JP3989882B2 - Driving method and driving circuit for liquid crystal display panel - Google Patents

Description

  The present invention relates to a driving method and a driving circuit for a liquid crystal display panel, and more particularly, to a driving method and a driving circuit for a liquid crystal display panel for driving a liquid crystal display device (LCD) using a pre-charging method. It is about.

  A currently known liquid crystal display device (LCD) is composed of a plurality of pixels arranged in a matrix, and the liquid crystal in each pixel is controlled by the voltage difference on it. Thus, the desired gradation can be realized on the screen by changing the transmittance of the liquid crystal.

  FIG. 3 shows a schematic diagram of an equivalent circuit of a conventional liquid crystal display panel (hereinafter referred to as “LCD panel”) and its peripheral drive circuit. As shown in FIG. 3, the LCD panel 1 is formed by vertically and horizontally intersecting data electrodes (D1, D2,..., Dm) and gate electrodes (G1, G2,..., Gn). ing. Each combination of data electrode and gate electrode controls one display unit. For example, the combination of the data electrode D1 and the gate electrode G1 controls the display unit 200. As shown in the figure, the equivalent circuit of each display unit mainly includes thin film transistors (Q11 to Q1m, Q21 to Q2m,..., Qn1 to Qnm) for controlling the passage of data, and storage capacitors (C11). To C1m, C21 to C2m,..., Cn1 to Cnm). The gates and drains of these thin film transistors are connected to the gate electrodes (G1 to Gn) and the data electrodes (D1 to Dm), respectively. In such a connection, the scanning signal passing through the gate electrodes (G1 to Gn) can turn on / off all thin film transistors on the same column (ie, on the same scanning line), and thus the data electrode It is possible to control whether or not to write the video signal on (D1 to Dm) to the corresponding display unit. It must be explained that each display unit corresponds to only one bright spot on the LCD panel. Therefore, in the case of a single color LCD, each display unit corresponds to a single pixel, while in the case of a color LCD, each display unit is red (represented by R) and blue (represented by B). Or, each corresponds to a single subpixel that may be green (denoted by G). In other words, a set of sub-pixels (three display units) such as R, G, and B constitute one pixel.

  Further, FIG. 3 shows a drive circuit for the LCD panel 1. A gate driver 10 supplies scanning signals to the gate electrodes G1, G2,..., Gn according to a predetermined scanning order. When a scanning signal is applied to a certain gate electrode, the thin film transistors in all the display units on the same column or the same scanning line are turned on. When a certain scanning line is selected, the data driver 20 selects m display units in which the corresponding video signal is connected to the column via the data electrodes D1, D2,... Dm based on the video data to be displayed. To supply. When the gate driver 10 finishes scanning the n scanning lines, the display operation for one frame is completed. Therefore, when the scanning of each scanning line is repeated and the video signal is further transmitted, continuous display of images is achieved. In FIG. 3, a signal CTR represents scanning control data received by the gate driver 10, a signal LD represents a data latch signal of the data driver 20, and a signal DATA represents input video data.

  By the way, generally, the video signal transferred by the data electrodes D1, D2,... Dm is based on the relationship with the common electrode voltage VCOM, and a positive video signal (positive video signal) and a negative video signal (negative video). signal). The positive video signal has a voltage higher than the common electrode voltage VCOM, and the actual voltage varies between the voltage Vp1 and the voltage Vp2 based on the gradation value represented by the positive video signal (normally) The closer to the common electrode voltage VCOM, the lower the gradation value). On the other hand, the negative video signal has a voltage lower than the common electrode voltage VCOM, and the actual voltage fluctuates between the voltage Vn1 and the voltage Vn2 based on the gradation value represented by the negative voltage video signal. (Similarly, the closer to the common electrode voltage VCOM, the lower the gradation value). When the same gradation is expressed by the positive polarity video signal and the negative polarity video signal, respectively, the same display effect can be basically obtained, but in reality, there are some differences. In addition, in order to prevent the life of the liquid crystal molecules from being shortened by continuing to apply a voltage having the same polarity, video signals having opposite polarities are alternately supplied to the same display unit in the odd and even frames.

