JPH02204720A - Display device and its driving method - Google Patents

Abstract

PURPOSE:To improve the uniformity of a display screen by driving corresponding to common inversion driving and to attain display with high picture quality by connecting the 2nd capacitor between a wiring connected to a counter electrode and a common electrode and transmitting a signal impressed to the common wiring to the counter electrode through the 2nd capacitor. CONSTITUTION:In a liquid crystal display device holding liquid crystal 24 between a glass base 22 for an active matrix array base having the 1st image signal holding capacitors connected to the common wiring in respective picture elements and a glass base for the counter electrode, the 2nd capacitor 21 is connected between an electrode 26 connected to the common wiring and an electrode 27 connected to a wiring 29 connected to the counter electrode through a conductive paste 28 and the device is mounted on a driving circuit with common inversion driving to obtain the display device. When a conventional signal is impressed to the common wiring and a signal through the 2nd capacitor 21 is impressed to the counter electrode, characteristics on the upper and lower parts of the display screen almost coincide with each other, the inclination of brightness is not observed, the uniformity of an image is increased, and display performance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a method for driving display materials such as liquid crystal using an active matrix array substrate having a matrix of switching elements such as thin film transistors, pixel electrodes, and capacitors for holding image signals. The present invention relates to a display device and a method for driving the same.

BACKGROUND OF THE INVENTION A typical case of a liquid crystal display device will be described with reference to the drawings.

FIG. 4 is a circuit diagram of a main part of a liquid crystal display device using an active matrix array substrate having an image signal holding capacitor (first capacitor).

The display section surrounded by the broken line ABCD has a large number of pixels (the part surrounded by the broken line 1) repeated in a matrix. Each pixel is equipped with a thin film transistor (hereinafter referred to as TPT) 2 as a switching element.
The gate electrode of the PT is connected to the scanning signal line 7, the source electrode is connected to the image signal line 8, and the drain electrode is connected to the image signal holding capacitor 3 (first capacitor; Cs) and the pixel electrode 4. Image signal holding capacitor 3
is also connected to the common wiring 9. The liquid crystal 6 is the counter electrode 5
and the pixel electrode 4 and are driven. Note that among the constituent elements of these pixels, the components other than the counter electrode 5 and the liquid crystal 6 are built on the active matrix array substrate. In addition, the counter electrode 5 is composed of one wide electrode that covers the entire display area, and is built on the counter substrate (note that the number of wiring is small in the drawing, but when performing TV display etc., the scanning signal is The number of wiring lines 7 and image signal wiring lines 8 exceeds several hundreds).

The part surrounded by the broken line EFGH is a display panel whose main components are an active matrix array substrate, a counter substrate, and a liquid crystal, and a liquid crystal display device is configured by mounting this on drive circuits 1°, 11, and 12. . FIG. 5 shows an example in which a display panel is mounted on a part of a drive circuit. 13 is an active matrix array substrate, 14
is a counter substrate, and liquid crystal is sealed between these two substrates to form a display panel. 15 is a mounting electrode built on the active matrix array substrate, and using this mounting electrode, the display panel is connected to the driving IC 1.
7 is mounted on a printed circuit board 18 via a flexible substrate 16 on which the circuit board 7 is mounted.

19 is a connector for further connecting to an external circuit.

The liquid crystal display turns on the TPT by sequentially applying scanning signals to the scanning signal wiring 7 in FIG.
The image signal applied to the pixel electrode 4 is transmitted to the pixel electrode 4.
This is done by driving the liquid crystal 8 using a voltage difference between the voltage difference between the voltage and the counter electrode 5. The image signal holding capacitor 3 (first capacitor) is used to hold the signal during the off period of the TPT 2 and as an application path for various modulation signals in driving the liquid crystal. is suitable for displaying high-quality images.

