JP2003215536A - Liquid crystal display device and driving method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a liquid crystal display device from being deteriorated in picture quality due to optical leak current. <P>SOLUTION: A plurality of signal lines 11, scanning lines 12, correction signal lines 13, and inverted scanning lines 14 are arranged in a matrix form, and two pieces of TFT 1 and TFT 2 are provided in the vicinity of intersection points of the signal lines 11 and the scanning lines 12. Further, TFT 3 which the drain (D) is connected with the connection point of TFT 1 and TFT 2, the gate (G) is connected with the inverted scanning line 14, and the source (S) is connected with the correction signal line 13, is arranged; this TFT 3 supplies a correction signal for generating an optical leak current (inverted optical leak current), generated by a signal generating circuit 15, for reversing the positive and negative polarities to the connection point of TFT 1 and TFT 2 when TFTs 1, 2 are in the OFF state; and the optical leak current is switched to the inverted optical leak current to be reduced on average by reversing the positive and negative polarities. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device, and more particularly to a liquid crystal display device capable of reducing the influence of light leakage current on the display and its driving method.

[0002]

2. Description of the Related Art A conventional active matrix liquid crystal display device (conventional liquid crystal display device) includes two glass substrates and a liquid crystal sandwiched between the glass substrates.

In an equivalent circuit of a conventional liquid crystal display device, signal lines 111 and scanning lines 112 as shown in FIG. 4 are arranged in a matrix on one glass substrate.

A switching element 102, for example, a thin film transistor (TFT) 102 is arranged near the intersection of the signal line 111 and the scanning line 112. Also,
The pixel electrode 107 is connected to the drain (D) of the thin film transistor 102. A counter electrode 108 is formed on the other substrate.

In such a conventional liquid crystal display device, the liquid crystal 10 provided between the pixel electrode 107 and the counter electrode 108 via the signal line 111 and the switching element 102.
A display signal is applied to 6 for display.

Specifically, the pixel electrode 107 and the counter electrode 1
08, a display signal voltage (display signal voltage) is applied to change the alignment state of the liquid crystal 106, and the amount of light transmitted through the liquid crystal 106 is controlled to perform display. . A storage capacitor 105 is also provided between the pixel electrode 107 and the counter electrode 108.

In addition to the thin film transistor (TFT) 102, a non-linear element such as a diode is used as the switching element. Above all, a polysilicon T that can be integrally formed with a driving circuit of a liquid crystal display device and has a high response speed.
FT is commonly used.

However, in the active matrix type liquid crystal display device as described above, when the TFT 102 is irradiated with light, the depletion layer portion of the pn junction (pn diffusion junction) thereof is
A pair of electrons and holes is generated, and a current (light leak current) flows between the source (S) and the drain (D).

Therefore, even when the TFT 102 is turned off, a light leak current is generated, causing crosstalk and contrast reduction. Further, when the amount of light leakage current in each TFT 102 varies due to the difference in the diffusion state of each TFT 102, problems such as uneven display on the liquid crystal display and deterioration of display quality occur.

As a technique for solving this problem, there is, for example, JP-A-58-171860.
The technique of this publication reduces the source-drain voltage applied to the switching element by connecting the switching elements in the liquid crystal display device in series, and reduces the light leakage current by the amount of the reduction in the source-drain voltage. There is.

In this technique, however, the diffusion length (length of the diffusion junction) is longer than the length of the depletion layer, and the area of the diffusion junction is
When the length is constant (that is, when the diffusion length is constant regardless of the source-drain voltage), the photoleakage current does not depend on the source-drain voltage. Therefore, there is a problem that it becomes difficult to reduce the light leak current.

For example, as shown in the relationship diagram between the source-drain voltage of the TFT and the generated light leakage current in FIG. 5, the light leakage current gradually increases until the source-drain voltage reaches about 0.4V. Although increasing, when the source-drain voltage is 0.4 or more, the photoleakage current is almost saturated, and the photoleakage current does not depend on the source-drain voltage. That is, the light leak current is constant regardless of the bias condition for the source-drain voltage.

Therefore, as a technique for reducing (reducing) the light leak current even when the light leak current does not depend on the source-drain voltage, see, for example, Japanese Patent Laid-Open No. 10-2.
21675 publication is mentioned.

This technique discriminates a moving image or a still image on the display screen of a liquid crystal display device, and in the still screen state, the switching element is always turned off, and the potential (voltage) of the signal line at that time is set to a pixel. The potential of the signal line is inverted (reverse driving), that is, the potential of the signal line is set to the opposite polarity (negative polarity / positive polarity) to the positive polarity / negative polarity of the pixel electrode. As a result, a current reverse to the generated light leakage current (reverse light leakage current) can be passed. Therefore, the light leak current can be invalidated (cancelled), so that the potential fluctuation of the pixel electrode hardly occurs.

Further, in the technique of Japanese Patent Laid-Open No. 2000-180899, as shown in FIG. 6, in a liquid crystal display device having a layered structure, a channel portion 202 located below a gate electrode 201 of a switching element (TFT) is The upper light shielding layer 203 and the tapered lower light shielding layer 204 are sandwiched between them. Therefore, the light irradiation amount to the channel portion 202 can be reduced, and the light leak current generated in the switching element can be reduced.

