JP2897779B2 - Method and apparatus for driving liquid crystal panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding a liquid crystal panel driving method, when a liquid crystal panel having a simple matrix structure is driven by using a voltage averaging method, occurrence of luminance unevenness depending on a display pattern for each line is suppressed. For the purpose, a matrix-type liquid crystal panel provided with data electrodes and scan electrodes crossing each other is applied with a predetermined voltage V applied to the selected data electrodes based on a voltage applied to the selected scan electrodes, (1-2a) V is applied to the unselected data electrodes, and (1-1 / a) V is applied to the unselected scan electrodes, and a positive voltage application mode period is applied to the selected data electrodes. Based on the voltage, a negative voltage is applied to apply V to the selected scan electrode, apply (2 / a) V to the unselected data electrode, and apply (1 / a) V to the unselected scan electrode. Drive in the voltage application mode period In this method, the magnitude of the correction voltage is determined in accordance with the ratio of light and dark of the data displayed on the selected scan electrode for each scan electrode driving time, and this correction voltage is applied to the positive voltage application mode period and the negative voltage application. Driving is performed with the polarity opposite to that in the mode period and added to the selection voltage of the scan electrode.

Further, in the method of driving the liquid crystal panel, if the ratio of lightness and darkness of data displayed on the selected scan electrode is calculated by performing weighting on each data in accordance with a distance from the scan driver output, the display is performed. A correction voltage that can further reduce unevenness can be obtained.

Further, a driving device for a simple matrix type liquid crystal panel including a data electrode driver and a scan electrode driver for performing the above-described method includes a selection voltage and a non-selection voltage for a positive voltage application mode period and a negative voltage application mode period, A power supply circuit for applying a selection voltage and a non-selection voltage in the positive voltage application mode period and the negative voltage application mode period to the scan electrode driver, a control circuit for sending a data signal to the data electrode driver and a scan signal to the scan electrode driver, and the control circuit , A positive voltage application mode period,
A voltage polarity switching circuit for switching between a negative voltage application mode period, a correction parameter generation circuit for measuring a light / dark ratio of data displayed on a selected scan electrode for each scan electrode driving time, and generating a correction parameter; The power supply circuit includes a correction voltage generation circuit that generates a correction voltage having a magnitude corresponding to the correction parameter, and a voltage addition circuit that adds the correction voltage to a scan voltage when the power supply circuit is selected.

[Industrial applications]

The present invention relates to a method and a device for driving a liquid crystal panel having a simple matrix structure.

In recent years, with the spread of personal computers, word processors, and the like, the adoption of a liquid crystal display device that is lightweight, thin, and can be driven by a battery has become remarkable as a display device instead of a large-sized and power-consuming CRT. Driving methods of liquid crystal display devices are roughly classified into simple matrix type and active matrix type, but active matrix type is difficult to structure because each pixel requires a non-linear element. Display devices generally employ a simple matrix structure.

However, in a display device having a simple matrix structure, as the display capacity is increased, display unevenness (crosstalk) depending on the display pattern occurs due to its characteristics, and display quality deteriorates. Therefore, it is strongly desired to eliminate the display unevenness. ing.

[Conventional technology]

FIG. 8, in the liquid crystal panel of simple matrix structure shown in FIG. 9, "bright" when the write (of the liquid crystal display is a liquid crystal display device of the entire line as the X ₁ row and X ₂ columns ○ ), And the driving waveform of the liquid crystal panel when writing “dark” (the display of the liquid crystal is ●). In FIG. (A) is X ₁ column of data voltage application waveform (thick line),
X is a data voltage application waveform (dotted line) of _two columns, and (b) is Y ₁
Scan voltage waveform applied row, and (c) Y ₂ rows of scan voltage waveform applied, it is (d) the drive voltage waveform of the cell alpha (thick line), the driving voltage waveform of the cell beta (dotted line).