FIG. 6 shows a typical example of a drive signal applied to the display panel section of the display device of the type shown in FIG. 4. The figure represents a signal related to one pixel on the screen. FIG. 6(a) is called common constant drive, in which the potential Vc of the counter electrode 5 is kept at a constant potential, and a signal Vs containing the image signal VsIg is applied to the image signal wiring 8, and the scanning signal is Display is performed by applying a scanning signal Vg to the wiring 7. Note that the signal Vs includes image signals to all pixels connected to the scanning signal wiring of interest in time series.

Although not shown in the figure, the potential of the common wiring 9 is always kept at a constant potential. FIG. 6(b) is called common inversion drive, in which the potential Vc of the counter electrode 5 is changed at a constant period (NT
SC TV signals are usually changed in units of 1 field or 1 frame), and in this case, the common wiring 9
The potential of is kept at the same potential as Vc. The advantage of common inversion drive is that the dynamic range of the signal Vs can be reduced, power consumption can be reduced, and low-cost ICs with low breakdown voltage can be used.

Regarding the above, see, for example, N. Matsumoto; Electronic Display Device (1984), Ohmsha, and Television, 7 Academic Magazine Vol. 1.42. No. 1 (1988).

Problems to be Solved by the Invention As described above, a display device equipped with an image signal holding capacitor is suitable for displaying high-quality images such as on a TV display due to the function of the signal holding capacitor. Further, power consumption can be reduced by performing common inversion drive.

However, when the display device of the type shown in FIG. 4 is driven as shown in FIG.
Even when inputting sig, a phenomenon occurs in which the brightness of the screen changes continuously from the top to the bottom of the screen. For example, FIG. 7 shows a normally black liquid crystal display panel (LCD panel for TR-3LTi manufactured by Matsushita Electric Industrial Co., Ltd.).
89280 pixels, 1 pixel size 160 μll x 19
0μm.

Capacity of signal holding capacitor per pixel Cs=I
PF+ Amorphous S 1TFT (W/L=5
．． 5) shows the experimental results of investigating the relationship between the image signal and screen brightness when common constant driving is used. The figure shows the brightness difference depending on the display location, and the same image signal Vs1gl
It has been measured that even when TI is applied, a difference in TI brightness (brightness slope) occurs between the top and bottom of the screen. Furthermore, the exact same liquid crystal display panel is driven by common inversion drive (counter electrode potential V
Fig. 8 shows the results when the amplitude of c was 5.5 V). In this case, the brightness gradient is even greater, and a brightness difference of T2 occurs between the top and bottom of the screen for the same image signal V sfg2. This brightness gradient impairs the uniformity of the screen and is a major impediment to high quality display.

The brightness gradient is a manifestation of changes in the retention characteristics of image signals due to differences in scanning timing due to differences in location. Therefore, it is theoretically possible to correct the problem by making complex signal corrections according to the timing (for each location), but this not only complicates the circuit, but also requires the development of a dedicated IC, the addition of a power supply circuit, and the reduction of power consumption. This is not a good idea as it will lead to an increase in the number of people.

The present invention is a signal holding capacitor (first capacitor)
Adding a simple configuration to the display device and
The purpose of this invention is to improve the uniformity of the display screen and realize higher-quality image display using drive similar to common inversion drive that consumes less power than conventional drives.

Means for Solving the Problems A second capacitor is installed between the opposing electrode and the common wiring, and the signal applied to the common wiring is configured to be transmitted to the opposing electrode via the second capacitor.

The present invention uses the simple means of installing a second capacitor to compensate for the loss component of the image signal when the potential of the common wiring changes, while performing drive similar to common inversion with low power consumption. This makes it possible to realize a uniform image with little brightness gradient. There is no need to add complicated circuits, power supply circuits, or develop ICs, and it can be driven using conventional drive circuits, so it is very effective in practice.

Specific means for installing the second capacitor are as follows: 1) Mounting the capacitor directly on the drive circuit (printed board, etc.) or directly on the display panel.

2) A capacitor is built into the counter board during the process of creating the counter board.

3) A capacitor is built into the active matrix array substrate during the manufacturing process of the active matrix array substrate.

