JPH09325348A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a flicker, obtain a high aperture rate, and make an active matrix type liquid crystal display device small-sized. SOLUTION: Of the active matrix type liquid crystal display device, a counter electrode 11 on a substrate facing an active matrix substrate is composed of inter-digital electrodes 11a and 11b formed by connecting electrodes A1 -A3 and B1 -B3 corresponding to pixel electrode rows each at one end. A voltage V1 or V2 is applied to the inter-digital electrodes 11a and 11b and a signal having the polarity corresponding to V1 or V2 applied to the opposite inter- digital electrodes is applied to the corresponding pixel electrode rows; and V1 or V2 applied to the inter-digital electrodes 11a and 11b and the signal voltage applied to the pixel electrodes are periodically inverted in polarity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device characterized by a counter electrode facing a pixel electrode.

[0002]

2. Description of the Related Art In recent years, a so-called flat display has attracted attention as a display which can replace a large and heavy cathode ray tube. Among them, liquid crystal display devices are currently being actively researched and developed because of their low power consumption, compact size, and the like, and some of them have already been commercialized.

Among the liquid crystal display devices, the mainstream type at present is the so-called active matrix type which can display a high-definition image. An active matrix type liquid crystal display device has a structure in which liquid crystal is arranged between a pixel electrode connected to an active switching element and a counter electrode facing the pixel electrode arranged in a matrix, and a voltage is applied between both electrodes. The display is performed by controlling the alignment state of the liquid crystal. In such a liquid crystal display device, generally, a signal voltage is applied to the pixel electrode row every horizontal scanning period.
There are several methods for applying a voltage to the pixel electrode and the counter electrode facing the pixel electrode.

For example, Japanese Laid-Open Patent Publication No. 1-138590 proposes a method of inverting the potential applied to the counter electrode in two values in synchronization with the field period (hereinafter referred to as "common field inversion"). With this method, the amplitude of the input image signal can be reduced. Further, in JP-A-55-120095, the counter electrode is divided into
A driving method is disclosed in which a counter electrode divided for each horizontal scanning period is sequentially inverted with a binary voltage (hereinafter, referred to as “divided common 1H inversion”). Hereinafter, this Japanese Patent Laid-Open No. 55-
The method disclosed in No. 120095 will be described.

FIG. 9 is a schematic sectional view of a liquid crystal display device 1 disclosed in Japanese Patent Application Laid-Open No. 55-120095. In the figure, 91 is an active matrix substrate on which a transistor having a source 92, a drain 93 and a gate 95 is formed. Reference numeral 96 denotes a pixel electrode, and on the opposite side of the pixel electrode 96, a counter electrode 97 provided on a counter substrate 94 via a liquid crystal 99 is arranged. Each gate is connected to the scanning line for each pixel electrode row, and the source is commonly connected to the signal line for each pixel electrode column. The counter electrode 97 is composed of a transparent electrode and is connected in the same direction as the scanning line, but is insulated in the same direction as the signal line and is divided into strips.

FIG. 10 is an equivalent circuit diagram of the liquid crystal display device shown in FIG. In the figure, 101 is a transistor, 102 is a signal storage capacitor (additional capacitance), 1
Reference numeral 03 is a liquid crystal (capacity). X _i is a scanning line, Y _i is a signal line, and Z _i is a counter electrode (corresponding to 97 in FIG. 9).
It is. In the liquid crystal display device shown here, the counter electrode is line-sequentially scanned in synchronization with the scanning line X _i .
AC voltage is applied by applying a binary voltage to the counter electrode.

When the driving method disclosed in Japanese Patent Laid-Open No. 55-120095 is used, crosstalk is reduced,
It is said that image blurring will be reduced.

On the other hand, the driving method which is currently the mainstream is
The counter electrode is fixed to a constant potential, and the video signal voltage is inverted with this potential as an intermediate potential (hereinafter referred to as "common constant voltage").

Such a divided common 1H inversion driving method,
By using the common constant voltage driving method, flicker can be extremely reduced.

[0010]

However, it has been made clear by the inventors that the liquid crystal display device using the above-mentioned driving method has technical problems to be solved as described below.

