The driving of LCD is used to adjust the phase, peak value and frequency of the potential signal applied on the electrode of the LCD, and establish the driving electric field to achieve the display effect of the LCD. There are many kinds of driving methods for LCD, the common driving methods are static driving method and dynamic driving method. Let’s introduce it to you.
1. Static driving method
Static driving method is the most basic method to obtain the best display quality, which is suitable for driving pen Segment LCD. In the electrode structure of this kind of liquid crystal display device, when multiple digits are combined, the back electrodes BP of each digit are connected together. In the circuit of static driving method, the pulse signal of oscillator is directly applied to the back electrode BP of LCD after frequency division, while the pulse signal of segment electrode is generated by the combination of display selection signal and timing pulse.
When a display pixel is selected for display, the pulse voltage phase difference between the two electrodes on the display pixel is 1800, and a voltage pulse sequence of 2V is generated on the display pixel, so that the LCD display pixel presents display characteristics; when a display pixel is selected for non display, the pulse voltage phase of the two electrodes on the display pixel is equal, and the synthesized voltage pulse on the display pixel is 0V, so as to realize the display The effect of the display. This is the static driving method. In order to improve the contrast, adjust the pulse voltage appropriately.
2. Dynamic driving method
When there are many display pixels on LCD (such as dot matrix LCD), in order to save huge hardware driving circuit, the fabrication and arrangement of LCD electrodes are processed, and the matrix structure is implemented, that is, the back electrodes of a group of horizontal display pixels are connected together and led out, which is called row electrode; the section electrodes of a group of vertical display pixels are connected The electrodes are connected and drawn out together, which is called column electrode. In LCD, each pixel is uniquely determined by the position of its column and row. In the driving mode, the grating scanning method similar to CRT is adopted. The dynamic driving method of LCD is to apply the selection pulse to the row electrode cyclically, and at the same time, the column electrode of all display data gives the corresponding selection or non selection driving pulse, so as to realize the display function of all display pixels in a certain row. This kind of row scanning is carried out row by row in sequence, and the cycle period is very short, which makes the LCD display show a stable display The scanning driving mode of crystal display is called dynamic driving mode.
The selection time of each row in a frame is equal. Suppose that the number of scanning lines of a frame is n and the scanning time is 1, then the selection time occupied by a line is 1 / N of the time of a frame. In the driving method of LCD, this value, that is, the reciprocal of the number of line scans in a frame, is called the duty of LCD driving, which is expressed by D. Under the same voltage, the increase of the number of scanning lines will reduce the duty cycle of LCD, which leads to the decrease of the effective value of the variable electric field voltage and reduces the display quality. Therefore, with the increase of the display screen and the number of display lines, in order to ensure the quality of the display, it is necessary to appropriately increase the driving voltage or adopt the double screen electrode arrangement structure to improve the voltage effective value or the duty cycle of the electric field.
In the dynamic driving mode, the display mechanism of the display pixel on a certain position of LCD is realized by the combination of row selection voltage and column display data voltage, that is, to make a position such as (I, J) display, it is necessary to apply selection voltage on the i-th column and j-th row at the same time, so as to maximize the variable electric field of the point. But at this time, except for (I, J), all the other points on column I and row J also bear a certain voltage. These points are called semi selection points. If the effective voltage on the semi selection point is greater than the threshold voltage, there will be an undesirable display on the screen, which will reduce the contrast. This phenomenon is called “cross effect”.
In the dynamic driving method, the method to solve the “cross effect” is the average voltage method, that is, to average the voltage of the half selected point and the non selected point, and moderately increase the voltage of the non selected point to offset part of the voltage of the half selected point, so that the voltage of the half selected point decreases and the contrast of the display is improved. Because the average voltage appears a quantity called bias ratio (bias), expressed by B.
The dynamic driving waveform of LCD module can be described from three aspects
(1) Driving voltage of LCD module (V LCD module)
The driving voltage of LCD module is the difference between the segment voltage and the common voltage
(2) Duty cycle
In order to reduce the number of electrodes on the LCD module, multi-channel driving is adopted. The voltage of the LCD module is AC waveform, and the duty cycle duty of the LCD module is the ratio of the part higher than the threshold voltage in a cycle.
(3) Bias ratio (bias)
The driving waveform of LCD module is composed of several levels. In order to prevent the non-uniformity of contrast, a certain voltage is still applied on the corresponding electrode of the non illuminated pixel, which is very important to reduce the cross interference caused by the illuminated pixel and prevent the non-uniformity of contrast. In LCD module, the ratio (1 / N) between the RMS voltage of non illuminated pixel (non selected point) and the RMS voltage of illuminated pixel (selected point) is called bias ratio.
The above is today’s Huatian Xinke small series for you to introduce the LCD commonly used driving method.