JPH08137441A - Liquid crystal display device and its driving method - Google Patents

Abstract

PURPOSE: To reduce burning with a simple method by making a voltage polarity of a data signal in a current impressed period of a scanning signal the voltage polarity opposite to the voltage polarity of the scanning signal in the current impressed period. CONSTITUTION: The current impressed period I(n) previous to a selective period S(n) of negative polarity is divided to four discontinuous sub-sections in e.g. the scanning signal ϕ(n). Further, the scanning signal takes selective potential Va1, Va2 of different polarities at the same potential alternately in respective sub-sections. Then, the voltage polarity of the data signal D(m) in the sub-section constituting the current impressed period I(n) of the scanning signal takes the voltage polarity opposite to the voltage polarity of the scanning signal in the current impressed period. For instance, the data signal takes data potential Vd2 of negative polarity in the sub-section where the scanning signal takes the selective potential Va1 of positive polarity, and the data signal takes the data potential Vd1 of negative polarity in the sub-section where the scanning signal takes the selective potential Va2 of negative polarity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION Liquid crystal display devices are widely applied as low power consumption flat panel displays. Among them, the active matrix system in which a switching element is built in each pixel and driven is being used as a large-capacity and high-quality display element in televisions, information terminals, and the like. A three-terminal type TFT (thin film transistor) and a two-terminal type diode or a non-linear resistance element such as MIM are used as the switching element. The 2-terminal type is easier to manufacture than the 3-terminal type and is expected in the future. The present invention relates to a two-terminal type active matrix liquid crystal display device using a two-terminal type switching element and a driving method thereof.

[0002]

2. Description of the Related Art FIG. 2 shows a block diagram of an active matrix liquid crystal display device using a two-terminal type switching element. The matrix display panel 3 has data lines D1 and D
2 ,. ． , DM and scan lines S1, S2 ,. ． , SN are arranged in a matrix. A liquid crystal pixel 1 and a two-terminal switching element 2 are installed corresponding to the intersection.
A data signal is supplied from the data line driver circuit 4 to the data line, and a scanning signal is supplied from the scanning line driver circuit 5 to the scanning line. The data line driver circuit 4 and the scanning line driver circuit 5 are connected to a control circuit and a power supply circuit 6 for processing a clock and an image signal 7. The two-terminal type switching element has a metal-insulator-metal (conductor) structure and has a non-linear current-voltage characteristic.
Is often used. A typical structure of the MIM is a lower electrode Ta, and an insulating film is an anodic oxide film (Ta) of the Ta.
Ox), ITO (transparent conductor) as the upper electrode, 2
It can be manufactured with one pattern (mask).

FIG. 3 shows a scanning signal waveform and a data signal waveform in a conventional method for driving a two-terminal type active matrix liquid crystal display device such as a diode or MIM (Japanese Patent Laid-Open No. 59-57288). φ (n), φ (n + 1),
φ (n + 2) is the nth line, the n + 1th line, and the n + 2 line, respectively.
This is a scanning signal applied to the first scanning line. Negative polarity selection periods H (n), H '(n + 1), H (n +)
2) and positive polarity selection periods H ′ (n), H (n + 1),
The selection potentials Va2 and Va1 are set at H '(n + 2), and the holding potentials Vb2 and Vb1 are set at the other non-selection periods. The data signal D (m) applied to the m-th data line is the data potential Vd1.
And Vd2. Gradation display uses either amplitude modulation or pulse width modulation, and the latter example is shown in FIG. VG is a reference potential and is drawn as a constant potential in this figure, but even if it fluctuates throughout the system, it is equivalent in principle, so it is often varied depending on the relationship of the power supply voltage of the driver circuit. In the figure, Va1, Va2 and Vb1, Vb2 are shown symmetrically with respect to the reference potential, but they may be asymmetrical when the characteristics of the two-terminal switching element are asymmetrical. In this example, the nth, n + 1th, and n + 2th consecutive selection periods H (n), H (n + 1), H (n + 2) and the selection periods H ′ (n), H ′ (n + 1), H ′ (n + 2). The polarity of the selection potential in) corresponds to the example of row-by-row inversion, but field-by-field inversion often occurs.

The biggest problem in an active matrix liquid crystal display device using a two-terminal switching element, especially when using MIM as a switching element, is image sticking or an afterimage phenomenon. This image sticking will be described with reference to FIG. In the case of normally white display, the change in the transmittance shown in FIG. 4A, that is, in the case of sequentially displaying white, halftone, black, and halftone, the actual change in transmittance is as shown in FIG. 4B. The change in the transmittance of the ideal image does not match that in FIG. When changing from white to halftone, an image that is slightly darker than halftone is burned in for a certain period such as 11, and when it is changed from black to halftone, an image that is slightly brighter than halftone is burned in for a certain period such as 12. This is because the threshold voltage Vth of the switching element changes. This change depends on the amount of current flowing through the switching element, and if there is a large amount of current, the threshold voltage Vth tends to increase and conversely Vth tends to decrease for small amounts of current.

