JP2851314B2 - Driving method of two-terminal type active matrix liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] Liquid crystal display devices are widely applied as low power consumption flat panel displays. Among them, an active matrix method in which a switching element is formed in each pixel and driven is being used as a large-capacity, high-quality display element in televisions, information terminals, and the like. 3 for switching element
A terminal type TFT (thin film transistor) and a non-linear resistance element such as a two-terminal type diode or MIM are used. Commercialization is 3
Terminal type TFTs preceded, but the two terminal type is easier to manufacture than the three terminal type, and future prospects are expected.

The present invention relates to a method for driving a two-terminal type active matrix liquid crystal display device using two-terminal type switching elements.

[Conventional technology and its problems]

FIGS. 2 and 3 show the basic arrangement of pixels of an active matrix liquid crystal display device using two-terminal switching elements.

FIG. 2 shows a system called a diode ring (JP-A-59-57273). C1, C2, C3 are data lines 5, R1, R
2, R3 are scanning lines 6 arranged in a matrix. The liquid crystal display pixel 10 corresponds to the intersection of the data line 5 and the scanning line 6.
And diode ring 20 as a two-terminal switching element
And are arranged. Each diode ring is a diode group 23 connected in the forward direction and a diode group connected in the reverse direction.
It consists of 22. Each diode 21 is usually formed by a pin junction or a Schottky junction of amorphous silicon.

FIG. 3 shows a two-terminal type active matrix liquid crystal display device of the MIM system. C1, C2, and C3 are data lines 5, R1, R2, and R3 are scanning lines 6, and are liquid crystal display pixels 10 and two-terminal switching elements corresponding to intersections of the data lines 5 and scanning lines 6.
MIM30 is arranged. MIM is a two-terminal switching element having a metal-insulator-metal (conductor) structure and having nonlinear current-voltage characteristics. A typical structure is a lower electrode Ta, an insulating film is an anodic oxide film (TaOx) of this Ta, and an upper electrode is ITO (transparent conductor), which can be manufactured with two patterns (masks).

FIG. 4 shows a scanning signal waveform in a conventional driving method of an active matrix liquid crystal display device such as a diode ring or MIM (Japanese Patent Laid-Open No. 59-57288).

The scanning signals φ ₁ , φ ₂ , φ ₃ correspond to the respective fields T _A
And T _B are signals for selecting line-sequential in the sections T _A1 , T _A2 , T _A3 and T _B1 , T _B2 , T _B3 . As for the scanning signals phi _1, a positive write section T _W1 in positive write voltage V _W1 is negative write section T _W2 negative write voltage V _W2 in the positive static period T _H1 in the positive hold voltage V _H1 In the negative holding section _TH2 , a negative holding voltage _TH2 is applied.

A problem occurs in the conventional driving method when the driving capability of the liquid crystal display pixel of the two-terminal switching element is not sufficient. There are the following two problems in the driving capability of the two-terminal switching element.

(B) Capacitance ratio α = C _LC / C _SW C _SW ; Two-terminal switching element capacitance C _LC ; Liquid crystal display pixel capacitance (b) Current drive capability in the write section If these two values are not sufficient, The problem arises in the write characteristics (dynamic range) and the retention characteristics (crosstalk) in the retention section. Regarding crosstalk, it is possible to make the whole uniform and the contrast is reduced, but it is not fatal. However, the writing characteristics are problematic in that display is not possible in extreme cases.

The capacitance ratio α has no problem in a design in which the liquid crystal display pixel is large and _CLC / _CSW can be 4 to 5 or more. However, C _LC / C _SW 3 or less in the liquid crystal projectors, liquid crystal Shipping Accessories finder such as a small high-density applications, extreme cases can not be handled by even occur prior driving method case dividing 1.

The current drivability in the writing section is good for a diode ring or the like, but poses a problem for small and high-density applications with a small element area. Furthermore, it is very problematic when MIM having a simpler structure is used in consideration of productivity.

It is aimed at overcoming the disadvantages of the prior art scheme of the present invention. That is, an object of the present invention is to provide a driving method of a two-terminal type active matrix liquid crystal display device which can be driven even by a two-terminal type switching element having insufficient capacity ratio and current driving capability in a writing section.

[Means for solving the problem]

The present invention improves the conventional method of driving a two-terminal type active matrix liquid crystal display device by modifying the scanning signal. That is, before the writing section, a scanning signal having a reset section having a reset voltage having a polarity opposite to the writing voltage and having a voltage having an absolute value equal to or greater than the writing voltage and having an absolute value greater than or equal to the writing voltage is used. It is characterized by things.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is an embodiment of a scanning signal waveform in a method for driving a two-terminal type active matrix liquid crystal display device according to the present invention.

