JPH0980385A - Liquid crystal display device using two-terminal non-linear resistance element - Google Patents

Abstract

(57) Abstract: To eliminate the burn-in by making the drift of the voltage-current characteristic of the non-linear resistance element due to the difference in display pattern uniform. In a liquid crystal display device using a two-terminal type non-linear resistance element as a switching element, a horizontal scanning period is time-divided into at least three, for example, four periods, and a scanning voltage and the signal voltage are divided into second and fourth periods. The polarity -VOff in the third period is controlled to be different with respect to the waveform VOn, and the polarities of the scanning voltage and the signal voltage are inverted every horizontal scanning period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to driving a liquid crystal display device using a two-terminal type non-linear resistance element as a switching element.

[0002]

2. Description of the Related Art Liquid crystal display devices are used in displays such as OA equipment and TVs by taking advantage of the features of thinness, light weight and low power consumption. Further, large capacity display and high quality display can be realized at low cost. Is desired.

As such a liquid crystal display device, a TN (Twisted Nematic) mode or STN using a nematic liquid crystal is used.
Although there is a display device of (Super Twisted Nematic) mode, in particular, the STN uses the steepness of the threshold characteristic in the electro-optical characteristic of the liquid crystal itself, so that the display portion (O
In terms of the contrast ratio between the N, on-pixel) and the non-display part (OFF, off-pixel), it is insufficient even if there are about 200 scanning electrodes. Furthermore, the scanning electrode has a large scale of 400 or more and a large capacity. When performing the matrix display of
The decrease in contrast ratio was fatal. In addition, the response speed is as slow as 100 msec to 300 msec, which is not suitable for advanced use such as a terminal display of a computer.

As a method of improving this, individual pixels are directly switch-driven. A thin film transistor (TFT) or a two-terminal non-linear resistance element (MIM) is used as a switching element.
Since the structure is simpler and the manufacturing is easier than T,
There is an advantage that the cost of the device can be reduced.

[0005]

In the two-terminal type liquid crystal display device, since the switching characteristic of the voltage-current characteristic is utilized, a high contrast ratio can be obtained. However, since writing is performed during a short period of time, which is the selection period (horizontal scanning period), even if the characteristics of the non-linear resistance element slightly change, the voltage that controls the liquid crystal changes and this is reflected in its transmittance. It is considered that this is because the voltage-current characteristics of the non-linear resistance element are different between the pixel that was ON-displayed and the pixel that was OFF-displayed. The voltage of the non-linear resistance element is affected by the charge during the previous frame period (vertical scanning period).
As a result of a slight difference in the current characteristics, there is a problem in that there is a difference in brightness, which is observed as burn-in. Before switching the two-terminal non-linear resistance element and applying the ON voltage to the signal electrode, a technique has been proposed in which a reverse current is applied to the non-linear resistance element with a voltage of opposite polarity to clear the state of the previous frame period. However, there is a problem that the adjustment is delicate.

The present invention has been made in view of the above problems, and provides a liquid crystal display device in which a change (drift) in the voltage-current characteristics of a non-linear resistance element is made uniform and image sticking is eliminated.

[0007]

According to the present invention, a plurality of scan electrodes which are arranged in a display region forming a plurality of pixels and extend in a line direction of the region, and extend in a direction intersecting with the scan electrodes. A plurality of signal electrodes, a two-terminal non-linear resistance element connected to the signal electrode for each pixel, a pixel electrode connected to the two-terminal non-linear resistance element and arranged for each pixel, the scanning electrode and the pixel Two terminals including a liquid crystal display element having a liquid crystal layer sandwiched between electrodes; a scan electrode drive circuit for applying a scan voltage to the scan electrodes; and a signal electrode drive circuit for applying a signal voltage to the signal electrodes In a liquid crystal display device using a non-linear resistance element, one vertical scanning period of a drive waveform for driving the liquid crystal display element is composed of horizontal scanning periods of a plurality of lines, and each horizontal scanning period of the plurality of lines is at least Divided time periods consists at 3 N,
A means for controlling the scanning voltage and the signal voltage so that the polarities of the (N-1) th period are different from the Nth period; and the scanning voltage and the signal voltage of one or more horizontal scanning periods. A liquid crystal display device using a two-terminal type non-linear resistance element, characterized in that it has means for inverting the polarity.

