JPH0635002A - Driving method for liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device of high display quality by suppressing the generation of a domain. CONSTITUTION:When an AC image signal Vs which is applied to a source bus line 5 is applied to each pixel electrode 1, an AC counter electrode signal Vco which is inverted in polarity is applied to each counter electrode 6 through an opposite signal wire 14 in synchronism with the AC image signal Vs. At this time, each auxiliary capacity electrode 7 is applied with an AC synchronizing auxiliary capacity signal Vcs which is different in amplitude from each counter electrode signal Vco through an auxiliary capacity wire 15. Consequently, an electric field which crosses an electric field produced between the pixel electrode 1 and the auxiliary capacity electrode 7, etc., provided on the same substrate with the pixel electrode 1 is produced between the counter electrode 6 and auxiliary capacity electrode 7.

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 display device having an active matrix substrate.

[0002]

2. Description of the Related Art In an active matrix liquid crystal display device, picture element electrodes are arranged in a matrix, and an active matrix substrate having switching elements connected to the picture element electrodes and a counter electrode for the active matrix substrate are provided. Further, a liquid crystal panel is provided in which the counter substrates are opposed to each other with the liquid crystal layer interposed therebetween.

FIG. 11 is an equivalent circuit diagram of a liquid crystal panel.

The liquid crystal panel 23 has a plurality of source bus lines 25 on the active matrix substrate and a plurality of gate bus lines 24 arranged so as to be orthogonal to the source bus lines 25. A thin film transistor (Thin-Film-Transisto) as a switching element is provided near each intersection of the bus lines 24 and 25.
r, hereinafter abbreviated as TFT) 22 is provided.

As shown in FIG. 12, each TFT 22 has a gate 11 connected to a gate electrode 24 'on a gate bus line 24.
1 is connected, and the source 112 is connected to the source electrode 25 ′ on the source bus line 25. further,
The drain 113 of the TFT 22 is connected to the pixel electrode 21.

Each picture element electrode 21 faces a counter electrode 26 disposed on a counter substrate with a liquid crystal layer sandwiched therebetween, and is provided in a liquid crystal layer portion between each picture element electrode 21 and the counter electrode 26. A liquid crystal capacitance C _LC is formed. Further, in the active matrix substrate, the auxiliary capacitance electrode 27 is opposed to a part of each pixel electrode 21 with the insulating film 116 interposed therebetween.
A storage capacitor C is provided between each pixel electrode 21 and the storage capacitor electrode 27.
_S is formed. Each auxiliary capacitance electrode 27 is put together,
It is connected to the counter electrode wiring 114, and the counter electrode 26 is also connected to the counter electrode wiring 114. An alternating counter electrode signal Vco is applied to the counter electrode 26 and each auxiliary capacitance electrode 27 through the counter electrode wiring 114.

All source bus lines 25 are connected to a source driver 28. The source driver 28 is
The input analog image signal or video signal is read by the shift register at predetermined time intervals, held by the sample hold circuit for a certain period of time, and then the image signal is supplied to each source bus line 25 via the output buffer. It is like this.

Further, all the gate bus lines 24 are connected to a gate driver 29, and the gate driver 29 sends a scan pulse of a predetermined cycle generated by a shift register and a level shifter to each gate bus via an output buffer. The lines 24 are sequentially output.

The gate driver 29 and the source driver 28 are connected to the control circuit 110, and the control circuit 110 causes the gate driver 29,
A control signal is sent to the source driver 28 so that each driver 2
Control 8 and 29.

The liquid crystal panel 23 having such a structure is driven as follows. Each signal voltage waveform is shown in FIG. When a pulse signal is selectively applied to one gate bus line 24 by the gate driver 29 and an AC signal is applied to a predetermined source bus line 25 by the source driver 28, the source to which each signal is applied. T connected to the bus line 25 and the gate bus line 24
The potential Vg of the gate 111 of the FT22 becomes "H" level, and the TFT22 thereof is turned on. During the period in which the TFT 22 is on (one horizontal scanning cycle), the AC image signal Vs is applied to the source 112 of the TFT 22 via the source bus line 25, and the potential Vd of the drain 113 of the TFT 22 is the image of the AC. Since it becomes equal to the signal Vs, the potential of the pixel electrode 21 becomes equal to the AC image signal Vs applied to the source 112.

At this time, the counter electrode wiring 114 is synchronized with the AC image signal Vs applied to the source bus line 25.
Is applied with an AC counter electrode signal Vco, the counter electrode 26 and each auxiliary capacitance electrode 27 facing each picture element electrode 21.
The AC counter electrode signal Vco is simultaneously applied to.

