JP3351660B2 - Liquid crystal display - 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,
In particular, TFT (Thin Film Transist)
The present invention relates to a technique which is effective when applied to a common drive circuit when a liquid crystal display panel is driven by an AC driving method.

[0002]

FIG. 9 shows a conventional liquid crystal display module (MD).
L) is an exploded perspective view showing each component part, SHD is a frame-shaped shield case (metal frame) made of a metal plate, LCW is a display window thereof, PNL is a liquid crystal display panel,
SPB is a light diffusion plate, LCB is a light guide, RM is a reflection plate, B
L is a backlight, LCA is a backlight case, and the components are stacked in a vertical arrangement as shown in the figure to assemble a module MDL.

[0003] The module MDL is a shield case SH.
The entirety is fixed by claws and hooks provided on D.

[0004] The driving circuit board PCB1 is a liquid crystal driving IC.
A drive circuit board on which a chip is mounted by tape automated bonding (TAB), a tape carrier package (TCP), a capacitor, etc., for a video signal drive circuit (drain driver) and a scan signal drive circuit. (Gate driver).

[0005] The drive circuit board PCB2 has electronic components such as ICs, capacitors, and resistors mounted thereon.

The drive circuit board PCB2 has a common electrode drive circuit (common drive circuit) for the liquid crystal display panel PNL,
A power supply circuit for obtaining a plurality of divided and stabilized voltage sources from one voltage source, and converts information for a CRT (cathode ray tube) from a host (upper processing unit) to information for a TFT liquid crystal display device. A circuit including a circuit and the like is mounted.
The drive circuit board PCB2 has a connector connecting portion (not shown) for connecting to the outside.

The backlight case LCA includes a backlight fluorescent tube BL, a light diffusion plate SPB, a light guide LCB, and a reflection plate R.
M, and the light of the backlight fluorescent tube BL disposed on the side surface of the light guide LCB is transmitted to the light guide LC.
B, a reflective plate RM, and a light diffuser plate SPB make a uniform backlight on the display surface, and the light is emitted to the liquid crystal display panel PNL side.

FIG. 10 is a circuit diagram showing a schematic configuration of a conventional common drive circuit, which comprises a common voltage generation circuit 219 and a common driver 1001.

The common voltage generating circuit 219 has a trapezoidal wave having an amplitude of 2.8 V, which is the sum of the forward voltage of diodes 203 and 204 and the forward voltage of diodes 205 and 206 connected in series. Is output centering on the reference voltage VOP.

On the other hand, the common driver 1001 outputs the output of the common voltage generating circuit 219 to an amplification factor -R ₂ A (ω) / set by the resistors R ₁ (208) and R ₂ (209).
At (R ₁ + R ₂ + R ₁ A (ω)), a trapezoidal wave amplified around the reference voltage VOP was output, and a common drive voltage was supplied to the electrode facing the thin film transistor.

Where ω is the angular frequency of the common drive signal,
A (ω) indicates the gain of the operational amplifier when the signal of the angular frequency ω is input, respectively.

Also, the TFT liquid crystal display panel 101
The glass substrate on which the FT 106 is formed (hereinafter, referred to as a glass substrate)
It is described as "TFT side glass substrate". ) Is connected to a substrate on which a color filter, a black matrix, and a common electrode as a counter electrode are formed (hereinafter, referred to as a “color filter side glass substrate”). And an anisotropic conductive film 218.

[0013]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

In the conventional liquid crystal display device, since one common driver 1001 drives all the pixels of the TFT liquid crystal display panel 101, the common drive signal is a signal from the output of the common drive circuit to the TFT liquid crystal display panel. The common signal is attenuated and distorted by the wiring resistance of the line, the connection resistance of the anisotropic conductive film 218, the wiring resistance of the common signal line, and the capacitance and stray capacitance of the pixel connected to the common signal line. "Waveform dulling" occurred.

For this reason, the contrast ratio decreases due to the decrease in the writing rate due to the voltage difference between the drain electrode and the common electrode becoming smaller than a predetermined value, and in particular, crosstalk in the horizontal direction of the screen called horizontal smear occurs. There is a problem that a streak-like image appears, and the visibility of the liquid crystal display device is reduced.

