JP2002098957A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device, having a backside light source suited for a moving image display by solving disadvantages caused by a fluorescent tube. SOLUTION: An EL(electroluminescence) backlight 400 comprising an organic EL material is arranged as a flat surface light source for white light emission, on the surface of a second electrode substrate 200 (or a first electrode substrate 100) on the side which is not brought into contact with a liquid crystal layer 300, and the EL backlight 400 is divided into strips at a prescribed pitch to form EL emission parts 401-404.

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, and more particularly, to a technique for improving a back light source in a transmission type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used in various fields by utilizing characteristics such as thinness, light weight, and low power consumption. Of these, notebook PCs and desktop P
In a transmission type liquid crystal display device used for C or the like, a back light source is incorporated on the back side of a liquid crystal panel. The most common back light source is a so-called light guide system in which a cylindrical fluorescent tube is arranged at the end of a liquid crystal panel, and light emitted from this fluorescent tube is used as a surface light source by a light guide. It is.

[0003]

The light guide system includes:
The fluorescent tube has the advantages of high brightness, long life, and color adjustment. However, there are disadvantages in that the number of components is large and the cost is high, and the overall efficiency as a light source is lower than that of the reflector type, and it is heavy and thick. In addition, since the rear light source using the fluorescent tube is always used while being turned on, there is a problem that unnecessary light emission hinders the display of a moving image in a moving image display such as a TV display.

On the other hand, as a back light source other than a fluorescent tube, for example, there is a light source of a small-sized white LED made into a planar shape by a transparent resin, or a light source using an inorganic EL material. Therefore, there is a problem that the use is limited.

An object of the present invention is to solve the disadvantages of the fluorescent tube and to provide a liquid crystal display device having a back light source suitable for displaying moving images.

[0006]

In order to achieve the above object, according to a first aspect of the present invention, a plurality of signal lines and a plurality of scanning lines crossing each other are connected to each intersection of these two lines via a switch element. A first electrode substrate including a pixel electrode to be connected, a storage capacitor line connected via a storage capacitor electrically connected in parallel with the pixel electrode, and a second electrode including a counter electrode facing the plurality of pixel electrodes. In a liquid crystal display device including an electrode substrate and a liquid crystal layer held between the two electrode substrates, an organic EL material is formed on a surface of the first or second electrode substrate on a side not in contact with the liquid crystal layer. A white light emitting flat light source is provided.

According to a second aspect of the present invention, in the first aspect, the planar light source is divided into strips in parallel with the scanning lines, and the divided light emitting portions are synchronized with the driving timing of the scanning lines. It is characterized by sequentially emitting light one after another.

According to a third aspect of the present invention, in the first aspect, the light-emitting portion divided into strips emits light sequentially for each of a plurality of portions, and is synchronized with the driving timing of the scanning line.
It is characterized in that the light emitting position moves by each light emitting portion.

According to a fourth aspect of the present invention, in the second or third aspect, the light emission of the light emitting portion divided into strips does not include a position where the scanning line is selected.

According to a fifth aspect of the present invention, in the second, third or fourth aspect, the non-light-emitting portion excluding the light-emitting portion divided into the strip shape and the auxiliary capacitance line are arranged at positions substantially in plan. The width of the non-light emitting portion is smaller than the width of the auxiliary capacitance line.

According to a sixth aspect of the present invention, in any of the second to fifth aspects, the light emission luminance of the light emitting portion divided into the strip shape changes according to the maximum value of the signal voltage applied to the corresponding pixel electrode. I do.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a liquid crystal display according to the present invention is applied to an active matrix type liquid crystal display will be described below.

FIG. 1 is a schematic sectional view of a liquid crystal display device according to this embodiment. The liquid crystal display device 10 includes a first electrode substrate 100, a second electrode substrate 200, and a liquid crystal layer 300 held between these substrates.

The first electrode substrate 100 is composed of a transparent glass substrate 101, and has scanning lines 102, signal lines 103 (not shown in FIG. 1), and pixels on the surface in contact with the liquid crystal layer 300. An electrode 104, a TFT 105 (not shown in FIG. 1), an auxiliary capacitance 106 (not shown in FIG. 1), and an auxiliary capacitance line 107 are formed.

FIG. 2 shows an equivalent circuit diagram of a display pixel formed on the first electrode substrate 100. A TFT 105 is connected as a switching element at an intersection of the scanning line 102 and a signal line 103 arranged to intersect the scanning line 102. The gate electrode of the TFT 105 is connected to the scanning line 102, and the source electrode (or drain electrode) is connected to the signal line 10.
3 and a drain electrode (or source electrode)
Are connected to the pixel electrode 104. The pixel electrode 104 is electrically connected in parallel with an auxiliary capacitor 106 for holding a charge. The auxiliary capacitance 106 forms a capacitance Cs between the pixel electrode 104 and the auxiliary capacitance line 107. The auxiliary capacitor 107 is supplied with a constant potential from an external control circuit (not shown).