That is, in the common field inversion driving method, flicker of 1/2 of the field period, that is, frame period is large, and the breakdown voltage of the transistor (TFT) is substantially required to be 3 times or more of the signal amplitude. Further, when the divided common 1H inversion driving method is used, the number of divided counter electrodes becomes substantially equal to the number of horizontal or vertical pixels, so that the connection between the electrode wiring and the external drive circuit is very complicated. However, it was not always practical. Further, in the common constant voltage driving method, high-speed driving becomes difficult as the number of pixels increases because the amplitude of the data signal voltage becomes large. Then, when the number of pixels increases and the interval between pixels becomes narrower, a horizontal electric field caused by an inversion signal applied to an adjacent pixel electrode causes a bright line region (in the case of TN liquid crystal, a white bright line, a dispersion type PDLC, a PNLC, NCA
In the case of P, a black bright line) is generated, which lowers the aperture ratio.

An object of the present invention is to provide a liquid crystal display device that solves the above technical problems. Another object of the present invention is to provide a compact and practical liquid crystal display device that can obtain a large aperture ratio substantially without causing flicker.

[0013]

The liquid crystal display device of the present invention, which solves the above-mentioned technical problems and achieves the above-mentioned objects, has a construction to be described below.

That is, the liquid crystal display device of the present invention corresponds to an active matrix substrate having a plurality of pixel electrodes arranged in rows and columns and a plurality of switching elements provided corresponding to the pixel electrodes, and the pixel electrodes. In a liquid crystal display device configured by disposing a liquid crystal between a counter substrate having a counter electrode and a counter electrode, a long electrode corresponding to a row of the pixel electrodes is commonly connected at one end. It is characterized by being configured by combining a plurality of comb-teeth shaped electrodes.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIG. 1 is a plan view of a counter electrode used in a reflective liquid crystal display device according to a first embodiment of the present invention. FIG.
Among, 11 is a transparent counter electrode made of ITO or the like, formed by connecting A ₁ to A ₃ and the comb-tooth electrodes 11a formed by connecting at one end to B ₁ .about.B ₃ corresponding to the pixel electrode row at one end 11
b are alternately arranged so as to face each other, and are wired so that the potentials of V ₁ and V ₂ are applied respectively.

FIG. 2 is a schematic cross-sectional view of the display portion of the liquid crystal display device of this embodiment, which is a cross section in a direction parallel to the pixel electrode row. In the present embodiment, a thin film transistor (TFT) is used as a switching element, and a TFT is provided for each pixel row.
The gates and the sources of each column are commonly connected to form an active matrix circuit.

In the figure, reference numeral 21 denotes an active matrix substrate. In this embodiment, a polycrystalline silicon TFT is formed on a glass substrate, or a polycrystalline silicon TFT or a single crystal silicon TFT is formed on a semiconductor substrate. be able to. On the active matrix substrate 21, there are reflective pixel electrodes 22 that form each pixel.
It is connected to the drain of the FT. Opposed to the active matrix substrate 21 is an opposed substrate 23 made of a transparent material such as glass. On the opposed substrate 23, the opposed electrode 11 made of the comb-teeth shaped electrodes 11a and 11b shown in FIG. Is formed.

A liquid crystal 24 is injected between the active matrix substrate 21 and the counter substrate 23 with a sealing material 25 sandwiched so that the distance between the counter electrode 11 and the pixel electrode 22 is constant.

In this embodiment, the light from the light source is the counter substrate 2.
The light enters from the 3 side and is scattered / non-scattered by the liquid crystal oriented depending on the driving voltage, and the non-scattered light is reflected by the surface of the pixel electrode 22 and emitted to the counter substrate 23 side.

FIG. 3 shows an equivalent circuit of the display portion of the liquid crystal display device of this embodiment. In the figure, 30 is a display pixel portion, 31 is a vertical scanning circuit, 32 is a horizontal scanning circuit, and 33 is a sampling circuit for sampling the input image signal V _in with pulse signals (H ₁₁ , H _12, ...) From the horizontal scanning circuit. is there. FIG.
In this circuit, the image signal sampled by the sampling circuit 33 is transferred and written in the pixel electrode row selected by the vertical scanning circuit 31.