In the conventional driving method, the voltage averaging method shown in FIG. 10 is employed, in which the first cycle is selected during one frame period, and the second cycle is selected in the next frame, Switching between the first period and the second period every several lines is practically used, and a DC component is not applied to the liquid crystal to realize highly reliable driving without deteriorating the panel characteristics.

The switching between the first cycle and the second cycle is called polarity inversion, and the control signal thereof is called a polarity inversion signal.

[Problems to be solved by the invention]

However, in the conventional driving method, for example, as shown in FIG. 11, the “bright” (）) display of the cell A immediately after displaying a large number of “dark” (●) on a certain scan electrode and the “bright” There is a problem that the cell A becomes brighter than the cell B when compared with the "bright" display of the cell B immediately after the large number of display.

This problem will be described in more detail with reference to FIGS. It is known that the apparent resistance of the liquid crystal cell is lower in the "bright" display than in the "dark" display, and therefore, a larger current flows to the scan electrode in the "bright" display. Flow in. Therefore, as shown in FIG.
When liquid crystal cells 1 to N are connected to one scan electrode via resistors R, respectively, the potential difference Vd between both ends of the scan electrode can be expressed by the following equation.

Here, the "dark" display at the time of _{i K (K = 1~N) =} i B, "bright" display at the time of _{i K (K = 1~N) =} i W, and if put, "bright" display of The fact that a larger current flows into the scan electrode at the time can be expressed by i _W = i _B + Δi. Then, the potential difference VdB of the scan electrode when all the cells 1 to N perform the “dark” display is: , And “light” in cells X to Y (1 ≦ X <Y ≦ N)
The potential difference VdPW of the scan electrode at the time of display is further reduced by the following formula by displaying “bright” in the cells X to Y in the aforementioned potential difference VdB, It is because the amount is added.

Therefore, the scan voltage becomes “dark” as shown in FIG.
The difference between the case where many displays are performed (thick line) and the case where many “bright” displays are performed (dotted line) is different. When the “bright” display is performed, the selection voltage level of the scan voltage application waveform is the first. It increases in the cycle and decreases in the second cycle. Then the 14th
As shown in FIG. 15 and FIG. 15, the voltage level during the selection period of the cell drive waveform fluctuates, and the effective voltage decreases in both the “bright” display and the “dark” display cells.

As a result, the cells on the scan electrode displaying a large number of “bright” have a darker display than the cells on the scan electrode displaying a large number of “dark”.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal panel driving method and a liquid crystal panel driving method capable of suppressing the occurrence of luminance unevenness in the conventional simple matrix liquid crystal display device.

[Means for solving the problem]

FIG. 1 shows the principle configuration of an apparatus for implementing the liquid crystal panel driving method of the present invention which solves the above-mentioned conventional problems. The device of the present invention is a device for driving a simple matrix type liquid crystal panel 3 provided with a data electrode driver 1 and a scan electrode driver 2, wherein the data electrode driver 1 selects between a positive voltage application mode period and a negative voltage application mode period. A power supply circuit 4 for applying a voltage and a non-selection voltage, a selection voltage and a non-selection voltage to the scan electrode driver 2 during the positive voltage application mode period and the negative voltage application mode period, a data signal to the data electrode driver 1, and a scan to the scan electrode driver 2 A control circuit 5 for transmitting a signal; a voltage polarity switching circuit 6 for switching between a positive voltage application mode period and a negative voltage application mode period in accordance with a signal from the control circuit 5; A correction parameter generation circuit 7 for measuring a ratio of light and dark of data displayed on the scan electrode to generate a correction parameter; Includes a correction voltage generation circuit 8 that generates a correction voltage of a magnitude corresponding to the correction parameter is, the voltage addition circuit 9 adds the correction voltage to the scan voltage during selection of the power supply circuit 4.