[0016] In recent years, TFs are being actively developed.
Since the driving frequency of the liquid crystal tends to be further increased in the high definition and multi-gradation of the T liquid crystal display panel 101, the wiring resistance and the stray capacitance of the common signal line are reduced, and the time constant is reduced. It is very difficult to reduce the dullness of the signal by reducing it.

An object of the present invention is to provide a technique capable of reducing dullness of a common drive signal in a TFT liquid crystal display panel.

Another object of the present invention is to provide a technique capable of reducing dullness of a common waveform in a liquid crystal display panel without adding a special circuit.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0020]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

(1) A TFT liquid crystal display panel having at least a plurality of thin film transistors provided in a matrix, a common drive circuit for outputting a common drive signal for driving a common signal line of the TFT liquid crystal display panel, and a computer unit The common drive circuit generates a differential signal having a predetermined time constant in the TFT liquid crystal display device including at least a display control device for controlling the circuits based on the input control signal and display data. A differential signal superimposing means for superimposing a signal on the common drive signal is provided.

(2) In the means of the above (1), the common drive circuit includes a feedback amplifier, and the differential signal superimposing means is an integration circuit including a resistor and a capacitor inserted in a feedback loop of the feedback amplifier. It is characterized by the following.

(3) In the means of (2), the resistance is a wiring resistance of a signal line from an output of the common drive circuit to a TFT liquid crystal display panel and a wiring resistance of a common signal line, and the capacitor is Is a stray capacitance of a signal line and a common signal line from the output of the common drive circuit to the TFT liquid crystal display panel.

[0024]

According to the means (1), the differential signal superimposing means connects the wiring resistance of the signal line from the output of the common drive circuit to the TFT liquid crystal display panel, the wiring resistance of the common signal line, and the common signal line. Pixel capacity, and
A differential signal having a time constant equivalent to the time constant of the RC circuit composed of the stray capacitance is superimposed on the common drive signal, so that a signal line from the output of the common drive circuit to the TFT liquid crystal display panel is provided. The wiring resistance of the common signal line and the wiring resistance of the pixel connected to the common signal line,
Further, even if the common drive signal is attenuated by the stray capacitance, a predetermined common drive signal can be applied to the common electrode.

As a result, it is possible to prevent a decrease in the writing rate due to a potential difference applied to the common electrode and the drain electrode being smaller than a predetermined value, which causes a decrease in contrast ratio or horizontal smear.

As described above, a voltage equivalent to the waveform blunting (waveform distortion) of the common drive signal in the TFT liquid crystal display panel is generated in advance by the differential signal superimposing means, and this signal is superimposed on the common drive signal to form a common electrode. , It is possible to prevent a decrease in the contrast ratio of the liquid crystal display device or the occurrence of horizontal smear caused by a decrease in the writing rate due to a dull common signal in the TFT liquid crystal display panel.

According to the means (2), the common drive circuit is constituted by the feedback amplifier and the integrating circuit including the resistor and the capacitor inserted in the feedback loop of the feedback amplifier. The output waveform is an output waveform obtained by adding an output waveform obtained by amplifying the input waveform applied to the input resistor to a differential waveform of the integration circuit that cancels the waveform dullness.

That is, the time constant of the integrating circuit is determined by changing the wiring resistance of the signal wiring from the output of the common driving circuit to the liquid crystal display panel, the wiring resistance of the common signal line, the capacitance of the pixel connected to the common signal line, and With a value equivalent to the stray capacitance, a predetermined drive signal is applied to the common electrode.

As described above, the feedback voltage applied to the feedback resistor of the common drive circuit of the feedback amplifier is blunted by the integration circuit to generate a common drive signal obtained by adding a differential waveform to the output of the common drive circuit. By driving the common electrode of the TFT liquid crystal display panel with a signal, the TFT
In the liquid crystal display panel, it is possible to prevent the contrast ratio of the liquid crystal display device from decreasing and the occurrence of horizontal smear due to the decrease in the writing rate due to the common drive signal becoming dull from a predetermined drive waveform.