[0016]

However, JP-A-10-
In the technology of Japanese Patent No. 2216675, for example, when only a part of the personal computer display screen is in a moving image state and most of the other screen (pixel) states are still images, the effect of canceling the light leak current is deteriorated. . for that reason,
There is a problem that it is difficult to suppress deterioration of quality such as display unevenness in a certain display screen area.

For example, FIG. 7 shows an example of Japanese Unexamined Patent Publication No. 10-22167.
In the liquid crystal display device using the technique of Japanese Patent Publication No. 5, the applied voltage (liquid crystal applied voltage) to the liquid crystal when displaying a moving image and the transmittance
It shows a relationship with display unevenness. In this figure, the above relationship is obtained in a normally white mode liquid crystal display device.

For example, in a certain pixel, a switching element writes positive polarity (+ polarity) display data to a pixel electrode (pixel). Then, due to the inversion driving, the negative polarity (-polarity) data (-polarity data) is present in the signal line for a certain period T (for example, in the case of the inversion driving of one horizontal line, about 1/2 frame period). It has become.

Then, a light leak current flows through the switching element for a certain period of time to the pixel electrode having the potential of the initial writing state (the potential of the initial pixel electrode), and the potential of the pixel electrode is on the negative polarity side (white). Level side).

The change amount ΔVlc of the voltage of the pixel electrode (pixel voltage) at this time is the pixel capacitance Clc (liquid crystal + auxiliary capacitance).
And the light leak current I, ΔVlc = (I × T) / Clc (equation).

Further, when the display data of the signal line is returned to the positive polarity, the variation amount ΔVlc of the pixel voltage becomes the difference voltage across the TFT.

However, since the difference voltage is very small, only the change due to the-polarity data is added as a result.

Here, based on the measurement example of the light leakage current shown in FIG. 5 [the light leakage current is about 3 pA when the source-drain voltage is 2 V, the pixel capacitance Clc (liquid crystal + auxiliary capacitance)]
Is 50 fF and the frame period is 60 Hz (wavelength: about 16 m
s), the liquid crystal applied voltage (difference between the pixel electrode and the counter electrode) ±
In the case of full-screen display of 1V, a voltage (pixel voltage) + 1V is applied to a certain pixel electrode, and the influence of the light leak current I is ΔVl.
Calculating c from the above equation, the decrease ΔVlc (−) of the inversion drive voltage (−1V) in one frame period
Is as follows.

ΔVlc (−) = ((3 [pA] × 16 [ms]) / 50 [fF]) / 2 = 480 [mV] ... (Formula) Further, the liquid crystal applied voltage is + 1V, which is the same as the pixel voltage. When,
A light leak current is generated in a direction to alleviate the decrease ΔVlc (−). However, as can be seen from the measurement example of the light leak current shown in FIG. 5 (see bright (maximum)), the light leak current is in the linear region (the region where the light leak current is saturated) and is obtained by the formula. The average light leakage current between 480 mV and 0 mV is about 1.5 pA.

The relaxation amount ΔVlc (+) is as follows.

ΔVlc (+) = ((1.5 [pA] × 16 [ms]) / 50 [fF]) / 2 = 240 mV (Equation) As a result, reduction and relaxation due to light leakage current during reverse driving The total effect of both trends and is calculated from the difference and is as follows. ΔVlc = ΔVlc (+) − ΔVlc (−) = 240 [mV] −480 [mV] = − 240 [mV] In other words, when the liquid crystal applied voltage is 1V, the change amount ΔVlc (−240mV) is 1V above when it occurs
The transmittance of 88% (point A) at that time changes to 94% (point B) after one frame period, which causes a problem of deterioration of display quality.

Even when the negative polarity display data is written to the pixel electrode, the change in the pixel voltage shows the same change except that the polarity is reversed. Further, in the normally white mode display device, it changes to the white side (liquid crystal applied voltage “0V” side), similarly to the normally black mode display device, to the black side (liquid crystal applied voltage “0V” side). Change. That is, in both cases, the applied voltage to the pixel shows a change to the 0V side.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 2000-180899, even if the amount of light applied to the TFT in the liquid crystal display device is reduced, the light passing through the portion where the light shielding film is not formed is not reflected in the liquid crystal display device. The TFT is reflected by an externally formed part (for example, a lens, a polarizing plate, a mirror, etc. in the projection) or an inner wall of the liquid crystal display device,
May come back to your side. Particularly when used in a transmission type projection display device, very strong light is applied to the liquid crystal panel surface in order to enlarge and project an image using a small liquid crystal panel. Therefore, the amount of light (reflected light) returning from the TFT side is large in addition to the amount of direct incident light.
There is a problem that a light leak current of T is generated, which adversely affects the deterioration of display quality.

The present invention has been made to solve the above conventional problems. And the purpose is
An object of the present invention is to provide a liquid crystal display device and a method for driving the liquid crystal display device, in which the display quality is prevented from being degraded by a light leak current.