[Action]

According to the present invention, the amount of voltage level variation of the waveform applied to the liquid crystal cell depending on the display pattern for each line is obtained from the display pattern, and when there are many "bright" displays, the selection voltage level of the scan electrode is changed in the first cycle. The power supply circuit is controlled to increase in the second cycle so as to increase. As a result, even when the display pattern changes, the selection voltage level of the scan electrode does not fluctuate, thereby suppressing luminance unevenness.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a circuit diagram showing a configuration of an embodiment of a liquid crystal panel driving device embodying the present invention. In the figure, a data electrode driver (X driver) 21 is applied to a data electrode of a liquid crystal panel 23, and a scan electrode driver (Y driver) is applied to a scan electrode.
Drivers) 22 are connected respectively. Reference numeral 24 denotes a power supply circuit which divides between two power supplies V _CC and V _DD by a plurality of resistors to generate voltages V _{1 to} V ₆ . The voltage V ₁ ~V ₆ is the voltage needed to perform the voltage averaging method described in Figure 10, the _{value, V 1 = V V 4 =} (2 / a) V V 2 = (1-1 _{/ a) V V 5 = (} 1 / a) V V 3 = (1-2 / a) is a V V ₆ = 0, where a is a number determined by the duty ratio.

The data electrode driver 21 is supplied with the voltages V ₁ , V ₃ , V ₄ , and V ₆ from the power supply circuit 24, and the scan electrode driver 22 receives the voltages from the power supply circuit 24 through a correction voltage addition circuit 29 described later. Each potential of V ₁ , V ₂ , V ₅ and V ₆ is applied. A liquid crystal panel controller 26 is connected to the data electrode driver 21 and the scan electrode driver 22. The liquid crystal panel control device 26 sends X data XDATA and Y data YDATA, which are liquid crystal panel display data, to the data electrode driver 21 and the scan electrode driver 22 in response to a command from a control device such as a personal computer 25. , And a signal DF for switching between the positive voltage application mode period and the negative voltage application mode period (hereinafter, an example in which switching is performed for each frame will be described). It is.

The data electrode driver 21 and the scan electrode driver 22 receive X data XDATA from the liquid crystal panel controller 26,
Each data electrode of the liquid crystal panel 23 according to the Y data YDATA,
And the aforementioned voltage V ₁ from the power supply circuit 24 to each scan electrode.
Providing by selecting one of ~V _6. That is, during the positive voltage application mode, the data electrode driver 21 outputs the X data XD
0 is applied to the data electrode selected based on the ATA, and (2 / a) V is applied to the non-selected data electrode. The scan electrode driver 22 applies the selected scan electrode to the selected scan electrode based on the Y data YDATA. V for non-selected scan electrodes (1 / a)
V is applied. Similarly, during the negative voltage application mode period, the data electrode driver 21 applies V to the data electrode selected based on the X data XDATA and (1) to the unselected data electrode.
−2 / a) V is applied, and the scan electrode driver 22 applies 0 to the selected scan electrode based on the Y data YDATA.
And (1-1 / a) V is applied to unselected scan electrodes.

In this embodiment, in addition to the above configuration, a correction parameter generation circuit 27, a D / A conversion circuit 28, and a correction voltage addition circuit 29 are provided. Correction parameter generation circuit 27
X data XDAT in synchronization with the data clock signal DCLK
Data latch circuit 271 for capturing A and data latch circuit
A data detection circuit 272 for detecting “on” data from the output of the data clock signal 271 and the data clock signal DCLK;
The number of "ON" data is obtained in response to the output of
Consists of three. A scan synchronization signal SSYNC for synchronizing scan electrode driving is connected to the initialization input RST of the counter 273, and the counter 273 is reset and set to an initial state every one scan drive period. The D / A conversion circuit 28 generates a correction voltage, and converts a digital count result output from the counter 273 into a voltage value corresponding to the digital count result. Further, the correction voltage addition circuit 29 and the adder circuit 291 for adding the correction voltage to the scan electrode selection voltage V ₁ of the power supply circuit 24, an inverting circuit 292 for inverting the correction voltage, to the scan electrode selection voltage V ₆ of the power supply circuit 24 An addition circuit 293 for adding the inverted correction voltage is provided.