4) When assembling the display panel, build in capacitors using both the counter substrate and the active matrix array substrate.

etc. are possible. Each method has its advantages, and which method to adopt can be selected according to the desired display performance and manufacturing process.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(a) shows an explanatory view of the main parts of a liquid crystal display device according to a first embodiment of the present invention, which corresponds to the invention described in claim 1. A second capacitor 21 is directly mounted on a display panel 20 similar to the conventional one.

A partial cross-sectional view of the part where the capacitor 21 is mounted is shown in Figure 1 (
Shown in b). 22 is a glass substrate for the active matrix array substrate, 23 is a glass substrate for the counter substrate, 24 sandwiched between them is a liquid crystal, and 25 is a sealing material for sealing the liquid crystal (because the drawing is complicated, the alignment film is (not shown). One end of the second capacitor 2 is connected to the electrode 26 connected to the common wiring, and the other end is connected to the electrode 27 and the conductive paste 2.
8 to a wiring 28 connected to the counter electrode.

In this example, the configuration of the display section itself is exactly the same as that used for measuring the conventional results shown in FIGS. 7 and 8, and a second capacitor (10000 pF) is installed on the display panel.
is directly mounted, and this is further mounted in the same common inversion drive circuit as the conventional one to create a display device. At this time, a conventional signal was applied to the common wiring, and a signal was applied to the opposing electrode via the second capacitor. Figure 2 shows the characteristics in this case. The characteristics at the top and bottom of the screen are almost the same, the brightness gradient is no longer visible, the image is more uniform, and the display performance is improved.

FIG. 3 shows an equivalent circuit centered on capacitive components for one pixel (the same components as in FIG. 4 are denoted by the same reference numerals, so the explanation of those parts will be omitted). Although not shown in FIG. 4, there are actually many capacitance components.Let us consider the principle of the present invention based on this fact. 1st for signal holding
Cs is the capacitance of the capacitor, CIc is the capacitance between the pixel electrode and the counter electrode, Cgds is the capacitance between the pixel electrode and the scanning signal line, and Csd is the capacitance between the pixel electrode and the image signal line.
, the capacitance between the counter electrode and the scanning signal wiring is defined as CCgl, and the capacitance between the counter electrode and the image signal wiring is defined as Ccs. Further, 30 is a component per pixel of the second capacitor, and the capacitance value is 02. Furthermore, regarding the potential relationship, the potential of the scanning signal wiring is Vgt, and the potential of the image signal wiring is V8m.
The potential of the pixel electrode is Vd, and the potential of the counter electrode is Vc'. During driving, a signal Vc is applied to the common wiring 9 and one end 81 of the second capacitor 30 to the opposing electrode during conventional common inversion driving.
(See FIG. 6) will be applied.

When common inversion driving is performed in this circuit network and the value of VC changes by ΔV, the potential (lVc'-Vdl) applied to the liquid crystal decreases by the value X expressed by the following equation due to capacitive coupling.

X=△V[Cs (Ccs+ Ccg) −C2(Cg
d+ C5d)]/Y However, Y=C1c(Ccs+Ccg+C2+Cgd+Csd+
Cs)+(Ccs+Ccg+C2)e (Cgd+Cs
d+C5) (In this equation, when C2=0, it represents the increase in brightness slope when the potential loss changes from common constant to common inversion.) Therefore, Cs (Ccs+Ccg) -C2(Cgd
By installing C2 such that +C5d)=0, the brightness gradient that occurs during common inversion driving is canceled out. Furthermore, C2
It is thought that if the value is set to the optimum value, the brightness gradient during constant common driving can also be canceled out. In the system of this embodiment, when calculating the value of X when 10,000 pF is attached as a second capacitor during common inversion drive and when it is not attached (design values are used as each capacitance value; C1c per pixel = 0. 24
．． C5=1.00. Ccs=0.019t
Ccg=0.006. Cgd=0.10. Cs
d:=0.001. C2 = 0.11 or 0; unit pF), the value when C2 is attached is 1 of the value when not attached
/3. In reality, the experimental results (Fig. 2) cannot be completely explained due to the deviation from the capacity estimation and design value on the drive circuit side, but by attaching the second capacitor as described above, it is possible to It can be inferred that the drive signal loss is reduced and the brightness gradient is alleviated.