According to the means (3), the integration circuit inserted into the feedback loop of the feedback amplifier is provided with a wiring resistance of a signal wiring from an output of the common drive circuit to a liquid crystal display panel and a wiring resistance of a common signal line. And the signal from the output of the common drive circuit to the liquid crystal display panel and the stray capacitance of the common signal line, so that a common drive signal different for each liquid crystal display panel is added without adding a special circuit. Waveform dullness can be canceled.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments.

In all the drawings for explaining the embodiments, parts having identical functions are given same symbols and their repeated explanation is omitted.

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of a liquid crystal display device of Embodiment 1.

In FIG. 1, 101 is a TFT liquid crystal display panel (TFT-LCD), 102 is a drain driver,
103 is a gate driver, 104 is a controller (display control device), 105 is a common drive circuit, 106 is a thin film transistor (TFT), 108 is a drain line, 109 is a gate line, 110 is a common signal line, 111 is a green pixel, 112 Indicates a blue pixel, and 113 indicates a red pixel.

As shown in FIG. 1, the liquid crystal display device according to the first embodiment includes a drain driver 10 on which a drain drive circuit (not shown) is mounted above a TFT liquid crystal display panel 101.
2. A gate driver 103 on which a gate drive circuit (not shown) is mounted on a side surface portion, and a controller 104 and a common drive circuit 105 are arranged on a side surface portion opposite to the gate driver 103.

The drain driver 102, the gate driver 103, the controller 104, and the common drive circuit 105
Are mounted on dedicated printed circuit boards, respectively.

The output of the drain driver 102 is a TFT
The output of the gate driver 103 is connected to the drain line 108 connected to the drain terminal of the
It is connected to the gate line 109 connected to the gate terminal of T106.

By controlling “ON” and “OFF” of the TFT 106 based on a control signal input to the controller 104 from an information processing device (not shown),
A gradation voltage is applied to 11 to 113.

The output of the common drive circuit 105 is first supplied to the drain driver 102 and the TFT liquid crystal display panel 1.
By using a part of the flat cable for connecting to the TFT 01, it is connected to a TFT-side glass substrate (not shown).

Next, the output of the common drive circuit 105 was formed on the filter-side glass substrate through an anisotropic conductive film (not shown) provided between the TFT-side glass substrate and the filter-side glass substrate. Common signal line 1
10 is connected.

The TFT liquid crystal display panel 101 has a 6
It is composed of 40 × 3 × 480 pixels.

FIG. 2 shows the common drive circuit 105 of the first embodiment.
2 is a circuit diagram showing a schematic configuration of
9, 215 and 216 are resistors, 202 and 211 are operational amplifiers, 203 to 206 are diodes, 207, 210 and 2
Reference numerals 14 and 217 denote capacitors, 212 denotes an NPN transistor, 213 denotes a PNP transistor, 218 denotes an anisotropic conductive film, 219 denotes a common voltage generation circuit, 220 denotes a common driver, and 221 denotes an integration circuit (differential signal superimposing means).

Referring to FIG. 2, common voltage generating circuit 219
When a high-level square wave is input (applied) from the M signal terminal (alternating signal input terminal), a current flows through the resistor 201 and the capacitor 207, and the capacitor 2
07 is charged, the output voltage (output voltage of the operational amplifier 202) gradually decreases, and the capacitor 20
When the potential difference between both ends of the capacitor 7 exceeds the forward voltage of the series-connected diodes 203 and 204 connected in parallel with the capacitor 207, the diodes 203 and 204 conduct, and the output voltage becomes low. It has a constant voltage value.

On the other hand, when a low-level square wave is input to the M signal terminal, a current flows through the resistor 201 and the capacitor 207 in a direction opposite to that at the time of the high level, and the capacitor 207 has a polarity opposite to the above. , The output voltage gradually increases, and the capacitor 207
When the potential difference between both ends exceeds the quasi-direction voltage of the series-connected diodes 205 and 206 connected in parallel with the capacitor 207, the diodes 205 and 206 conduct, and the output voltage becomes constant on the high potential side. Voltage value.

By repeating the above operation, a trapezoidal alternating signal having a reference voltage VOP as the center level of the amplitude is output, and the trapezoidal alternating signal is applied to the resistor 208.

