JP3617896B2 - Liquid crystal display device and driving method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low power consumption liquid crystal display device used in a portable computer or the like.
[0002]
[Prior art]
An example of a liquid crystal display device according to a conventional example is Japanese Patent Publication No. 1-37911. FIG. 11 shows an equivalent circuit diagram of the liquid crystal display device according to the conventional example, which is formed by a plurality of signal lines, scanning lines, and intersections between the signal lines and the scanning lines arranged in a matrix form via switch elements. The pixel electrode has a liquid crystal cell between the pixel electrode and the counter electrode, and an auxiliary capacitor between the pixel electrode and the auxiliary capacitor line. A video signal is supplied to each pixel electrode in a frame cycle via a signal line and a switch element. Since the liquid crystal molecules are polarized with respect to a DC voltage to lower the display quality, the video signal uses an AC signal whose polarity is inverted every frame period.
[0003]
When used as a display device for office automation equipment, most of the time is still image display, for example, in the case of word processing. In the case of a liquid crystal display device, as shown in the conventional example, since the video signal is held in the pixel capacity, in principle, it is not necessary to supply the video signal to the pixel electrode as long as the still image display continues. The scanning of the device can be stopped. Since the power consumption for scanning is about 40% of the power consumption of the entire liquid crystal display device, the power consumption can be greatly reduced by stopping the scanning.
[0004]
However, in practice, scanning cannot be stopped even in the case of still image display. This is because a leak current flows through the switch element and the pixel electrode potential changes with time. For this reason, a driving method is used in which the frame rate is 60 frames / second and the polarity is inverted every frame.
[0005]
On the other hand, Japanese Patent Application Laid-Open No. 58-23091 discloses an example in which a digital memory cell is formed in a pixel electrode and the influence of the pixel potential due to the leakage current of the switch element is eliminated. FIG. 12 shows an equivalent circuit diagram of a pixel portion of the liquid crystal display device according to the conventional example. A digital memory is formed by two inverter elements after the switch element, and data is held at a high or low level. The liquid crystal cell is AC driven by applying an exclusive OR signal of the data value of the digital memory and the Vcom signal to the pixel electrode. For this reason, still image display can be performed without scanning the X and Y drivers. In this way, the conventional example can stop scanning when still images are displayed, and power consumption during still image display is greatly reduced.
[0006]
[Problems to be solved by the invention]
Although the conventional example can stop scanning and reduce power consumption when displaying a still image, there is a problem that only a binary image can be handled as a display image.
Therefore, the present invention solves the problem that only a binary image can be handled as a display image, which is a problem of the conventional example, and stops scanning at the time of display even when halftone display is possible and halftone still image display is performed. An object of the present invention is to provide a high-performance, low power consumption liquid crystal display device.
[0007]
[Means for Solving the Problems]
The above-described problems are caused by crossing a plurality of signal lines and scanning lines wired in a matrix, signal lines and scanning line driving circuits for driving the signal lines and scanning lines, and the signal lines and scanning lines. A first electrode substrate having a pixel electrode formed through a switch element; a second electrode substrate having a counter electrode formed opposite to the pixel electrode; the first electrode substrate and the second electrode substrate; In a liquid crystal display device having a liquid crystal layer sandwiched between electrode substrates, a control means for switching a driving method of the signal line and scanning line driving circuit depending on whether or not a display image changes between image frames. And the control means includes means for holding the scanning line at a potential at which the switch element is turned off and switching the potential of the signal line at a certain period when the display image does not change between the frames. It can be solved by using a liquid crystal display device comprising and.
[0008]
When displaying a still image whose display image does not change between the frames, the potential of the scanning line is held at a low level so that all the switch elements are turned off. In order to compensate for the light leakage current of the switch element, the signal lines of the white level and the black level are alternately supplied to the signal lines at a constant cycle. Therefore, scanning is not performed during still image display.
[0009]
The switching cycle of the signal line potential is 1/60 second or less. Alternatively, the phase of the potential of the signal line that is switched for each predetermined period is reversed between adjacent signal lines. The luminance of each pixel changes with a period of 1/60 seconds or less and the average luminance value becomes substantially constant, or the direction of luminance change of adjacent pixels is reverse and the average value becomes substantially constant.