Therefore, the potential difference Vs-Vco between the pixel electrode 21 to which the image signal Vs is applied and the potential Vco of the counter electrode 26.
Therefore, the liquid crystal capacitance C of the liquid crystal layer portion between the electrodes 21 and 26 is
_The charge is accumulated in _LC , and also the charge is accumulated in the auxiliary capacitance C _S between the electrodes 21 and 27 due to the potential difference Vs−Vco between the pixel electrode 21 and the potential Vco of the auxiliary capacitance electrode 27. As a result, the display signal is written in the picture element electrode 21.

When the potential Vg of the gate 111 becomes "L" level, the TFT 22 turns off, and the voltage applied during the on period while the TFT 22 is off is held by the charges of the liquid crystal capacitance C _LC and the auxiliary capacitance C _S. It In this way
The liquid crystal is driven over one field.

[0014]

As the liquid crystal of the liquid crystal panel 23, a TN (Twisted Nematic) type is usually used. As shown in FIG. Are arranged regularly with a constant rising angle θ1. In such a state, when a voltage is applied between the picture element electrode 21 and the counter electrode 26 so that a vertical electric field E is formed, the liquid crystal molecules 17 are
Usually, as shown in FIG. 14 (b), it regularly rises in a direction in which the angle between the molecular axis and the electric force line is small, and approaches the electric force line. The rising angle θ2 of the liquid crystal molecules 17 at this time changes according to the strength of the electric field E, and the liquid crystal panel 23 changes according to the magnitude of the rising angle θ2.
The light transmittance of changes.

However, as shown in FIG. 15A, since the auxiliary capacitance electrode 26, the gate electrode 24 'and the source electrode 25' of the TFT 22 are provided on the substrate on which the pixel electrode 21 is arranged. 15B, an electric field E ′ that intersects the electric field E between the pixel electrode 21 and the counter electrode 26 is formed between these electrodes and the pixel electrode 21. As a result, the liquid crystal molecule 17 rises so as to approach an electric field E ′ where the angle between the molecular axis and the line of electric force is small, and a domain is generated.

Such a domain is usually formed by the pixel electrode 2
Although it occurs only in a partial area of the liquid crystal layer portion driven by No. 1, even if it is minute, in the area where the domain occurs, the phenomenon of inversion in the viewing angle direction with respect to the normal area occurs, and Optical rotation is lost at the boundary between the area and the normal area, so that the display quality of the liquid crystal panel 23 is significantly impaired.

The present invention has been made in order to solve the problems of the prior art, and it is an object of the present invention to provide a driving method of a liquid crystal display device having excellent display quality by suppressing the generation of domains. To aim.

[0018]

According to a method of driving a liquid crystal display device of the present invention, a plurality of signal wirings arranged in parallel on a transparent insulating substrate and a plurality of signal wirings arranged orthogonal to each signal wiring. Scanning lines, picture element electrodes connected to respective regions surrounded by the respective signal wirings and the respective scanning wirings through switching elements, and auxiliary capacitance electrodes opposed to the respective picture element electrodes with an insulating film interposed therebetween. And an opposite substrate in which an opposite electrode facing each of the picture element electrodes is provided on an insulating substrate opposite to the active matrix substrate with a liquid crystal layer interposed therebetween. A method of driving a liquid crystal display device, wherein an AC image signal is applied to each signal wiring, and a synchronous AC signal synchronized with a polarity inversion cycle of the AC image signal is applied to the counter electrode. Cage, Luo, will be characterized by driving the counter electrode and the auxiliary capacitance electrode as an electric field is formed between the counter electrode and the auxiliary capacitance electrode, thereby the objective described above being achieved.

[0019]

According to the present invention, the influence of the electric field formed between the auxiliary capacitance electrode on the insulating substrate on which each picture element electrode is arranged and each picture element electrode on the liquid crystal layer is suppressed,
An electric field is formed between the auxiliary capacitance electrode and the counter electrode.

[0020]

EXAMPLES Examples of the present invention will be described below.

[First Embodiment] The driving method of the present invention is used for driving an active matrix type liquid crystal display device having the liquid crystal panel shown in FIG. The liquid crystal panel is
It has an active matrix substrate 31 and a counter substrate 33 which is arranged to face the active matrix substrate 31 with a liquid crystal 34 in between.