Each pixel includes a first switch circuit 40, a memory capacity 41, a second switch circuit 42, an additional capacity 43, a liquid crystal (capacity) 44, and a clear switch circuit 45. First
The gates of the transistors of the switch circuit 40 are commonly connected to the scanning lines for each pixel electrode row, and are controlled by the pulses (V ₁ , V ₂ ...) From the vertical scanning circuit 31. The memory capacitor 41, the additional capacitor 43, and the other end 46 of the clear switch circuit 45 are divided counter electrodes. The gates of the clear switch circuit 45 are commonly connected in the screen, so that the batch clearing is possible. In addition, the gates of the second switch circuits 42 are commonly connected in the entire screen, and memory signals can be collectively transferred to the liquid crystal pixels. Each switch may be composed of a single element or a plurality of elements. When a plurality of elements are connected in series, the resistance at the time of non-conduction can be increased, the leakage current is small, and the number of defects is small. Can be configured.

FIG. 4 is a drive timing chart of the circuit shown in FIG. In FIG. 4, for simplification, the timing in the case of 3 × 3 pixels is illustrated.

First, the holding voltage of each pixel is cleared at once by φC. After that, the potential of the counter electrode is reversed, and then φT
Then, the memory signal is collectively transferred from the memory capacity 41 of each pixel to each pixel. In this embodiment, since the potential of the counter electrode is changed after clearing, the change range of the pixel voltage is almost the amplitude of the signal, and the withstand voltage of the TFT may be small. This starts full-screen display.

An image signal is stored in the memory capacity 41 in the next one vertical scanning period. Vertical scanning circuit 31 according to φV _s
Starts scanning, and scan pulse V ₁ is generated every horizontal scanning period.
V ₂ ... Is output. The horizontal scanning circuit 32 starts scanning with φH _s , and within one horizontal scanning period, the scanning pulse H ₁₁ ,
H ₁₂ ... Is output, and the image signal V _in is sequentially sampled and transferred to each memory capacitor 41 of the pixel electrode row selected by the scanning pulse. After the end of one vertical scanning period, the image signal is accumulated in the memory capacity of all pixels.

The above operation is repeated every vertical scanning period.

FIG. 5 shows the overall circuit configuration. The image signal that has been subjected to the γ processing or the like in the signal processing circuit 54 is output to the inverting circuit 5
At φ2, it is inverted every horizontal scanning period by the φH pulse.
The inversion signal is input to the sampling circuit 33 and transferred to the memory capacity of each pixel row in each horizontal scanning period.

Voltages V ₁ and V ₂ are applied to the comb-teeth-shaped electrodes. V ₁ and V ₂ are supplied from the control circuit 53 to the voltage switching circuit 51.
Is supplied with a pulse φF _v , V ₁ →
It switches from V _{2 to} V ₁ . The control circuit 53 supplies φV _s to the vertical scanning circuit 31 of the active matrix substrate, φH _s to the horizontal scanning circuit 32, pixel reset pulse φC, and memory transfer pulse φT.

FIG. 6 shows a signal waveform diagram applied to each electrode. In the figure, (A) shows the voltage waveform applied to the comb-shaped electrodes,
(B) is an image signal waveform applied to the pixel electrode. Further, F1, F2 ... Are each vertical scanning period, and H1, H2 ... Are each horizontal scanning period. Voltages V _A and V _B are applied to the comb-shaped electrodes in each vertical scanning period. V _A and V _B are switched to the values of V ₁ and V ₂ for each vertical scanning period. If V ₁ is GND and V ₂ is 10 V, the black signal is 1 V (9 V) and the white signal is It is 9V (1V).
Inverted signals are in parentheses.

On the other hand, the polarity of the image signal is inverted every horizontal scanning period as shown in FIG. H1, the potential of the comb-tooth electrodes H3 ... signal in corresponding to a pixel row to be applied is V _A, H2, H4 ... in a V _B.

In the present embodiment, the amplitude of the signal applied to the pixel electrode is about 8 V, and the signal can be driven at about 1/2 of the common constant voltage method.

[Second Embodiment] FIG. 7 shows a waveform of an image signal applied to a liquid crystal display device according to a second embodiment of the present invention. The present embodiment is an example in which different comb-teeth shaped electrodes are made to correspond to every two pixel electrode rows. Therefore, the polarity of the image signal waveform is inverted every two horizontal scanning periods as shown in FIG.

[Embodiment 3] FIG. 8 shows a partial schematic view of a third embodiment of the present invention. In this embodiment, the source of the switching element is commonly connected to each pixel electrode row, and the gate is commonly connected to each pixel electrode column, corresponding to the comb-teeth shaped electrodes which are different for each pixel electrode row. Therefore, in this embodiment, horizontal scanning is sequentially performed for each pixel electrode column, and the polarity of the image signal input for each pixel electrode row is inverted by the inversion circuit 81 during each horizontal scanning period.