Further, a liquid crystal display device using a two-terminal type non-linear resistance element in which the scanning voltage and the signal voltage are inverted in polarity every 1 / N horizontal scanning period within one horizontal scanning period is obtained.

Further, the signal voltage applied to the signal electrode within one horizontal scanning period is the same voltage in the odd-numbered period and the even-numbered period, and the signal electrode drive circuit determines the pulse width of the signal voltage. The gradation display is controlled by modulation, and when K gradations are to be obtained, the kth gradation (k: 1 ≦ k
≦ K, a natural number of ≦ K is displayed, the signal electrode is turned on (ON) with a width of 1- (k−1) / (K−1) with respect to the 1 / N horizontal scanning period in the odd-numbered period. ) Signal voltage is applied, the ON signal voltage is applied to the signal electrode with a width of (k-1) / (K-1) in the even-numbered period, and the signal electrode is applied to the signal electrode in the odd-numbered period. A liquid crystal display device using a two-terminal type non-linear resistance element, wherein the sum of the ON time of the applied signal voltage and the ON time of the signal voltage applied to the signal electrode during the even-numbered period is equal. I will get it.

[0010]

According to the present invention, at least a pair of forward and reverse pulse voltages is applied to the preceding stage of the ON signal (voltage for controlling the pixel to the display state) of the signal voltage in one horizontal scanning period (selection period). In this case, the pulse before the ON signal is OF of the opposite polarity to the ON signal.
An F pulse (a voltage that does not change display or non-display of pixels) can be used, and a previous pulse having the same polarity as the ON signal can form part of the ON signal.

That is, when one horizontal scanning period (selection period) is set to N periods (3 ≦ N: natural number), in the case of ON display writing, the voltage is turned on at ON in the (N−2) th and Nth periods. The (N-1) th period is an OFF polarity inversion voltage. In the case of OFF display writing, the (N−2) th and Nth periods are set to the OFF voltage, and the (N−1) th period is set to the ON voltage of the opposite polarity.

The two-terminal type non-linear resistance element is generally Ta
A laminated structure of (Metal) -TaO (Insulator) -Ta (Metal) is used, and the nonlinearity of the voltage-current characteristics is used as a switch. The insulating layers that are stacked have drifts due to changes in polarization that occur with the application of voltage, but the application of a pair of forward and reverse pulse voltages contributes to the elimination of this drift, and allows the nonlinear resistance element to operate uniformly. Set to state.

As described above, the effective value of the voltage applied to the pixel becomes the same in all the pixels in the selected period, and is applied to the two-terminal type non-linear resistance element due to the difference in display pattern. The difference in the time integral value of the voltage is also small. Therefore, even when different displays are continuously displayed for a certain two pixels for a long time, it is possible to make the drift of the voltage-current characteristics of the non-linear resistance element connected to each pixel uniform and to prevent the occurrence of burn-in. Can be suppressed.

The present invention is also effective when halftone display is performed by frame control or the like.

Further, it can be applied to an operation system in which a scanning voltage is applied to the signal electrode of the display element and a signal voltage is applied to the scanning electrode.

[0016]

【Example】

(Embodiment 1) FIG. 1, FIG. 2, FIG. 6, FIG. 7 and FIG. 8 show Embodiment 1 of the present invention.

In FIG. 6A, a liquid crystal display element 1 has a display area 2 which serves as a display screen, and is connected to and driven by a scan electrode drive circuit 3 and a signal electrode drive circuit 4. These drive circuits are driven by the current voltage generation circuit 5 and the drive signal generation circuit 6.

As shown in FIG. 7, the liquid crystal display element 1 has a large number of transparent stripe-shaped scanning electrodes 13 (M, for example 320) extending on the inner surface of the observation side substrate 11 in the line direction of the display screen. , Are arranged in parallel. On the surface of the counter substrate 12 facing this, the signal electrodes 14 are arranged to intersect with the scanning electrodes 13 in an orthogonal relationship on the screen, and the transparent pixel electrodes 15 formed for each pixel region are provided for each pixel electrode. The two-terminal type non-linear resistance element 16 of the MIM element is connected.