FIG. 5 shows a scanning signal waveform and a data signal waveform in a conventional example for reducing burn-in in a driving method of a two-terminal type active matrix liquid crystal display device.
φ (n), φ (n + 1), and φ (n + 2) are scanning signals applied to the nth scanning line, the n + 1th scanning line, and the n + 2th scanning line, respectively. The selection period H (n) of positive polarity,
In H '(n + 1), H (n + 2) and negative selection periods H' (n), H (n + 1), H '(n + 2), the selection potentials Va1 and Va2 are held and in the other non-selected periods, the holding potential Vb.
Take 1, Vb2. The data signal D (m) applied to the m-th data line has a potential between the data potentials Vd1 and Vd2. The drive waveform of FIG. 5 is different from the drive waveform of FIG. 3 in that the scanning signals φ (n), φ (n + 1), and φ (n + 2) are positive selection periods H (n), H ′ (n + 1), and H, respectively. (N +
2) and a negative polarity selection period H ′ (n), H (n + 1),
Before H '(n + 2), the current application period I of opposite polarity is applied.
(N), I ′ (n + 1), I (n + 2) and negative selection periods I ′ (n), I (n + 1), I ′ (n + 2). In this conventional example, it is expected that the characteristic change of the element is saturated by the current forcibly passed through the switching element during the current application period and the image sticking is suppressed.

[0006]

As described above, in a two-terminal type active matrix using a switching element whose element characteristic changes depending on the amount of current flowing, image burn-in and afterimage caused by the characteristic change pose a problem. FIG.
In the conventional driving method, the amount of current flowing through the switching element varies depending on the gradation displayed on the liquid crystal pixel, and this phenomenon cannot be eliminated. On the other hand, in the driving method shown in FIG. 5, it is aimed to suppress the burn-in by saturating the characteristic change of the element by forcing a current to flow through the switching element by providing a current application period, but it is difficult to obtain the expected effect. For example, as shown in FIG. 6, current application periods I ′ (n) and I ′ (n +
1), the voltage of I '(n + 2) is in the previous selection period S
When the selection voltages of (n), S (n + 1), and S (n + 2) have the same polarity and the same voltage, the current does not flow in the current application period in the two-terminal switching element ideally having the nonlinear current-voltage characteristic. In reality, the non-linear characteristic of the switching element is not ideal, so a small amount of current flows, but it is difficult to obtain the effect until the characteristic change of the element is saturated and seizure is suppressed. Current application period I '(n), I' (n + 1), I '
The voltage of (n + 2) is applied to the previous selection period S (n), S (n
If it is set to a value larger than the selection voltage of +1) and S (n + 2), the effect of saturating the characteristic change and suppressing the image sticking can be obtained. However, an independent high-voltage power supply is required, and the load is large in terms of circuit scale and breakdown voltage. An object of the present invention is to provide a driving method capable of increasing the amount of current flowing in a switching element without increasing the circuit scale and breakdown voltage as compared with the conventional example and improving image burn-in and afterimage phenomenon. There is something to do.

[0007]

In order to achieve the above object, in the two-terminal type active matrix liquid crystal display device and its driving method of the present invention, a selection period as a scanning signal, a current application period preceding the selection period, and a selection period of the current application period. The current application period has a holding period following the selection period, and the current application period is composed of a plurality of discontinuous small sections. The voltage polarity in the current application period of the scan signal of the data signal is the same as that of the scan signal of the current application period. The above problem is solved by setting the voltage polarity opposite to the voltage polarity.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the driving method of the present invention. φ (n) and φ (n + 1) are the nth line,
The scanning signal is applied to the (n + 1) th scanning line and the (n + 2) th scanning line. An example of so-called row-by-row inversion is clearly shown by the voltage polarities of the selection periods S (n) and S (n + 1). Of course, the present invention is not limited to line-by-line inversion, but is also effective in frame inversion and inline inversion. The scanning signal φ (n) has a negative selection period S (n) and a positive selection period S ′.
(N), the scanning signal φ (n + 1) is a positive selection period S
(N + 1) has a negative polarity selection period S ′ (n + 1), and the selection potential Va1 is positive and the selection potential Va2 is negative.
have. The retention period H is the period following each selection period.
(N), H (n + 1) or H '(n), H' (n +
Corresponding to 1), the holding potential Vb1 is set in the holding period following the positive selection period, and the holding potential Vb2 is set in the holding period following the negative selection period. In this embodiment, the selection periods S (n) and S '
In (n), the selection potentials Va1 and Va2 are all taken, but some of them may take other potentials, for example, the holding potentials Vb1 and Vb2.