A thin film transistor is used for the switch element. This is particularly effective when a poly-Si film is used for the active layer of the thin film transistor.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a liquid crystal display device and a driving method according to the present invention will be described below with reference to the drawings. FIG. 1 is an equivalent circuit diagram showing a first configuration of a liquid crystal display device according to the present invention.
[0011]
A plurality of signal lines 20 and scanning lines 21 are arranged in a matrix, and pixel electrodes 23 are formed at intersections of the signal lines 20 and the scanning lines 21 via switch elements 22. A liquid crystal cell 24 is formed by inserting a liquid crystal between the pixel electrode 23 and a counter electrode formed to face the pixel electrode.
[0012]
The signal line 20 is connected to a video bus 27 c via an analog switch 26 controlled by an X driver 25. In the video bus 27c, the digital video signal 27a is converted into an analog signal by the D / A conversion circuit 28, and converted into an AC signal (usually for each frame) for driving the liquid crystal cell 24 by the polarity inversion circuit 29a. A video signal is sent. In FIG. 1, only one video bus 27c is shown for simplicity. However, when color display is performed, video buses corresponding to R, G, and B are separately prepared. The scanning line 21 is connected to a Y driver 30.
[0013]
As the external input, in addition to the digital video signal 27a, a horizontal synchronizing signal 32, a vertical synchronizing signal 33, and an M / S signal 34 are prepared, and a driving method according to whether the display image changes between frames or not changes. Switching is performed by the control circuit 31 inserted in the input stage. The control circuit 31 includes a gate array (G / A). The M / S signal 34 is a control signal for identifying whether the transmitted video signal is a moving image or a still image. For example, in the case of a personal computer, the M / S signal 34 can be generated by detecting whether or not the frame buffer is rewritten. .
[0014]
Next, the operation principle of the liquid crystal display device and the driving method according to the present invention will be described.
For the pixel switch 22 in FIG. 1, a thin film transistor (hereinafter abbreviated as TFT) that can be formed on a glass substrate which is a transparent insulating substrate is used. As the active layer of the TFT, amorphous Si or poly-Si that can be formed by a low-temperature process of 600 ° C. or lower is used. Among them, the mobility of the poly-Si TFT is 100 cm. ² Peripheral drive circuits can be integrally formed on a glass substrate by about 2 to 3 orders of magnitude larger than / Vs and amorphous Si, and are not limited by the mounting pitch of external LSIs. Yes.
[0015]
The leakage current of the poly-Si TFT includes a dark leakage current generated by heat or an electric field and a light leakage current generated during light irradiation. Among these, the influence on the pixel potential fluctuation can be sufficiently reduced by using the hydrogen passivation or the LDD (Lightly Doped Drain) structure for the former. On the other hand, the latter light leakage current can be reduced by inserting a light shielding layer, but there is no appropriate light shielding layer, or a sufficient size is required for the light shielding layer in view of multiple scattering, so that the aperture ratio is However, there are problems such as being unrealistic. For this reason, the leakage current of the switch element is mainly caused by the optical leakage current, and in order to solve the problem, it is necessary to suppress the fluctuation of the pixel electrode potential due to the optical leakage current.
[0016]
FIG. 2 is a cross-sectional view showing the configuration of the pixel switch 22. 90 is a gate, 91 is a source, 92 is a drain, 93 is a depletion layer, 94 is an active layer, and 95 is a region where a diffusion current is generated. The light leakage current is a current caused by photogenerated carriers (minority carriers) generated in the depletion layer 93 at the drain-biased drain junction and at the distance of the diffusion length from the end of the depletion layer 93. In a poly-Si TFT having high mobility, the depletion layer Since the diffusion length is longer than the length 93 and the diffusion length is constant regardless of the drain voltage, the dependence of the light leakage current on the drain voltage is small. For the same reason, there is almost no dependency on the gate voltage. For this reason, the light leakage current can be regarded as almost constant regardless of the bias condition of the TFT. Therefore, if the potential of the TFT constituting the switch element 22 on the signal line 20 side is swung up and down with respect to the potential of the pixel electrode 23 at regular intervals, substantially equal amounts of current flow in opposite directions in each cycle. In other words, the pixel electrode potential after one cycle is equivalent to the pixel electrode potential at the time before one cycle, and the pixel potential does not fluctuate.
