KR20040047242A - Method for driving a Liquid Crystal Display of large panel and high resolution - Google Patents

Abstract

PURPOSE: A method for driving a large scale high resolution liquid crystal display device is provided to solve the charge error due to the RC delay and the non-uniformity of the liquid crystal display device. CONSTITUTION: A method for driving a large scale high resolution liquid crystal display device is characterized in that it is driven by differently adjusting the voltage application times for the pixels in response to the data line lengths between the source drivers for supplying the voltage to the pixels and the pixels.

Description

{Method for driving a Liquid Crystal Display of large panel and high resolution}

The present invention relates to a method for driving a large-area high-resolution liquid crystal display device. More particularly, the present invention provides a method of varying a voltage application time for the pixels according to a source line providing a voltage to the pixels and a data line length between the pixels. The present invention relates to a method for driving a liquid crystal display device, characterized in that for adjusting and driving.

Liquid crystal display (LCD), one of the flat panel display devices for displaying letters, symbols, or graphics, is a display that combines liquid crystal technology and semiconductor technology by using the optical properties of liquid crystals whose molecular arrangement is changed by an electric field. Device. A thin film transistor (TFT) liquid crystal display uses a TFT as a switching element for turning an internal pixel on and off, and the pixels are turned on and off as the TFT is turned on and off. In a typical TFT liquid crystal display device, as shown in FIG. 1, cells 130 constituting pixels are arranged in an array, and each cell has a liquid crystal cell 134, a storage capacitor (CST), and a switch function. It consists of TFT 132 which makes.

The source electrodes of each TFT are commonly connected in the column direction to form data lines D1 to D _N , and then connected to the data driver 120, and the gate electrodes of each TFT are rowed. The scan lines S1 to _{S M} are connected in common to each other, and then connected to the gate driver 110 to implement a display device having N × M resolution. The data driver 120 may also be referred to as a source driver or a column driver, and the gate driver may also be referred to as a row driver or a scan driver.

When driving the pixel array, if voltage is applied to only one direction of the liquid crystal of the pixel, the degradation of the liquid crystal is promoted, and thus the image data voltage applied to the liquid crystal should be periodically inverted to the opposite polarity. The period in which the data voltage is applied in the opposite direction to the normal direction is changed every field. The field inversion or frame inversion method of inverting the voltage polarity of all the pixels of the panel at once in each field, inverting by row line The line inversion method, the column inversion method to invert by column line, and the dot inversion method to invert by each pixel, etc. are mentioned. In either case, the pixel voltage (the voltage applied to the pixel electrode connected to the drain of the TFT) is alternately changed so that the pixel voltage (the voltage applied to the pixel electrode connected to the drain of the TFT) is positive or negative with respect to the common voltage Vcom.

2 illustrates a data driver of a general liquid crystal display device. In Fig. 2, the data driver is composed of a latch unit 200 composed of a shift register, a sampling latch and a holding latch, a D / A converter, an output buffer, a data latch (not shown), a bidirectional polarity inversion circuit (not shown), and the like. . The shift register generates a clock for latching data in the sampling latch, and the data signal for one line sequentially stored in the sampling latch is transferred to the holding latch and provided to the D / A converter, and the D / A converter provides digital data. Convert to an analog signal. The output buffer receives the output of the D / A converter and drives the data lines D1, D2, ....

Such a liquid crystal display device has various advantages, such as ultra-thin, high resolution, and low power consumption, compared to a CRT (cathode ray tube).

3 illustrates a voltage application waveform (scan waveform) of a general liquid crystal display device. In general, a liquid crystal display device is driven by sequentially selecting G1 row, G2 row, and G3 row to turn on the TFT of the pixel for a uniform time, and outputting from the source driver during the time (scan time) of the TFT of the pixel. The data signal voltage is applied to the pixel to charge it.

However, when the area of the liquid crystal display device is increased and the resolution is increased, the length of the signal line (that is, the data line or the source line) of the liquid crystal display device is increased, thereby increasing the resistance and capacitance of the signal line and transferring the signal lines to the signal line. It causes RC delay of the signal.

Figure 4 illustrates the effect of the resistors and capacitors on the data line on the signal. In FIG. 4, assuming that the waveform before passing through the RC equivalent data line 420 is the data signal 410 output from the source driver, the data signal 430 passing through the data line is the data line 420. It can be seen that the charge and discharge time increases due to the RC delay caused by the resistor and the capacitor.

As such, if a signal delay occurs due to the RC, the RC-affected data signal does not fully charge the pixel during a given scan time, that is, a time for turning on the TFT of the pixel, thereby causing a charging error.