Next, operations of the correction parameter generation circuit 27, the D / A conversion circuit 28, and the correction voltage addition circuit 29 configured as described above will be described. The X data XDATA output from the liquid crystal panel control device 26 is sent to the data electrode driver 21 and simultaneously taken into the data latch circuit 271 therein by the correction parameter generation circuit 27 in synchronization with the data clock signal DCLK. Output immediately. And
In the data detection circuit 272, the AND of the output of the data latch circuit 271 and the data clock signal DCLK is obtained, so that a pulse is output from the data detection circuit 272 only when the X data XDATA is "ON". A scan synchronization signal SSYNC for synchronizing scan electrode driving is input to an initialization input RST of the counter 273 to which this output is input, and the counter 273 is reset every one scan driving period. In, the number of “ON” in the X data XDATA in one scan drive period is counted by the number of rising or falling edges of the pulse output from the data detection circuit 272, and the result is output as a correction parameter.

This correction parameter output is converted into a voltage by a D / A conversion circuit 28, which is a subsequent correction voltage generation circuit, and output as a correction voltage. This correction voltage is applied to a correction voltage addition circuit.
Is directly input to the adder 291 in the 29, the scan electrode selection voltages V ₁ is corrected. Also, this correction voltage is
292 is inverted is input to the addition circuit 293 through the scan electrode selection voltage V ₆ in the opposite direction is corrected to the correction of the scan electrode selection voltage V _1. This correction voltage is the X data XDATA
The value becomes larger as the number of “on” in the inside increases.

FIG. 3 shows a scan voltage waveform according to the present invention when a large number of "dark" and a large number of "bright" are displayed. FIG. 3 (a) shows the operation waveform of the scan voltage when there are many "dark" displays. At this time, since the correction voltage is hardly generated, the maximum value of the scan electrode selection voltage is V and the minimum value is 0, The waveform is the same as before. On the other hand, as shown in FIG. 3 (b), when the "bright" display is large, a large correction voltage is generated, so that the maximum value of the scan electrode selection voltage is larger than V and the minimum value is smaller than 0. . Third
FIG. 5C shows a change in voltage at each position of the scan electrode according to the present invention, as compared with the related art. conventionally,
The potential difference between the "dark" display and the "bright" display on the side far from the scan electrode power supply was large, but in the present invention, the potential difference on the side far from the scan electrode power supply was "dark" display. It can be seen that there is not much difference between time and when there are many "bright" displays.

As described above, in the present invention, the drive waveform of the conventional scan electrode does not change when there are many "dark" displays, and the voltage at the time of selecting the scan electrodes changes compared to the conventional case when there are many "bright" displays. Then, as "bright" is displayed more, the scan selection voltage is corrected in a direction to increase the effective voltage, so that there is no drop in the cell drive voltage at this time, and the effective voltage is reduced because "bright" is displayed. Therefore, a high quality display can be obtained.

FIG. 4 is a circuit diagram showing the configuration of a second embodiment of the present invention. The same members as those in the circuit of FIG. 2 are denoted by the same reference numerals. This device differs from the device of FIG. 2 in that the output of the correction parameter generating circuit 47 is inverted by an inverting circuit 471 so that X data XDATA in one scan driving period is obtained.
The point that the number of “ON” data in the circuit is obtained, and that when the correction voltage is applied to the addition circuits 291 and 293 in the correction voltage addition circuit 49, the polarity is maintained for the addition circuit 293 and the addition circuit The point that the polarity is reversed for 291 by passing through an inversion circuit 491.

In this configuration, as shown in FIG. 5B, when a large number of “bright” characters are displayed, the maximum value of the scan electrode selection voltage becomes smaller than V and the minimum value becomes larger than 0, as in the conventional case. . Then, as shown in FIG.
Are displayed, a correction voltage is generated, the maximum value of the scan electrode selection voltage is lowered below V, and the minimum value is made larger than 0. As a result, the scan selection voltage is corrected in a direction in which the effective voltage becomes lower as more "dark" is displayed. As a result, the same correction effect as that of the apparatus of FIG. 2 is obtained, and display unevenness is suppressed. it can.

