JPH09305150A - Driving method for display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissolve cross talk phenomenon caused by characteristics of liquid crystal by reversing polarity of an applied electric field to liquid crystal of pixels in one vertical scanning period and mixing pixels to which electric fields of both polarities are applied. SOLUTION: A polarity of a (i-1)th scanning signal is set to a ground potential or positive making the prescribed DC potential a border, a polarity of a (i)th scanning signal is set to negative, and a polarity of the (i+1)th scanning signal is set to positive. This is a condition in which a polarity of a scanning signal is reversed for each signal. On the other hand, in voltage waveform Vci of a picture signal electrode Ci also, a polarity of applied voltage is reversed for each scanning signal electrode when a scanning signal and a picture signal are constituted. A voltage waveform applied to a selected pixel is made a waveform shown with VRI-Vci , and low frequency components are eliminated. This is due to that a driving frequency of a picture having a low frequency component near a frame frequency with which cross talk is caused frequently is frequency-converted to a high frequency side, cross talk phenomenon is improved by this effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a liquid crystal panel in which pixels are formed at the intersections of scanning signal electrodes and image signal electrodes, and more particularly to a high duty time division driving method for a liquid crystal display.

[0002]

2. Description of the Related Art Recently, research has been conducted into the practical application of a so-called liquid crystal television which is small and lightweight and uses a liquid crystal display instead of a conventional cathode ray tube. A liquid crystal display device used for a liquid crystal television is required to have much more severe performance than a conventional device for displaying numbers and characters used in watches, calculators and the like. That is, the number of display pixels is remarkably large, and fast response characteristics and contrast characteristics required for gradation change are indispensable. In particular, high performance is required for all characteristics such as response characteristics, contrast characteristics, viewing angle characteristics, temperature characteristics, and frequency characteristics of liquid crystals. Conventionally, as a method of driving a liquid crystal display, a so-called voltage averaging method, a two-frequency driving method,
Although there is a switch matrix method and the like, the voltage averaging method is the only method that is currently in practical use because it consumes the least power and can reduce the manufacturing cost.

FIG. 1 shows an electrode matrix used for a liquid crystal television display. In the figure, R _{1 to} R
_N represents a scan signal electrodes, C ₁ -C _M represents an image signal electrode. The liquid crystal pixel selected by the i-th scanning signal electrode and the j-th image signal electrode is represented by A (i, j).
And

When a liquid crystal television display device is driven in a time-division manner by a matrix of scanning signal electrodes and image signal electrodes as shown in FIG. 1, the number of display pixels is tens of thousands.
If the duty ratio is 1 / n, it is inevitable that n ≧ 64. For such a large value of n, a so-called crosstalk phenomenon is likely to occur, and in a liquid crystal television image, this crosstalk phenomenon significantly reduces image quality, and is the most problematic defect.

FIG. 2 shows a typical crosstalk phenomenon.
The figure shows a simple pattern in which a black background 2 exists in a white background 1 in a normal case. However, due to a crosstalk phenomenon, a portion 3 which should be a white gradation is slightly changed in gray. . The crosstalk phenomenon remarkably appears in such a simple pattern, in other words, in an image having a display signal in which most of it is a low frequency component.

The causes of the crosstalk are roughly classified into two: an imbalance in drive voltage and a frequency characteristic of a liquid crystal threshold. Among them, a particular problem occurs when the rear liquid crystal threshold value changes in the used image display frequency band. The image display frequency band differs depending on the driving method.
Hereinafter, the relationship between the frequency band and the crosstalk of the two conventionally used driving methods will be described with reference to the applied driving voltage waveforms.

Conventionally, the driving method of the voltage averaging method is 2
Various driving methods (for example, refer to Japanese Patent Application Laid-Open No. 56-44438) are known. One is a so-called low-frequency driving method, and the driving voltage waveform is shown in FIG. The other is a high-frequency driving method, and FIG. 4 shows a driving voltage waveform.