As shown in FIG. 2, the active matrix substrate 31 includes a transparent insulating substrate 30 and the insulating substrate 3
0 has a plurality of source bus lines 5 arranged in parallel with each other and a plurality of gate bus lines 4 arranged orthogonal to the respective source bus lines 5. A pixel electrode 1 for driving liquid crystal and a TFT 2 for driving the pixel electrode 1 are provided in respective regions surrounded by the gate bus lines 4 and the source bus lines 5. An auxiliary capacitance electrode 7 is arranged in parallel with each gate bus line 4 in proximity to each gate bus line 4.

Gate bus line 4 and auxiliary capacitance electrode 7
Are provided in contact with the insulating substrate 30, and an insulating film 16 is provided over the entire surface of the insulating substrate 30 so as to cover each gate bus line 4 and the auxiliary capacitance electrode 7.

Part of each picture element electrode 1 is laminated on the auxiliary capacitance electrode 7 with the insulating film 16 interposed therebetween.
The auxiliary capacitance C _s is formed in the laminated portion of the auxiliary capacitance electrode 7 and the auxiliary capacitance electrode 7.

The other counter substrate 33 is a counter electrode 6 that covers the entire insulating substrate 32 on a transparent insulating substrate 32.
Are laminated, and each picture element electrode 1 faces the counter electrode 6.

Each TFT 2 has a source 12 as shown in FIG.
Is connected to the source electrode 5 ′ of the source bus line 5, and the gate 11 is connected to the gate electrode 4 ′ of the gate bus line 4.
, And the drain 13 is further connected to the pixel electrode 1.

FIG. 4 is a drive circuit diagram of the liquid crystal panel 3.
All the source bus lines 5 in the liquid crystal panel 3 are connected to the source driver 8. Source driver 8
Is the input analog image signal or video signal,
After being read by the shift register at predetermined time intervals and held by the sample hold circuit for a certain time, an alternating-current image signal Vs of a predetermined cycle is supplied to each source bus line 5 via an output buffer. .

All the gate bus lines 4 are connected to the gate driver 9, and this gate driver 9
Is configured to sequentially output the scanning pulse having a predetermined cycle generated by the shift register and the level shifter to each gate bus line 4 via the output buffer.

Gate driver 9 and source driver 8
Is connected to the control circuit 10, and the control circuit 10 sends control signals to the gate driver 9 and the source driver 8 to control the drivers 8 and 9, respectively.

An alternating counter electrode signal Vco is supplied to the counter electrode 6 provided on the counter substrate 33 by the counter electrode wiring 14, and each pixel electrode 1 of the active matrix substrate 31 is supplied. Each auxiliary capacitance electrode 7 overlapping with a part is collectively connected to the auxiliary capacitance line 15, and each auxiliary capacitance electrode 7 is connected through the auxiliary capacitance line 15.
An AC auxiliary capacitance signal Vcs is supplied to the.

The alternating counter electrode signal Vco and the auxiliary capacitance signal Vcs have the same period as the image signal Vs, and the alternating counter electrode signal Vco and the auxiliary capacitance signal Vcs are different so that a potential difference is formed. It is driven by a voltage value, and in this embodiment, the amplitude of the counter electrode signal Vco is larger than the amplitude of the auxiliary capacitance signal Vcs.

A liquid crystal 34 between each pixel electrode 1 and the counter electrode 6
The portion of is a liquid crystal capacitance C _LC , and the auxiliary capacitance C _S is provided between each pixel electrode 1 and the auxiliary capacitance electrode 7, and charges are respectively stored therein.

The liquid crystal display panel 3 having such a structure is driven as follows.

The signal voltage waveform of each electrode is shown in FIG. When the liquid crystal panel 3 is driven, an AC counter electrode signal Vco is applied to the counter electrode wiring 14, and the counter capacitor signal Vco has the same period and the same polarity and different amplitude as the counter electrode signal Vco. The auxiliary capacitance signal Vcs is applied. Therefore, due to the voltage difference between the counter electrode signal Vco applied to the counter electrode 6 and the auxiliary capacitance signal Vcs applied to each auxiliary capacitance electrode 7, a space between both electrodes 6 and 7 is perpendicular to both electrode surfaces. An electric field is created.

In such a state, the gate driver 9 selectively applies the scanning signal Vg to one gate bus line 4 in a pulsed manner, and the source bus line 5 selected by the source driver 8 receives an alternating current. Image signal Vs
Are applied in synchronization with the scanning signal Vg.