A fixed space is formed between the scanning electrode 13 and the pixel electrode 15, and the liquid crystal layer 17 is sandwiched between them. Alignment films 18 and 19 are applied on the electrodes of both substrates, and the liquid crystal molecules of the liquid crystal layer 17 are aligned by rubbing. The liquid crystal layer 17 is made of nematic liquid crystal and has liquid crystal molecules of 270 °.
A twisted STN type display element is constructed.

These electrode arrangements are shown in a planar circuit arrangement in FIG. 6 (b). A plurality of stripe-shaped scanning electrodes 13 extending in the line direction of the screen of the display region 2, that is, the horizontal direction in the drawing are arranged in parallel, and a plurality of signal electrodes 14 are arranged in a direction orthogonal to the scanning lines, that is, in the vertical direction in the drawing. Books should be placed at equal intervals. The pixel electrodes 15 are arranged in, for example, 480 × 320 matrix-shaped pixel regions surrounded by the scanning electrodes 13 and the signal electrodes 14. The capacitance is shown in the figure, and one end of the pixel electrode is connected to the signal electrode 14 via the two-terminal type non-linear resistance element 16. There is a liquid crystal layer between the pixel electrode and the scanning electrode, and a capacitance is formed between them.

A signal voltage as data is applied in parallel to each signal electrode 14 from the signal electrode drive circuit 4, and the display area is line-sequentially scanned by the application of the scan voltage by the scan electrode drive circuit 3.

FIG. 1 shows a waveform when the display area is displayed in binary. This waveform represents a drive waveform applied to one pixel on the screen, for example, P11. FIG. 1A shows a case of ON display, and FIG. 1B shows a case of OFF display. One horizontal scanning period, that is, the selection period N is divided into four sections.

In the case of ON display, writing is performed with the OFF voltage in the first period (N-3) and the third period (N-1), and the first period is written in the second period (N-2) and the fourth period (N). Writing is performed with an ON voltage having a polarity opposite to that in the third period.

Further, when the OFF display is performed, the first and the third
During the period, writing is performed with an ON voltage, and during the second and fourth periods, writing is performed with an OFF voltage of opposite polarity.

These voltages are V0>V1> shown in FIG.
Six-level potentials of V2>V3>V4> V5 are obtained from the current-voltage generating circuit 5 generated by resistance division of the input power supply voltage V by the resistance elements R3 and R4 of the potentiometer. In the figure, reference numeral 51 indicates a buffer.

V0, V1, V4 and V5 are for the scan electrode driving circuit 3, and V0, V2, V3 and V5 are for the signal electrode driving circuit 4.
Is supplied to.

If the selection potential is V, the scan electrode drive circuit 3 is V
A voltage of 0 (V5 when the polarity is inverted) or V4 (V1 when the polarity is inverted) is output to the scan electrodes when the potential is non-selective.
), The voltage of V3 (V2 when the polarity is inverted) is output to the signal electrode when the display is OFF.

FIG. 2 shows the voltages input to the scan electrodes and the signal electrodes in order to obtain the drive waveform of FIG. 1, and the drive waveform of FIG. 1 is obtained by combining them. Each waveform in FIGS. 1 and 2 is 2
The frame is shown, and the inversion is performed for each frame and the inversion is performed for each line. In this case, m (1 ≦ m ≦ M)
It can also be applied to line-by-line inversion.

One frame (vertical scanning period) consists of a horizontal scanning period (selection period) of 320 lines (M = 320), which is time-divided into first to fourth periods.

In the case of ON display, as shown in FIG. 2A, in the first frame period, the scan electrode V5 and the signal electrode V2 are (V5-V2) =-VOff during the first and third periods, In the second and fourth periods, the scan electrode V0 and the signal electrode V5
Then, (V0-V5) = VOn. The frame-inverted second
In the frame period, the scan electrodes V0, in the first and third periods,
At the signal electrode V3, (V0-V3) = VOff, and in the second and fourth periods, the scan electrode V5 and the signal electrode V0 (V5-
V0) =-VOn.