[0030]

In order to solve the above-mentioned problems, the liquid crystal display device of the present invention has signal lines for transmitting display signals, scanning lines for transmitting scanning signals, arranged in a matrix. A pixel electrode; a first transistor having a source connected to the signal line and a gate connected to the scanning line;
A source is provided to the drain of the transistor, a gate is connected to the scanning line, and a second transistor having a drain connected to the pixel electrode is provided, and a display signal is applied to the pixel electrode when the first and second transistors are turned on by the scanning signal. A liquid crystal display device for supplying, correction signal generating means for generating a correction signal for generating a light leak current having a positive / negative polarity inversion with respect to a light leak current generated between the signal line and the pixel electrode, A correction signal supply means is provided for supplying the correction signal to a connection point between the first transistor and the second transistor when the display signal is not supplied to the pixel electrode by the first and second transistors. It is characterized by being.

In order to solve the above problems, the driving method of the liquid crystal display device according to the present invention includes a signal line for transmitting a display signal, a scanning line for transmitting a scanning signal, and pixels arranged in a matrix. An electrode, a first transistor having a source connected to the signal line, and a gate connected to the scanning line;
A source is provided to the drain of the transistor, a gate is connected to the scanning line, and a second transistor having a drain connected to the pixel electrode is provided, and a display signal is applied to the pixel electrode when the first and second transistors are turned on by the scanning signal. A method of driving a liquid crystal display device to be supplied, wherein, with respect to a light leak current generated between the signal line and the pixel electrode,
When a display signal is generated by the first and second transistors and a display signal is not supplied to the pixel electrode, the correction signal is generated by generating a correction signal that causes a positive and negative polarity inversion of the light leakage current. It is characterized in that it is supplied to a connection point with two transistors.

Usually, scanning lines and signal lines are wired in an active matrix type liquid crystal display device. Then, in response to the application (supply) of the ON voltage of the scanning signal transmitted through the scanning line (in accordance with the ON timing of the scanning signal),
A switching element such as a transistor for supplying a display signal transmitted through the signal line to the pixel electrode is provided. Then, after the display signal is supplied to the pixel electrode, the display signal is stored in the liquid crystal / storage capacitor through the pixel electrode.

In the above structure, two consecutive (two consecutive) first and second transistors are provided for the pixel electrode. Then, the generated correction signal is supplied to the connection point of these two transistors.

Further, in the liquid crystal display device of the present invention, the correction signal is generated by the correction signal generating means and supplied to the connection point by the correction signal supplying means.

Therefore, when the display signal is not supplied to the pixel electrode (when not writing), that is, after the display signal is stored in the liquid crystal / storage capacitor through the pixel electrode, for example, the pixel electrode and the signal line. A correction signal for generating a light leakage current (reversed light leakage current) that inverts the positive / negative polarity with respect to the light leakage current generated between and is supplied to the connection point.

As a result, the source of the second transistor
It is possible to generate the above-described light leakage current (inversion light leakage current) in which the positive and negative polarities are inverted between the drains.

As a result, the above-mentioned photoleakage current is switched to the inversion photoleakage current, and the photoleakage current is reduced on average due to the reversal of the positive and negative polarities. Therefore, it is possible to prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current.

Further, unlike the prior art, it is possible to prevent the deterioration of the display quality of the liquid crystal display device due to the light leak current without providing a light shielding film or the like for blocking the light incident on the transistor inside the liquid crystal display device. .

Further, in the liquid crystal display device of the present invention, in addition to the above configuration, it is preferable that the correction signal is a signal whose polarity is inverted at the same period as the display signal or at a period equal to or higher than the frame frequency. .

Further, in the driving method of the liquid crystal display device of the present invention, in addition to the above configuration, the correction signal is a signal whose polarity is inverted at the same period as the display signal or at a period equal to or higher than the frame frequency. It is preferable.

According to the above configuration, for example, when a display signal oscillating at a constant cycle (for example, every horizontal line) is supplied to the signal line, the signal line and the pixel are generated at the constant cycle. Inversion light leakage current can be generated immediately after the generation of light leakage current between the electrodes.

Therefore, for example, the voltage of the liquid crystal / storage capacitor repeats a slight increase / decrease around the initial write voltage, and the voltage fluctuation can be reduced on average. Therefore, it is possible to further prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current.

Further, the fluctuation of the electric potential of the pixel electrode, which is changed by the light leak current, appears to the human eye as a flicker phenomenon when it becomes a certain amount. However, if the correction signal has a cycle of a frame frequency (generally 1/60 seconds) or more, it is possible to suppress not only the pixel potential fluctuation due to the light leak current but also the pixel potential fluctuation due to the correction signal. Therefore, the liquid crystal display device can be driven without the flicker phenomenon being felt by human eyes.

Further, in the liquid crystal display device of the present invention, in addition to the above configuration, the correction signal generating means applies to the pixel electrode rather than the difference between the voltage applied to the pixel electrode and the voltage of the display signal. It is preferable that the voltage value of the correction signal is set so that the difference between the applied voltage and the voltage of the correction signal becomes large.

In addition, in the method for driving a liquid crystal display device according to the present invention, in addition to the above configuration, the voltage applied to the pixel electrode is more than the voltage applied to the pixel electrode and the voltage of the display signal. It is preferable to set the voltage value of the correction signal so that the difference from the voltage of the correction signal becomes large.

For example, when a display signal (black level display signal or white level display signal) for making the display screen of the liquid crystal display device black display or white display is supplied to the pixel electrode, the signal line and the pixel electrode Since the potential difference between the two becomes large, the light leakage current also becomes a large value. In particular, the light leak current in this case is in a saturated state (saturated current value).

According to the above structure, the voltage value of the correction signal is higher than the difference between the voltage applied to the pixel electrode and the voltage of the display signal, and the voltage applied to the pixel electrode and the voltage of the correction signal. Is set to be large. Then, even if the voltage applied to the pixel electrode for white display or black display is applied, the reverse light leakage current (saturated current value) generated by the voltage difference between the voltage applied to the pixel electrode and the voltage of the correction signal. Is decreased on average due to the reversal of positive and negative polarities.

Therefore, the reverse light leakage current can be generated more reliably, and the deterioration of the display quality of the liquid crystal display device can be prevented.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows an equivalent circuit diagram of the liquid crystal display device of the present embodiment (the present liquid crystal display device).

In the present liquid crystal display device, a plurality of signal lines 11
Scanning lines 12, correction signal lines 13, and inverted scanning lines 14 are arranged in a matrix.

Further, the source driver 21 connected to the signal line 11 to generate a display signal and the scanning line 1 described above.
2. A gate driver 22 connected to the reverse scanning line 14 to generate a scanning signal / reverse scanning signal, and a correction signal generating circuit 15 (correction signal generating means) connected to the correction signal line 13 to generate a correction signal. It is provided.

Two switching elements (TFT; Thin) are provided near the intersection of the signal line 11 and the scanning line 12.
Film Transistor) 1 and 2 (first transistor and second transistor) are provided.

In the TFTs 1 and 2, both gates (G) are connected to the scanning line 12, while the drain (D) of the TFT 1 and the source (S) of the TFT 2 are connected.
The source (S) of the TFT1 is connected to the signal line 11, and the drain (D) of the TFT2 is connected to the pixel electrode 7. That is, it can be said that the TFTs 1 and 2 are two TFTs 1 and 2 in which the source (S) is connected to the signal line 11 and the drain (D) is connected to the pixel electrode 7.

Further, the drain (D) is connected to the connection point (middle point) with the TFTs 1 and 2, the gate (G) is connected to the inversion scanning line 14, and the source (S) is connected to the correction signal line 13 (the correction signal supply). Means) is provided.

A storage capacitor (auxiliary capacitor) 5 and a liquid crystal 6 are arranged (connected) between the pixel electrode 7 and a counter electrode 8 formed so as to face the pixel electrode 7. There is.

In the present liquid crystal display device, a display signal controlled by the source driver 21 (a display signal forming display data) is supplied to the signal line 11 as a signal transmission path for liquid crystal display. The display signal is supplied to the pixel electrode 7 via the TFT1 and the TFT2 at the scanning timing by the gate driver 22 (timing at which the ON voltage of the scanning signal is output). Specifically, the display signal is supplied by changing the ON voltage of the scanning signal to the TFT1.T.
It is performed when FT2 is turned on.

Further, the correction signal transmitted through the correction signal line 13 can be supplied to the middle point of TFT1 and TFT2 via the TFT3. The TFT3 is TF
When T1 and TFT2 are turned on, they are turned off, and TFT1
-It can be controlled so that the TFT 2 is turned on when it is off (details will be described later).

The correction signal is based on the potential between the source and drain (both ends) of the TFT 2 with the potential of the pixel electrode 7 as a reference.
For example, the signal has a constant (for example, a cycle of ½ frame frequency or more) positive (+) polarity or negative (−) polarity (+ inversion driving or −inversion driving).

The operation of one pixel portion of the present liquid crystal display device will be described with reference to the timing chart of FIG. First, a description of each signal will be given below. For the members such as the TFTs 1, 2 and 3 in the following description, refer to the equivalent circuit diagram of the present liquid crystal display device shown in FIG.

Scanning signal Vg ... Transmitting scanning line 12 and transmitting 1F
One pulse signal that turns on once every (frame) period.

Display signal Vdata ... A signal (inverted signal) which is transmitted through the signal line 11 and whose voltage is changed (oscillated) every 1H (horizontal line) period based on the display data.

Inverted scan signal Vgb ... A signal of one pulse which is transmitted through the inverted scan line 14 and turned off once for each 1F period. Note that this signal is a signal obtained by inverting the scanning signal Vg generated by the gate driver 22 by the inverter 22a.

Correction signal Vdb: a signal which is transmitted through the correction signal line 13 and whose positive and negative polarities are inverted in a constant cycle (for example, every 1H). That is, the correction signal Vdb is the display signal Vdat.
It is a signal whose polarity is inverted at the same cycle as the cycle a or at a cycle of the frame frequency (generally 60 Hz) or higher.

The adjustment to the positive / negative polarity inversion and the setting of the voltage value are performed by the correction signal generation circuit 15.

Specifically, as shown in the circuit diagram of the correction signal generating circuit shown in FIG. 3, it is used for timing control from a general gate driver which generates a scanning signal (ON signal) of a driving transistor every 1H. Using the clock signal,
Inversion cycle control of the correction signal is performed.

Further, the positive / negative voltage of the correction signal has a voltage range wider than the voltage range applied to the pixel electrode (white display signal voltage (white display voltage) or black display signal voltage (black display voltage)) from the outside. Just supply it.

According to the light leak characteristic shown in FIG. 5, for example, if the voltage range applied to the pixel electrode is wider by ± 0.5 V or more, the light leak current is in the saturation region.

Further, the correction signal Vdb is, for example, after the display signal Vdata is supplied to a certain pixel X, the next pixel Y is displayed.
When the display signal Vdata is supplied to the pixel X, it is supplied to the certain pixel X.

Also, in FIG. 2, the display signal V
Correction signal Vd, which has a polarity opposite to that of data
An example of b is shown. Further, in FIG. 2, the correction signal Vdb
In order to make it easy to understand the relationship between the display signal Vdata and the display signal Vdata, the display signal Vdata is indicated by a dotted line and the correction signal Vd
It is displayed on top of b. However, where the solid line of the correction signal Vdb and the dotted line of the display signal Vdata overlap and are difficult to see, the phase of the display signal Vdata indicated by the dotted line is shifted.

It should be noted that Vlc1 is a voltage change of the storage capacitor 5 and the liquid crystal 6 connected to the pixel electrode 7 in the present liquid crystal display device, and Vlc2 is a voltage change of the storage capacitor 105 and the liquid crystal 106 of the conventional configuration. .

First, the ON voltage of the scanning signal Vg changes to the TFT 2
Of the display signal Vdata which changes every 1H at the timing (Vg timing) applied to the gate (G) of
It is once supplied to the source (S) of the TFT 2 via T1 (on once).

Then, the display signal Vdata is supplied to the pixel electrode 7. Then, the stored data is stored in the storage capacitor 5 and the liquid crystal 6 sandwiched between the pixel electrode 7 and the counter electrode 8, and the display data is displayed on the liquid crystal 6.

On the other hand, the off voltage of the scanning signal Vg is applied to the gate (G) of the TFT2, and the display signal Vdata is not supplied to the pixel electrode 7 via the TFT2.

Further, writing of display data to the pixel electrode 7 through the TFT 2 (supply of display signal Vdata)
The OFF voltage of the inversion scanning signal Vgb is applied to the gate (G) of the TFT 3 only when the above is performed, and the TFT 3 is once turned off.

However, after the writing of the display data to the pixel electrode 7 is completed, the TFT 3 is controlled by the inversion scanning signal Vgb so as to be always turned on until the writing timing of the pixel electrode 7 in the next frame.

That is, the ON voltage of the inverted scanning signal Vgb is applied to the gate (G) of the TFT 3 until the timing of writing the display data to the pixel electrode 7 of the next frame.

Then, while the ON voltage of the reverse scanning signal Vgb is applied to the gate (G) of the TFT 3, the correction signal Vdb generated by the correction signal generating circuit 15 is generated.
Are supplied to the middle point of TFT1 and TFT2 via TFT3.

As described above, after the display data has been written to the pixel electrode 7, while the display signal Vdata is being supplied to the signal line 11, the display signal V is supplied via the TFT 3.
The correction signal Vdb, which has the polarity opposite to that of the data, is supplied to the midpoint.

Therefore, between the source and drain of the TFT 2, a light leak current (reversed light leak current) in which the positive / negative polarity is inverted with respect to the light leak current generated between the pixel electrode 7 and the signal line 11 is generated. You can

As a result, the above-mentioned photoleakage current is switched to the inversion photoleakage current, and the photoleakage current decreases on average due to the inversion of positive and negative polarities. Therefore, it is possible to prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current.

Further, unlike the prior art, the liquid crystal display device is not provided with a light shielding film or the like for blocking the incident light to the TFT (switching element), and the display quality of the liquid crystal display device is deteriorated due to the light leak current. Can be prevented.

The correction signal Vdb generated so as to invert (oscillate) the polarity is the same as when the display signal Vdata is not written in the pixel electrode 7, that is, the inverted scanning signal Vdb.
When the on-voltage of gb is applied to the gate (G) of the TFT3, the TFT1 · T is periodically (for example, every 1H).
It is supplied to the midpoint of FT2.

Therefore, a light leak current between the signal line 11 and the pixel electrode 7 generated by the display signal Vdata being oscillated at a constant cycle (for example, every 1H) is supplied to the signal line 11. Inversion light leakage current can be generated correspondingly immediately after.

Therefore, as shown in FIG. 2, the voltage (display data) held in the storage capacitor 5 and the liquid crystal 6 connected to the pixel electrode 7 does not decrease as shown in the conventional Vlc2 and is shown in the Vlc1. As described above, a slight increase / decrease is repeated around the initial write voltage. That is, the fluctuation of the voltage described above becomes small on average. Therefore, it is possible to further prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current.

Further, the potential fluctuation of the pixel electrode changed by the light leak current appears as a flicker phenomenon to human eyes when it becomes a certain amount. However, if the correction signal has a cycle of a frame frequency (generally 1/60 seconds) or more, it is possible to suppress not only the pixel potential fluctuation due to the light leak current but also the pixel potential fluctuation due to the correction signal. That is, the liquid crystal display device can be driven without the flicker phenomenon being felt by human eyes.

Further, for example, when the display screen is black display or white display (the potential of the pixel electrode 7 is a black level potential or a white level potential), the voltage of the correction signal Vdb is larger than the voltage of the display signal Vdata. A value (large amplitude) is preferable.

That is, since the difference between the potential of the pixel electrode 7 (pixel electrode potential) and the potential of the correction signal Vdb (potential difference) becomes larger than the difference between the pixel electrode potential and the potential of the display signal Vdata, light leakage occurs. A light leakage current (reversed light leakage current) that inverts the positive / negative polarity with respect to the current is generated.

Even when the display signal Vdata (black level display signal or white level display signal) for making the display screen black display or white display is supplied to the pixel electrode 7,
Inversion light leakage current (saturated current value) is generated due to the difference voltage between the voltage applied to the pixel electrode 7 and the voltage of the correction signal Vdb.

Therefore, for example, when the amplitude of the correction signal Vdb is made larger than the amplitude of the display signal Vdata transmitted through the signal line 11 which is the range of the voltage applied to the pixel electrode 7, the pixel electrode of the black level potential or the white level potential. The inversion light leakage current between No. 7 and the correction signal line 13, that is, the inversion light leakage current having a saturated current value, decreases on average due to the inversion of positive and negative polarities.

That is, the voltage value of the correction signal Vdb (for example, the positive polarity value and the negative polarity value) is a value (voltage value) that can bring the inverted light leakage current generated in the TFT 2 into a saturated state (saturated current value). Has become.

Therefore, the reverse light leakage current can be generated more reliably, and the deterioration of the display quality of the liquid crystal display device can be prevented.

Note that FIG. 5 may be referred to as an example showing the relationship between the light leak current having the saturated current value and the voltage difference (potential difference).

Further, the display change of the liquid crystal display device due to the voltage change of the pixel electrode 7 often appears remarkably in the display at the halftone level due to the visual characteristics. That is, in the display of an extreme white level or black level, for example, it may be difficult for the display quality to be affected by display unevenness.

Therefore, if the switching to the inversion light leakage current using the correction signal Vdb is performed when the display of the liquid crystal display device represents the halftone level, the display quality of the liquid crystal display device is most effectively obtained. Can be prevented.

In the display of such a halftone level,
When the correction signal Vdb is supplied, the amplitude of the correction signal Vdb may be smaller than the amplitude of the correction signal Vdb supplied in the above black level or white level display.

This is because the electric potential of the pixel electrode 7 is an electric potential of a halftone level, which is smaller than the amplitude voltage at the black level or the white level, and it is possible to sufficiently prevent the deterioration of the display quality.

In the present embodiment, the TFT, which is a switching element, may have a leak current (dark leak current) due to heat or an electric field.

However, the dark leakage current (dark current) can reduce the influence of the potential fluctuation due to the LDD (Lightly Doped Drain) structure of the liquid crystal display device.

The effect of this embodiment is that the pixel electrode 7
It can be said that the apparent average voltage of the pixel electrodes 7 becomes constant irrespective of the inversion driving of the liquid crystal by repeating a slight increase / decrease around the initial write voltage to.

In addition, the display signal Vda of white or black level
When ta is transmitted to the signal line 11, the correction signal line 1
The correction signal Vdb transmitting 3 can also be expressed as a white or black level correction signal Vdb.

Further, the black display voltage can be expressed as a Hi side voltage and the white display voltage can be expressed as a Lo side voltage.

Further, the fluctuation of the potential of the pixel electrode, which is changed by the light leak current, appears as a flicker phenomenon to the human eye when it becomes large to some extent. However, it can be said that the pixel potential fluctuation due to the correction signal (light leak current) can be suppressed if the correction signal has a cycle of a frame frequency (generally 1/60 seconds) or more.

The liquid crystal display device of this embodiment can also be expressed as follows.

In the liquid crystal display device, the signal lines / scanning lines arranged in a matrix, the correction signal lines, the inversion scanning lines for transmitting the inversion signal of the scanning lines, and the intersections of the signal lines / scanning lines are arranged. Both gates are scanning lines, one source is signal line,
The other drain is disposed at the intersection of the two switching elements connected to the pixel electrode and the correction signal line / inversion scanning line, the gate is the inversion scanning line, and the one source is the correction signal line,
A switching element having the other drain connected to the midpoint of the above two switching elements, a substrate having a drive circuit for controlling various signals of the switching element, and a counter electrode arranged to face the pixel electrode are provided. A liquid crystal display device comprising a substrate having the liquid crystal and a liquid crystal sandwiched between the two substrates, wherein after applying a display signal to a pixel electrode for image display,
It can also be said that it has a means for transmitting a correction signal to the midpoint of the above two switching elements.

Further, in the liquid crystal display device, the control means is provided with a switching element which is always on except when the display data of each pixel is written, and the correction signal which is inverted at a constant cycle is switched in the above two series. It can be said that the voltage can be applied to the midpoint of the device.

Further, in the liquid crystal display device, even when the potential of the pixel electrode is black or white, the light leak current between the midpoint of the two switching elements and the pixel electrode is saturated. Therefore, it can be said that the positive and negative values of the correction signal are set.

[0108]

As described above, in order to solve the above-mentioned problems, the liquid crystal display device of the present invention has a matrix of signal lines for transmitting display signals and scanning lines for transmitting scanning signals. A pixel electrode, a first transistor having a source connected to the signal line and a gate connected to the scanning line, and the first transistor.
A source is provided to the drain of the transistor, a gate is connected to the scanning line, and a second transistor having a drain connected to the pixel electrode is provided, and a display signal is applied to the pixel electrode when the first and second transistors are turned on by the scanning signal. A liquid crystal display device for supplying, correction signal generating means for generating a correction signal for generating a light leak current having a positive / negative polarity inversion with respect to a light leak current generated between the signal line and the pixel electrode, A correction signal supply means is provided for supplying the correction signal to a connection point between the first transistor and the second transistor when the display signal is not supplied to the pixel electrode by the first and second transistors. It is a configured structure.

Further, in order to solve the above-mentioned problems, the driving method of the liquid crystal display device of the present invention, the signal line for transmitting the display signal, the scanning line for transmitting the scanning signal, and the pixels arranged in a matrix form. An electrode, a first transistor having a source connected to the signal line, and a gate connected to the scanning line;
A source is provided to the drain of the transistor, a gate is connected to the scanning line, and a second transistor having a drain connected to the pixel electrode is provided, and a display signal is applied to the pixel electrode when the first and second transistors are turned on by the scanning signal. A method of driving a liquid crystal display device to be supplied, wherein, with respect to a light leak current generated between the signal line and the pixel electrode,
When a display signal is generated by the first and second transistors and a display signal is not supplied to the pixel electrode, the correction signal is generated by generating a correction signal that causes a positive and negative polarity inversion of the light leakage current. It is a configuration in which it is supplied to a connection point with two transistors.

According to this, two continuous (two continuous) first and second transistors are provided for the pixel electrode. Then, the generated correction signal is supplied to the connection point of these two transistors.

In the liquid crystal display device of the present invention, the correction signal is generated by the correction signal generating means and is supplied to the connection point by the correction signal supplying means.

Therefore, when the display signal is not supplied to the pixel electrode (when not writing), that is, after the display signal is stored in the liquid crystal / storage capacity through the pixel electrode, for example, the pixel electrode and the signal line. A correction signal for generating a light leak current (reversed light leak current) in which the positive and negative polarities are inverted with respect to the light leak current generated between and is supplied to the connection point.

Thus, the source of the second transistor
It is possible to generate the above-mentioned inverted light leak current between the drains.

As a result, the above-mentioned photoleakage current is switched to the inversion photoleakage current, and the photoleakage current decreases on average due to the inversion of positive and negative polarities. Therefore, it is possible to prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current.

Further, unlike the conventional case, it is possible to prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current without providing a light shielding film or the like inside the liquid crystal display device for shielding the light incident on the transistor. Has the effect.

Further, in the liquid crystal display device of the present invention, in addition to the above configuration, it is preferable that the correction signal is a signal whose polarity is inverted at the same period as the display signal or at a period equal to or higher than the frame frequency. .

In addition, in the method for driving a liquid crystal display device of the present invention, in addition to the above configuration, the correction signal is a signal whose polarity is inverted at the same period as the display signal or at a period equal to or higher than the frame frequency. It is preferable.

According to this, for example, when a display signal vibrating at a constant cycle (for example, every horizontal line) is supplied to the signal line, the signal line and the pixel electrode are generated at the constant cycle. An inversion light leakage current can be generated immediately after the occurrence of the light leakage current between them.

Therefore, for example, the voltage of the liquid crystal / storage capacity is repeatedly increased and decreased around the initial write voltage, and the voltage fluctuation can be reduced on average. Therefore, it is possible to further prevent the deterioration of the display quality of the liquid crystal display device due to the light leakage current.

Further, the fluctuation of the potential of the pixel electrode, which is changed by the light leak current, appears as a flicker phenomenon to the human eye when it becomes large to some extent. However, if the correction signal has a cycle of a frame frequency (generally 1/60 seconds) or more, it is possible to suppress not only the pixel potential fluctuation due to the light leak current but also the pixel potential fluctuation due to the correction signal. Therefore, the liquid crystal display device can be driven without the flicker phenomenon being felt by human eyes.

Further, in the liquid crystal display device of the present invention, in addition to the above structure, the correction signal generating means applies to the pixel electrode rather than the difference between the voltage applied to the pixel electrode and the voltage of the display signal. It is preferable that the voltage value of the correction signal is set so that the difference between the applied voltage and the voltage of the correction signal becomes large.

In addition, in the method for driving a liquid crystal display device according to the present invention, in addition to the above structure, the voltage applied to the pixel electrode is more than the voltage applied to the pixel electrode and the voltage of the display signal. It is preferable to set the voltage value of the correction signal so that the difference from the voltage of the correction signal becomes large.

For example, even when a display signal (black level display signal or white level display signal) for making the display screen of the liquid crystal display device black display or white display is supplied to the pixel electrode, it is applied to the pixel electrode. The inversion light leak generated by the voltage difference between the voltage and the voltage of the correction signal becomes saturated (saturated current value).

According to this, the voltage value of the correction signal is
The difference between the voltage applied to the pixel electrode and the voltage of the correction signal is set to be larger than the difference between the voltage applied to the pixel electrode and the voltage of the display signal. Then, even if the voltage applied to the pixel electrode for white display or black display is applied, the reverse light leakage current (saturated current value) generated by the voltage difference between the voltage applied to the pixel electrode and the voltage of the correction signal. Is decreased on average due to the reversal of positive and negative polarities.

Therefore, the light leakage current is switched to the inversion light leakage current, and the light leakage current decreases on average due to the inversion of positive and negative polarities.

[Brief description of drawings]

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

FIG. 2 is a timing chart of each signal in the equivalent circuit shown in FIG.

FIG. 3 is a circuit diagram of a correction signal generation circuit shown in FIG.

FIG. 4 is an equivalent circuit diagram of a conventional liquid crystal display device (conventional liquid crystal display device).

FIG. 5 is a diagram showing a relationship between a light leak current and a source-drain voltage of a TFT.

FIG. 6 is a cross-sectional view showing a conventional liquid crystal display device in which a TFT is shielded from light.

FIG. 7 is a diagram showing a relationship between a liquid crystal applied voltage and a transmittance / display unevenness level.

[Explanation of symbols]

1 TFT (first transistor) 2 TFT (second transistor) 3 TFT (correction signal supply means) 5 liquid crystal 6 storage capacity 7 pixel electrode 8 Counter electrode 11 signal line 12 scan lines 13 Correction signal line 14 Reverse scan line 15 Correction signal generation circuit (correction signal generation means) Vdata display signal Vgb inverted scan signal Vg scan signal Vdb correction signal

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 624 G09G 3/20 624B 624Z 3/36 3/36 F term (reference) 2H093 NA16 NA32 NC34 NC40 NC49 NC67 ND05 ND09 ND10 NE05 NH15 5C006 AC11 AC21 AF44 BB16 BC20 BF34 EC11 FA36 5C080 AA10 BB05 DD10 FF11 JJ03 JJ04 JJ05 JJ06

Claims (6)

[Claims] 1. A first line in which a signal line transmitting a display signal, a scanning line transmitting a scanning signal, pixel electrodes arranged in a matrix, a source connected to the signal line, and a gate connected to the scanning line. A transistor and a second transistor having a source connected to the drain of the first transistor, a gate connected to the scan line, and a drain connected to the pixel electrode are provided, and when the first and second transistors are turned on by a scan signal. In a liquid crystal display device that supplies a display signal to a pixel electrode, a correction signal that generates a correction signal that generates a light leakage current that inverts the positive / negative polarity with respect to the light leakage current that occurs between the signal line and the pixel electrode. When the display signal is not supplied to the pixel electrode by the generating means and the first and second transistors, the correction signal is supplied to the first transistor. The liquid crystal display device characterized by static and the correction signal supply means for supplying to the connection point of the second transistor is provided. 2. The liquid crystal display device according to claim 1, wherein the correction signal is a signal whose polarity is inverted at the same period as the display signal or at a period equal to or higher than the frame frequency. 3. The correction signal generating means has a difference between a voltage applied to the pixel electrode and a voltage of the correction signal larger than a difference between a voltage applied to the pixel electrode and a voltage of the display signal. The liquid crystal display device according to claim 1, wherein the voltage value of the correction signal is set as described above. 4. A first line in which a signal line for transmitting a display signal, a scanning line for transmitting a scanning signal, pixel electrodes arranged in a matrix, a source for the signal line and a gate for the scanning line are connected. A transistor and a second transistor having a source connected to the drain of the first transistor, a gate connected to the scan line, and a drain connected to the pixel electrode are provided, and when the first and second transistors are turned on by a scan signal. In a method of driving a liquid crystal display device that supplies a display signal to a pixel electrode, a correction signal that generates a light leak current that inverts the positive / negative polarity with respect to the light leak current that occurs between the signal line and the pixel electrode is generated. However, when the display signal is not supplied to the pixel electrode by the first and second transistors, the correction signal is supplied to the first transistor and the first transistor. The driving method of a liquid crystal display device and supplying to the connection point between the transistors. 5. The method of driving a liquid crystal display device according to claim 4, wherein the correction signal is a signal whose polarity is inverted at the same period as the display signal or at a period equal to or higher than the frame frequency. 6. The correction signal is adjusted so that the difference between the voltage applied to the pixel electrode and the voltage of the correction signal is greater than the difference between the voltage applied to the pixel electrode and the voltage of the display signal. The method for driving a liquid crystal display device according to claim 4, wherein a voltage value is set.