Here, the operation of the equivalent circuit diagram shown in FIG. 2 will be briefly described. When a video signal is sampled on the signal line 103 and a row selection pulse is output to the scanning line 102 in synchronization with the sampling, the source and the drain of the TFT 105 become conductive, and the video signal sampled on the signal line 103 is transferred to the TFT 105. Is written to the pixel electrode 104 via the. The video signal is charged as a signal voltage between the counter electrode (202), which will be described later, and the liquid crystal layer 300 responds to the video signal to display a video.

The second electrode substrate 200 includes the first electrode substrate 10
It is composed of a transparent glass substrate 201 like 0,
On the surface in contact with the liquid crystal layer 300, a counter electrode 202 facing the pixel electrode 104 is formed on the entire surface.

On the surface of the glass substrate 201 which is not in contact with the liquid crystal layer 300, an EL backlight 400 is formed as a planar light source composed of organic EL (electroluminescence). The EL backlight 400 is formed of a thin film, and in parallel with the scanning line 102,
It is divided into strips at the pixel pitch (the pitch of the pixel electrodes 104). In FIG. 1, the EL backlight 400 divided into strips is used as EL light emitting portions 401, 402, and 40.
3, 404. This EL backlight 4
00 is supplied with a predetermined power supply voltage from an external control circuit (not shown).

Between each of the EL light emitting portions 401 to 404,
Non-light-emitting portions 411 and 4 where no EL light-emitting portion is formed
12, 413 are provided. This non-light emitting portion 41
The positions of 1, 412, and 413 are substantially opposed to the auxiliary capacitance line 107 in plan view, and the width thereof is set to be smaller than the width of the auxiliary capacitance line 107.

Next, the light emission operation of the EL backlight 400 in the liquid crystal display device 10 configured as described above will be described.

FIG. 3 is a timing chart showing the operation of the EL backlight 400 with the row selection pulse. In FIG. 3, the upper part is a video signal in an arbitrary frame, the middle part is the row selection pulse at time T1, and the emission luminance of the corresponding EL emission portion, and the lower stage is the row selection pulse at time T2 and the emission of the corresponding EL emission portion. The luminance is shown.
Since the display screen is scanned in the vertical direction in order of one scanning line from the upper end to the lower end, the horizontal axis (time) indicates the operation in the vertical direction of the screen. In this embodiment, the EL light emitting portions are controlled so as to emit light one by one in synchronization with the row selection pulse output to the scanning line 102, and the row selection pulse moves from the upper end to the lower end as the time advances. As a result, the EL light-emitting portions move one step at a time after the row selection pulse. In the lower stage, the light emission luminance of the EL light emitting portion is increased in accordance with the maximum value of the video signal (broken line portion). However, the signal voltage of the video signal is changed in accordance with the light emission luminance, and the portion other than the peak portion of the waveform is changed. Needless to say, the display needs to be constant.

In the liquid crystal display device 10 having the above configuration, since the EL backlight 400 formed of a thin film is used as a back light source, the thickness of this portion can be reduced to about 1 μm or less. In addition, EL backlight 400
Is disposed outside the second electrode substrate 200, a substrate as a back light source is not required. Therefore, as compared with the case where a fluorescent tube is used as the back light source, the number of components is small and the cost is low, and the back light source itself can be light and thin.

In addition, since light is emitted for each EL light emitting portion in synchronization with the scanning line drive timing, unnecessary light emission does not hinder moving image display, and clear moving image display can be performed. By the way, in order to display clear moving images, it is important to give an illusion to the observer's eyes. For that purpose, it is not necessary to use a light source that constantly emits light such as a fluorescent tube, but to use it as in the above embodiment. It is desirable to control the light source to emit light only for a short period of time so that the cycle of writing the video signal and the cycle of light emission are shifted. That is, by emitting light so as not to include the position of the scanning line selected by the row selection pulse, it is possible to prevent a display in a transient state in which the content is rewritten by writing a video signal, so that the display quality is reduced. Can be increased.

Further, when the light emission luminance of the EL light emitting portion is changed in accordance with the video signal, the light emission brightness is changed in accordance with the maximum value of the signal voltage applied to the pixel electrode. The dynamic range can be increased, and a liquid crystal display device suitable for displaying moving images can be provided.

Further, the non-light-emitting portion is substantially opposed to the auxiliary capacitance line in a plane, and the width thereof is set smaller than that of the auxiliary capacitance line, so that the divided portion of the EL backlight is not seen from the observer side. Display quality can be further improved.

The configuration of the above embodiment can be changed as appropriate. For example, in the embodiment, the EL backlight 40 is used.
Although 0 is formed outside the second electrode substrate 200 (on the side not in contact with the liquid crystal layer 300), it may be formed outside the first electrode substrate 100 or formed on a third substrate (not shown). You may.