The common driver 220 includes resistors 208 and 2
09, the operational amplifier 211, and the NPN transistor 21
2 and an output buffer composed of a PNP transistor 213. The negative feedback amplifier has a basic configuration and outputs a common drive signal necessary for driving the common electrode of the TFT liquid crystal display panel 101 from the output voltage of the common voltage generation circuit 218. Generate.

When the resistance of the resistor 215 is sufficiently smaller than the resistance of the resistor 209, the output voltage Eout of the common driver 220 is calculated by the following equation (1).

[0048]

(Equation 1)

Where Ein is the output of the common voltage generation circuit, ω is the angular frequency of Ein, A (ω) is the gain of the operational amplifier 211 at the angular frequency ω, R ₁ is the resistance of the resistor 208, and R ₂ is the resistance of the resistor 208. 209 indicates a resistance value.

At this time, the integration circuit 221 is connected to the resistor 209 (hereinafter referred to as the feedback resistor 20) connected to the output buffer.
9 ". ), The output waveform of the common driver 220 is blunted to output a common drive signal obtained by adding a differential waveform signal of a time constant composed of the resistors 215, 216 and the capacitor 217.

That is, when the output of the common driver 220 becomes High, a current flows through the resistors 215 and 216 and the capacitor 217, so that the feedback resistor 209
Is a voltage obtained by dividing the output voltage of the common driver 220 by the resistors 215 and 216, the output voltage of the common driver 220 is expressed by the following equation (1).
Is the voltage calculated from

When the charging of the capacitor 217 proceeds and the potential at the point A rises, the current flowing through the resistor 215 decreases, and the voltage applied to the feedback resistor 209 approaches the output voltage of the common driver 220. The voltage approaches the value calculated by Equation 1, and the output voltage becomes a constant value when the charging of the capacitor 217 is completed.

On the other hand, when the output voltage of the common driver 220 goes low, the H
When the electric charge at the time of the high is discharged, the potential at the point A becomes the voltage value calculated by the equation (1).

At this time, the voltage applied to the feedback resistor 209 is the same as that in the case of High described above.
Since the voltage is divided by 6, the output voltage of the common driver 220 at this moment has a voltage value obtained by calculating the divided voltage by the equation (1).

When the discharge of the capacitor 217 proceeds and the potential at the point A decreases, the voltage applied to the feedback resistor 209 approaches the output voltage of the common driver 220 accordingly. When the value approaches the value, the output voltage becomes constant at the end of discharging of the capacitor 217.

As described above, the output of the common driver 220 is changed from Low to High level or from High to Lo.
When the level changes to the w level, a current flows through the resistors 215 and 216 and the capacitor 217, and the voltage applied to the feedback resistor 209 rises or falls exponentially by charging and discharging the capacitor 217. ,
Common driver 220 (NPN transistor 212 and P
The output waveform of the NP transistor 213) is, as shown in FIG.
Output waveform 3 to which a voltage (differential waveform) corresponding to the delay of the feedback voltage by the integration circuit including the capacitor 217 is added.
01.

The differential waveform portion of the output 301 indicates the wiring resistance from the common drive circuit 105 to the TFT liquid crystal display panel 101, the anisotropic conductive film 218, the wiring resistance of the common signal line 110, and the common signal. The TFT is attenuated by a time constant caused by the capacitance of the green / blue / red pixels 111 to 113 connected to the line 110 and the stray capacitance.
A trapezoidal wave obtained by integrating the differential waveform portion is applied to the common electrode of the liquid crystal display panel 101.

When the common drive circuit 105 of the output 301 drives the common electrode of the TFT liquid crystal display panel 101, the result of measuring the common drive signal applied to the common electrode is shown in FIG. A common drive signal waveform by the common drive circuit 402 is a common drive waveform by the common drive circuit 105 of the first embodiment.

As is apparent from FIG. 4, the bluntness of the waveform when the common drive signal rises and falls is improved.

FIG. 5 is a graph showing the relationship between the horizontal smear occurrence ratio and the contrast ratio of the first embodiment and the drive frequency of the common drive signal, and is applied to the common electrode as the drive frequency increases. The effect of the voltage on which the differential signal is superimposed (hereinafter, referred to as “boost voltage”) becomes remarkable. In particular, as for the contrast ratio, the effect becomes large in the region where the driving frequency is 20 MHz or more. Since the driving frequency of the liquid crystal needs to be increased in the TFT liquid crystal display panel to be adjusted, the effect is particularly enhanced.