  FIG. 4 is a diagram showing the relationship between the voltage difference applied to the liquid crystal and the time of each frame. FIG. 4 shows the time of the initial video signal. In this example, when the frame rate is 60 Hz, the time of each frame is 16.6 ms. Become. At that time, the voltage (pixel voltage) accumulated by the storage capacitor (liquid crystal) gradually approaches the applied voltage difference as shown by the dotted line in the figure, and finally reaches the voltage difference.

  Therefore, in order to increase the speed at which the pixel voltage reaches the video signal level, the level of the data electrode can be increased in advance. Such a method is executed by precharging the data electrode level until the positive / negative voltage reaches a voltage value that maximizes the gradation change of the liquid crystal molecules. In short, according to such pre-charging technology, the target pixel voltage can be reached in a shorter time by changing the voltage in advance, so that the LCD can express gradation more faithfully. Become.

  However, the above-described conventional precharging technique that charges / discharges data electrodes in advance for both positive and negative polarity has such drawbacks. In other words, as a result of charging / discharging in advance, there is a possibility that the charging / discharging is excessive, so that it becomes necessary to correct the last pixel voltage to the target voltage. It is a point to end up. Therefore, it is necessary to carefully consider the timing for pre-charging.

In determining the timing for executing the precharge, it can be determined by the amount of drain current Id flowing through the source / drain of the thin film transistor. The reason is that the amount of drain current Id directly affects the charge / discharge speed of liquid crystal molecules. The current value of the drain current Id depends on the gate, drain and source voltages of the thin film transistor. The relationship can be expressed by the following formula 1.
(Equation 1)
Id = μ (W / L) Cins (Vgs−Vth) Vds
Where μ represents the electron transfer rate, W and L represent the width and length of the thin film transistor, respectively, Cins represents the capacitor at the gate of the thin film transistor, Vgs represents the voltage difference between the gate and source of the thin film transistor, Vth represents a threshold voltage for turning on the thin film transistor, and Vds represents a voltage difference between the drain and the source of the thin film transistor.

As can be seen from Equation 1, Vgs decreases as the source voltage approaches the gate voltage, so Id also decreases. When an N-type thin film transistor is taken as an example, when the level of the video signal supplied from the data driver 20 is higher than the voltage of the liquid crystal pixel, the liquid crystal pixel is charged. Is the pixel voltage. On the other hand, when the level of the video signal supplied from the data driver 20 is lower than the voltage of the liquid crystal pixel, the discharge operation is performed on the liquid crystal pixel, so that the source voltage of the thin film transistor becomes the level of the video signal. Therefore, Vgs is a voltage difference between the gate voltage Vg _(on) and the smaller value between the video signal level Vvideo and the pixel voltage Vpixel. This is expressed by the following formula 2.
(Equation 2)
Vgs = Vg _(on) − (Min [Vvideo, Vpixel])
Here, Vg _{(on) is set} to 12V, and Vvideo and Vpixel are in the range of 1.5V to 8.9V. In the case of negative polarity, Vvideo is 1.5 V, and Vpixel at that time is larger than Vvideo, so Vgs is 10.5 V. This voltage difference is sufficient to supply a sufficient current Id to the thin film transistor. On the other hand, in the case of the positive polarity, Vgs becomes small as the gate voltage Vg _(on) approaches Vvideo or Vpixel, and the change in the pixel voltage at that time is as follows.

That is, when the liquid crystal pixel is charged, Vvideo at that time is 8.9 V and Vpixel is 7.4 V, so Vgs is 4.6 V (Vgs = Vg _(on) −Vpixel = 4.6 V). It becomes. Furthermore, as the pixel voltage Vpixel gradually rises due to charging, Vgs gradually decreases and Id decreases, so the charging time required for the pixel voltage Vpixel to reach the target voltage level becomes longer.

On the other hand, when the liquid crystal pixel is discharged, Vvideo at that time is 7.4 V and Vpixel is 8.9 V, so Vgs is 4.6 V (Vgs = Vg _(on) −Vvideo = 4.6 V). It becomes. Further, as the pixel voltage Vpixel is discharged to the level of Vvideo, Vgs gradually increases and Id gradually increases. Therefore, the discharge time required for the pixel voltage Vpixel to reach the target voltage level is relatively long. short.