FIG. 9 is an explanatory diagram of the main parts of a liquid crystal display device according to a second embodiment of the present invention, which corresponds to the invention set forth in claim 3. represents.

When performing liquid crystal display, a light shielding layer (black matrix) is sometimes provided to prevent light from leaking from a non-display area between adjacent pixel electrodes. In this embodiment, the second capacitor is installed using this black matrix. 9th
FIG. 9(a) shows the shape of the black matrix 32 formed in the counter substrate, and FIG. 9(b) is a sectional view of that portion of the display panel. The counter substrate is a glass substrate 33 with metal C.
A black matrix 32 is formed by r, and a dielectric layer 3 is formed.
5 and a counter electrode 34 is formed therebetween. Further, 37 is a glass substrate for an active matrix array substrate, 38 is a pixel electrode, and 38 is a liquid crystal (components not directly related to the present invention are omitted in the drawings). In this configuration, a capacitor 36 is formed between the counter electrode and the black matrix. In this embodiment, the capacitor 36 is used as a second capacitor, and a display panel having this configuration is mounted on the same common inversion drive circuit as the conventional one to obtain a display device. When the common wiring (not shown) and the black matrix 32 were driven by applying Vc of the conventional common inversion drive, the characteristics at the top and bottom of the screen almost matched as in the first embodiment, and the image Uniformity has increased and display performance has improved. In the structure of this embodiment, since a dyed layer of a color filter or the like can be used for the dielectric layer 35, it has the feature that it can be implemented without increasing the production process or the number of constituent materials.

FIG. 10 is an explanatory diagram of the main parts of a liquid crystal display device according to a third embodiment of the present invention, which corresponds to the invention set forth in claim 4, and shows the same parts as FIG. 1(b). ing.

40 is a glass substrate for an active matrix array substrate, 41 is a glass substrate for a counter substrate, and 4 is sandwiched between them.
8 is a liquid crystal, and 49 is a sealing material. The electrode 42 and the electrode 44 connected to the common wiring form a second capacitor 47 by sandwiching a dielectric layer 43 therebetween. The electrode 44 is connected via a conductive paste 45 to a wiring 46 connected to a counter electrode. A display panel with this configuration was mounted on the same common inversion drive circuit as the conventional one to produce a display device. In this embodiment, when driving was performed by applying the conventional common inversion drive voltage Vc to the electrode 42 connected to the common wiring as in the first embodiment, the uniformity of the image increased as in the first embodiment, and the display Improved performance. In this embodiment, the dielectric layer 43 is made of TP.
It is formed at the same time as the gate insulating layer of T, and the electrode 44
The electrodes 42 and 42 are also formed at the same time as the gate electrode and source electrode of the TPT are formed, respectively, and they have the characteristic that they can be carried out without increasing the number of steps or constituent materials.

FIG. 11 is an explanatory diagram of the main parts of a liquid crystal display device according to a fourth embodiment of the present invention, which corresponds to the invention set forth in claim 5, and shows the same parts as FIG. 9(b). ing.

50 is a glass substrate for an active matrix array substrate, 51 is a glass substrate for a counter substrate, and 5 is sandwiched between them.
2 is a liquid crystal. 53 is a black matrix, 54 is a dyed layer for color filters, and 55 is a counter electrode. 6
6 is a pixel electrode, and 57 is an electrode connected to the common wiring.