As described above, the common driver 22
Integrating circuit of the stray capacitance and wiring resistance of the common signal line and a time constant corresponding to the connection resistance of the anisotropic conductive film for connecting the common driver 220 and the TFT liquid crystal display panel 101 to the negative feedback resistance portion of 0. By setting 221 in advance, the output of the common driver is an output that takes into account a voltage equivalent to a portion whose output waveform becomes dull with a time constant composed of the stray capacitance of the common signal line and the wiring resistance.
Since the dulling of the common driving signal due to the time constant can be corrected, the contrast of the liquid crystal display device is reduced due to the decrease in the writing rate due to the dulling of the common driving signal within the TFT liquid crystal display panel due to the dulling below a predetermined voltage, and The generation of smear can be prevented.

(Embodiment 2) FIG. 6 is a circuit diagram showing a schematic configuration of a common drive circuit according to Embodiment 2 of the present invention.
8, 209 are resistors; 202, 211 are operational amplifiers;
3 to 206 are diodes, 207, 210 and 214 are capacitors, 212 is an NPN transistor, and 213 is a PN
P transistor 218 is an anisotropic conductive film, 219 is a common voltage generation circuit, 601 is a feedback terminal, and 602 is a common driver.

In FIG. 6, common voltage generating circuit 218
Has the same configuration as that of the first embodiment, and a description thereof will be omitted.

The common driver 602 includes resistors 208 and 2
09, the operational amplifier 211, and the NPN transistor 21
Is a negative feedback amplifier having a basic configuration of an output buffer composed of a PNP transistor 2 and a PNP transistor 213. However, the feedback voltage of the operational amplifier 211 is not directly fed back from the output of the common driver 602, but the TFT liquid crystal display panel 60
3 is configured to perform feedback from the feedback terminal 601 provided.

At this time, the output of the common driver 602 includes the resistance of the anisotropic conductive film for connecting the TFT liquid crystal display panel 603 and the common drive circuit 105, the resistance of the common signal line in the TFT liquid crystal display panel 603, and Of the common signal due to the stray capacitance of the common signal line
01 is fed back to the feedback resistor 209 of the common driver 602, and based on the feedback voltage, the output becomes the voltage value shown in Expression 1. Therefore, the common drive signal at the feedback terminal 601 is obtained by converting the output of the operational amplifier 202 by Expression 1. It becomes a trapezoidal wave of the calculated voltage value.

As described above, the common driver 60
By applying a voltage to be applied to the feedback resistor 209 of the TFT 2 from a predetermined place provided on the common signal line of the TFT liquid crystal display panel 603 instead of applying the voltage from its output, T
The dullness of the common drive signal in the FT liquid crystal display panel 603 is corrected.

That is, the connection resistance of the anisotropic conductive film for connecting the TFT liquid crystal display panel 603 and the output of the common driver 602, and the feedback terminal 60
By feeding back the output considering the wiring resistance of the common signal lines up to 1 and their stray capacitances to the feedback amplifier of the common driver 602, the dullness of the common drive signal in the TFT liquid crystal display panel 603 is corrected.

With the above-described configuration, it is possible to prevent a decrease in contrast ratio and the occurrence of horizontal smear due to dull common drive signals without increasing the number of components used.

Furthermore, since the number of components used is not increased, the common driver 602 can be configured with the same driver area as the conventional liquid crystal display device.

Although the feedback terminal 601 of the second embodiment uses a part of a conventional terminal for inputting a common drive signal, the feedback terminal 601 is used.
Obviously, by taking a feedback signal from a position where the stray capacitance value of the common signal line of the FT liquid crystal display panel 603 is in the middle of the panel, it is possible to further prevent a decrease in the contrast ratio and the occurrence of horizontal smear.

(Embodiment 3) FIG. 7 is a block diagram showing a schematic configuration of a liquid crystal display device of Embodiment 3.