[0008]

Problems to be Solved by the Invention In FIGS. 3 and 4,
t _L indicates one horizontal scanning period, and V _{Ri-1 to} V _{Ri + 1} are voltage waveforms of the scanning signal electrodes.
The polarity is inverted within one horizontal period. V _cj indicates the voltage waveform on the image signal electrode C _j . The voltage waveforms V _{Ri-1 to} V _{Ri + 1 of} the scanning signal electrodes and the voltage waveform V ^cj of the image signal electrodes shown in both figures are voltage waveforms viewed from the ground potential or a certain predetermined DC potential. . The voltage waveform applied to the pixel A (i, j) selected by the scanning signal electrode voltage V _Ri and the image signal electrode voltage V _{cj in} both figures is V _Ri −
It is indicated by V _cj . Here, in order to clarify the driving frequency bands of both, the selection point A (i,
j) is a lighting state, and the other pixels A (k, j) (where k is i
Is not equal to ) Shows the case of the non-lighting state. Both display the same, but their driving frequency bands are significantly different, as is clear from FIGS.

[0009] frequency band f _D uses of both, when defining a frame period of time for scanning one scanning signal electrodes R ₁ to R _N in FIG. 1, the frame frequency f _F is the inverse of the frame period, the N As for the number of scanning signal electrodes, in the case of the low frequency drive system of FIG. 3, f _F / 2 ≦ f _D ≦ Nf _F / 2 (1) In the high frequency drive system of FIG. 4, polarity inversion is performed once within t _F. In this case, Nf _F / 2 ≦ f _D ≦ Nf _F (2)

Here, in the case of the low-frequency driving of (1), the frequency variation ratio is N, whereas in the case of the high-frequency driving of (2), it is 2.

Therefore, when the threshold value of the liquid crystal fluctuates with frequency, the high-frequency driving method is advantageous for crosstalk because the frequency fluctuation ratio is small. However, in the case of high-frequency driving, there is a disadvantage that power consumption increases because the number of times of switching is greatly increased. Since the main power source of a liquid crystal television that emphasizes portability is a battery, an increase in power consumption is a serious problem.

As described above, the liquid crystal used in the liquid crystal television is required to have higher performance than before in all characteristics. Many actual liquid crystals do not have excellent overall characteristics, and usually have some display defects. A certain type of liquid crystal is inferior to other liquid crystals only in the frequency characteristic of the threshold value, but has a property that the contrast characteristic is superior to other liquid crystals. In this case, the use of the conventional driving method has to be abandoned, or the power consumption has to be sacrificed, which has been a major obstacle to the practical use of the liquid crystal television.

[0013]

According to the present invention, a plurality of scanning signal electrodes and a plurality of image signal electrodes are arranged in a matrix, and a plurality of scanning signal electrodes and a plurality of image signal electrodes are provided at intersections thereof. A driving method of a liquid crystal panel in which a pixel is provided and an electric field of a difference voltage between a scanning signal supplied to the scanning signal electrode and an image signal supplied to the image signal electrode in one vertical scanning period or a liquid crystal of the pixel is applied That is, in one vertical scanning period, the scanning signal electrode to which the scanning signal of the first type having the one polarity as the scanning signal is supplied with respect to the ground potential or the predetermined DC potential and the other A scan signal is supplied to the plurality of scan signal electrodes so as to have the scan signal electrode to which a second type scan signal having a polarity is supplied, and the scan signal is supplied to the liquid crystal of the pixel within one vertical scan period. The polarity of the electric field, characterized in that reversing each other in the pixel scanning signal of the second type and pixel scanning signal of the first type is applied is applied.

A plurality of scanning signal electrodes and a plurality of image signal electrodes are arranged in a matrix, and a plurality of pixels are provided at the intersections of the plurality of scanning signal electrodes and the plurality of image signal electrodes. A method of activating a liquid crystal panel in which an electric field of a difference voltage between a scanning signal supplied to the scanning signal electrode and an image signal supplied to the image signal electrode in a period is applied to the liquid crystal of the pixel, which is one vertical scanning period. The polarity of the scanning signal with reference to the ground potential or a predetermined DC potential is inverted every one or more horizontal scanning periods, and the polarity of the image signal with reference to the ground potential or a predetermined DC potential is scanned. It is characterized in that it is inverted in synchronization with the inversion of the polarity of the signal.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings.

