixel is 0V, so as to achieve the effect of not displaying. This is the static drive method. In order to improve the contrast of the display, adjust the voltage of the pulse appropriately.
2. Dynamic drive method When the LCD device displays a large number of pixels, such as the dot matrix LCD device, in order to save the huge hardware drive circuit, the production and arrangement of the electrodes of the LCD device are processed, and the matrix structure is implemented, that is, the back electrodes of a horizontal group of display pixels are connected together, which is called the row electrode. The section electrodes of a longitudinal group of display pixels are connected together to lead out, which is called the column electrode. Each display pixel on a liquid crystal display is uniquely determined by the position of the column and row in which it is located. In the driving mode, the grating scanning method similar to CRT is adopted accordingly. The dynamic driving method of liquid crystal display is to apply the selection pulse to the row electrode in a cycle, and at the same time, all the column electrodes for the display of data are given the corresponding selection or non-selection of the driving pulse, so as to achieve the display function of all the display pixels in a row, this line scan is carried out line by line, the cycle period is very short, so that the liquid crystal display screen presents a stable image. We call the scanning drive mode of liquid crystal display dynamic drive method.