In FIG. 7, reference numeral 701 denotes a transverse electric field type TF.
T liquid crystal display panel (TFT-LCD), 102 is a drain driver, 103 is a gate driver, 104 is a controller (display control device), 705 is a common drive circuit, 1
06 is a thin film transistor (TFT), 108 is a drain line, 109 is a gate line, 706 is a common signal line, 702
Indicates a green pixel, 703 indicates a blue pixel, and 704 indicates a red pixel.

As shown in FIG. 7, the liquid crystal display device of the third embodiment has a drain driver 102 on which a drain drive circuit (not shown) is mounted above a lateral electric field type TFT liquid crystal display panel 701, and a gate (not shown) on a side surface. Gate driver 103 on which drive circuit is mounted, and gate driver 1
The controller 104 and the common drive circuit 705 are arranged on a side surface opposite to the side 03.

The drain driver 102, the gate driver 103, the controller 104, and the common drive circuit 705
Are mounted on dedicated printed circuit boards, respectively.

The output of the drain driver 102 is a TFT
It is connected to the drain line 108 connected to the drain terminal of 106.

The output of the gate driver 103 is
The signal “O” of the TFT 106 is connected to the gate line 109 connected to the gate terminal of the TFT 106 based on a control signal input to the controller 104 from an information processing device (not shown).
By controlling “N” and “OFF”, the pixel 702 is controlled.
A gradation voltage is applied to 704.

The common drive circuit 705 has the same circuit configuration as the common drive circuit 105 shown in the first embodiment.

The common signal line 706 is formed in the shape of a comb and has a large wiring resistance and its stray capacitance, that is, a particularly large integration time constant that causes waveform dulling. growing.

FIG. 8 is a graph showing the relationship between the boost voltage of the TFT liquid crystal display panel (vertical electric field VGA) of the first embodiment and the TFT liquid crystal display panel (horizontal electric field VGA) of the third embodiment and the generation ratio of the horizontal smear. In the case of the liquid crystal display device according to the first embodiment, when the boost voltage is about 3 to 5 V, the occurrence rate of the horizontal smear becomes the lowest at about 3.8, and when the voltage is higher or lower than this voltage, the occurrence rate of the horizontal smear is obtained. Increases.

On the other hand, in the case of the liquid crystal display device of the third embodiment, when the boost voltage is about 2.4 to 3 V, the occurrence ratio of the horizontal smear is 0, that is, the horizontal smear completely disappears.
Even when the voltage is higher or lower than this voltage, the rate of occurrence of horizontal smear increases.

As is apparent from this figure, it is understood that the contrast ratio and the rate of occurrence of horizontal smear are improved irrespective of the driving method of the TFT liquid crystal display panel.

In particular, the lateral electric field type TFT shown in Embodiment 3
In the liquid crystal display panel, the common electrode and the common signal line are comb-shaped in structure, so that the effect is great, and it can be seen that the horizontal smear is completely eliminated especially when the boost voltage is around 3V.

Regardless of the driving method, it can be seen from the fact that the occurrence ratio of the lateral smear is increased except for the above-described boost voltage, and it is apparent that an optimum boost voltage exists.

For details of the in-plane switching TFT liquid crystal display panel of this embodiment, refer to Japanese Patent Application No. 7-105862 “Liquid Crystal Display Device” of the same applicant.

In the third embodiment, the operation of the liquid crystal display device of the first embodiment in which the in-plane switching mode TFT liquid crystal display panel is applied has been described. However, the operation is also applicable to the liquid crystal display device of the second embodiment. Needless to say, the effect of signal correction is further enhanced by using the voltage at the center of the TFT liquid crystal display panel as the feedback voltage.

In the above embodiment, a negative feedback amplifier is used as a feedback amplifier. However, it goes without saying that a positive feedback amplifier can also be used.

As described above, the invention made by the present inventor is:
Although the present invention has been described in detail with reference to the embodiment, the present invention is not limited to the embodiment, and it is needless to say that various changes can be made without departing from the scope of the invention.