FIG. 5 shows the voltage waveform of the scanning signal electrode, the voltage waveform of the image signal electrode, and the voltage waveform applied to a certain pixel selected by them for explaining the first embodiment of the present invention. . In the figure, t _L indicates one horizontal scanning period. V _{Ri-1 to} V _{Ri + 1} represent the voltage waveform of the scanning signal electrode, V _cj is the voltage waveform on the image signal electrode C _j , and is selected by R _i and C _j as in FIGS. 3 and 4. Pixels turned on and other A (k, j) (where k is not equal to j).
Corresponds to the state in which the pixel is not illuminated. In the figure, the i-th
The polarity of the -1 scanning signal is set to be positive with respect to the ground potential or a predetermined DC potential, the polarity of the i-th scanning signal is set to be negative, and the polarity of the i + 1-th scanning signal is set to be positive. It represents a state in which the polarity is reversed for each one.

On the other hand, when the voltage waveform V _cj of the image signal electrode C _j also constitutes the scanning signal and the image signal, the scanning signal electrode 1
The polarity of the applied voltage is inverted every time. Selected pixel A
The voltage waveform applied to (i, j) is V _Ri −V _{cj in} FIG.
The waveform shown by. In this applied voltage waveform, a low frequency component is largely removed as compared with the applied voltage waveform of the conventional low frequency driving method shown in FIG.

This is because the drive frequency of an image having a low frequency component near the frame frequency at which crosstalk appears prominently is frequency-converted to the high frequency side, and this effect significantly reduces the crosstalk phenomenon. To be improved.

The drive frequency of the first embodiment of the present invention is 1/2 of the drive frequency of the conventional high frequency drive system shown in FIG. Therefore, the present embodiment enables low power consumption driving.

By the way, even if the polarities of the scanning signal and the corresponding image signal in this embodiment are opposite to those shown in FIG. 5, the effect of the above-mentioned embodiment does not change at all. That is, by inverting the polarity of the applied voltage for each scanning signal electrode,
Crosstalk can be improved with low power consumption.

Next, FIG. 6 shows a voltage waveform of a scanning signal electrode, a voltage waveform of an image signal electrode, and a voltage waveform applied to a pixel selected by them for explaining a second embodiment of the present invention. Indicates. In the figure, t _L represents one horizontal scanning period. V _{Ri-1 to} V _{Ri + 2} are voltage waveforms of the scanning signal electrodes, the polarities of which are inverted between every two scanning signal electrodes with the ground potential or the used DC potential as a boundary. V _Cj is a voltage waveform on C _j on the image signal electrode. As in FIGS. 3, 4, and 5, the pixel selected by R _i and C _j is lit, and other A (k, j) (however, , K is not equal to j.)
Corresponds to a state in which the pixel is not lit. When the scanning signal and the image signal are configured in this way, the scanning signal electrode 2
The polarity of the applied voltage is inverted every time.

The voltage waveform applied to the selected pixel A (i, j) is V _Ri -V _cj . The effect of this embodiment is the same as that of the first embodiment.
Compared with the embodiment described above, the driving frequency is halved, so that the power consumption is further reduced. Generally, when the N scanning signal electrodes are configured to invert the polarity of the scanning signal at a repetition cycle of every L scanning electrodes, the optimum value of L is obtained by experiment from the conditions of the degree of cancellation of crosstalk and the power consumption.
As an example, in an experiment using an azoxycyanoester-based mixed liquid crystal, when the frame time is 1/60 seconds and N = 64, the crosstalk phenomenon is not observed when L ≦ 4, and from the condition of the minimum power consumption, L = 4 was determined.

By the way, in the above embodiment, the case where the polarity distribution of the applied voltage within the frame period has a fixed cycle is shown, but the present invention is not limited to this, and the polarity distribution is It need not be periodic, and the number of scanning signals of each polarity may not be equal.

However, since no particular advantage can be found in constructing the non-periodic distribution, in practice, the periodic distribution has an advantage in that the configuration of the drive circuit is facilitated. .