When the scanning signal Vg is applied to the gate bus line 4, the TFT 2 connected to the gate bus line 4
The potential Vg of the gate 11 of the
2 turns on. During the period when the TFT 2 is on (one horizontal scanning period), a voltage equal to the image signal Vs applied to the source 12 of the TFT 2 is applied to the drain 13, so that the pixel electrode 1 is applied to the source 12. Image signal Vs is applied.

Therefore, due to the voltage difference Vs-Vco between the picture element electrode 1 to which the image signal Vs is applied and the potential Vco of the counter electrode 6, charges are accumulated in the liquid crystal capacitance C _LC between both electrodes and the picture element charge to the storage capacitor C _S between the electrodes by the voltage difference Vs-Vcs between the electrode 1 and the potential Vcs of the auxiliary capacitance electrodes 7 are accumulated. As a result, the display signal is written in the picture element electrode 1.

The scanning signal Vg of the gate bus line 11 is L
When the level is reached, the TFT 2 is turned off, and while the TFT 2 is off, the voltage applied while the TFT 2 is on is held by the charges of the liquid crystal capacitance C _LC and the auxiliary capacitance C _S. In this way, the liquid crystal is driven over one field.

While the liquid crystal is being driven, the counter electrode signal Vco and the auxiliary capacitance signal Vcs having different voltage values are supplied to the counter electrode 6 and the auxiliary capacitance electrode 7 through the counter electrode wiring 14 and the auxiliary capacitance wiring 15, respectively. Therefore, an electric field is vertically formed between the electrodes 6 and 7. Therefore, due to this electric field, the rising angle of the liquid crystal molecules located between the pixel electrode 1 and the counter electrode 6 is slightly increased.

Moreover, the picture of the lines of electric force of the electric field formed between the auxiliary capacitance electrode 7, the gate electrode 4'in the TFT 2 and the source electrode 5'on the substrate on which the picture element electrode 1 is arranged. It functions to correct the inclination with respect to the pixel electrode 1 so as to be upright with respect to the pixel electrode 1. Therefore, the generation of domains in the liquid crystal molecule layer is suppressed. To suppress such domains, the phase of the AC electric field applied between the counter electrode 6 and the auxiliary capacitance electrode 7 is equal to the phase of the AC electric field applied between the counter electrode 6 and the source electrode 5. Moreover, the larger the potential difference, the more remarkable. As described above, since the driving method of the present invention suppresses the generation of domains, the quality of the liquid crystal display device is significantly improved.

[Second Embodiment] In the first embodiment, each of the counter electrode signal Vco and the auxiliary capacitance signal Vcs is a synchronous AC signal whose polarity is inverted from that of the AC image signal Vs.
In addition, the storage capacitor electrode voltage Vcs is higher than the counter electrode signal Vco.
Although the electric field is formed between the counter electrode 6 and the auxiliary capacitance electrode 7 by decreasing the amplitude of the counter electrode, in the present embodiment, only the counter electrode voltage Vco is applied to the signal electrode 5 as shown in FIG. The alternating image signal Vs to be generated is a synchronous alternating signal whose polarity is inverted, and the auxiliary capacitance signal Vcs is applied with a DC voltage having a potential corresponding to the center potential of the amplitude of each of the image signal Vs and the counter electrode voltage Vco. Has become. Also in this embodiment, the signal electrode 5 is provided between the counter electrode 6 and the auxiliary capacitance electrode 7.
Since the AC electric field is applied in synchronization with the cycle of the AC image signal Vs, the generation of domains is suppressed.

[Third Embodiment] FIG. 8 is an equivalent circuit diagram of a liquid crystal panel in a third embodiment of the present invention, FIG. 9 is a plan view thereof, and FIG. 9 is a sectional view taken along line AA ′. The figures are respectively shown in FIG. In the liquid crystal panel of the present embodiment, the auxiliary capacitance electrode 7 is of the Cs-On-Gate system in which a part of the gate bus line 4 is used. Therefore, the auxiliary capacitance electrode 7 has the gate bus line 4 Thus, the scanning signal Vg applied to each gate electrode 4 is applied as the auxiliary capacitance signal Vcs. The other structure is the same as that of the liquid crystal panel of the first embodiment.