[0017]
This operation will be described with reference to FIG. FIG. 3 is an explanatory diagram showing the relationship between the voltage applied to the liquid crystal cell and the transmittance, and shows an example when a twisted nematic cell is operated in a normally white mode.
[0018]
When the switch element 22 is OFF, the pixel potential of the pixel electrode 23 is at point A in the initial state, and if the signal line potential of the signal line 20 is Vb (black level) at that time, the pixel potential is at point B after a certain period T. come. At this time, the potential difference ΔV1 between A and B is expressed as follows, assuming that the pixel capacitance is Cpix and the leakage current is I.
ΔV1 = I * T / Cpix
It becomes. Next, considering the pixel potential after the signal line potential is set to Vw (white level) and held for a certain period T, a current -I in the reverse direction flows during T, so the change amount ΔV2 of the pixel potential during this period is
ΔV2 = −I * T / Cpix
And the final pixel potential fluctuation is
ΔV1 + ΔV2 = 0
It becomes.
[0019]
In the above operation, the pixel potential varies in a 2T cycle. For this reason, if ΔV1 is larger than a certain level, flicker is detected by human eyes. However, even in this case, the frequency of polarity inversion of the signal line potential is increased to 2T <1/60 (sec), or the polarity inversion phase is changed between adjacent pixels as described later, and one pixel is transmitted. When moving in the direction in which the rate increases, the adjacent pixels may move in the direction in which the transmittance decreases, and as a result, the flicker component may be canceled between the adjacent pixels.
[0020]
When the above operation is performed during still image display, the switch element 22 of the pixel portion is always in the OFF state, and it is sufficient that the polarity inversion period of the signal line 20 is about twice the frame frequency or the frame frequency. In this case, the Y driver 30 is kept stationary (the switch element 22 is kept OFF), and the X driver 25 only needs to be scanned once or twice per frame. For this reason, the power consumption of the drive circuit can be reduced by almost three orders of magnitude compared to the normal operation for the Y driver 30 and the AC component for the X driver 25 as compared with the normal operation. For this reason, the power consumption by the drive circuit can be significantly reduced by adopting a configuration in which no current flows during DC operation, such as a CMOS configuration of the drive circuit.
[0021]
The driving method is changed between the case where the display image changes between frames and the case where the display image does not change. When the display image changes, normal scanning is performed. A power consumption liquid crystal display device can be realized.
[0022]
Next, the operation of the liquid crystal driving circuit of FIG. 1 according to this embodiment will be described with reference to the timing charts of FIGS. FIG. 4 is a flowchart showing the overall operation of the liquid crystal driving circuit of FIG. The vertical synchronizing signal 33 (Vsyn) is a signal generated for each pulse, the x driving signal 35 (φx) is generated for one pulse for each pixel, and the y driving signal 38 (φy) is generated for one pulse for each scanning line. is there. A region indicated by hatching in the figure indicates that the signal voltage changes within the hatched portion.
[0023]
In the case of moving image display in which the display image changes between frames, that is, during normal operation, the M / S signal is at a high level and normal scanning is performed. In this case, clock signals 35 and 36 synchronized with the data rate of the video signal and a start signal 37 synchronized with the horizontal synchronizing signal Hsyn are supplied to the X driver, and a clock signal 38 synchronized with the horizontal synchronizing signal 32 is supplied to the Y driver. , 39 and a start signal 40 synchronized with the vertical synchronization signal 33 is supplied from the control circuit 31. At this time, an analog video signal is supplied to the video bus 27c at a data rate (around 30 MHz in the case of VGA). The analog video signal is supplied to the counter electrode potential (Vcom) for each frame by the polarity inversion circuit 29. The polarity is inverted so as to be AC driven.
[0024]
For the signal line 20, a signal obtained by sampling the signal of the video bus 27c by the analog switch 26 once in one horizontal scanning period is supplied, and for the pixel electrode 23, the pixel switch 22 is turned on once in one vertical scanning period. The signal line potential at that time is written and held in the pixel electrode 23.
