LCD display drive circuit

The internal structure of the STN-LCD color screen module: the upper part of it is an LCD screen composed of polarizer, glass, and liquid crystal, and the white LED and backlight board are underneath it. It also includes an LCD driver IC and a stable power supply for the LCD driver IC. Low dropout regulator (LDO), two to eight white LEDs and boost regulator IC driven by LEDs. LCD is a kind of flat panel display, and can be divided into static drive (Static), simple matrix drive (Simple Matrix) and active matrix drive (Active Matrix) according to the driving mode. Among them, the simple matrix type can be divided into twisted nematic (Twisted Nematic, TN), super twisted nematic (Super Twisted Nematic, STN), and other passive matrix-driven liquid crystal displays. The active matrix type can be roughly divided into thin film transistor type (ThinFilmTransistor, TFT) and two-terminal diode (Metal/Insulator/Metal, MIM). TN, STN and TFT type liquid crystal displays have different advantages in viewing angle, color, contrast and animation display quality due to the different principle of twisting liquid crystal molecules, which makes them have obvious differences in product application range classification. In terms of the current scope and level of application of liquid crystal display technology, active matrix drive technology is based on thin-film transistors as the mainstream, and is mostly used in notebook computers and animation and image processing products; pure matrix drive technology is currently based on twisted nematic As well as STN-based, STN liquid crystal displays can display the three primary colors of red, green, and blue respectively through color filters, and then through the harmony of the three primary colors, it can display the true color of the full-color mode. At present, the applications of color STN-LCD are mostly consumer products such as mobile phones, PDAs, digital cameras, video game consoles, and word processors.

STN liquid crystal display principle

The STN type display principle is similar to TN. The difference is that the liquid crystal molecules of the TN twisted nematic field effect rotate the incident light by 90 degrees, while the STN super twisted nematic field effect rotates the incident light by 180 to 270 degrees. What I want to explain here is that the pure TN liquid crystal display itself has only two situations (or black and white), and there is no way to change the color. The STN liquid crystal display involves the relationship between liquid crystal materials and the interference of light, so the color tones displayed are mainly light green and orange. But if you add a color filter to the traditional monochrome STN liquid crystal display, and divide any pixel (pixel) of the monochrome display matrix into three sub-pixels, pass the color filter separately Display the three primary colors of red, green and blue, and then through the harmony of the ratio of the three primary colors, the colors of the full color mode can also be displayed. In addition, if the display screen of the TN-type liquid crystal display is made larger, the contrast of the screen will appear poor, but the improved technology of STN can make up for the lack of contrast. The driving method of the LCD screen ---the simple matrix driving method is composed of vertical and horizontal electrodes. The part to be driven is controlled by the horizontal voltage, and the vertical electrodes are responsible for driving the liquid crystal molecules. In the TN and STN type liquid crystal displays, the method of simply driving the electrodes is driven by the intersection of the X and Y axes. Therefore, if the display part becomes larger and larger, the reaction time of the electrode in the center part may be It will be longer. In order to make the screen display consistent, the overall speed will be slower. To put it simply, it seems that the screen update frequency of the CRT monitor is not fast enough, that is, the user will feel the screen flickering and beating; or when fast 3D animation is required, the display speed of the monitor cannot keep up. The effect may be delayed. Therefore, the early liquid crystal displays have certain limitations in size, and they are not suitable for watching movies or playing 3D games. ---The driving method of the active matrix is to let each pixel correspond to a group of electrodes. Its structure is a bit like a DRAM loop method. The voltage is scanned (or called a certain time charging) method to represent each pixel status. In order to improve this situation, the liquid crystal display technology was later driven by active-matrix addressing, which is currently an ideal device for achieving high-density liquid crystal display effects with extremely high resolution. The method is to use the silicon transistor electrode made of thin film technology, and use the scanning method to select any display point (pixel) on and off. This actually uses the non-linear function of the thin film transistor to replace the non-linear function of the liquid crystal which is difficult to control. In the TFT type liquid crystal display, the conductive glass is drawn with small net-like lines, and the electrodes are matrix switches arranged by thin-film transistors. There is a control box where each line intersects, although the driving signal is fast The ground is scanned at each display point, but only the selected display point in the transistor matrix on the electrode gets enough voltage to drive the liquid crystal molecules, so that the liquid crystal molecular axis turns to a "bright" contrast, and the unselected display points are naturally It is the "dark" contrast, and therefore avoids the dependence of the display function on the ability of the liquid crystal electric field effect.