JP2000338936A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of preventing the gray level of an apparent image from becoming too conspicuous, even when a low-temperature poly-silicon liquid crystal is used, and capable of improving an image quality characteristic of a display image in the case of using the poly-silicon liquid crystal. SOLUTION: In this liquid crystal display device, during a vertical blanking period after an image display period on a liquid crystal panel 111, a driving signal generated from a driving circuit 119 for the vertical blanking period is supplied to a controller circuit 118, to execute liquid crystal driving, and hereby even in the vertical blanking period on each field or in each frame, a switching transistor for pixel driving is driven, to prevent decline of its source potential. Therefore, the gray level on a line in the horizontal scanning direction generated by decline of a pixel voltage caused by current leakage of a pixel transistor is equalized relative to a time on each horizontal line of the same field unit on each field or in each frame.

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 which is used as a display device of a portable device terminal device or the like and drives a liquid crystal in a liquid crystal panel to display an image.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device for driving a liquid crystal in a liquid crystal panel to display an image has been used in a computer system including a portable terminal device, a television receiver, and the like because of its light weight, space saving, and low power consumption. Widely used as display devices, built-in driver circuits that directly drive the liquid crystal panel, and drive those driver circuits to reduce costs, reduce the number of components, and further reduce power consumption The drive circuits to be controlled are being built in rapidly.

Among them, a driver circuit and a drive circuit using a conventional transistor element formed of amorphous silicon are difficult to be built in, and as a replacement therefor, a low-temperature process has recently attracted attention. A driver circuit and a drive circuit using a polycrystalline silicon transistor element formed by the processing. A liquid crystal panel in which the driver circuit and the drive circuit are incorporated has been commercialized, and further improvements are being made, and attention is being paid.

A schematic configuration and an operation of such a liquid crystal display device will be described below. FIG. 3 is a block diagram showing a configuration of a conventional liquid crystal display device. In FIG. 3, reference numeral 411 denotes a liquid crystal panel.
1 denotes a plurality of scanning electrodes 420 and a plurality of signal electrodes 42
1 and 422, a pixel 423 formed of liquid crystal
Is an image display medium on which an image is displayed by driving the pixel 423.

Reference numeral 412 denotes a plurality of signal drivers 412 ₁ , 4
12 _2, ..., a signal driver circuit composed of 412 _n-1, 412 _n. The signal driver circuit 412 includes a plurality of signal drivers 412 ₁ , 412 ₂ ,..., 4 when the driving circuit is formed of an IC or an element outside the liquid crystal panel 411.
12 _n−1 , 412 _n are configured as individual ICs packaged in blocks corresponding to the respective signal electrodes 421, 422, and the number of blocks is configured in units of one to several tens. It is generally done.

Reference numeral 414 denotes a signal driver circuit that operates in the same manner as the signal driver circuit 412. The signal driver circuit 414 has a plurality of signal drivers 414 ₁ , 414 ₂ ,. _n-1 ,
414 _{n. The} number of block units is one to several tens. The configuration such as the signal driver circuits 412 and 414
According to the configuration of the signal driving wiring for the eleven pixels 423, for example, the liquid crystal panel 411 provided with the signal electrode 421 and the signal electrode 422 on both upper and lower sides of the liquid crystal panel 411 as signal electrodes is applied. In many cases, a signal electrode (for example, the signal electrode 421) is provided on only one side of the liquid crystal panel 411 as an electrode. The signal driver circuits 412 and 414 operate based on the image data corresponding to the image signals input from the outside.
The pixel 423 operates to drive current through the signal electrodes 421 and 422.

Reference numeral 413 denotes a plurality of scan drivers 413 ₁ , 4
13 _2, ... made of 413 _n, by each of the scanning electrodes in the liquid crystal panel 411 is connected to the gate terminal of each TFT on the same horizontal line for pulse application 420
And a scanning driver circuit for driving the same, and the number of blocks is one to several units. The scanning driver circuit 413 includes a plurality of signal drivers 41.
_{2 1, 412 2, ...,} 412 n-1, 412 n and a plurality of signal drivers _{414 1, 414 2, ...,} 414 n-1, 414 n
The liquid crystal panel 41 through the signal electrodes 421 and 422
1 signal driver circuits 412 and 4 for inputting image data
With 14, the pixel 423 on the liquid crystal panel 411 operates to control the drive timing for image display.

