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Design and development of LCD control driver

2020-08-10

For LCD screens, it usually consists of a glass substrate, an ITO(Indium Tin Oxide) film, a directional film, and a polarizing board, with two layers above and below. Each sandwich consists of electrodes and grooves formed on the alignment film, with the upper and lower glass substrates aligned at 90 degrees. Liquid crystals are placed in the upper and lower layers, and the liquid crystals are arranged in the direction of the grooves. On the whole, the liquid crystal molecules are arranged like a spiral twist. When an electric field is added to the glass substrate, the molecular configuration of liquid crystals changes and becomes vertical. When the liquid crystal molecules stand erect, light cannot pass through, resulting in black on the display. Liquid crystal display (LCD) will be based on the voltage, the control of liquid crystal molecular alignment direction, so that the panel to achieve the display effect.

There are various classification methods for LCD. Usually according to its display mode can be divided into segment, dot character, dot matrix, etc. In addition to black and white display, there are many grayscale and color display. When driven by LCD, ac voltage is applied to the segment electrode and the common electrode. If only DC voltage is applied to the electrode, the liquid crystal itself degrades. Liquid crystal driving mode includes static driving, dynamic driving and other driving modes.

Static drive: Each segment has a separate drive circuit, indicating a continuous voltage applied between the segment electrode and the common electrode. It is suitable for LCD with simple control.

Multiple drive mode: a matrix electrode is formed, and the number of common terminals is N. The common terminals are driven in sequence according to the time sequence of 1/ N. Corresponding to the driving sequence, all segment signal electrodes are selected to drive. This method is suitable for LCD with more complex control. In the multiplexed mode, pixels can be divided into selective point, half - selective point and non - selective point. In order to improve the display contrast and reduce cross-talk, duty and bias should be selected reasonably.


Multiplexed drive can be divided into point reversal drive and frame reversal drive. The point reversal driver is suitable for low duty cycle applications. It reverses the data when each piece of data is output. The frame reversal driver is suitable for high space ratio applications. It reverses the data when each frame is output.

Frame - frequency control (FRC) and pulse width modulation (PWM) methods are usually used for multi - gray and color display control. Frame frequency control is to reduce the number of frame output, control the effective value of the output signal, to achieve multi-gray and color control. By changing the pulse width of the output signal and controlling the effective value of the output signal, the multi-gray and color control is realized.

The display mode changes from simple segment type, dot character type to complex dot matrix type and order type. The display color changes gradually from black and white to color. The Response Time of the display screen is gradually shortened from small to large, and STN display has advantages in cost and consumption current. TFT displays have advantages in contrast and animation corresponding speed.

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