In the OFF display, as shown in FIG. 2B, the scan electrode V5 and the signal electrode V0 are supplied in the first and third periods.
(V5-V0) =-VOn, and (V3-V0) = VOf for the scan electrode V0 and the signal electrode V3 in the second and fourth periods.
becomes f. The second frame period in which the frame is inverted is the first
In the third period, the scan electrode V0 and the signal electrode V5 (V0
-V5) = VOn, and (V5-V2) =-VOff for the scan electrode V5 and the signal electrode V2 during the second and fourth periods.

The remaining frame period is a non-selection period and includes a selection period of another adjacent pixel P12 on the same signal electrode, and the voltage applied to the pixel P11 during this period is that P11 is ON.
In the case of display, the first period and the third period are (V4-V3), and the second period and the fourth period are (V1-V0) according to the first to fourth periods of the pixel P12. Also, the pixel P11
Is OFF, the first period and the third period are (V5-V4), and the second period and the fourth period are (V2-V1) according to the first to fourth periods of P12.

Here, the pixel P12 is driven by line inversion.
1 and 2 show waveforms applied to the pixel P11 when the other pixels are inversely driven line by line in the non-selection period.

In this embodiment, the display pattern was fixed and displayed for 1 hour, and then the display was switched to the halftone raster display. However, the previously displayed pattern was completely erased and the burn-in was removed. Was observed.

(Embodiment 2) FIGS. 3 and 4 explain this embodiment, and are applied to a display device using the two-terminal type non-linear resistance element of the MIM element shown in FIG.

FIG. 3A shows a case of ON display, and FIG.
(B) shows the case of OFF display. In FIG. 3, the selection period is divided into four sections.

In the case of the ON display shown in FIG. 3A, the OFF voltage is used for writing in the first and third periods, and the ON voltage is used for writing in the second and fourth periods. Further, the polarities of the respective periods are opposite in polarity in the third period before the fourth period and the other periods.

Further, in the OFF display of FIG. 3B, the ON voltage is used for writing in the first and third periods, and the OFF voltage is used for writing in the second and fourth periods. Further, the polarities of the respective periods are opposite in polarity in the third period before the fourth period and the other periods.

FIG. 4 shows the voltage waveforms applied to the scanning electrodes and the signal electrodes of the liquid crystal display element for two frames to obtain the driving waveforms of FIG. 3, and the solid line in FIG. 4A is applied to the scanning electrodes. The scanning voltage in ON display, the dotted line in FIG. 4A is the signal voltage in ON display applied to the signal electrode, and FIG.
The solid line in (b) is the scanning voltage for OFF display applied to the scanning electrodes, and the dotted line in FIG. 4 (b) is the OF applied to the signal electrodes.
The signal voltage in F display is shown. In the case of the present embodiment as well, as in the first embodiment, the inversion is performed for each frame and for each line.

In this example, as in Example 1, no seizure phenomenon was observed.

(Embodiment 3) FIG. 5 shows drive waveforms during halftone display drive by the pulse width modulation method in the configuration of FIG.

FIG. 5B shows the twelfth gradation (k = 1) when the 16-gradation display signal electrode drive circuit (K = 16) is used.
It is a drive waveform when displaying 2).

In the first and third periods, ON transmission is output as a signal voltage in the period of 4/15 of the 1/4 horizontal scanning period, and in the second and fourth periods, it is 11 of the 1/4 horizontal scanning period. /
The ON voltage is output in the period of 15. FIG. 5A shows the scanning voltage (solid line) and the signal voltage (dotted line) at this time. That is, in order to obtain K gradations, when displaying the kth gradation (k: natural number of 1 ≦ k ≦ K), in the odd-numbered period, the signal electrode is set to 1 with respect to the 1 / N horizontal scanning period. An ON signal voltage having a width of − (k−1) / (K−1) is applied, and an ON signal voltage having a width of (k−1) / (K−1) is applied to the signal electrode in an even-numbered period. Is applied.

Here, the ON time of the signal voltage applied to the signal electrode in the odd-numbered period and the ON time of the signal voltage applied to the signal electrode in the even-numbered period are equalized.

Each of the first to fourth periods is A, the odd-numbered period ON voltage period is B, and the even-numbered period ON voltage period is C.
Then, A: B = 1: (1- (k-1) / (K-1)) A: C = 1: (k-1) / (K-1).

In this embodiment, the first halftone pattern was completely disappeared from the moment the first halftone pattern was displayed for one hour and then the display was switched to the second halftone pattern. It was confirmed that it was removed.