FIG. 6 shows only the configuration of a correction parameter generating circuit 57 which is different from the configuration of FIG. 2 in the configuration of the third embodiment of the present invention. In the device of this embodiment, the X data XDATA is taken into the data latch circuit 271, the output of which is input to the U / D terminal of the up / down counter 571, and the data clock signal DCLK is counted. Therefore, if the X data XDATA is “ON”, the count is up, and if the X data XDATA is “OFF”, the count is down, and the result is output from the up / down counter 571 as a correction parameter. Then, correction is performed based on the difference between the numbers of “ON” and “OFF”. That is, if the number of “bright” displays and the number of “dark” displays are the same, no correction is performed, and the direction of increasing the effective voltage when there are many “bright” displays and the direction of increasing the effective voltage when there are many “dark” displays , The correction works in the direction of lowering, and the same effect can be obtained.

FIG. 7 shows only the configuration of a correction parameter generation circuit 67 different from the device of FIG. 2 in the configuration of the fourth embodiment of the present invention. In the apparatus of this embodiment, X data DCLK
Measurement circuit 671 that counts the number and outputs the X coordinate of data
And a weighting circuit 672 that receives the output and outputs a value weighted by coordinates, and a weighting circuit 672 based on an output from the data latch circuit 271 when there is “ON” data in the X data XDATA. And a integrating circuit 674 for integrating the output during one scan drive period.

The difference between this device and the device of Fig. 2 is that X data XDAT
Even if the same “ON” data exists in A, the “ON” data displayed on the scan electrode closer to the power supply circuit 24 is counted as a small value and displayed on the scan electrode farther from the power supply circuit 24 The "on" data is counted as a large value. This has a small effect on the voltage drop of the "bright" display scan electrode of the liquid crystal cell connected to the scan electrode closer to the power supply circuit 24.
"Akira" of the liquid crystal cell connected to the scan electrode far away from 24
This is because the influence on the voltage drop of the scan electrode for display is large. With this device, it is possible to cope with a phenomenon in which the amount of change in the scan selection voltage varies depending on the position where “bright” is displayed on the same scan electrode, and more appropriate correction can be performed.

Further, the bias ratio a is set to a theoretical optimum value. (However, D is a duty ratio). This method is disclosed in JP-A-59-160124, and has an effect of improving the contrast ratio in addition to the effect of reducing the driving voltage described in the publication. However, when this method is used alone, there is a problem in that the drive margin is narrowed, and the transmittance is largely changed by a slight change in the effective voltage, and crosstalk is likely to occur. Therefore, by suppressing the fluctuation of the effective voltage due to the display pattern in combination with the present invention, the problem of crosstalk can be solved, the driving voltage can be reduced, and the contrast ratio can be improved.

Incidentally, in the illustrated _{embodiment, V 1 = V V 4 =} (2 / a) V V 2 = (1-1 / a) V V 5 = (1 / a) V V 3 = (1-2 / a Although V V ₆ = 0, V ₁ -V ₆ may be increased or decreased by a fixed voltage value, since the voltage averaging method only requires that the difference between the voltages satisfies this relationship. .

Further, in the above-described embodiment, “ON” is displayed in the “ON” display data.
The explanation has been given using a liquid crystal display device corresponding to the display as an example,
For a liquid crystal display device that corresponds to “ON” display data with “dark” display, the “bright” display description is changed to “dark” display and the “dark” display
The same can be applied by replacing the display description with the “bright” display.