  Therefore, it is necessary to perform pre-charging only when the positive polarity signal charges the liquid crystal pixel. The example examined above is an example in which the thin film transistor is N-type, but if the thin film transistor is P-type, only when a negative signal discharges to the liquid crystal pixel. It is necessary to perform pre-charging.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to make a pixel reach a predetermined voltage level at a higher speed by appropriately selecting a timing for executing pre-charging. An object of the present invention is to provide a driving circuit and a driving method for a liquid crystal display panel.

In order to achieve the above object, the present invention includes a plurality of display units, and a plurality of N-type thin film transistors respectively connected to the common electrode voltage, the data electrode, and the gate electrode and corresponding to the display unit. A method of driving a liquid crystal display panel applied to a liquid crystal display panel, comprising: supplying a precharge pulse and a video signal to the data electrode; and supplying a scanning signal to the gate electrode. And the level of the precharge pulse is higher than the common electrode voltage when the display unit is positive, and is a voltage value that maximizes the gradation change of the display unit, On the other hand, when the display unit has a negative polarity, it is lower than the common electrode voltage and maximizes the gradation change of the display unit. In such a voltage higher voltage value than the value, i.e., it is achieved as a negative halftone value of the voltage value and the common electrode voltage that is the maximum change in gradation of the display unit .
The present invention is also applicable to a liquid crystal display panel including a plurality of display units and a plurality of P-type thin film transistors connected to the common electrode voltage, the data electrode, and the gate electrode, respectively, and corresponding to the display units. A method for driving a liquid crystal display panel, comprising: supplying a precharge pulse and a video signal to the data electrode; and supplying a scanning signal to the gate electrode. The level of the display unit is higher than the common electrode voltage when the display unit is positive and lower than a voltage value that maximizes the gradation change of the display unit, that is, the display unit. positive a halftone value, whereas, the display unit is negative voltage value, such as to maximize the change in gradation between the said common electrode voltage When it is achieved as a voltage value that is the maximum gradation changes in and the display unit at a lower than the common electrode voltage.

The present invention further includes a liquid crystal display comprising a plurality of display units and a plurality of N-type or P-type thin film transistors respectively connected to the common electrode voltage, the data electrode, and the gate electrode and corresponding to the display unit. A driving circuit for a liquid crystal display panel applied to the panel, a gate driver for supplying a scanning signal to the gate electrode, and a precharge pulse generator for supplying a precharge pulse to the data electrode And a data driver for supplying a video signal to the data electrode, and the level of the precharge pulse is determined when the thin film transistor is N-type and the display unit is positive. A voltage that is higher than the common electrode voltage and lower than a voltage value that maximizes the gradation change of the display unit. , And the other hand, when the display unit is negative, the common electrode voltage and in what lower gradation change of said display unit at a voltage value that is a maximum, i.e., the gradation of the display unit If the voltage value that maximizes the change is a negative halftone value of the common electrode voltage, and the level of the prior power reception pulse is P-type, the display unit is positive If the voltage is higher than the common electrode voltage and lower than the voltage value that maximizes the gradation change of the display unit, that is, the gradation change of the display unit is maximized. A positive halftone value between the common electrode voltage and the common electrode voltage. On the other hand, when the display unit is negative, the display unit is lower than the common electrode voltage and Change is achieved as a voltage value that is the maximum.

  According to the driving method and driving circuit of the liquid crystal display panel according to the present invention, when the N-type thin film transistor is used, the liquid crystal pixel is not precharged when the negative polarity is used, whereas the P-type thin film transistor is used. In this case, since the liquid crystal pixels are not precharged at the positive polarity, the time for the pixel voltage to reach the target level can be shortened, and the display quality of the liquid crystal display device can be improved.