[0047]

In the liquid crystal display device using the two-terminal type non-linear resistance element as the switching element, the drift of the voltage-current characteristics of the non-linear resistance element due to the difference in the display pattern can be made uniform and the image sticking can be eliminated. .

[Brief description of drawings]

FIG. 1 illustrates Example 1 of the present invention, in which (a) is O
N display, (b) voltage waveform diagram for OFF display,

FIG. 2 illustrates Example 1 of the present invention, in which (a) is O
N display, (b) voltage waveform diagram for OFF display,

FIG. 3 illustrates Example 2 of the present invention, in which (a) is O
N display, (b) voltage waveform diagram for OFF display,

FIG. 4 illustrates Example 2 of the present invention, in which (a) is O
N display, (b) voltage waveform diagram for OFF display,

5A and 5B are voltage waveform diagrams for explaining a third embodiment of the present invention,

FIG. 6 shows the configuration of Examples 1 to 3 of the present invention,
(A) is a block diagram, (b) is a circuit layout diagram of the display area,

FIG. 7 is a schematic sectional view of a liquid crystal display element,

FIG. 8 is a circuit diagram showing a configuration of a current voltage generation circuit.

[Explanation of symbols]

 1: Liquid crystal display element 2: Display area 3: Scan electrode drive circuit 4: Signal electrode drive circuit 5: Current voltage generation circuit 6: Drive signal generation circuit 13: Scan electrode 14: Signal electrode 15: Pixel electrode 16: 2 terminal type Non-linear resistance element 17: Liquid crystal layer P11, P12 ...: Pixel

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenshi Tsuchiya, 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company, Toshiba Yokohama Office (72) Inventor Kazushi Miyake, 8-shin-sugita-cho, Isogo-ku, Yokohama, Kanagawa Company Toshiba Yokohama Office

Claims (3)

[Claims] 1. A plurality of scan electrodes which are arranged in a display area in which a plurality of pixels are formed and which extend in the line direction of the area,
A plurality of signal electrodes extending in a direction intersecting the scan electrodes, a two-terminal type non-linear resistance element connected to the signal electrode for each pixel, and a two-terminal type non-linear resistance element connected to the two-terminal type non-linear resistance element and arranged for each pixel. A liquid crystal display element having a pixel electrode, and a liquid crystal layer sandwiched between the scanning electrode and the pixel electrode;
A liquid crystal display device using a two-terminal type non-linear resistance element, comprising: a scan electrode drive circuit that applies a scan voltage to the scan electrodes; and a signal electrode drive circuit that applies a signal voltage to the signal electrodes. One vertical scanning period of a drive waveform for driving the plurality of lines is composed of a horizontal scanning period of a plurality of lines, and each horizontal scanning period of the plurality of lines is time-divided into N periods of at least 3, and the scanning voltage and the signal voltage are Means for controlling the polarities of the (N-1) th period with respect to the Nth period; and means for inverting the polarities of the scanning voltage and the signal voltage for each of the one or more horizontal scanning periods. A liquid crystal display device using a two-terminal type non-linear resistance element. 2. A liquid crystal display device using a two-terminal type non-linear resistance element according to claim 1, wherein the scanning voltage and the signal voltage are inverted in polarity every 1 / N horizontal scanning period within one horizontal scanning period. . 3. The signal voltage applied to the signal electrode in one horizontal scanning period is the same voltage in the odd-numbered period and the even-numbered period, and the signal electrode drive circuit determines the pulse width of the signal voltage. It modulates and controls the gradation display.
In order to obtain K gradations, when displaying the kth gradation (k: natural number of 1 ≦ k ≦ K), in the odd-numbered period, 1 / N horizontal scanning period is applied to the signal electrode. 1-
An ON signal voltage having a width of (k-1) / (K-1) is applied, and (k-1) / is applied to the signal electrode during the even-numbered period.
An ON signal voltage having a width of (K-1) is applied, and the signal voltage applied to the signal electrode during the odd-numbered period is ON.
The liquid crystal display using the two-terminal non-linear resistance element according to claim 1 or 2, wherein the sum of the time and the ON time of the signal voltage applied to the signal electrode during the even-numbered period is equal. apparatus.