The driving method of STN liquid crystal display

ST LCD screenadopts passive matrix electrode structure with many electrodes, and it is impossible to maintain a continuous electric field during the display time of the pixel. Therefore, it is generally not used for static driving, but for dynamic driving. The dynamic driving schematic diagram of the liquid crystal screen is shown as in Fig. 1. The passive matrix in the figure consists of multiple row electrodes (also called horizontal electrodes, scan electrodes, scan lines or X electrodes) and column electrodes (also called vertical electrodes, address electrodes, It is composed of gate electrode, data line or Y electrode), the row electrode will add a series of scanning pulse voltages in chronological order, the column electrode and the row electrode are synchronized, and the gate voltage waveform and the non-gated voltage waveform are input respectively; the input is synchronized on both sides At a moment of the driving voltage waveform, a driving waveform will be synthesized on the pixel at the intersection of the row and each column electrode, so that the corresponding pixel on the row is selected. All the rows are scanned once, and all the selected pixels form a picture, but the pixels of each row on this picture are strobed in different time periods, so this method is also called 'time division display' or APT (progressive) drive method. Since each display pattern is instantaneously combined by pixels displayed in different time divisions, there is no real continuous display state on the pixels, so it is also called dynamic driving. Figure 1 Schematic diagram of dynamic driving of STN LCD screen. Generally, the time for applying a scanning voltage to all scanning row electrodes is called one frame; the number of frames scanned per second is called frame rate; the ratio of the electrode strobe time per scanning row to the frame period Called the duty cycle, it is equal to the reciprocal of the number of row electrodes, that is, 1/N. Dynamic drive is the most commonly used drive method for ST LCD screens. If a matrix is u200bu200bcomposed of m rows and knife columns, there are m×n pixels, and only m + watts of electrode leads are required for dynamic driving, which can not only greatly reduce electrode leads, but also greatly reduce the cost of peripheral driving circuits. Therefore, the application Very extensive. Method skills The dynamic driving method is not only widely used in STN liquid crystal displays, but also widely used in pen-segment TN liquid crystal displays (liquid crystal digital tubes). For 1 to 2 pen-segment digital tubes, there are fewer curved segments, and static driving method can be used. However, if multiple pen-segment digital tubes are used, since there are many pen-segment pixels, it is impossible to set a separate outer lead on each pixel. In this case, dynamic driving can be used. For example, for six digital tubes, the back electrode can be led out separately as a row electrode, and the corresponding positions of the front electrode can be connected together (that is, six pen-segment type six a are connected together, and six b are connected together. Together... a total of seven paragraphs), and then lead out separately as column electrodes. Therefore, the total number of electrode leads is 6+7u003d13. When working, the voltages on the back electrodes (row electrodes) are turned on sequentially, which is called scanning. For example, the back electrode of the fourth digital tube is 'turned onHowever, the back electrode of these digital tubes is not 'connectedIn this way, the back electrode is turned on in turn, and the pen segments on it are displayed accordingly. If there are six digital tubes, each display time is only 1/6; if the scanning speed of the back electrode is fast enough (per second Take turns 50 times or more), due to the 'persistence of vision' feature of the human eye, you can't feel the flicker of the display, what you see is the six numbers displayed continuously.

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