Reference numeral 417 denotes a power supply circuit, and the liquid crystal panel 41
A signal driver circuit 412 for driving the signal electrodes 421 and 422 and the scanning electrode 420 for displaying an image on
The power of a required voltage is supplied to the scan driver circuit 414 and the scan driver circuit 413. 418 is a signal driver circuit 412, 4
14 and a scanning driver circuit 413 to generate a control signal including a driving signal and a driving timing signal necessary for displaying an image on the liquid crystal panel 411 by the controller circuit 415. A power source supply line 416 for supplying a predetermined voltage to the scan driver circuit 412 and 414 and the scan driver circuit 413 are connected to the signal driver circuits 412 and 414 and the scan driver circuit 413 from the controller circuit 418.
This is a control line for supplying a control signal necessary for displaying an image on the liquid crystal panel 411.

[0009]

However, in the above-mentioned conventional liquid crystal display device, the performance of the driver itself and the characteristics of the transistors constituting the driver circuit itself,
There are problems with various image quality characteristics due to current leakage caused by deterioration of the off characteristics of the pixel transistors constituting the pixels of the liquid crystal panel, and problems with the reliability and quality of the liquid crystal panel due to such problems. There is a problem different from the case where a transistor element is used.

That is, in the conventional liquid crystal display device, since the same polarity is displayed every horizontal line through all the fields, the potential of the signal electrode is lowered due to the leak current particularly caused by the deterioration of the off characteristic in the pixel transistor. As a result, a decrease in pixel voltage results in horizontal stripes of black and white line shading for each horizontal line, and this state becomes particularly noticeable in halftone display, and the degree of this shading is particularly high in vertical blanking. The period is determined by the source potential level of the pixel transistor during the period, and increases as the TV characteristic of the liquid crystal material becomes steeper, such as low-temperature polysilicon liquid crystal.

The present invention solves the above-mentioned conventional problems. Even when a low-temperature polysilicon liquid crystal is used, the black and white shading in the horizontal direction is reduced, so that the shading of an apparent image is not significantly noticeable. And a liquid crystal display device capable of improving image quality characteristics in a display image when a polysilicon liquid crystal is used.

[0012]

In order to solve the above-mentioned problems, a liquid crystal display device according to the present invention supplies a drive signal generated from a drive circuit for a vertical blanking period to a controller circuit during a vertical blanking period. In order to prevent the source potential from lowering by driving the switching transistor for driving the pixel even during the vertical blanking period for each field or each frame by performing the liquid crystal driving, the pixel voltage due to the current leakage of the pixel transistor is reduced. The shading on the line in the horizontal scanning direction caused by the drop in
It is characterized in that, for each field or each frame, the same is temporally the same on each horizontal line in the same field unit to reduce the shading in the display image.

As described above, even when the low-temperature polysilicon liquid crystal is used, the black and white shading in the horizontal direction can be reduced so that the shading of the visual image can be made remarkably inconspicuous. Image quality characteristics of a display image can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display device according to a first aspect of the present invention comprises a liquid crystal panel having a plurality of scanning electrodes, a plurality of signal electrodes, and pixels formed of liquid crystal, and a plurality of scanning electrodes. A plurality of scan drivers for driving; and a plurality of signal drivers for driving the plurality of signal electrodes. The plurality of scan electrodes and the plurality of signal electrodes are driven by the plurality of scan drivers and the plurality of signal drivers, respectively. A liquid crystal display device that drives the pixel through and displays an image on the liquid crystal panel by driving the pixel,
The plurality of scanning drivers and the plurality of signal drivers,
A drive timing signal for driving each of them, a controller circuit for supplying a drive signal, and a drive timing signal from the controller circuit and a vertical blanking after a drive period for the liquid crystal panel for displaying the image by the drive signal. A vertical blanking period driving circuit that generates a signal for further driving the liquid crystal panel during the vertical blanking period, and wherein the vertical blanking period includes a vertical blanking period driving circuit. Is supplied to the controller circuit, and the controller circuit drives the liquid crystal from the plurality of scan drivers and the plurality of signal drivers through the plurality of scan electrodes and the plurality of signal electrodes. A period driving circuit is configured.

According to a second aspect of the invention, a liquid crystal display device comprises a drive timing signal from the controller circuit according to the first aspect and the generation of a drive signal in a vertical blanking period after the drive period by the drive signal to form a display image. The vertical blanking period drive circuit is configured to perform this operation every vertical blanking between frames. According to the above configuration,
In the vertical blanking period, the drive signal generated from the vertical blanking period drive circuit is supplied to the controller circuit to drive the liquid crystal, so that the pixel drive for the field can be performed even in the vertical blanking period for each field or frame. In order to prevent the source potential of the switching transistor from lowering, the shading on the line in the horizontal scanning direction caused by the reduction of the pixel voltage due to the current leak of the pixel transistor is applied to the same field unit for each field or frame. Are made temporally the same on each horizontal line to reduce the shading in the displayed image.

Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be specifically described with reference to the drawings.
First, the configuration and operation of the liquid crystal display device of the present embodiment will be described. FIG. 1 is a block diagram showing a configuration of the liquid crystal display device of the present embodiment. In FIG. 1, reference numeral 111 denotes a liquid crystal panel. The liquid crystal panel 111 passes through a plurality of scanning electrodes 120 and a plurality of signal electrodes 121 and 122.
This is an image display medium in which a pixel 123 formed of liquid crystal is driven and an image is displayed by driving the pixel 123.

Reference numeral 112 denotes a plurality of signal drivers 112 ₁ , 1
12 _2, ..., a signal driver circuit composed of 112 _n-1, 112 _n. This signal driver circuit 112 includes a plurality of signal drivers 112 ₁ , 112 ₂ ,..., 1 when the driving circuit is formed of an IC or an element outside the liquid crystal panel 111.
12 _n−1 and 112 _n are configured as individual ICs packaged in blocks corresponding to the respective signal electrodes 121 and 122, and the number of blocks is configured in units of one to several tens. It is generally done.

Reference numeral 114 denotes a signal driver circuit that operates in the same manner as the signal driver circuit 112. The signal driver circuit 114 has a plurality of signal drivers 114 ₁ , 114 ₂ ,. _n-1 ,
114 _n , and the number of block units is one to several tens. In the configuration like the signal driver circuits 112 and 114, the signal electrode 121 and the signal electrode 122 are used as the signal electrodes, for example, by the configuration of the signal driving wiring for the pixel 123 of the liquid crystal panel 111 as in the related art. This is applicable to the liquid crystal panels 111 provided on both upper and lower sides of the liquid crystal panel 111.
The signal driver circuits 112 and 114 apply the signal electrodes 1 to the pixels 123 of the liquid crystal panel 111 based on the image data corresponding to the image signals input from the outside.
21 and 122 to drive the current.

Reference numeral 113 denotes a plurality of scanning drivers 113 ₁ , 1
13 _2, ... made of 113 _n, by each of the scanning electrodes 120 connected to the pulse applied to the gate terminal of each TFT on the same horizontal line in the liquid crystal panel 111
And a scanning driver circuit for driving the same, and the number of blocks is one to several units. The scanning driver circuit 113 includes a plurality of signal drivers 11
_{2 1, 112 2, ...,} 112 n-1, 112 n and a plurality of signal drivers _{114 1, 114 2, ...,} 114 n-1, 114 n
Liquid crystal panel 11 through signal electrodes 121 and 122
Signal driver circuits 112, 1 for inputting image data to 1
With 14, the pixel 123 on the liquid crystal panel 111 operates to control the drive timing for image display.

When the transistor elements formed of amorphous silicon are used for the signal driver circuits 112 and 114 and the scan driver circuit 113, they are each constituted by an individual IC. Reference numeral 117 denotes a power supply circuit, and signal driver circuits 112 and 114 and a scan driver circuit 11 for driving the signal electrodes 121 and 122 and the scan electrode 120 for displaying an image on the liquid crystal panel 111.
3 is supplied with the required voltage. Reference numeral 118 denotes signal driver circuits 112 and 114 and a scan driver circuit 113
And a control circuit 115 for generating a control signal including a drive signal and a drive timing signal necessary for displaying an image on the liquid crystal panel 111 by the control circuit. A power supply line for supplying power of a predetermined voltage to the circuit 113.
And a control line for supplying a control signal necessary for displaying an image on the liquid crystal panel 111 to the signal driver circuits 112 and 114 and the scanning driver circuit 113.

Reference numeral 119 denotes a drive timing signal from the controller circuit 118 and a vertical blanking operation after the drive period for the liquid crystal panel 111 for displaying an image based on the drive signal. From the signal driver circuits 112 and 114 and the scan driver circuit 113 to the signal electrodes 121 and 122.
And a driving circuit for a vertical blanking period for generating a driving signal through the scanning electrode 120. The vertical blanking period drive circuit 119 supplies a drive signal to the controller circuit 118 during a vertical blanking period after the drive period for the liquid crystal panel 111 for image display, and the controller circuit 118 causes the plurality of scans to be performed. driver _{113 1, 113 2, ...,} 113 n and a plurality of signal drivers _{112 1, 112 2, ...,} 112 n-1, 11
2 _n and a plurality of signal drivers 114 ₁ , 114 ₂ ,.
The liquid crystal in the pixel 123 is driven from 114 _n−1 and 114 _n through a plurality of scanning electrodes 120 and a plurality of signal electrodes 121 and 122.