In this configuration, by assembling the display panel, a capacitor 5 is placed between the counter electrode 55 formed on the counter substrate side and the electrode 57 formed on the active matrix substrate side.
8 is formed and used as the second capacitor. A display panel with this configuration was mounted on the same common inversion drive circuit as the conventional one to produce a display device. Then, when driving was performed by applying Vc of the conventional common inversion drive to the common wiring and the electrode 57 as in the first example, the uniformity of the image increased and the display performance improved as in the first example. This embodiment is characterized in that the electrode 57 can be formed at the same time as the TPT light-shielding layer (not shown), etc., and can be implemented without increasing the number of steps or constituent materials. Furthermore, in the past, it was necessary to directly connect the electrode on the opposing board to the outside using a conductor (for example, use conductive paste to create an electrical connection between the two boards), but in this example, The potential on the opposing substrate side is determined by the action of the second capacitor, and there is no need to connect directly to the outside with a conductor, making the manufacturing process simpler than before.

Effects of the Invention According to the present invention, a uniform image with a small brightness gradient can be realized using a very simple implementation means of adding a capacitor and a driving method similar to common inversion with low power consumption. There is no need to develop a complicated IC or add a correction circuit or power supply circuit, and it can be implemented by applying a conventional drive circuit, so it is very effective in practice.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view showing the configuration of a liquid crystal display panel according to the first embodiment of the present invention, FIG. 1(b) is an enlarged sectional view showing the main parts thereof, and FIG. A diagram showing the relationship between the image signal and screen brightness in the embodiment, FIG. 3 is an equivalent circuit diagram of the main part for explaining the present invention in detail, and FIGS. 4 and 5 are each a diagram showing a conventional liquid crystal display. A circuit diagram of the main part of the device and a perspective view showing the configuration of the main part, FIGS. 6(a) and (b) are driving signal waveform diagrams of the main part of a conventional liquid crystal display device, and FIGS. 7 and 8 are A diagram showing the relationship between image signals and screen brightness when displaying on a conventional liquid crystal display device, FIG. 9(a)
and (b) are respectively a plan view and a sectional view showing the configuration of the main parts of the display panel according to the second embodiment of the present invention, and FIG. 10 is a diagram showing the main parts of the display panel according to the third embodiment of the present invention. FIG. 11 is a sectional view showing the structure of a main part of a display panel according to a fourth embodiment of the present invention. 21.38.47.58.30...Second capacitor, 5,34.55...Counter electrode, 29,46...
... Wiring connected to the counter electrode, 9... Common wiring, 2
6.42.57... Electrode connected to common wiring. Name of agent: Patent attorney Shigetaka Awano 1 person 1 figure k2rXI Vsno

Claims (6)

[Claims] (1) An active matrix array substrate having a first capacitor for holding an image signal connected to a common wiring for each pixel, a counter substrate having a counter electrode formed therein, and the above-mentioned two
In a display device in which a display panel made of a display material sandwiched between seed substrates is mounted on a drive circuit, a second capacitor is mounted between a wiring connected to the counter electrode and a wiring connected to the common wiring. Characteristic display device. (2) The display device according to claim 1, wherein the second capacitor is mounted directly on the display panel. (3) an active matrix array substrate having a first capacitor for holding an image signal connected to a common wiring for each pixel; a counter substrate having a counter electrode formed therein;
In a display device in which a display panel made of a display material sandwiched between seed substrates is mounted on a drive circuit, the counter electrode is connected to the common wiring via a second capacitor built on the counter substrate. A display device characterized by: (4) an active matrix array substrate having a first capacitor for holding an image signal connected to a common wiring for each pixel; a counter substrate having a counter electrode formed therein;
In a display device in which a display panel made of a display material sandwiched between seed substrates is mounted on a drive circuit, the counter electrode is connected to the common wiring via a second capacitor built on the active matrix substrate. A display device characterized by: (5) an active matrix array substrate having a first capacitor for holding an image signal connected to a common wiring for each pixel; a counter substrate having a counter electrode formed therein;
In a display device in which a display panel made of a display material sandwiched between substrates is mounted on a drive circuit, the counter electrode is connected to the counter electrode via a second capacitor formed between the active matrix substrate and the counter substrate. A display device characterized by being connected to a common wiring. (6) A method for driving a display device according to claim 1, 3, 4 or 5, characterized in that a signal is applied from the drive circuit to the counter electrode via the second capacitor.