The feature of the present invention resides in the current application period preceding the selection period. For example, in the scan signal φ (n), the current application period I (n) preceding the negative polarity selection period S (n) is divided into four discontinuous small sections. In each of the small sections, the scanning signal alternates the selection potentials Va1 and Va2 having different polarities with the same potential. The voltage polarity in the small section of the current application period I (n) of the scanning signal of the data signal D (m) has a voltage polarity opposite to the voltage polarity of the scanning signal of the current application period. For example, in a small section in which the scanning signal has the positive selection potential Va1, the data signal has the negative data potential Vd2, and in the small section where the scanning signal has the negative selection potential Va2, the data signal has the negative data potential. It is taking Vd1.

FIG. 8 shows the relationship between the potential of the data signal and the image sticking in the embodiment of FIG. When a negative voltage, for example, Va2, is applied to the scanning signal in a small section that constitutes the current application period, the right end of the figure shows the case where the data signal takes the positive data potential Vd1, and the left end of the figure shows the negative side. Data potential V
The case where d2 is taken is shown. Burn-in is suppressed when the voltage polarity of the data signal is opposite to the voltage polarity of the scanning signal.

FIG. 9 shows the relationship between the number of small sections to which the current is applied and the seizure in the embodiment of FIG. It is assumed that the data signal satisfies the optimum condition at the left end of FIG. The ratio of the current application subsection and the selection period is 1: 3. The number of current application subsections is 3
The above effect is obtained, and it is saturated at about 10.

In the present invention, the data signal D (m) applied to the m-th data line has a potential between the data potentials Vd1 and Vd2 as in the conventional example of FIG. 3 as shown in FIG. Gradation display uses either amplitude modulation or pulse width modulation, and the latter example is shown in FIG. Reference numeral 22 is a reference potential, which is drawn as a constant potential in this figure, but may vary throughout the system.
Although Va1 and Va2 and Vb1 and Vb2 are shown symmetrically with respect to the reference potential in the figure, they may be asymmetrical. Further, although this example corresponds to an example of line-by-line inversion, field inversion or inline inversion may be performed.

In the above example, the potentials used during the current application period are the same as the selection potentials Va1 and Va2, which is very advantageous in terms of saving the number of power supplies in the circuit.

In principle, FIG. 7 is completely equivalent to FIG.
In this example, the reference potential VG of FIG. 1 is changed row by row like the reference potential VG of FIG. 7 to reduce the scanning signal amplitude. On the contrary, the data signal amplitude increases. The drive waveforms look different but are equivalent. The present invention is applicable to such an oscillating potential if the reference potential is fixed and equivalent.

FIG. 10 shows the scanning signal waveform of another embodiment of the present invention. This is an example of a television that displays a video signal, and a horizontal retrace line section is used as the current application subsection of the scanning signal. Since the video information of the video signal is not transmitted in the blanking section, it is possible to efficiently apply the current without affecting the signal processing by using this section.

Further, the current application small section is 1 compared to the selection section.
Since it is / 3 or less, it is possible to reduce the deterioration of the driving ability.

[0017]

As described with reference to FIG. 4, the problem of the conventional driving method is that the biggest problem of the active matrix liquid crystal display device using the two-terminal type switching element is image sticking and afterimage phenomenon. This is because the threshold voltage Vth changes depending on the amount of current flowing. In the present invention, a current is forcibly applied to the switching element by the provided current application period, and the threshold value Vth is changed to stabilize the current, so that image sticking and afterimage are reduced as shown in FIG.

As described above, the liquid crystal display device of the present invention and the driving method thereof have the selection period as the scanning signal, the current application period preceding the selection period, and the holding period following the selection period.
The current application period is composed of a plurality of discontinuous small sections, and the voltage polarity of the scan signal of the data signal in the current application period is opposite to the voltage polarity of the scan signal of the current application period. Therefore, the image sticking can be reduced by a simple method.

[Brief description of drawings]

FIG. 1 is a driving waveform in one embodiment of a driving method of a two-terminal type active matrix liquid crystal display device of the present invention.

FIG. 2 is a block diagram of an active matrix liquid crystal display device using a typical two-terminal type switching element.

FIG. 3 is a driving waveform in a driving method of a conventional two-terminal type active matrix liquid crystal display device.

FIG. 4 is an explanatory diagram of a burn-in problem in a conventional driving method.

FIG. 5 is an explanatory diagram showing a voltage waveform applied to a switching element and a current waveform flowing through the switching element in the conventional driving method and the driving method of the present invention.