FIG. 2 is a timing waveform chart showing the operation of the liquid crystal display device shown in FIG. In FIG. 2, ST
V is a vertical synchronizing signal output from the controller circuit 118 or a signal equivalent to the vertical synchronizing signal corresponding to the vertical blanking period after the driving period for the liquid crystal panel 111 for image display. CVA and CVB are synchronized with the vertical synchronization signal STV, and the scan electrodes 1 of the liquid crystal panel 111 are
20 is a pulse for driving the scan driver 20 through the scan driver circuit 113. OE is a pulse for distinguishing between an even field and an odd field of the display image. OEV is a write pulse for writing one horizontal period data to the liquid crystal panel 111. With the pulse OEV, S-DATA becomes image data for writing an image signal from a source electrode of a pixel transistor (TFT). VSIG is the liquid crystal panel 111
Is a charging pulse for driving.

As described above, conventionally, the liquid crystal panel was not driven during the vertical blanking period.
In the present embodiment, in the vertical blanking period, a drive signal generated from the vertical blanking period drive circuit is supplied to the controller circuit to perform liquid crystal driving, so that in the vertical blanking period for each field or frame, In order to prevent the source potential of the switching transistor from lowering by driving the pixel driving switching transistor, the shading on the line in the horizontal scanning direction caused by the lowering of the pixel voltage due to the current leak of the pixel transistor is determined for each field or frame. Each time, it is possible to reduce the shading in the display image by making the same temporally on each horizontal line in the same field unit.

As a result, in order to maintain a uniform pixel voltage for each field and frame of a display image, a voltage difference between signal electrodes due to a current leak or the like in a pixel transistor or the like is canceled out and uniformized. Even when used, it reduces the black and white shading in the horizontal direction,
It is possible to make the appearance of the image look less noticeable, and to improve the image quality characteristics of the display image when using the polysilicon liquid crystal.

[0025]

As described above, according to the present invention, during the vertical blanking period, the driving signal generated from the vertical blanking period driving circuit is supplied to the controller circuit to drive the liquid crystal, thereby making it possible to drive each field. Alternatively, even in a vertical blanking period for each frame, a line in the horizontal scanning direction generated by a decrease in the pixel voltage due to a current leak of the pixel transistor in order to drive the switching transistor for driving the pixel and prevent a decrease in the source potential thereof. The upper and lower shades are made identical temporally on each horizontal line in the same field unit for each field or frame,
Shading in a display image can be reduced.

Therefore, even when the low-temperature polysilicon liquid crystal is used, the black-and-white shading in the horizontal direction can be reduced to make the shading of the visual image remarkably inconspicuous. Image quality characteristics of an image can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a timing chart showing an operation of the liquid crystal display device of the embodiment.

FIG. 3 is a block diagram showing a circuit configuration of a conventional liquid crystal display device.

[Explanation of symbols]

 111 Liquid Crystal Panel 112, 114 Plural Signal Drivers 113 Plural Scan Drivers 117 Power Supply Circuit 118 Controller 119 Drive Circuit for Vertical Blanking Period

Claims (2)

[Claims] 1. A liquid crystal panel having a plurality of scan electrodes, a plurality of signal electrodes, and pixels formed of liquid crystal, a plurality of scan drivers for driving the plurality of scan electrodes, and a drive for the plurality of signal electrodes. A plurality of signal drivers, wherein each of the plurality of scan drivers and each of the plurality of signal drivers drive the pixel through the plurality of scan electrodes and the plurality of signal electrodes. A controller circuit for supplying a drive timing signal and a drive signal for each of the plurality of scan drivers and the plurality of signal drivers to the plurality of scan drivers and the plurality of signal drivers; and a drive timing from the controller circuit. Vertical blanking after a driving period for the liquid crystal panel for displaying the image by a signal and a driving signal A vertical blanking period driving circuit for generating a signal for further driving the liquid crystal panel during the vertical blanking period for each of the vertical blanking periods.
During the vertical blanking period, a drive signal from the vertical blanking period drive circuit is supplied to the controller circuit, and the controller circuit causes the plurality of scan electrodes and the plurality of signal drivers to output the plurality of scan electrodes and A liquid crystal display device, wherein the driving circuit for the vertical blanking period is configured to drive the liquid crystal through a plurality of signal electrodes. 2. A vertical blanking method according to claim 1, wherein a drive signal is generated in a vertical blanking period after a drive period based on a drive timing signal and a drive signal from a controller circuit, for each vertical blanking between frames forming a display image. 2. The liquid crystal display device according to claim 1, wherein a driving circuit for the ranking period is configured.