[0033]

According to the present invention, since the counter electrode is composed of a plurality of comb-teeth shaped electrodes, the number of external terminals is increased by at least one as compared with the common constant voltage method, and the connection is simple. . Further, by dividing the counter electrode, the amplitude of the data signal applied to the image electrode can be suppressed small, and the peripheral circuit can be configured at high speed, low cost, and low power consumption even if the number of pixels is increased. Further, since the signal amplitude is small, the lateral electric field between the pixel electrode rows can be suppressed to be small, the generation of the bright line region can be prevented, and the aperture ratio can be increased. Furthermore, TF which is a switching element of the pixel
As T, a material having a small breakdown voltage can be used.

In the present invention, the polarity of the image signal applied to each pixel electrode row is inverted so that the flicker can be suppressed below the detection limit and the image quality can be improved.

[Brief description of drawings]

FIG. 1 is a plan view of a counter electrode used in a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a display unit of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a display unit of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 4 is a drive timing chart of the circuit shown in FIG.

FIG. 5 is an overall circuit configuration diagram of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 6 is a signal waveform diagram applied to each electrode of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 7 is a data signal waveform diagram applied to a signal line of the liquid crystal display device according to the second embodiment of the present invention.

FIG. 8 is a partial schematic view of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 9 is a schematic sectional view of one pixel of a conventional liquid crystal display device.

10 is an equivalent circuit diagram of the liquid crystal display device shown in FIG.

[Explanation of symbols]

 11 Counter Electrodes 11a and 11b Comb-Shaped Electrodes 21 TFT Substrate 22 Pixel Electrode 23 Cover Glass 24 Liquid Crystal 25 Sealing Material 30 Display Pixel Part 31 Vertical Scan Circuit 32 Horizontal Scan Circuit 33 Sampling Circuit 40 First Switch Circuit 41 Memory Capacity 42 Second Switch circuit 43 Additional capacity 44 Liquid crystal (capacity) 45 Clear switch circuit 46 Counter electrode 51 Voltage switching circuit 52 Inversion circuit 53 Control circuit 54 Signal processing circuit 81 Inversion circuit 91 Active matrix substrate 92 Source 93 Drain 94 Counter substrate 95 Gate 96 Pixel electrode 97 counter electrode 99 liquid crystal 101 transistor 102 signal storage capacitor (additional capacity) 103 liquid crystal (capacity)

Claims (9)

[Claims] 1. An active matrix substrate having a plurality of pixel electrodes arranged in rows and columns and a plurality of switching elements provided corresponding to the pixel electrodes, and a counter substrate having a counter electrode corresponding to the pixel electrodes. A liquid crystal display device in which a liquid crystal is disposed between the counter electrodes, and the counter electrode is formed by combining a plurality of comb-teeth electrodes formed by connecting long electrodes corresponding to the rows of the pixel electrodes at one end. A liquid crystal display device characterized by the above. 2. The liquid crystal display device according to claim 1, wherein the counter electrode is configured by alternately arranging the plurality of comb-teeth electrodes in a staggered manner. 3. The liquid crystal display device according to claim 2, wherein the comb-teeth-shaped electrodes respectively corresponding to the adjacent pixel electrode rows are different. 4. The liquid crystal display device according to claim 1, wherein the potential applied to the comb-teeth-shaped electrode and the polarity of the signal voltage applied to the pixel electrode row corresponding to the comb-teeth-shaped electrode are different. 5. The liquid crystal display device according to claim 4, wherein different potentials are applied to the individual comb-teeth electrodes that form the counter electrode. 6. The liquid crystal display device according to claim 5, wherein the polarity applied to the comb-teeth electrode and the polarity of the signal voltage are periodically inverted. 7. The liquid crystal display device according to claim 1, wherein the switching element is a transistor. 8. The liquid crystal display device according to claim 8, wherein a gate of the transistor is commonly connected to a scanning line for each pixel electrode row, and a source is connected for each pixel electrode column. 9. The liquid crystal display device according to claim 8, wherein a gate of the transistor is commonly connected to a scanning line in each pixel electrode column, and a source is connected to each pixel electrode row.