The auxiliary capacitance line 107 is formed separately from the scanning line 102 (Cs independent structure), but a capacitance Cs is formed between the immediately preceding scanning line 102 and the pixel electrode 104 adjacent thereto. (Cs-on-gate structure). In this case, the non-light emitting portion and the scanning line 102 are arranged so as to face each other in a plane, and the width of the non-light emitting portion is set to be smaller than the width of the scanning line 102.

Further, in the embodiment, E divided into strips is described.
The L light emitting portions are controlled so as to emit light one by one. The EL light emitting portions are caused to emit light sequentially for each of a plurality of portions.
The light emission position may be controlled to move by one EL light emitting portion. As described above, in the case where the EL light emitting portion emits light in order for each of the plurality of portions, the light emitting time can be lengthened and the light emitting luminance of the EL light emitting portion can be relatively reduced, so that the display device is easy for the observer's eyes. Can be provided. That is, if the light emission time is short, a high light emission luminance is required to maintain the light emission luminance of the entire screen, so that the observer's eyes instantaneously receive strong light. However, this can be avoided by relatively lowering the emission luminance by emitting light with relatively weak light for a long time.

The pitch at which the EL light-emitting portion is divided does not necessarily have to be the pixel pitch, and may be set to an integral multiple thereof. For example, in the case of a high-definition screen,
Three times is appropriate. When the color filters (not shown) are arranged in a horizontal stripe arrangement, the color filters need to be set to a multiple of three. In addition, the EL light emitting portion may be divided at the same pitch as the scanning line.

Further, when the light emission luminance of the EL light emitting portion is changed according to the video signal, the change is made not according to the maximum value of the signal voltage applied to the pixel electrode, but according to the average value of the writing voltage to the pixel electrode corresponding to the EL light emitting portion. You may.

[0031]

As described above, in the liquid crystal display device according to the present invention, the disadvantage of the fluorescent tube is solved by using the EL backlight made of a thin film as the back light source, and the cost is reduced. A liquid crystal display device having a back light source suitable for moving image display, because not only can a light and thin back light source be used, but also unnecessary light emission does not hinder moving image display and clear moving image display can be performed. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device according to an embodiment.

FIG. 2 is an equivalent circuit diagram of a display pixel formed on a first electrode substrate.

FIG. 3 is a timing chart showing the operation of a row selection pulse and an EL backlight.

[Explanation of symbols]

10: liquid crystal display device, 100: first electrode substrate, 101,
201: glass substrate, 102: scanning line, 103: signal line, 104: pixel electrode, 105: TFT, 106: auxiliary capacitance, 107: auxiliary capacitance line, 300: liquid crystal layer, 400:
EL backlight, 401, 402, 403, 404 ...
EL light emitting portion, 411, 412, 413 ... non-light emitting portion

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/36 G02F 1/1335 530 F-term (Reference) 2H091 FA44Z LA11 2H093 NC10 NC16 NC34 NC42 ND42 ND54 NE06 5C006 AA22 AC02 AF69 AF71 AF78 BB16 BB29 BC06 EA01 FA51 FA54 5C080 AA10 BB05 CC03 DD01 DD27 EE32 FF09 JJ02 JJ04 JJ06 KK02 5G435 AA03 AA16 BB12 CC09 EE30 GG25 HH01 LL08

Claims (6)

[Claims] 1. A plurality of signal lines and a plurality of scanning lines crossing each other, a pixel electrode connected to each intersection of these two lines via a switch element, and an auxiliary electrically connected in parallel with the pixel electrode. A first electrode substrate including an auxiliary capacitance line connected via a capacitor, a second electrode substrate including a counter electrode facing the plurality of pixel electrodes, and a liquid crystal layer held between the two electrode substrates. A liquid crystal display device comprising: a white light-emitting flat light source made of an organic EL material disposed on a surface of the first or second electrode substrate that is not in contact with the liquid crystal layer. apparatus. 2. The flat light source is divided into strips in parallel with the scanning lines, and the divided light emitting portions emit light one by one in synchronization with the driving timing of the scanning lines. The liquid crystal display device according to claim 1. 3. The light-emitting portion divided into strips sequentially emits light for each of a plurality of portions, and a light-emitting position moves by one light-emitting portion in synchronization with a drive timing of the scanning line. Item 2. The liquid crystal display device according to item 1. 4. The liquid crystal display device according to claim 2, wherein light emission of the light-emitting portion divided into strips does not include a position where the scanning line is selected. 5. A non-light-emitting portion excluding the light-emitting portion divided into strips and the auxiliary capacitance line are arranged at positions substantially facing each other in a plane, and the width of the non-light-emitting portion is equal to the width of the auxiliary capacitance line. 5. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is narrower than the liquid crystal display device. 6. The light emission luminance of the light-emitting portion divided into strips according to a maximum value of a signal voltage applied to the corresponding pixel electrode.
The liquid crystal display device according to the above.