[0088]

The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

(1) The differential signal superimposing means is integrated with the wiring resistance and the stray capacitance from the common drive circuit to the TFT liquid crystal display panel, and the portion where the drive waveform becomes dull is preliminarily superimposed on the common drive signal. Output, the dullness of the common waveform in the common electrode liquid crystal display panel can be reduced, so that the contrast of the liquid crystal display device is reduced due to the decrease in the writing rate due to the common drive signal becoming duller than a predetermined voltage. Further, occurrence of horizontal smear can be prevented.

(2) A feedback voltage (output voltage) applied to a feedback resistor of a common drive circuit including a feedback amplifier
Since the output of the common drive circuit is obtained from the common signal line of the liquid crystal display panel, the output of the common drive circuit includes an integral multiplier that causes waveform dulling due to wiring resistance and stray capacitance until reaching the TFT liquid crystal display panel. It is possible to reduce the dullness of the common waveform in the liquid crystal display panel without adding a special circuit, and as a result, the contrast of the liquid crystal display device accompanying the decrease in the writing rate due to the dulling of the common signal below a predetermined voltage is reduced. And the occurrence of horizontal smear can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram illustrating a schematic configuration of a common drive circuit according to the first embodiment.

FIG. 3 is a diagram illustrating an output of the common drive circuit according to the first embodiment.

FIG. 4 is a diagram illustrating measurement of common drive signals of a conventional common drive circuit and a common drive circuit according to the first embodiment in a TFT liquid crystal display device.

FIG. 5 is a graph showing the relationship between the occurrence ratio of horizontal smear and the contrast ratio in the liquid crystal display device of Example 1 and the drive frequency of the common drive signal.

FIG. 6 is a circuit diagram illustrating a schematic configuration of a common drive circuit according to a second embodiment.

FIG. 7 is a block diagram illustrating a schematic configuration of a liquid crystal display device according to a third embodiment.

FIG. 8 shows a TFT liquid crystal display panel (HA507) according to the first embodiment.
7 is a graph showing the relationship between the boost voltage and the occurrence rate of horizontal smear of the TFT liquid crystal display panel (lateral electric field VGA) of Example 3 and the TFT liquid crystal display panel (lateral electric field VGA) of Example 3.

FIG. 9 is an exploded perspective view showing components of a conventional liquid crystal display module.

FIG. 10 is a circuit diagram illustrating a schematic configuration of a common drive circuit of a conventional liquid crystal display device.

[Explanation of symbols]

101, 603, 701 ... TFT liquid crystal display panel, 10
2 ... Drain driver, 103 ... Gate driver, 10
4 Controller, 105, 705 Common drive circuit,
106: thin film transistor, 108: drain line, 10
9: gate line, 110, 706: common signal line, 11
1,702: green pixels, 112, 703: blue pixels, 113, 704: red pixels, 201, 208, 2
09, 215, 216 ... resistor, 202, 211 ... operational amplifier, 203-206 ... diode, 207, 210,
214, 217: capacitor, 212: NPN transistor, 213: PNP transistor, 218: anisotropic conductive film, 219: common voltage generating circuit, 220, 602
1001 common driver, 221 integration circuit, 601
... Return terminal.

Continued on the front page (72) Inventor Yasuyuki Mishima 3300 Hayano Mobara-shi, Chiba Pref. Electronic Device Division, Hitachi, Ltd.

Claims (3)

(57) [Claims] 1. A TFT liquid crystal display panel having at least a plurality of thin film transistors provided in a matrix, a common drive circuit for outputting a common drive signal for driving a common signal line of the TFT liquid crystal display panel, and an input from a computer unit. And a display control device for controlling each of the circuits based on the control signal and the display data. The common drive circuit generates a differential signal having a predetermined time constant, A liquid crystal display device comprising a differential signal superimposing means for superimposing a signal on the common drive signal. 2. The method according to claim 1, wherein the common drive circuit includes a feedback amplifier, and the differential signal superimposing means is an integration circuit including a resistor and a capacitor inserted in a feedback loop of the feedback amplifier. Liquid crystal display device as described. 3. The resistance is a wiring resistance of a signal line from an output of the common driving circuit to a TFT liquid crystal display panel and a wiring resistance of a common signal line, and the capacitor is a wiring resistance of an output of the common driving circuit. 3. The liquid crystal display device according to claim 2, wherein the stray capacitance is a signal line and a common signal line up to the TFT liquid crystal display panel.