Scanning signal _{^{φ 1 *, φ 2 *,}} φ 3 * in each field T _A and T interval T _A1 of _B, T _A2, T _A3 and T _B1, T _B2, line-sequentially the signal selected by the T _B3 is there. Looking at the scanning signal φ ₁ ^* , in the positive write period T _W1 , the positive write voltage V
_W1 is a negative writing period T _W2 negative write voltage V _W2 in,
In the positive holding section T _H1 , the positive holding voltage V _H1 is changed to the negative holding section T.
_{At H2} , a negative holding voltage V _H2 is applied. In this regard, the fourth
This is the same as the conventional example shown in FIG. A feature of the scanning signal of the present invention is that a reset section is provided before the write section, in which a reset voltage of a voltage having a polarity opposite to the write voltage and having an absolute value greater than or equal to the absolute value of the write voltage is obtained. It is in. That is, a negative reset section T _R1 is provided before the positive write section T _W1 , and a positive reset section T _R2 is provided before the negative write section T _W2 , and the respective reset voltages are made higher in absolute value than the write voltage. Is set to

 FIG. 7 shows a scanning signal according to another embodiment of the present invention.

FIG. 1Z shows the maximum voltage 11 and the minimum voltage 12 at each timing of the scanning signal group of the embodiment of FIG. In this embodiment, since the so-called row-by-row inversion method is used, the maximum voltage 11 and the minimum voltage 12 vary depending on the polarity of the write voltage of the scanning signal. The difference between the maximum voltage and minimum voltage programming voltage is positive timing V _R2 -V _H2, V _H1 -V-negative timing
It becomes _R1 . To save the operating voltage of the driving circuit, the operating voltage of the driving circuit is calculated by subtracting the operating voltage of this driving circuit from the maximum voltage and the minimum voltage.
It is known that V _R2 −V _H2 (V _H1 −V _R1 ) can be set. For this purpose, the voltage difference between these two timings V _R2 −V _H1 (V
_H2 -V _R1) a having signal (Fig. 7 X) a seventh view of a scanning signal phi ₁ ^** by subtracting from the scanning signal of FIG. 1, phi ₂ ^**,
φ ₃ ^** , and the operating voltage can be reduced by V _R2 −V _H1 (V _H2 −V _R1 ).

In this embodiment, the timing of the reset section is set in the immediately preceding write section of the scanning line, but may be independently or staggered.

The effect of the present invention is greater when the length of the reset section is longer than that of the write section as shown in FIG. 6 described later.

〔The invention's effect〕

 Next, the effects of the present invention will be described.

FIG. 5 is an explanatory diagram showing a voltage state in a writing section in a conventional example. When the data signal and V _D, write section T _W1
Holding period T _H2 in the holding voltage V _H2 + data voltage V _D of the front of,
In the holding section T _H1 after the writing section, the holding voltage V _H1 + the data voltage V _D is applied. In the write section _TW1 , V _W1 + V _D (OFF) is applied when the data signal is OFF, and V _W1 + V _D (ON) is applied when the data signal is ON.

The voltage applied to the liquid crystal display pixels in the holding section _TH2 is defined as Va. When the data signal is OFF in the writing section _TW1 , a voltage of V _W1 + V _D (OFF) is applied, and if the capacitance ratio C _LC / C
_{When SW} is 1, the voltage instantaneously applied to the liquid crystal display pixel by the capacitive coupling becomes _Vd2 . As described above, when the capacitance ratio is not sufficient, the voltage V _W1 + V _D (OFF) −Va normally applied to the two-terminal switching element is C _LC / (C _SW + C
_LC ). Even this may be at the current drive capability of the write period of the two-terminal type switching element is sufficient, but no current in the write period T _W1 if insufficient is injected into the liquid crystal display pixel, the liquid crystal display pixel after the writing Cannot be sufficiently obtained between the voltage _Ve2 applied to the memory _cell and the voltage _Vd2 before writing. Similarly, when the data signal is ON, V _W1 + V
A voltage is applied _D (ON), the voltage applied to the liquid crystal display pixel difference between the voltage V _e1 and before writing voltage V _d1 applied next V _d1, a liquid crystal display pixel after the writing is not sufficiently taken . When the voltage becomes the holding voltage V _H1 + the data voltage V _{D in the} holding section, the voltages applied to the liquid crystal display pixels become V _f1 and V _{f2 due} to capacitive coupling. This voltage drives the liquid crystal display pixels, but when the capacity ratio and the current driving capability in the writing section are not sufficient as described above, the liquid crystal driving voltage _Vf1 for ON writing and the liquid crystal driving voltage _VOFF for OFF writing A sufficient difference in the liquid crystal drive voltage _Vf2 cannot be obtained, and a sufficient contrast cannot be obtained.