FIG. 6 is an explanatory diagram showing a burn-in reduction effect by the driving method of the present invention.

FIG. 7 is a driving waveform in another embodiment of the driving method of the present invention.

FIG. 8 is a diagram showing a relationship between burn-in reduction and the polarity and potential of a data signal in the driving method of the present invention.

FIG. 9 is a diagram showing a relationship between burn-in reduction and the number of current application subsections in the driving method of the present invention.

FIG. 10 is a driving waveform in another embodiment of the driving method of the present invention.

[Explanation of symbols]

 φ (n), φ (n + 1) scanning signal D (m) data signal D1, D2, DM data line S1, S2, SN scanning line 1 liquid crystal pixel 2 2 terminal type switching element S (n), S '(n) Selection period I (n), I '(n) Current application period

Claims (14)

[Claims] 1. A scanning line, comprising a plurality of data lines and a plurality of scanning lines, a liquid crystal pixel and at least one two-terminal switching element provided corresponding to an intersection of the data lines and the scanning lines. In a liquid crystal display device in which a liquid crystal pixel is driven according to a scanning signal applied and a data signal applied to a data line, the scanning signal is applied to a selection period, a current application period preceding the selection period, and the selection period. The current application period has a continuous holding period, and the current application period is composed of a plurality of discontinuous small sections, and the voltage polarity in the current application period of the scanning signal of the data signal is
A liquid crystal display device having a voltage polarity opposite to that of a scanning signal in the current application period. 2. The data signal takes the data potentials Vd1, Vd2 or a potential between them in the selection period of each scanning signal, and the data potential V in the small section which constitutes the current application period of each scanning signal.
2. A liquid crystal display device according to claim 1, wherein either d1 or Vd2 is set. 3. A plurality of sub-sections forming a current application period of the scanning signal are both sub-sections having the same voltage polarity as the voltage polarity of the selection period and sub-sections having the opposite voltage polarity. The liquid crystal display device according to claim 1. 4. The current application period is composed of a plurality of four or more small sections, and the plurality of small sections have two or more small sections having the same voltage polarity as the voltage polarity of the selection period and an opposite voltage polarity. The liquid crystal display device according to claim 3, wherein the liquid crystal display device comprises two or more small sections. 5. The scanning signal is a selection potential Va1 in the selection period,
Va2 is taken and the holding potential Vb is held in the holding period following the selection period.
2. The liquid crystal display device according to claim 1, wherein 1 and Vb2 are set, and selection potentials Va1 and Va2 are set in a current application period preceding the selection period. 6. The liquid crystal display device according to claim 1, wherein a horizontal blanking period of the video signal is used as the current application period. 7. The length of a small section constituting the current application period is one-third or less of the selection period.
The described liquid crystal display device. 8. A scanning line comprising a plurality of data lines and a plurality of scanning lines, a liquid crystal pixel and at least one two-terminal switching element provided corresponding to an intersection of the data lines and the scanning lines. In a method of driving a liquid crystal display device in which liquid crystal pixels are driven according to a scan signal applied and a data signal applied to a data line, the scan signal is a selection period and a current application period preceding the selection period. The current application period has a holding period following the selection period, and the current application period is composed of a plurality of discontinuous small sections. The voltage polarity in the current application period of the scan signal of the data signal is the same as that of the scan signal of the current application period. A method for driving a liquid crystal display device, which has a voltage polarity opposite to that of the voltage polarity. 9. The data signal takes the data potentials Vd1, Vd2 or a potential therebetween in the selection period of each scanning signal, and the data potential V in the small section which constitutes the current application period of each scanning signal.
9. The method of driving a liquid crystal display device according to claim 8, wherein either d1 or Vd2 is set. 10. The plurality of small sections forming the current application period of the scanning signal are both small sections having the same voltage polarity as the voltage polarity of the selection period and small sections having the opposite voltage polarity. The method for driving a liquid crystal display device according to claim 8. 11. The current application period comprises a plurality of four or more small sections, and the plurality of small sections have two or more small sections having the same voltage polarity as the voltage polarity of the selection period and an opposite voltage polarity. 11. The method for driving a liquid crystal display device according to claim 10, wherein the method comprises two or more small sections. 12. The scanning signal has a selection potential Va in a selection period.
9. The method of driving a liquid crystal display device according to claim 8, wherein the holding potentials Vb1 and Vb2 are set in a holding period subsequent to the selection period and 1 and Va2, and the selection potentials Va1 and Va2 are set in a current application period preceding the selection period. 13. The method of driving a liquid crystal display device according to claim 9, wherein a horizontal blanking period of the video signal is used as the current application period. 14. The method of driving a liquid crystal display device according to claim 8, wherein the length of the small section constituting the current application period is one third or less of the selection period.