This RC delay is greatest in the output data signal of the source driver which performs the inversion driving due to the characteristics of the LCD. In particular, the RC delay of the signal is greater in pixels that are far from the output of the source driver. Due to the RC delay of this data line, there is a problem in that the data signal to be charged in the pixel cannot be charged within the scan time of the TFT, and thus the desired data signal cannot be displayed in the pixel.

Therefore, the present inventors have studied to solve the problem of insufficient charging time of the data signal due to the RC delay of the signal line, which is the biggest problem in the large-area and high-resolution liquid crystal display device as described above. In the case of driving the voltage application time for the pixels differently according to the data line length between the pixels, for example, the data signal is charged to the pixels with less RC influence and the remaining scan time is not affected by the RC influence. In addition to the time required for charging the large pixels, the signal delay due to the RC delay can be compensated for, and the charging error and the large-area high resolution LCD display panel can be compensated for by applying a voltage during the time required for charging. It was confirmed that the problem of non-uniformity of gradation could be solved, and the present invention was completed.

Accordingly, it is an object of the present invention to provide a novel driving method for driving a large area high resolution liquid crystal display device.

1 shows a typical TFT-LCD,

2 illustrates a data driver of a general liquid crystal display device.

FIG. 3 illustrates a typical voltage application waveform (scan waveform) when the liquid crystal display is driven.

4 illustrates a delay result of a signal due to RC influence of a data line,

5 illustrates a scan waveform in the driving method according to the present invention,

6 is a layout of unit pixels for obtaining capacitance values of a data line and a gate line.

7 is an equivalent circuit model of a unit pixel,

8 is a model of the resistance and capacitance of the gate line as a T3 equivalent circuit,

9 shows a modeled equivalent circuit of a panel of a liquid crystal display,

10 is a result of simulating the charging time for each block required to charge the capacitor by HSPICE,

FIG. 11 illustrates scan time per block when the scan time per block is adjusted differently by applying the driving method according to the present invention.

<Explanation of symbols for the main parts of the drawings>

110: gate driver 120: data driver

130: pixel configuration cell 132: TFT

134: liquid crystal cell

410: data signal output from the source driver

420: RC equivalent data line

430: data signal after passing through the data line

The present invention provides a method of driving a large-area, high-resolution liquid crystal display device, by adjusting a voltage application time (scan time) for the pixels differently according to a data line length between the pixels and a source driver for providing a voltage to the pixels. The present invention relates to a liquid crystal display driving method.

In the above driving method, the voltage application time is shortened for pixels that are located close to the source driver and are less affected by the RC delay of the data line, and are located far from the source driver so that the RC of the data line can be located. By increasing the voltage application time for the pixels affected by the delay, the insufficient charging time may be compensated for by the RC delay.

Preferably, the voltage application time for the pixels is preferably determined in proportion to the RC delay according to the data line length between the pixels and the source driver.

In general, in a liquid crystal display, since the data line lengths between the pixels of the same row and the source driver are the same, the voltage application time is made the same by applying the voltage to the pixels of the same row at the same time. Also, it is preferable that the sum of the voltage application times for the pixels in each row is equal to the frame period.

On the other hand, when the total of the voltage application time is less than one frame period, it is possible to increase the driving frequency. One frame period is the time taken to generate the entire screen by scanning it once. For example, in the case of driving at 60 Hz, one frame period is the time for displaying 60 screens on the screen in one second, that is, the time of 1/60 second. it means. As a result of applying the driving method according to the present invention, if the charging time of the entire panel is less than 1/60 sec, it is possible to drive at a driving frequency higher than the driving frequency of 60 Hz.

Hereinafter, an embodiment of a method of driving a large area high resolution liquid crystal display according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited by the following examples.

5 illustrates a scan waveform in a method of driving a large area high resolution liquid crystal display according to the present invention.

As shown in FIG. 5, the driving time is adjusted by differently adjusting the voltage application time for the pixels according to the source line providing the voltage to the pixels and the data line length between the pixels. That is, the voltage application time is shortened for pixels (for example, pixels in the G1 row) that are located close to the source driver and are less affected by the RC delay of the data line. On the contrary, the voltage application time is extended for the pixels (eg, pixels in the Gn row) which are located far from the source driver and greatly affected by the RC delay of the data line. Therefore, the insufficient charging time can be compensated for by the RC delay.

Hereinafter, a driving method according to the present invention will be described through a simulation experiment for driving a large area high resolution liquid crystal display device.

1. Experimental conditions

end. Modeling of LCD Panel

In order to confirm the effect of the driving method according to the present invention, a simulation was performed to drive a large-resolution high-resolution TFT-LCD of the 30-inch UXGA class (1600 × 1200), which was electrically modeled.