The biggest problem of the conventional example is that a sufficient voltage is not applied to the two-terminal switching element in the initial state of the writing section.

FIG. 6 is an explanatory diagram showing a voltage state in a writing section according to the embodiment of the present invention. In the present invention, the reset section T _R1 in which the reset voltage V _R1 of the opposite polarity is applied before the write section T _W1.
Is different from the conventional example. At the beginning of the reset period, the voltage instantaneously applied to the liquid crystal display pixel by capacitive coupling is V _b
^* , The current is injected into the liquid crystal display pixel in the reset period, and finally becomes V _c ^* . Data signal is turned off at write _TW1
The liquid crystal display voltage applied to the pixel V _d2 ^*, the V _d1 ^* when the ON when the. What should be noted here is the voltage V of the conventional example.
This is the difference between _d1 and _Vd2 and the voltages _Vd1 ^* and _Vd2 ^* of the embodiment of the present invention. With the addition of the reset section, the voltages V _d1 ^* and V _d2 ^* of the embodiment of the present invention are considerably smaller than the voltages V _d1 and V _d2 of the conventional example. As a result, the voltage applied to the two-terminal switching element during the writing period increases. As described above, according to the present invention, the greatest problem of the conventional example can be greatly improved. As a result, the voltage finally applied to the liquid crystal display pixel
The difference between V _f1 ^* and V _f2 ^* increases, and the contrast increases.

In the reset voltage V _R1 to the aforementioned reset period T _R1,
In order to obtain the effect of the present invention, the write voltages _VW1 and _VW2 must be equal to or greater than the absolute values. When the reset voltage is smaller than the write voltage, V _d1 ^* and V _d2 ^*
It becomes equal to V _d1 and V _d2, and the effect of the present invention cannot be obtained.

As described above, according to the present invention, it is possible to drive a high-contrast two-terminal switching element having a low capacitance ratio and a low current driving capability, which has not been able to obtain sufficient contrast.

In this embodiment, the reset section is provided immediately before the write section. However, even if another voltage section is inserted therebetween, the effects of the present invention are not changed and are included in the present invention.

Further, in this embodiment, the writing sections T _A1 , T _A2 , T _A3 and T _B1 , T _B2 , T _B3 of the scanning signals φ ₁ ^* , φ ₂ ^* , φ ₃ ^* are made continuous, but an appropriate section is provided therebetween. May be inserted.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing a scanning signal in an embodiment of a method for driving a two-terminal type active matrix liquid crystal display device of the present invention, and FIGS. 2 and 3 are all typical two-terminals according to the prior art. FIG. 4 is a circuit diagram showing a basic structure of a liquid crystal display device of the active matrix type, FIG. 4 is a waveform diagram showing a scanning signal in a driving method of a two-terminal type active matrix liquid crystal display device according to the prior art, and FIG. FIG. 6 is a waveform diagram showing the state of voltage application to the liquid crystal display pixel before and after the writing period. FIG. 6 is a waveform diagram showing the state of voltage application to the liquid crystal display pixel before and after the writing period in the embodiment of the present invention. FIG. 9 is a waveform chart showing another embodiment of the scanning signal of the driving method of the present invention. 5 ...... data line, 6 ...... scanning lines, 10 ...... liquid crystal display pixels, 20 ...... diode ^{_{ring, 30 ...... MIM, φ 1 *}} , φ 2 *, φ 3 * ...... scan signal.

Claims (3)

(57) [Claims] 1. A scanning device comprising: data lines and scanning lines arranged in a matrix; a liquid crystal display pixel provided at an intersection of the data lines and the scanning lines; and at least one two-terminal switching element; In a method for driving a two-terminal active matrix liquid crystal display device in which a liquid crystal display pixel is driven by a scanning signal applied to a line and a data signal applied to the data line, the two-terminal switching element is a non-linear resistance element. The scanning signal has a write section having positive and negative write voltages, and before the write section, has a polarity opposite to the write voltage and equal to or greater than the absolute value of the write voltage. A method for driving a two-terminal type active matrix liquid crystal display device, comprising a reset section of a voltage having an absolute value of: 2. The method of driving a two-terminal active matrix liquid crystal display device according to claim 1, wherein the two-terminal switching element is a MIM element. 3. The method of driving a two-terminal active matrix liquid crystal display device according to claim 1, wherein the capacitance of the two-terminal switching element is larger than one third of the capacitance of the display pixel.