JP3080054B2 - Liquid crystal display device - Google Patents

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 displays images by arranging liquid crystal display elements in an XY matrix, for example.

[0002]

2. Description of the Related Art For example, it has been proposed to display a television image using a liquid crystal (see Japanese Patent Application Laid-Open No. 59-220793).

That is, in FIG. 3, an input terminal 1 is supplied with, for example, a video signal of a television. The video signal from the input terminal 1 is, for example, N channel FE
Switching elements M _1, M ₂ vertical through ··· M _m (Y-axis) direction of the line L ₁ consisting of T, is supplied to the L ₂ ··· L _m. Note that m is a number corresponding to the number of pixels in the horizontal (X-axis) direction.

Further, an m-stage shift register 2 is provided, and clock signals Φ _1H and Φ _2H whose frequency is m times the horizontal frequency are supplied to the shift register 2. A drive pulse signal φ sequentially scanned by the clock signals Φ _1H and Φ _2H
1H , φ _2H ... Φ _Hm are supplied from respective output terminals of the shift register 2 to respective control terminals of the switching elements M _{1 to} M _m . The shift register 2 is supplied with a low potential (V _SS ) and a high potential (V _DD ), and a drive pulse of these two potentials is formed.

A switching element M ₁₁ composed of, for example, an N-channel FET is connected to each of the lines L _{1 to} L _m .
_{M 12 ··· M n1, M 12} , M 22 ··· M n2, ··· M 1m,
One end of M _2m ... M _nm is connected. Note that n is a number corresponding to the number of horizontal scanning lines. This switching element M ₁₁ ~
The other end of the M _nm are connected to the target terminal 3 through the liquid crystal cell C _11, C ₁₂ ··· C _nm, respectively.

Further, an n-stage shift register 4 is provided, and the shift register 4 is supplied with horizontal frequency clock signals Φ _1V and Φ _2V . The driving pulse signals φ _V1 , φ _V2 ... Φ _Vn sequentially scanned by the clock signals φ _1V and φ _2V are supplied from the output terminals of the shift register 4 to the gate lines G ₁ and G in the horizontal (X-axis) direction. ₂ ... G
Each column in the X-axis direction of the switching element M ₁₁ ~M _nm through _{n (M 11 ~M 1m),} (M 21 ~M 2m) ··· (M n1 ~
M _nm ). Note that the shift register 4 has the same voltage V _SS as the shift register 2.
And V _DD are supplied.

That is, in this circuit, clock signals Φ _1H , Φ _2H , Φ _1V , and Φ _2V as shown in FIGS. 4A and 4B are supplied to the shift registers 2 and 4, for example. Then, drive pulse signals φ _{H1 to} φ _Hm are output from the shift register 2 for each pixel period as shown in C of the figure, and the shift register 4 is driven for each horizontal period as shown in D of the figure. Pulse signals φ _{V1 to} φ _Vn are output. Further, a signal as shown by E in FIG.

For example, when the drive pulse signals φ _V1 and φ _H1 are being output, the switching elements M ₁ and M ₁₁ .
M _1m is turned on and input terminal 1 → M ₁ → L ₁ → M ₁₁ → C ₁₁
→ A current path for the target terminal 3 is formed. This potential difference between the signal and the target terminal 3 which is supplied to the input terminal 1 is supplied to the liquid crystal cell C _11.

[0009] For this reason capacity of the liquid crystal cell C _11, 1
The charge corresponding to the potential difference due to the signal of the second pixel is sampled and held. Then, the light transmittance of the liquid crystal is changed in accordance with this charge amount. The same cells C ₁₂ ~ and this
This operation is sequentially performed for C _nm , and when the signal of the next field is supplied, the charge amount of each cell C _{11 to} C _nm is rewritten.

In this way, the light transmittance of the liquid crystal cells C _{11 to} C _nm is changed corresponding to each pixel of the video signal, and this is sequentially repeated to display a television image.

[0011]

When a liquid crystal is used for display, an AC drive is generally used to increase the reliability and the life of the liquid crystal. For example, in displaying a television image, a signal obtained by inverting a video signal for each field or frame is supplied to the input terminal 1. Further, in a liquid crystal display device, a signal is inverted every horizontal period in order to prevent the pseudo-shooting of a display in a vertical direction.

Therefore, in the above-described device, the input terminal 1
Is supplied with a signal which is inverted every horizontal period and inverted every field or frame, for example, as shown in FIG.

However, in the above-described device, if the polarity inversion is performed every horizontal period as described above, for example, when the display image is all white (or all black), the image supplied to the input terminal 1 is displayed. For example, as shown in FIG. 5A, the signal has a white (or black) level Vp whose polarity is inverted every horizontal period with respect to the target voltage.

[0014] When the switching element M ₁ ~M _m in the driving pulse signal phi _H1 to [phi] _Hm as shown in the figure B is turned relative to, the potential of the line L ₁ ~L _m is in FIG. C, ie, each line L ₁
Potential of ~L _m will be 2Vp changed to one pulse period of the drive pulse signal phi _H1 to [phi] _Hm.

In this case, the pulse signals φ _{H1 to} φ _Hm
1 pulse period, the effective screen period of one horizontal period is 1 / m
This is a very short period of time,
To perform the voltage change of Vp, the switching elements M ₁ to
Must be lower on-resistance of the M _m, it is necessary to increase the size of each element.

However, increasing the size of such an element not only increases the chip area when the element is made on-chip, but also imposes restrictions on the design of the related horizontal scanning circuit (shift register 2) and the like. It is tough.