〔The invention's effect〕

As described above, according to the present invention, in a simple matrix type liquid crystal display device, “light”
Is displayed, the scan electrode selection voltage does not decrease, so that the display quality can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of a liquid crystal panel driving apparatus embodying the method of the present invention, FIG. 2 is a circuit diagram showing the structure of a first embodiment of the present invention, and FIG. 3 is shown in FIG. 4 is a waveform diagram showing the operation and effect of the first embodiment, FIG. 4 is a circuit diagram showing the configuration of the second embodiment of the present invention, and FIG. 5 is a waveform diagram showing the operation of the embodiment of FIG. FIG. 6 is a circuit diagram showing the configuration of only the correction parameter generation circuit portion of the third embodiment of the present invention. FIG. 7 is only the correction parameter generation circuit portion of the fourth embodiment of the present invention. FIG. 8 is a diagram showing driving voltage waveforms of cells α and β in FIG. 9, FIG. 9 is a diagram showing an example of a display pattern on a liquid crystal panel, and FIG. FIG. 11 shows another example of a display pattern on a liquid crystal panel. FIG. 12 shows a liquid crystal connected to one scan electrode. FIG. 13 is a waveform diagram showing a change in scan voltage according to the display pattern of FIG. 11, and FIGS. 14 and 15 show a case where a large number of “bright” are displayed. FIG. 9 is a diagram showing driving waveforms of the liquid crystal cell when a large number of “dark” are displayed. 21: Data electrode driver, 22: Scan electrode driver, 23: LCD panel, 24: Power supply circuit, 26: LCD panel controller, 27, 47, 57, 67: Correction parameter generation circuit, 28: … D / A conversion circuit, 29… Correction voltage addition circuit, 271… Data latch circuit, 272… Data detection circuit, 273 …… Counter, 291,293… Addition circuit 272,292,471,491… Inversion circuit, 571 …… Up / down Counter, 671… Coordinate measurement circuit, 672… Weighting circuit, 673… Control buffer, 674 …… Integration circuit.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Munehiro Haraguchi 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Takayuki Hoshiya 1015 Kamikodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (56) References JP-A-3-220591 (JP, A) JP-A-2-89 (JP, A) JP-A-60-126626 (JP, A) JP-A-3-21985 (JP, A) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/133 G09G 3/36

Claims (3)

(57) [Claims] A matrix-type liquid crystal panel provided with data electrodes and scan electrodes intersecting each other, applying a predetermined voltage V to selected data electrodes based on a voltage applied to the selected scan electrodes; Unselected data electrodes (1
−2 / a) V, and (1-1-1) is applied to the unselected scan electrodes.
/ a) With reference to the positive voltage application mode period in which V is applied and the voltage applied to the selected data electrode, V is applied to the selected scan electrode and (2 /
a) In a method in which V is applied and a non-selected scan electrode is driven in a negative voltage application mode period in which (1 / a) V is applied, display is performed on a selected scan electrode every scan electrode drive time The magnitude of the correction voltage is determined according to the ratio of light and dark of the data to be corrected, and the correction voltage is added to the selection voltage of the scan electrode with the opposite polarity between the positive voltage application mode period and the negative voltage application mode period. Characteristic liquid crystal panel driving method. 2. The liquid crystal panel driving method according to claim 1, wherein a ratio of lightness and darkness of data displayed on the selected scan electrode is calculated by weighting each data according to a distance from a scan driver output. A method for driving a liquid crystal panel. 3. A driving device for a simple matrix type liquid crystal panel (3) comprising a data electrode driver (1) and a scan electrode driver (2), wherein a positive voltage application mode period and a negative voltage are applied to the data electrode driver (1). A power supply circuit (4) for applying a selection voltage and a non-selection voltage during the voltage application mode period and a selection voltage and a non-selection voltage during the positive voltage application mode period and the negative voltage application mode period to the scan electrode driver (2); A control circuit (5) for sending a data signal to 1) and a scan signal to the scan electrode driver (2); and a positive voltage application mode period and a negative voltage application mode period according to a signal from the control circuit (5). A voltage polarity switching circuit (6) for switching the scan electrode, and a correction parameter for measuring the ratio of light and dark of data displayed on the selected scan electrode for each scan electrode driving time. A correction parameter generation circuit (7) for generating a correction voltage; a correction voltage generation circuit (8) for generating a correction voltage of a magnitude corresponding to the correction parameter; and a scan voltage when the power supply circuit (4) is selected. A driving circuit for a liquid crystal panel, comprising: