JP2000305063A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide a liquid crystal display device which prevents the occurrence of left and right unevenness depending on the display screen in a large screen, high definition liquid crystal display device. Kind Code: A1 A voltage level of a common voltage applied to a lead line of a left and right common electrode is changed in accordance with the frequency of display unevenness, and more specifically, a level generated when the gate shifts from an on state to an off state. The shift voltage is changed according to the difference between the left and right, the wiring distribution of the common electrode that differs between the left and right, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TFT liquid crystal display and, more particularly, to provide a TFT liquid crystal display with good display quality by reducing the occurrence of display unevenness that differs between left and right.

[0002]

2. Description of the Related Art A conventional liquid crystal display has a structure in which a TF having a pixel including a TFT, a pixel electrode, a liquid crystal, and a color filter is provided at an intersection of electrodes arranged in a matrix.
Color display is performed by applying a gradation voltage corresponding to display data to the T liquid crystal panel. As such a liquid crystal display device, for example, as described in Japanese Patent Application Laid-Open No. 3-71453, a method is used in which the value of the common electrode voltage is converted into an alternating voltage every horizontal scanning period.

[0003]

In the prior art, when a specific pattern is displayed, there is a problem that the display quality is different between the right and left sides of the screen. Hereinafter, this problem will be described in detail with reference to FIGS.

FIG. 13 is a diagram showing an applied voltage waveform in a TFT liquid crystal display panel having M rows and N columns. The lower diagram shows a pixel p located at the second row and first column shown in FIG.
(2,1) and pixel p (2, N) located in the second row and the Nth column
3 is an enlarged view of an applied voltage according to FIG.

FIG. 14 is an image diagram showing deterioration of display quality.

The problem to be solved by the present invention will be described in detail with reference to the above drawings.

In a liquid crystal display panel comprising M × N pixels, gate lines and drain lines intersect in a matrix.
A TFT is arranged at each intersection, and a gate electrode and a drain electrode of the TFT are connected to a corresponding gate line and drain line, respectively. The source electrode of the TFT faces the common electrode via the liquid crystal layer. Here, in each wiring, for example, C
An r alloy, an Al alloy, or the like is employed. However, even when any material is used, it is needless to say that the wiring has resistance and a parasitic capacitance is applied to each wiring during the manufacturing process.

In FIG. 5, the gate line is connected to the gate electrode driving circuit on the right side of the panel, and the drain line is connected to the drain electrode driving circuit on the upper side of the panel.
Therefore, the lead wire of the common electrode is p
And two places from the right. Therefore, the wiring resistance of the common electrode in the panel as viewed from the lead line will look different, and the waveform with respect to the voltage fluctuation will be different depending on the arrangement.

Further, when driving a TFT liquid crystal display panel, when the gate is turned off, a level shift voltage is generated by a dive current to the capacitance Cgs parasitic between the gate and the source of the TFT, and the potential of the source electrode is ΔVs before and after the gate is turned off. Will change. This value can theoretically be approximated by the following equation, assuming that no charge flows from the drain electrode to the source electrode when the gate of the TFT is turned off.

[0010]

ΔVs = (Vgon−Vgoff) × Cgs /
(Clcd + Cadd + Cgs) However, the charge actually flows during the transition from the gate ON to the OFF.

Since the amount of inflow depends on the transition time from gate on to off, the transition time on the left side of the screen is short in the driving waveform of the TFT liquid crystal display panel shown in FIG. On the right side, the charge inflow increases because of the length. Therefore, as shown in FIG.
ΔVs at p (2,1) is higher than ΔVs at pixel p (2, N).

As a result, the voltage value held in the liquid crystal layer differs between the left and right sides of the TFT liquid crystal panel.

As a result, for example, as shown in FIG. 13, a white display in which the current value with respect to the common electrode is maximum is displayed in the display area at the center of the screen, and a liquid crystal display is displayed in the other background area. In the case where halftone display, which is the steepest region in the applied voltage-luminance characteristic, is performed, for example, as shown in FIG. 7A, a good display without smear is obtained on the right side of the screen as shown in FIG. Even in such a case, display quality may deteriorate on the left side of the screen due to occurrence of smear.

If a good display without smears is realized on the left side to correct this, there is a problem that smears occur on the right side as shown in FIG. 7 (2).
This result is particularly prominent when the screen is large and high definition. In addition, the charge component jumping into the common electrode via the source electrode due to the voltage fluctuation of the drain line also depends on the load component of the common electrode, and this point is also considered to be a cause of display unevenness.

[0015]

According to the present invention, in order to solve the above-mentioned problems, in the present invention, a voltage is applied to the common electrode from the right-hand lead line, that is, from the gate substrate side and the drain substrate on the gate substrate side. It is characterized in that the common waveform and the common line applied from the left lead line, that is, the common waveform applied from the drain substrate side opposite to the gate substrate are different.

In order to realize the above, the liquid crystal display device of the present invention comprises a common voltage generating circuit for generating a voltage to be applied to the right lead line and a common voltage generating circuit for generating a voltage to be applied to the left lead line. Have.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a diagram showing the configuration of a liquid crystal display device according to the present invention. Reference numeral 101 denotes a TF constituted by pixels in M rows and N columns.
A T liquid crystal display panel 102 has N drain lead lines connected to the drain electrodes of the TFTs arranged in each column inside, and 103-1 to 103-m reference the TFT gate electrodes arranged in each row. M connected gate lead lines 104-1 to 104-p, 105-1 and 105-2 are common electrode lead lines.

Reference numeral 106 denotes a control circuit, 107 denotes an inverted signal, 108 denotes a drain drive circuit control signal, and 109 denotes a gate drive circuit control signal.
Generates and outputs these signals. 110 is a power supply circuit,
111 is a gradation reference voltage, 112 is a gate reference voltage, 1
13 is a common reference voltage.

The power supply circuit 110 generates these voltages by boosting and converting supply voltages from an external system (not shown). Reference numeral 114 denotes a gradation voltage generation circuit;
Is a gray scale voltage, and the gray scale voltage generation circuit 114 generates a gray scale voltage 115 based on the gray scale reference power supply 111 and the inverted signal 107.
Generate

Reference numeral 116 denotes a common voltage generation circuit, 117 denotes a common voltage generated by the common voltage generation circuit 116, and the common voltage generation circuit 116
And a common voltage 117 based on the common reference voltage 113.
Generate Reference numeral 118 denotes a common voltage correction circuit which corrects the voltage value of the common voltage 117 and
Output as

Reference numeral 120 denotes a selection circuit, 121 denotes a gate electrode driving circuit side common voltage, 122 denotes a gate driving circuit reverse side common voltage. The selection circuit 120 generates a common voltage 117 and a corrected common voltage 119 according to the polarity of the inverted signal 107. And outputs the same as the gate electrode drive circuit side common voltage 121 and the gate drive circuit reverse side common voltage 122.

Here, the gate driving circuit reverse common voltage 1
The voltage line 22 is connected to the common electrode lead line 105-2 on the opposite side of the gate lead line, and the gate electrode drive circuit side common voltage 121 is connected to common electrode lead lines other than 105-2.

Reference numeral 123 denotes a drain electrode driving circuit which generates a drain voltage based on the drain electrode driving circuit control signal 108 and the gradation voltage 115 and
02 is applied with a voltage. Reference numerals 124-1 to 124-m denote gate electrode drive circuits, and a gate electrode drive circuit control signal 1
09, a gate drive voltage is generated based on the gate reference voltage 112, and a voltage is applied to the gate lead lines 103-1 to 103-m.

FIG. 2 is a diagram showing a configuration of the common voltage generation circuit 116. VDD, VEE, Vref and VR in the figure
Is the common reference voltage 1 generated in the power supply circuit 110
13, M is an inverted signal 107, and Vcom is a common voltage 1 generated by a common voltage generation circuit 116.
Seventeen. 201 and 202 are inverting amplifier circuits, 203 is a current amplifier circuit composed of complementary transistors, R1 to R6 and Rb are resistors, and Cb is a capacitor.

FIG. 3 is a diagram showing the configuration of the common voltage correction circuit 118. Vcom 'indicates a corrected common voltage 119. Reference numeral 301 denotes a current amplifier circuit using complementary transistors, and Rd and Cd denote resistors and capacitors, respectively.

FIG. 4 is a diagram showing the difference between the common voltage waveforms.
, Vcom 'which is an output voltage of the common voltage generation circuit 116, and Vcom' which is an output of the common voltage correction circuit 118.

FIG. 5 is a diagram showing a voltage waveform applied to the TFT liquid crystal front panel 101. The pixel p (2,1) shown in FIG.
And a voltage value applied to the pixel p (2, N).

In the figure, Vd (1) and Vd (N) are pixels p (2,1), p (2,
N) Drain voltage applied to the drain electrode, Vg (1), V
g (N) is a gate voltage applied to the gate electrodes of the pixels p (2,1) and p (2, N), respectively.

FIG. 6 is an enlarged view of the voltage change during the period when the gate voltage is turned off in the applied voltage waveform shown in FIG. 5. For comparison, the pixel p (2,1) and the pixel
The voltage value applied to p (2, N) is also shown. here
Vs (2,1) and Vs (2, N) are voltage values held at the source electrodes of the TFTs located at pixel p (2,1) and pixel p (2, N), respectively. Also V
l (2,1) is the liquid crystal applied voltage held at pixel p (2,1), Vl (2,1)
N) is a voltage applied to the liquid crystal held in the pixel p (2, N), and the amount of light transmitted through the liquid crystal changes according to each voltage, thereby realizing gradation display.

The operation of the first embodiment will be described in detail with reference to the drawings.

In FIG. 1, an inversion signal 107, a drain drive circuit control signal 108, and a gate drive circuit control signal 109 are generated for a control circuit 106 based on a control signal group input through an external system (not shown). .

Here, the inversion signal 107 is a signal for determining the AC period of the voltage applied to the liquid crystal panel.
Here, it is assumed that the polarity changes every horizontal scanning period. Drain drive circuit control signal 108
Is composed of display data, a transfer signal, and a latch signal. The display data is a signal for determining the gradation level of each pixel, and is usually composed of 6 to 8 bits per pixel.

The transfer signal is transmitted to the drain electrode driving circuit 1 sequentially.
23 is a signal indicating the transfer timing of the display data input to 23. The transferred display data is subjected to selection of a corresponding voltage value from the gradation voltage 115 in the drain electrode drive circuit 123. When the transfer of the display data to all the columns of the drain lead line 102 is completed, the voltage value according to the display data is selected from the gradation voltages at the timing based on the latch signal, and the selected voltage value is set to the drain lead line 102. Is output to

The gate electrode drive circuit control signal 109 comprises a frame signal and a selection signal.
4-1 to 124-m scan by applying a gate-on voltage to the gate lines sequentially from the first row when the selection signal is input, and apply a gate-off voltage to the other gate lines. . Here, the gate-off voltage is a voltage having the same polarity as the common voltage as shown in FIG. When the scanning of all the rows is completed, the scanning is started again from the first row by applying the frame signal. The potentials applied to the pixel p (2,1) and the pixel p (2, N) by the above operation are the drain voltage Vd (1), the gate voltage Vg (1), and the drain voltage Vd (N), if the display data is equal. Vg (N) has a waveform as shown in FIG. The above operation is described in detail in the conventional example.

Next, the operation of generating the common voltage will be described. The common voltage generating circuit 116 couples the inverting amplifier circuits 201 and 202 as shown in FIG.
By appropriately setting the resistance value of the common voltage Vc
om. The current amplification circuit 203 is a circuit for supplying a sufficient current to the liquid crystal display panel.

In FIG. 2, when attention is paid to the second-stage inverting amplifier circuit 202, there are load components Rd and Cd in a feedback loop via R6 and R5. Therefore, when an input change occurs, a part of the current relating to feedback flows into Cd via Rd, and thus a phase delay occurs in the feedback component.

Since the inverting amplifier circuit 202 acts to cancel the phase delay, the resulting common voltage Vco
As shown in FIG. 4, m once changes to a high potential, and approaches the common voltage waveform without Rd and Cd as Cd is charged, as compared with the case without Rd and Cd. Become.

On the other hand, the common voltage correction circuit 118
Is as shown in FIG. Since the current amplifier circuit 301 is a circuit having low input and high output impedance, even if the output voltage Vcom ′ of the common voltage circuit correction circuit 118 changes, it does not affect the input voltage Vcom. A load component consisting of Rd and Cd is coupled to the output of the current amplification circuit 301. Therefore, as shown in FIG. 4, Vcom 'has a phase delay with respect to Vcom.

The common voltage 1 generated as described above
17. The selection circuit 120 selects whether to output the correction common voltage 119 to the gate electrode drive circuit side or the opposite side according to the polarity of the inverted signal 107 in the selection circuit 120. In this selection, a common voltage 117 is applied to the gate electrode when a voltage having a positive polarity (here, the positive polarity is a case where the source voltage is higher than the common voltage) is applied to the selected row. The correction common voltage 119 is applied to the circuit side common voltage 121 and the gate drive circuit reverse side common voltage 122
Output to

By using the above configuration, the input of the common voltage to the common electrode lead line on the side having the gate electrode drive circuit and the input of the common voltage to the opposite common electrode lead line in the TFT liquid crystal display panel are different. It becomes possible to close.

The method of generating a common voltage has been described above with reference to the first embodiment. Next, how the voltage applied to the pixel electrode according to this embodiment will be described with reference to FIG. .

As described in connection with the problem to be solved by the invention, in the conventional method, a difference occurs in the source voltage Vs even when the same gray scale display is performed on the left and right due to the occurrence of a delay when the gate is turned off. On the other hand, in the liquid crystal display device of the present embodiment, as shown in FIG.
Is higher in potential than VcomN, and conversely, in the case of negative polarity, VcomN can be higher in potential than Vcom1.

By this operation, even when the value of ΔVs due to the inrush current at the time of gate-off differs between the left and right sides of the liquid crystal display panel, the same difference can be given to the common voltage according to the potential difference.

(Second Embodiment) Hereinafter, a second embodiment will be described with reference to FIGS. It is to be noted that the important part in the present invention is the configuration of the common voltage generation circuit and the method of applying the same. Therefore, the configuration overlapping with the conventional example has the same configuration as the conventional example unless otherwise specified.

FIG. 7 shows a configuration in which a common voltage generating circuit is independently provided, and 701 is a common voltage generating circuit.

FIG. 8 is a diagram showing the configuration of the common voltage generation circuit 801. Reference numerals 801, 802 and 804 denote inverting amplifier circuits, and 803 and 805 denote current amplifier circuits. VcomR is a voltage applied to the common electrode lead line on the side opposite to the gate electrode drive circuit, and VcomL is a voltage applied to the common electrode lead line on the gate electrode drive circuit side.

The operation of the second embodiment will be described with reference to the above drawings.

In the second embodiment, the output voltage values VcomR and VcomL of the common voltage generation circuit 701 shown in FIG.

[0050]

## EQU2 ## Therefore, for example, if the resistance values in FIG. 8 are set as R3 = R6, R4 = R7, and R5 <R8, then VcomR <VcomL holds when VR> Vref.

Therefore, as shown in FIG. 9, the relationship between VcomR and VcomL is such that the amplitude values of the two are equal and the absolute values are different.
Different types of common voltage values can be obtained. The potential difference between the two is a level ΔVs (1) −ΔVs (N) which is a level shift voltage of the drain voltage of the left and right pixel electrodes when the gate is off.
If it is set equal to, the difference between the left and right of the level shift voltage can be absorbed by the difference between the common voltages, and a good image quality without display unevenness can be obtained.

Third Embodiment Next, a third embodiment will be described with reference to FIGS.

FIG. 10 is a diagram showing the configuration of a liquid crystal display device according to the third embodiment, wherein 1001 is a common voltage generation circuit, 1002 is a selection circuit, and 1003 is a common voltage selection signal. As shown in the second embodiment, the common voltage generation circuit 1001 generates two-level voltage values of VcomL and Vcom '. Here, it is assumed that VcomL> Vcom 'holds. The selection circuit 1002 is a common voltage generation circuit 10
01, and selects one of the voltage levels of VcomL and Vcom ′ according to the polarity of the common voltage selection signal 1003.

FIG. 11 is a diagram showing the configuration of the common voltage generation circuit 1001. Reference numerals 1101, 1102 and 1104 denote inverting amplifier circuits, and 1103 and 1105 denote current amplifier circuits. R1 to R6 are resistors, and ZD1 is a Zener diode.

FIG. 12 shows VcomL and Vco in the third embodiment.
FIG. 7 is a diagram showing voltage waveforms of m ′ and VcomR. Vg indicates a gate voltage.

The operation in the third embodiment will be described with reference to the above drawings.

In the third embodiment, a common voltage generation circuit 1001 shown in FIG. 10 generates a two-level common voltage waveform VcomL and Vcom '. As this configuration, in addition to the configuration shown in the second embodiment, the configuration shown in FIG. 12 can be used. A common voltage generation circuit 1001 shown in FIG. 12 generates a common voltage VcomL by using a configuration including two inverting amplifier circuits 1101 and 1102 and a current amplifier circuit 1103. On the other hand, for Vcom ', ZD1 and R6
Vcom ′ is obtained by feeding back a voltage reduced by a certain potential to the non-inverting amplifier circuit 1104 irrespective of the potential of VcomL determined by Vcom ′. So VcomL and Vco
The potential relationship of m 'has a waveform equivalent to the relationship between VcomL and VcomR in the second embodiment.

One of the VcomL and Vcom ′ generated in this way is selected by the selection circuit 1002 based on the polarity of the common voltage selection signal 1003. As shown in FIG. 12, the polarity of the common voltage selection signal 1003 is the inverted signal M that controls the polarity of the voltage level applied to the liquid crystal layer.
based on. Specifically, VcomR = VcomL is set during the rise time of the common voltage, and the polarity of the common voltage selection signal 1003 is changed before the gate is turned off, so that VcomR = Vcom ′.

By using the above configuration, it is possible to set the potential difference between the common voltages VcomR and VcomL equal to the level ΔVs (1) −ΔVs (N) which is the level shift voltage of the drain voltages of the left and right pixel electrodes when the gate is off. In addition, the difference between the left and right of the level shift voltage can be absorbed by the difference between the common voltages, and a good image quality without display unevenness can be obtained.

[0060]

According to the above invention, it is possible to make the value of the common voltage different between the left and right, and it is possible to suppress display unevenness occurring in the left and right directions.

According to the first embodiment, it is possible to use the same amplifier circuit as a source of the common voltage applied to the left and right, thereby providing a low-cost liquid crystal display device. Become.

According to the second embodiment, different generation circuits can always be used as a source of the common voltage applied to the left and right, thereby making it possible to shorten the charging time.

According to the third embodiment, the common voltage values applied to the left and right can be made different only when the gate is off, thereby realizing low power consumption.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a liquid crystal display device of the present invention.

FIG. 2 is a diagram illustrating a configuration of a common voltage generation circuit.

FIG. 3 is a diagram illustrating a configuration of a common voltage correction circuit.

FIG. 4 is a diagram showing a change in a common voltage waveform.

FIG. 5 is a diagram showing an applied voltage waveform.

FIG. 6 is an enlarged view of a voltage applied to a pixel electrode.

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

FIG. 8 is a diagram illustrating a configuration of a common voltage generation circuit.

FIG. 9 is a diagram showing a common voltage waveform in the second embodiment.

FIG. 10 is a diagram illustrating a configuration of a liquid crystal display device according to a third embodiment.

FIG. 11 is a diagram illustrating a configuration of a common voltage generation circuit according to a third embodiment.

FIG. 12 is a diagram showing a common voltage waveform in the third embodiment.

FIG. 13 is a diagram showing the influence of distortion of a gate waveform.

FIG. 14 is a diagram showing an example of display unevenness.

[Explanation of symbols]

101: TFT liquid crystal display panel, 102: drain lead line, 103-1 to 103-m: gate lead line, 1
04-1 to 104-p, 105-1, 105-2 ... common electrode lead wire, 106 ... control circuit, 107
... Inversion signal, 108 ... Drain drive circuit control signal, 10
9: gate drive circuit control signal, 110: power supply circuit, 11
1 ... gradation reference voltage, 112 ... gate reference voltage, 113
... Common reference voltage, 114 ... Grayscale voltage generation circuit, 115
... Grayscale voltage, 116 ... Common voltage generation circuit, 117 ... Common voltage, 118 ... Common voltage correction circuit, 119 ... Correction common voltage, 120 ... Selection circuit, 121 ... Gate electrode drive circuit side common voltage, 122 ... Gate drive circuit Reverse common voltage, 123 ... Drain electrode drive circuit, 124-1 to 124-1
124-m: gate electrode drive circuit, 201, 202: inverted amplifier circuit, 203: current amplifier circuit, 301: corrected common voltage, 701: common voltage generation circuit, 801: inverted amplifier circuit, 802: inverted amplifier circuit, 803 ... Current amplifying circuit, 804 ... inverting amplifying circuit, 805 ... current amplifying circuit, 1
001: common voltage generation circuit, 1002: selection circuit, 1
003: common voltage selection signal, 1101: inverting amplifier circuit, 1102: inverting amplifier circuit, 1103: current amplifier circuit, 1104: inverting amplifier circuit, 1105: current amplifier circuit.

 ──────────────────────────────────────────────────の Continued on front page (72) Inventor Yoshiaki Nakayoshi 3300 Hayano, Mobara-shi, Chiba Hitachi, Ltd.Electronic Device Division (72) Inventor Tsutomu Furuhashi 1099, Ozenji, Aso-ku, Kawasaki-shi, Kanagawa Hitachi, Ltd. Inside the System Development Laboratory (72) Inventor Hiroyuki Nitta 1099 Ozenji Temple, Aso-ku, Kawasaki City, Kanagawa Prefecture Inside Hitachi Systems Development Laboratory (72) Inventor Norio Manba 1099 Ozenji Temple, Aso-ku, Kawasaki City, Kanagawa Prefecture F-term in Hitachi, Ltd. System Development Laboratory (reference) 2H093 NA45 NA51 NB30 NC01 NC18 NC34 NC35 NC37 ND05 5C006 AC25 AC27 BB16 FA22 FA25 FA37 FA47 5C080 AA10 BB05 DD05 DD10 DD26 DD28 EE29 FF07 FF11 JJ02 JJ03 JJ04 JJ04

Claims (5)

[Claims] An active matrix type liquid crystal display panel in which switching elements and liquid crystals are arranged in a matrix in each pixel portion, display data is input, and a gradation voltage corresponding to the input display data is generated. A drain electrode driving circuit for applying the pixel data in the horizontal direction corresponding to the display data and one of the pixel units arranged in the vertical direction are sequentially selected, and a selection voltage is applied to the selected pixel unit. And a gate electrode driving circuit for applying a non-selection voltage to a non-selected pixel portion. In the active matrix type liquid crystal display panel, a common electrode which is one electrode via a liquid crystal layer is provided in at least a row. In a liquid crystal display device having a feature that is common in units, a gate electrode drive is applied to a common electrode of the active matrix type liquid crystal display panel. A liquid crystal display device comprising a common voltage applied from the circuit side, that occupy different value of the common voltage applied to the common electrode of the opposite side with respect to the row direction. The difference between the common voltage applied from the gate electrode drive circuit side and the value of the common voltage applied to the common electrode on the opposite side in the row direction is determined by the drain voltage when the gate voltage shifts from the on voltage to the off voltage. 2. The method according to claim 1, wherein the difference is substantially equal to a level shift voltage generated in the voltage.
The liquid crystal display device according to the above. 3. An active matrix type liquid crystal display panel in which switching elements and liquid crystals are arranged in a matrix in each pixel portion, display data is input, and a gradation voltage is generated according to the input display data. A drain electrode driving circuit for applying the pixel data in the horizontal direction corresponding to the display data and one of the pixel units arranged in the vertical direction are sequentially selected, and a selection voltage is applied to the selected pixel unit. And a gate electrode driving circuit for applying a non-selection voltage to a non-selected pixel portion. In the active matrix type liquid crystal display panel, a common electrode which is one electrode via a liquid crystal layer is provided in at least a row. In a liquid crystal display device having a feature that is common in units, at least 2
A liquid crystal display device having a circuit for generating a common electrode of a level, wherein a voltage value generated in the circuit for generating the common electrode is switched according to the polarity of the voltage level applied to the liquid crystal layer. 4. A liquid crystal display device according to claim 3, wherein one voltage level is applied to all common electrodes of the liquid crystal display panel for a certain period after the polarity is changed, and at least the gate is turned off from the on state. A liquid crystal display device characterized in that before shifting, a common voltage applied to a common electrode on a gate electrode drive circuit side and a common voltage applied to a common electrode on the opposite side are made different. 5. A liquid crystal display device according to claim 4, wherein a switching signal for switching a common voltage applied to said one common electrode and said switching signal are generated.