If the sizes of the switching elements M _{1 to} M _m are insufficient, the signal potentials of the lines L _{1 to} L _m do not rise sufficiently, and the rewriting of the charge amount of the liquid crystal cell is insufficient. Therefore, there is a problem that the image quality is extremely deteriorated, for example, the contrast of the displayed image is lowered.

This application has been made in view of the above points, and the problem to be solved is that in the conventional device, the on-resistance of the device must be reduced, and the size of the device is increased. Therefore, if the design restrictions are strict or the size of the element is insufficient, the image quality is extremely deteriorated such as the contrast of the displayed image is lowered.

[0019]

In Means for Solving the Problems The present invention for this, there is that so as to precharge the potential of the signal line to the intermediate potential for each inversion of the video signal, dot-sequentially supplied according to this The change width of the signal to be changed is reduced, the load on the switching element is reduced, and the deterioration of the image quality of the displayed image can be prevented even with a small element size.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a plurality of first signal lines arranged in parallel in the vertical direction, a plurality of second signal lines arranged in parallel in the horizontal direction, and A liquid crystal cell provided at each intersection of the first and second signal lines via a selection element; a shift register for sequentially scanning the second signal line to select one row of pixels; A liquid crystal display device having a shift register that generates a pulse signal for writing an image signal to one row of pixels, a unit that inverts the polarity of the image signal supplied to the first signal line at predetermined time intervals; Each inverted period of the image signal supplied in a dot-sequential manner
Means for precharging an arbitrary intermediate potential of the video signal of the first signal line to a first signal line by a switching element different from a shift register for generating a pulse signal for writing an image signal to pixels of one selected row. It is.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an example of a liquid crystal display device to which the present invention is applied.

FIG. 1 shows the structure of a single liquid crystal display device similar to that of FIG. 3. In FIG. 1, switching elements are provided at the lower ends of the lines L _{1 to} L _m in the vertical (Y-axis) direction. M _R1 , M _R2 ... M _Rm are provided. The target terminal 3 through these elements M _R1 ~M _Rm
And the control terminals of these elements M _{R1 to} M _Rm are connected to the reset terminal 5 to which the horizontal blacking pulse H _BLK is supplied. Other configurations are the same as those of the apparatus shown in FIG.

In this apparatus, for example, A in FIG.
Is supplied to the input terminal 1 and the driving pulse signal φ as shown in FIG.
_H1 to [phi] When the switching element M ₁ ~M _m is turned on by _Hm, horizontal blanking pulse H _BLK as shown in the figure C is supplied to the reset terminal 5, whereby the switching element M _R1 ~M _Rm is turned on.

For this reason, the potentials of the lines L _{1 to} L _m are precharged to the target voltage during each horizontal blanking pulse H _BLK , and the drive pulse signals φ _{H1 to} φ _Hm
Is changed from this target voltage to the potential of the video signal.

Therefore, in this device, the pulse signal φ _H1
Signal is changed to one pulse period to [phi] _Hm could be the half of the maximum Vp, and the conventional device. For this reason, the charge amount of the liquid crystal cell can be sufficiently rewritten even with a small element size, and deterioration of image quality due to a decrease in contrast of a displayed image or the like can be prevented. Further, there is no increase in the chip area due to the increase in the element size and no restriction on the design.

According to this device, by precharging the potential of the signal line to the intermediate potential every time the video signal is inverted, the width of the change of the signal supplied in a dot-sequential manner is reduced, and Such a load is reduced, and a load on the switching element is reduced, so that the image quality of the displayed image can be prevented from deteriorating even with a small element size.

In the above-described device, the switching element is not limited to the NMOS signal as shown, but may be a PMOS or CMOS element. The signal supplied to the reset terminal 5 is not limited to the horizontal blanking pulse, and may be any signal as long as the signal is in a non-effective period of the video signal. Further, the voltage for performing the precharge is not limited to the target voltage, and any intermediate potential of the video signal can be used.

[0028]

Therefore, according to the first aspect of the present invention, by precharging the potential of the signal line to the intermediate potential every time the video signal is inverted, the width of the signal supplied in a dot-sequential manner is reduced. Thus, the load on the switching element is reduced, and the image quality of the displayed image can be prevented from deteriorating even with a small element size.

As a result, in the conventional device, the on-resistance of the element must be low, and the design restrictions are strict in order to increase the size of the element. The present invention of the present application can easily solve these problems, which have had problems such as the image quality being extremely deteriorated such as the image contrast being lowered.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a liquid crystal display device to which the present invention is applied.

FIG. 2 is a diagram for explaining the operation.

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

FIG. 4 is a diagram for the explanation.

FIG. 5 is a diagram for explaining this.

[Description of References] L _{1 to} L _m ... vertical signal lines, G _{1 to} G _n are gate lines, M _{1
~M m, M R1 ~M Rm,} M 11 ~M nm switching element,
C _{11 to} C _nm : liquid crystal cell, 1: input terminal, 2, 4: shift register, 3 target terminal, 5: reset terminal

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein the plurality of first power supply units are arranged in parallel in a vertical direction.
A plurality of second signal lines disposed in parallel in the horizontal direction; a liquid crystal cell provided at each intersection of the first and second signal lines via a selection element; A liquid crystal display having a shift register that sequentially scans a second signal line to select one row of pixels, and a shift register that generates a pulse signal for writing an image signal to the selected one row of pixels. in the apparatus, the for each of the inverting means and said image signal point are sequentially supplied to reverse the polarity of the image signal supplied to the first signal line for each predetermined time period
An arbitrary intermediate potential of the inverted video signal in each period is converted into the first signal by a switching element different from a shift register that generates a pulse signal for writing an image signal to the selected one row of pixels. Pritch to line
And a means for di-, liquid crystal display device, characterized in that.