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Technology Center

Selection of Driver Chip for LCDs

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PenSegment code displayThe driver IC is generally HT 1621, which can drive 128 segments. If it exceeds 128 segments, 1622 can be used. Single chip microcomputer can also be selected, only for simple content and low price.

The display of liquid crystal is due to the electric field applied on the display pixel, and this electric field is generated by the synthesis of the potential signals on the front and back electrodes of the display pixel. It is very easy to establish a DC electric field on the display pixel, but the DC electric field will lead to the chemical reaction of the liquid crystal material and the aging of the electrodes, thus rapidly reducing the display life of the liquid crystal. Therefore, an AC driving electric field must be established, and it is required that the DC component in this AC electric field is as small as possible, and the DC component is usually required to be less50mV. In practical applications, due to the use of digital circuit drive, so the AC electric field is established by the pulse voltage signal.

When the effective value is greater than the threshold voltage of the liquid crystal, the pixel is in a display state; when the effective value is less than the threshold voltage, the pixel does not produce an electro-optic effect; when the effective value is near the threshold voltage, the liquid crystal will exhibit a weaker electro-optic effect, which will affect the contrast of the liquid crystal display device.

The driving of the liquid crystal display is used to adjust the phase, peak value, frequency, etc. of the potential signal applied to the electrode of the liquid crystal device to establish a driving electric field, so as to realize the display effect of the liquid crystal display device. There are many driving methods for liquid crystal display, and the commonly used driving methods are static driving method and dynamic driving method.

(1)static driving method

    The static drive method is the most basic method to obtain the best display quality, which is suitable for the drive of the pen segment liquid crystal display device.Move. The electrode structure of this kind of liquid crystal display device, when the multi-digit combination, the back electrode of each bit.BPare linked together. In the circuit of static driving method, the pulse signal of the oscillator is directly applied to the back electrode of the liquid crystal display device after frequency division.BPThe pulse signal of the segment electrode is generated by synthesizing the display selection signal and the timing pulse.

When a display pixel is selected for display, the pulse voltage phase difference between the two electrodes on the display pixel1800 , generated on the display pixel2VThe voltage pulse sequence, so that the display pixel presents display characteristics, when a display pixel is non-display selection, the pulse voltage phase of the two electrodes on the display pixel is equal, and the synthetic voltage pulse on the display pixel is.0VIn order to achieve the effect of display. This is the static drive method. In order to improve the contrast, the voltage of the pulse may be appropriately adjusted.

(2)dynamic driving method


    When a large number of pixels are displayed on a liquid crystal display device (such as a dot matrix liquid crystal display device), in order to save the huge hardware driveThe dynamic circuit is processed in the production and arrangement of the electrodes of the liquid crystal display device, and a matrix structure is implemented, that is, the back electrodes of a horizontal group of display pixels are connected together, called row electrodes, and the segment electrodes of a vertical group of display pixels are connected together, called column electrodes. Each display pixel on the liquid crystal display device is uniquely defined by the position of the column and row in which it is located. In the driving mode, the analogy is adopted accordingly.CRTThe raster scan method. The dynamic driving method of liquid crystal display is to apply selection pulses to row electrodes cyclically, and at the same time all column electrodes of display data give corresponding selection or non-selection driving pulses, so as to realize the display function of all display pixels in a row. This row scanning is carried out sequentially row by row, and the cycle period is very short, so that the liquid crystal display screen presents a stable display. People call the liquid crystal display scanning driving method dynamic driving method.

The selection time of each row in a frame is equal. Assume that the number of scan lines for a frame isNand the scan time is1, then the selection time occupied by a row is one frame of time.1/N. In the driving method of liquid crystal display, this value, that is, the reciprocal of the number of line scans per frame, is called the duty cycle of liquid crystal display driving (duty),dRepresentation. Under the same voltage, the increase of the number of scanning lines will reduce the duty cycle of the liquid crystal display, which leads to the decrease of the effective value of the variable electric field voltage and reduces the display quality. Therefore, as the display screen increases and the display lines increase, in order to ensure the display quality, it is necessary to appropriately increase the driving voltage or adopt a double-screen electrode arrangement structure to increase the voltage effective value of the electric field or increase the duty ratio.

In the dynamic driving mode, the display mechanism of the display pixel at a certain position of the liquid crystal display device is realized by the combination of the row selection voltage and the column display data voltage, that is, to make a position such (I , J) point display, you need to be in the firstIColumn and No.JA selection voltage is simultaneously applied to the row to maximize the variable field at that point. But at this time (I , J) outside the pointIColumn and No.JThe rest of the points on the line are also subjected to a certain voltage. These points are called half-selected points. If the effective voltage on the half-selected points is greater than the threshold voltage, undue display will appear on the screen, resulting in a decrease in contrast. This phenomenon is calledcross effect.

solved in dynamic drive methodcross effectThe method is the average voltage method, that is, the voltage of the half-selected point and the non-selected point is averaged, and the voltage of the non-selected point is moderately increased to offset a part of the voltage on the half-selected point, so that the voltage on the half-selected point drops and the contrast of the display is improved. Since the average voltage appears a quantity called bias ratio (bias),bRepresentation

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