In the liquid crystal panel of this embodiment, as shown in FIG. 7, since the scanning signal Vg of the gate electrode 4 is applied as the auxiliary capacitance signal Vcs applied to the auxiliary capacitance electrode 7,
While the TFT 2 is off, the auxiliary capacitance signal Vcs applied to the auxiliary capacitance electrode 7 has a constant DC level. An alternating image signal V applied to the pixel electrode 5 is applied to the counter electrode 6.
An alternating counter electrode signal Vco whose polarity is inverted while always maintaining a constant potential difference is applied to s. Therefore, TF
When T2 is off, an electric field whose voltage difference changes in synchronization with the counter electrode signal Vco is formed between the counter electrode 6 and the auxiliary capacitance electrode 7. In addition, when the TFT 2 is turned on, TF is provided between the counter electrode 6 and the auxiliary capacitance electrode 7.
An electric field having the opposite polarity to that when T2 is off is formed. As described above, also in this embodiment, the generation of domains is suppressed.

[0044]

As described above in detail, according to the present invention, the auxiliary capacitance electrode on the insulating substrate provided with the pixel electrode is formed by the electric field formed between the counter electrode and the auxiliary capacitance electrode. The generation of domains due to the electric field generated between the electrodes such as the above and the picture element electrodes is electrically suppressed. As a result, the display quality of the liquid crystal display device can be improved without changing the structure, the material, or the like.

[Brief description of drawings]

FIG. 1 is a sectional view of a TFT liquid crystal panel according to an embodiment of the present invention.

FIG. 2 is a plan configuration of a TFT liquid crystal panel according to an embodiment of the present invention.

FIG. 3 is a circuit configuration of one picture element portion of a TFT liquid crystal panel according to an embodiment of the present invention.

FIG. 4 is a schematic configuration of a drive circuit of a liquid crystal display device according to an embodiment of the present invention.

FIG. 5 is a signal waveform diagram of each electrode of the TFT liquid crystal panel in the first embodiment of the present invention.

FIG. 6 is a signal waveform diagram of each electrode of the TFT liquid crystal panel according to the second embodiment of the present invention.

FIG. 7 shows Cs-On-Gat in the third embodiment of the present invention.
The signal waveform diagram of each electrode of the e-type TFT liquid crystal panel.

FIG. 8 is an equivalent circuit diagram of the TFT liquid crystal panel.

FIG. 9 is a plan view of the TFT liquid crystal panel.

10 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 11 is a drive circuit diagram showing a schematic configuration of a liquid crystal display device in a conventional example.

FIG. 12 is a circuit diagram of a part of the TFT liquid crystal panel.

FIG. 13 is a signal waveform diagram of each electrode of the TFT liquid crystal panel.

FIG. 14A is a cross-sectional view showing an alignment state of liquid crystal molecules when an electric field is not applied to the TN type liquid crystal layer. FIG. 3B is a sectional view showing an alignment state of liquid crystal molecules when an electric field is applied to the TN type liquid crystal layer in the liquid crystal panel.

FIG. 15A is a cross-sectional view showing an alignment state of liquid crystal molecules when an electric field is not applied to a liquid crystal layer in a conventional liquid crystal panel. FIG. 3B is a cross-sectional view showing an alignment state of liquid crystal molecules when an electric field is applied to the liquid crystal layer.

[Explanation of symbols]

 1 pixel electrode 2 TFT 3 liquid crystal panel 4 gate bus line 4'gate electrode 5 source bus line 5'source electrode 6 counter electrode 7 auxiliary capacitance electrode 8 source driver 9 gate driver 10 control circuit 11 TFT gate 12 TFT source 13 Drain of TFT 14 Counter signal wiring 15 Storage capacitor electrode wiring 16 Insulating films 30, 32 Insulating substrate 31 Active matrix substrate 33 Counter substrate 34 Liquid crystal layer

Claims (1)

[Claims] 1. A plurality of signal wirings arranged in parallel on a transparent insulating substrate, a plurality of scanning wirings arranged orthogonally to the respective signal wirings, surrounded by each signal wiring and each scanning wiring. An active matrix substrate having picture element electrodes connected to respective regions via switching elements, and auxiliary capacitance electrodes facing each picture element electrode with an insulating film interposed therebetween, and a liquid crystal on the active matrix substrate. A method of driving a liquid crystal display device, comprising: an opposing substrate in which an opposing electrode facing each of the picture element electrodes is provided on an insulating substrate placed to face each other with a layer in between, and an alternating current is applied to each signal wiring. Image signal is applied to the counter electrode, and a synchronous AC signal synchronized with the polarity reversal period of the AC image signal is applied to the counter electrode, and further, between the counter electrode and the auxiliary capacitance electrode. Electric field shape The driving method of a liquid crystal display device and drives the counter electrode and the auxiliary capacitance electrode as.