In order that the present invention may be more fully understood, examples will be illustrated with reference to the drawings, and the present invention will be described in detail as follows. Needless to say, the embodiments described are not intended to limit the present invention.
FIG. 1 is a schematic diagram for explaining a display unit of a liquid crystal display device and a driving circuit thereof according to an embodiment of the present invention. Although only the circuit configuration of a single display unit is shown in FIG. 1, the overall circuit configuration of the liquid crystal display device is the same as that shown in FIG. One data electrode Dm and one gate electrode Gn control one display unit. As shown in FIG. 1, the equivalent circuit of each display unit is mainly composed of a thin film transistor Qmn for controlling the passage of display data and a storage capacitor Cmn. The gate and drain of the thin film transistor are connected to the gate electrode Gn and the data electrode Dm, respectively. In such a connection, the scanning signal passing through the gate electrode Gn can turn on / off all the thin film transistors on the same column (ie, on the same scanning line), and thus the image on the data electrode Dm. It is possible to control whether or not to write a signal (video signal) to the corresponding display unit. Further, the transfer gates 61 and 62 are used to control display of a predetermined area on the liquid crystal display panel, and are controlled by switching signals HSW and PSW, respectively. It must be explained that each display unit corresponds to only one bright spot on the LCD panel. Therefore, in the case of a single color LCD, each display unit corresponds to a single pixel, while in the case of a color LCD, each display unit is red (represented by R) and blue (represented by B). Or, each corresponds to a single subpixel that may be green (denoted by G). In other words, a set of sub-pixels (three display units) such as R, G, and B constitute one pixel.

  Next, the drive circuit portion will be described with reference to FIG. A gate driver 30 supplies a scanning signal (also referred to as a scanning pulse) to each gate electrode according to a predetermined scanning order. When a scanning signal is applied to a certain gate electrode, the thin film transistors in all the display units on the same column or the same scanning line are turned on. When a scanning line is selected, the data driver 40 supplies a corresponding video signal to m display units connected to the column via the data electrode Dm based on the video data to be displayed.

  In the embodiment of the present invention, the precharge pulse generator 50 is for supplying a precharge pulse to the data electrode Dm. As described above, the level of the precharge pulse is higher than the common electrode voltage VCOM when the display unit is positive, and the voltage value (maximum positive) that maximizes the gradation change of the display unit. Value). On the other hand, when the display unit has a negative polarity, the level of the precharge pulse is lower than the common electrode voltage VCOM and higher than a voltage value that maximizes the gradation change of the display unit, that is, This is not a voltage value (negative maximum value) that maximizes the gradation change of the display unit. Therefore, in the case of the negative polarity, the level of the precharge pulse may be a negative halftone value or the common electrode voltage VCOM, or the supply itself may not be performed.

  In the above-described embodiments, the N-type thin film transistor has been described as an example. However, in the case of the P-type thin film transistor, the level of the precharge pulse is the common electrode when the display unit is in the negative polarity. The voltage value is lower than the voltage VCOM and is a voltage value (maximum negative value) that maximizes the gradation change of the display unit. On the other hand, when the display unit is positive, the level of the precharge pulse is higher than the common electrode voltage VCOM and lower than a voltage value that maximizes the gradation change of the display unit, that is, This is not a voltage value (positive maximum value) that maximizes the gradation change of the display unit. Therefore, in the case of the positive polarity, the level of the precharge pulse may be the positive polarity intermediate gradation value or the common electrode voltage VCOM, or the supply itself may not be performed.

  FIG. 2 is a signal timing diagram of the liquid crystal display device according to the embodiment of the present invention. Here, an example in which a precharge pulse of 8.9 V is applied when the pixel voltage is positive and the target pixel voltage is 8.9 V is taken as an example. First, when a precharge pulse is supplied from the precharge pulse generator 50 to the transfer gate 62, and the switching signal PSW turns on the transfer gate 62, the level of the data electrode Dm is raised thereby, and the level of the precharge pulse 8. It reaches 9V. Next, when a high level gate scanning signal is applied to the gate electrode Gn, the level of the data electrode is slightly lowered and the pixel voltage is raised due to the capacitor coupling action. At the same time, the switching signal HSW is applied to the transfer gate 61. turn on. Thereafter, the video signal (8.9V) supplied from the data driver 40 continues to increase the levels of the data electrode and the pixel voltage until the target level of 8.9V is reached. Since the level of the precharge pulse is the same as that of the video signal, only the video signal is displayed in the figure.