In order to further clarify the difference between the present invention and the conventional method, an additional explanation will be given below. In the conventional high-frequency driving method, the polarity of the applied voltage is inverted at least once in one horizontal scanning period. However, in the present invention, the polarity inversion is not performed in one horizontal scanning period. Further, in the conventional low-frequency driving method, the polarity of the applied voltage is the same within the frame time, but in the present invention, both polarities are mixed.
Further, the driving frequency band of the present invention is not limited to the frequency band of the conventional low-frequency driving method shown in the above-mentioned formula (1) regardless of how the reversal frequency of the applied voltage is determined. Becomes possible.

As described above, the present invention is a novel display panel driving method, which is different from any of the conventional methods.

[0027]

As described above, according to the liquid crystal panel driving method of the present invention, by inverting the polarity of the electric field applied to the liquid crystal of the pixel within one vertical scanning period,
Pixels to which an electric field having both polarities are applied are mixed in the vertical scanning period, and the crosstalk phenomenon due to the characteristics of the liquid crystal can be eliminated. Further, since the polarity of the electric field applied to the liquid crystal is not reversed in units of one vertical scanning period, flicker can be reduced. Further, by setting the frequency of the polarity reversal of the applied electric field according to the magnitude of the crosstalk phenomenon, there is a great advantage over the conventional driving method that the power consumption can be optimized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a general display panel in time-division driving.

FIG. 2 is an explanatory diagram showing a crosstalk phenomenon.

FIG. 3 is a voltage waveform diagram of a conventional low frequency drive system.

FIG. 4 is a voltage waveform diagram of a conventional high frequency drive system.

FIG. 5 is a voltage waveform diagram of the first embodiment of the present invention.

FIG. 6 is a voltage waveform diagram of the second embodiment of the present invention.

[Explanation of symbols]

 1. ・ White gradation part 2 ・ ・ Black gradation part 3 ・ ・ White gradation part with changed gradation

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[Procedure amendment]

[Submission date] February 5, 1997

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[0027]

As described above, according to the driving method of the liquid crystal panel of the present invention, the polarity of the electric field applied to the liquid crystal of the pixel in one vertical scanning period is reversed, so that in one vertical scanning period. Pixels to which electric fields of both polarities have been applied are mixed, and it is possible to eliminate the crosstalk phenomenon due to the characteristics of the liquid crystal. Further, since the polarity of the electric field applied to the liquid crystal is inverted in a cycle shorter than one vertical scanning period unit, flicker can be reduced. Further, by setting the frequency of the polarity reversal of the applied electric field according to the magnitude of the crosstalk phenomenon, there is a great advantage over the conventional driving method that the power consumption can be optimized.

Claims (2)

[Claims] 1. A plurality of scanning signal electrodes and a plurality of image signal electrodes are arranged in a matrix, and a plurality of pixels are provided at intersections of the plurality of scanning signal electrodes and the plurality of image signal electrodes, and one vertical scanning is performed. A vertical scanning period of a liquid crystal panel, wherein an electric field of a difference voltage between a scanning signal supplied to the scanning signal electrode and an image signal supplied to the image signal electrode in a period is applied to the liquid crystal of the pixel. In the above, the scanning signal electrode to which the scanning signal of the first type in which the polarity of the scanning signal with respect to the ground potential or a predetermined DC potential is one polarity is supplied, and the second type scanning with the other polarity A scanning signal is supplied to the plurality of scanning signal electrodes so as to have the scanning signal electrode to which a signal is supplied, and the polarity of the electric field applied to the liquid crystal of the pixel in one vertical scanning period is set to the first The driving method of a display panel wherein there that is inverted with respect to each other in a pixel in which the pixel and the second type of scanning signals that the scan signals are applied in type is applied. 2. A plurality of scanning signal electrodes and a plurality of image signal electrodes are arranged in a matrix, and a plurality of pixels are provided at intersections of the plurality of scanning signal electrodes and a plurality of image signal electrodes, and one vertical scanning is performed. A method of operating a liquid crystal panel in which an electric field of a difference voltage between a scanning signal supplied to the scanning signal electrode and an image signal supplied to the image signal electrode in a period is applied to the liquid crystal of the pixel, which is one vertical scanning period. The polarity of the scanning signal with reference to the ground potential or a predetermined DC potential is inverted every one or more horizontal scanning periods, and the polarity of the image signal with reference to the ground potential or a predetermined DC potential is scanned. A method of driving a display panel, which is inverted in synchronism with polarity inversion of a signal.