In the 30-inch UXGA TFT-LCD, all values except the resistance value of the data line, the capacitance value, and the mobility of the TFT were fixed and simulated. This is because the resistance and capacitance values of the data line and the mobility of the TFT are the most dominant elements among the factors that can cause the charging error in the pixel. The channel width and channel length of the TFT were fixed to 20 μm and 4 μm, respectively.

In order to electrically model the panel of the 30-inch UXGA TFT-LCD, the resistance and capacitance values were calculated as follows.

In order to obtain the capacitance value, the unit pixels are laid out as shown in FIG. 6. An equivalent model of the unit pixel is illustrated in FIG. 7. In the equivalent model, C _gs is a gate-source overlap capacitor, C _gd is a gate-drain overlap capacitor, C _sd is a source-drain overlap capacitor, C _s is a storage capacitor, and C _LC is a load capacitor .

The parasitic capacitance of each unit pixel of the 30-inch UXGA liquid crystal display was extracted using Raphael ^™ , an RLC extraction simulator. Parasitic capacitances of the extracted unit pixels are shown in Table 1 below:

[Table 1] Parasitic capacitance of each unit pixel of 30-inch UXGA LCD

Capacitor Capacitance C _gs (gate-source overlap capacitor) 0.77fF C _gd (gate-drain overlap capacitor) 3.625fF C _sd (source-drain overlap capacitor) 0.0028 pF C _s (storage capacitor) 0.191 pF C _LC (load capacitor) 1.1 pF

By multiplying the parasitic capacitance value for the unit pixel by the number of pixels according to the resolution, it is possible to obtain the total capacitance value of the gate line and the data line.

The resistance values of the gate line and the data line were calculated assuming that the materials of the gate line and the data line were Al alloy and Mo (the specific resistivity of this material was 5.2 kcm and 12 kcm, respectively) and the line width was 10 m.

The resistance and capacitance values of the gate line and data line calculated as described above are shown in Table 2 below:

[Table 2] Resistance and capacitance values of gate lines and data lines

Resistance Capacitance value Gate line 10kΩ 266pF Data line 15kΩ 140 pF

The panel of the 30-inch UXGA LCD was electrically modeled using the resistance and capacitance values of Tables 1 and 2.

The resistance and capacitance of the gate line can be modeled with a T3 equivalent circuit. For example, when the resistance is R and the capacitance is C, it may be modeled as a T3 equivalent circuit as shown in FIG. 8.

The assumed TFT-LCD has a resolution of 1600 x 1200 UXGA, and the number of vertical pixels is 1200, so that there are 1200 gate lines. When the 1200 gate lines are divided into 20 blocks, each block has 60 pixels, which is modeled as an equivalent circuit using the assumed resistance value and capacitance value. The modeled panel was used to simulate HSPICE. The modeled equivalent circuit of the panel is shown in FIG. 9.

I. Scan time of one row

One frame time is the time taken to generate the entire screen by scanning it once. For example, in the case of driving at 60 Hz, one frame period is a time for displaying 60 screens on the screen in one second, that is, a time of 1/60 second. it means. Thus, the scan time of one row for simulation at UXGA resolution (with 1200 vertical pixels) is 1/60/1200 = 13.8 ms. However, the actual charging time for pixel charging is the information input to the selected one row of pixels. Should be determined as the time that does not affect the next row. Therefore, in consideration of the rising time and the falling time of the scan waveform generated during the scan of one row, 10 ms is set as the scan time of one row.

All. Definition of charging error

It is assumed that the voltage charged in the block pixel is inverted from the lowest voltage of the negative region to the highest voltage of the positive region in the range of 0.5V to 9.5V. Based on 7mV, which is less than 1/2 of the 1-gray spacing voltage among 256 grays implemented with 8 bits, it is defined that a charging error occurs when a larger voltage error occurs.

In addition, it is defined that a charging error occurs even when a voltage charging time required to charge a desired voltage in an arbitrary pixel is longer than the selection time (10 ms) of the one row.

2. Simulation

end. Setting resistance value and TFT mobility of data line

The resistance value of the data line of the 30-inch UXGA TFT-LCD was set to 15 kPa, and the mobility of the TFT was set to 0.65 cm ² / V · sec. Other values were simulated with the modeled values. This is because, as described above, the resistance of the data line and the mobility of the TFT are the most dominant elements among the factors that can cause the charging error in the pixel.

I. Charge time measurement

In order to measure the pixel charging time, HSPICE simulates the charging time required for each block to charge the capacitor through the TFT corresponding to the pixel in each block of the gate line modeled as 20 blocks as described above. It was.

10 shows the simulation results. As can be seen from Fig. 10, since the B1, B2, and B3 blocks, etc., which are close to the driving driver have little effect of resistance and capacitance, the charging time for charging the voltage is shorter than the scan time (10 ms) of a row. It can be seen that. However, as the pixel of the block moves away from the driver, it can be seen that the charging time is longer than the scan time of one row due to the influence of resistance and capacitance. Therefore, it can be seen that a charging error may occur when the general driving method is applied to the pixels that are charged over a predetermined scan time.

Table 3 below shows the charging time of the charging voltage charged in the pixels of each block:

[Table 3] Charging time of charging voltage charged in pixel of each block

Pixel block Charging time Extra time Total time Cumulative totaling time B1 8.47 1.53 91.8 91.8 B2 8.77 1.23 73.8 165.6 B3 8.96 1.04 62.4 228 B4 9.15 0.85 51 279 B5 9.31 0.69 41.4 320.4 B6 9.42 0.58 34.8 355.2 B7 9.53 0.47 28.2 383.4 B8 9.65 0.35 21 404.4 B9 9.76 0.24 14.4 418.8 B10 9.84 0.16 9.6 428.4 B11 9.91 0.09 5.4 433.8 B12 9.99 0.01 0.6 434.4 B13 10.03 -0.03 -1.8 432.6 B14 10.06 -0.06 -3.6 429 B15 10.14 -0.14 -8.4 420.6 B16 10.18 -0.18 -10.8 409.8 B17 10.2 -0.2 -12 397.8 B18 10.22 -0.22 -13.2 384.6 B19 10.22 -0.22 -13.2 371.4 B20 10.22 -0.22 -13.2 358.2

The charging time required in Table 3 represents the time required for charging each block pixel. The spare time is a value obtained by subtracting the charging time from the scan time (10 ms) of one row. The summation time is a time obtained by converting the spare time into a value for the entire pixel, that is, 60 pixels. The cumulative summation time is a time in which the summation time of each block is accumulated.

As can be seen from the above table, it can be seen that a charging error has occurred since the charging time takes longer than the scan time of one row in the pixels of blocks B13 to B20.

All. Adjusting Scan Time

According to the present invention, the scan time was adjusted in the following manner in order to drive the liquid crystal display by differently adjusting the scan time for the pixels:

First, a pixel block in which charging is completed within a selection time of one row was found. In the above experiment, B1 to B12 correspond.

Then, the remaining time after the blocks are fully charged, that is, the remaining time after subtracting the charging time from the actual scan time is obtained. Subsequently, the summation time obtained by converting the spare time into values for all the pixels, that is, 60 pixels, is calculated.

Then, the charging error generating pixel blocks which are charged by passing the selection time of one row are found (B13 to B20 in the above experiment), and the time required to fully charge these blocks is calculated.

Finally, the total time of the fully charged blocks is compared with the time required to fully charge the pixel block in which the charging error occurs. As a result of the comparison, when the summation time of the fully charged blocks is larger than the time required to fully charge the pixel blocks in which the charging error has occurred, the scan time may be adjusted and driven differently according to the present invention.

FIG. 11 illustrates scan time per block when the scan time per block is adjusted differently by applying the driving method according to the present invention. In FIG. 11, blocks B1 to B12 are charged with a charging time less than 10 ms, which is a scan time of one row, and blocks of B13 to B20 are charged for a longer time than this.

That is, the pixels with less RC influence are determined as the minimum scan time for full charging of the data signal, and the pixels with large RC influence are charged with the scan time as long as necessary for the full charging time. In this way, by compensating the effect of the RC of the data line, it is possible to represent the image while preventing the charging error when applying the data signal voltage.

In the case of driving with a conventional uniform row selection time, a pixel charging error occurs due to an increase in the resistance value and the capacitance value of the data line due to the large area of the LCD.

However, as can be seen from the above experiment, when driving a large-area high-resolution liquid crystal display device according to the driving method of the present invention, a signal delay due to RC delay, which is the biggest problem when driving a large-area high-resolution liquid crystal display device, is compensated. In addition, since charging is performed by applying a voltage for the time required for charging, the charging error due to the RC delay and the nonuniformity of the display of the liquid crystal display can be solved.

Claims (5)

In a large area high resolution liquid crystal display device driving method, And driving a voltage application time for the pixels differently according to a source driver for providing a voltage to the pixels and a data line length between the pixels. The method of claim 1, wherein the voltage application time is shortened for pixels that are located close to the source driver and are less affected by the RC delay of the data line, and are located far from the source driver. A method of driving a liquid crystal display device, wherein a voltage application time is extended for pixels that are greatly affected by a delay. The method of claim 1, wherein a voltage application time for the pixels is proportional to an RC delay according to a data line length between the pixels and a source driver. 2. The method of claim 1, wherein the data line lengths between the pixels in the same row and the source driver are the same, and voltages are simultaneously applied to the pixels in the same row. The method of driving a liquid crystal display device according to claim 4, wherein the sum of voltage application times for pixels in each row is equal to a frame period.