  By such a precharging operation, the level of the data electrode and the pixel can be increased in advance, so that the pixel voltage Vpixel can reach the target level in a shorter time. In the case of an N-type thin film transistor, it is not necessary to perform precharging when the display unit is negative. However, if precharging is performed, the value is lower than the negative maximum value of the common electrode voltage VCOM. Care must be taken not to charge until the pixel voltage reaches the target level with excessive precharging.

  Although the preferred embodiment of the present invention has been illustrated as described above, this is not intended to limit the present invention, and some modifications that can be made by those skilled in the art without departing from the spirit and scope of the present invention. It is possible to add or modify. Accordingly, the scope of the protection claimed by the present invention is based on the scope of the claims.

1 is a schematic diagram illustrating a display unit and a driving circuit of a liquid crystal display device according to an embodiment of the present invention. FIG. 5 is a signal timing diagram of the liquid crystal display device according to the embodiment of the present invention. It is the schematic which shows the equivalent circuit of the conventional thin-film transistor liquid crystal display panel and its peripheral drive circuit. It is a figure which shows the relationship between the voltage difference applied to a liquid crystal, and the time of each flame | frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 10, 30 Gate driver 20, 40 Data driver 200 Display unit 50 Precharge pulse generator 61, 62 Transfer gate D1, D2, D3, ..., Dm Data electrode G1, G2, ..., Gn Gate Electrodes HSW, PSW Switching signals Q11 to Q1, Q21 to Q2,..., Qn1 to Qnm Thin film transistors C11 to C1m, C21 to C2m,.

Claims (3)

Multiple display units;
A plurality of N-type thin film transistors respectively connected to the common electrode voltage, the data electrode, and the gate electrode and corresponding to the display unit;
A liquid crystal display panel driving method applied to a liquid crystal display panel comprising:
Supplying a precharge pulse and a video signal to the data electrode;
Supplying a scanning signal to the gate electrode,
The level of the precharge pulse is a voltage value that is higher than the common electrode voltage and maximizes the gradation change of the display unit when the display unit is positive. When the display unit has a negative polarity, the voltage value is lower than the common electrode voltage and higher than the voltage value that maximizes the gradation change of the display unit, that is, the gradation change of the display unit. A driving method for a liquid crystal display panel, characterized by having a negative halftone value between a maximum voltage value and the common electrode voltage . Multiple display units;
A plurality of P-type thin film transistors respectively connected to the common electrode voltage, the data electrode, and the gate electrode and corresponding to the display unit;
A liquid crystal display panel driving method applied to a liquid crystal display panel comprising:
Supplying a precharge pulse and a video signal to the data electrode;
Supplying a scanning signal to the gate electrode,
The level of the precharge pulse is a voltage value that is higher than the common electrode voltage and lower than a voltage value that maximizes the gradation change of the display unit when the display unit is positive . That is, it is a positive intermediate gradation value of the voltage value that maximizes the gradation change of the display unit and the common electrode voltage , while the common electrode when the display unit is negative A method for driving a liquid crystal display panel, characterized in that the voltage value is lower than the voltage and maximizes the gradation change of the display unit. Multiple display units;
A plurality of N-type or P-type thin film transistors respectively connected to the common electrode voltage, the data electrode, and the gate electrode and corresponding to the display unit;
A liquid crystal display panel drive circuit applied to a liquid crystal display panel comprising:
A gate driver for supplying a scanning signal to the gate electrode;
A precharge pulse generator for supplying a precharge pulse to the data electrode;
A data driver for supplying a video signal to the data electrode;
The level of the precharge pulse is higher than the common electrode voltage and maximizes the gradation change of the display unit when the thin film transistor is N-type and the display unit is positive. On the other hand, when the display unit is negative, the voltage value is lower than the common electrode voltage and maximizes the gradation change of the display unit when the display unit is negative . That is, a negative halftone value between the voltage value that maximizes the gradation change of the display unit and the common electrode voltage,
The level of the prior power reception pulse is higher than the common electrode voltage and maximizes the gradation change of the display unit when the thin film transistor is P-type and the display unit is positive. A voltage value lower than the voltage value, that is, a positive halftone value of the common electrode voltage and a voltage value that maximizes the gradation change of the display unit, while the display unit A driving circuit for a liquid crystal display panel, having a negative voltage and a voltage value lower than the common electrode voltage and maximizing a gradation change of the display unit .

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