[0025]
FIG. 5 is a timing chart showing the operation of the X driver 25 during this normal operation. When the x start signal φxST synchronized with the horizontal synchronizing signal Hsyn becomes high level, the x drive signals φx1, φx2,..., Φxn sequentially become high level for one pixel clock period in synchronization with the pixel clock φx. While the x drive signals φx1, φx2,..., φxn are at a high level, the analog switch 26 is turned on, and the video signal voltage at that time is supplied to the signal line 20.
[0026]
On the other hand, each of the scanning line signals φy1 to φyn of the Y driver 30 maintains a high level during one line scanning. That is, φy1 changes to high level during the first line scan, and φy2 changes to high level during the second line scan.
[0027]
When the still image display is performed in which the display image does not change between frames, the M / S signal changes to a low level. At this time, the Y driver 30 stops, and the X driver 25 is scanned for one line (φx1 to φxn) every ½ frame (every 1/120 second). Further, since the control signals 41 and 42 are alternately at a high level, the NOR circuit output is always at a low level, and the output of the D / A circuit 28 is in a high impedance state. By the control signals 41 and 42, the two switch elements 101 and 102 are alternately conducted. The switch element 101 is connected to a node 97 of a voltage divider composed of three resistors, and the switch element 102 is connected to a node 98. The potential of the node 97 is white level, and the potential of the node 98 is black level. Accordingly, black level and white level signals are supplied to the video bus 27b in a frame cycle. The polarity of the signal on the video bus 27b is inverted by the polarity inversion circuit 29a in accordance with the inversion signal P / N and supplied to the video bus 27c.
[0028]
FIG. 6 shows a specific circuit configuration example of the polarity inverting circuit 29a. A signal corresponding to the addition value of the signal Vcom and the signal 27b is generated at the output of the operational amplifier 50, and a signal corresponding to a subtraction value obtained by subtracting the signal 27b from the signal Vcom is generated at the operational amplifier 51. One of the outputs of the operational amplifiers 50 and 51 is selected by the analog switch 52 according to the inverted signal P / N, and is output as the signal 27c.
[0029]
With the above operation, black level and white level signals are supplied to the signal line 20 in the frame period, and the potential of the pixel electrode 23 changes according to the potential of the signal line 20 as shown in FIG. Since the amount of leakage current is constant, the average value is constant. Since the period of the pixel voltage fluctuation is a frame period and is 1/60 second, the flicker component due to the pixel voltage fluctuation is not perceived by human eyes.
[0030]
In this embodiment, no particular correction is performed on the assumption that the voltage fluctuation after 1/2 frame is sufficiently small. However, in order to make the average value coincide with the initial writing value, the first DC level application time is set to the normal 1/1 time. 2 is effective.
[0031]
When the still image display period is long, the video signal 27c is inverted in polarity at an arbitrary frame during the still image display period, and normal driving is performed. Thereafter, the still image driving is performed. This is because when the liquid crystal is DC-driven for a long time, polarization occurs and display defects such as image sticking occur. As the fixed period, for example, a time such as every 10 frames or every 1 second may be used. When the driving method is used, it is desirable to make the time for applying the positive signal and the negative signal uniform. There is no problem when the still image is driven for a long time, but when the moving image display and the still image display are frequently switched, the control circuit 31 adjusts the positive polarity application time and the negative polarity application time to be uniform. It will be necessary. For example, a stack-type counter (that is, an up / down counter) may be provided in the control circuit 31 so that the positive and negative polarity application periods during still image display are adjusted to be the same according to the counter value.
[0032]
FIGS. 7A and 7B show a plan view and a cross-sectional view of the pixel portion of this embodiment. The same components as those in FIG. 1 are denoted by the same reference numerals.
A plurality of signal lines 20 and scanning lines 21 are formed in a matrix on the first electrode substrate 53, and one end is connected to the signal line 20 at the intersection of the signal lines 20 and the scanning lines 21. A switch element 22 is formed of a thin film transistor using a part of 21 as a gate electrode. The video signal is supplied from the signal line 20, reaches the thin film transistor through the contact hole 54, and further reaches the pixel electrode 23 made of a transparent conductive film through the contact hole 55. In FIG. 7B, the signal line 20 is located above the contact hole 54. A liquid crystal 61 is inserted between the counter electrode 60 formed on the second electrode substrate 59 and the pixel electrode 23 to form a liquid crystal cell.
[0033]
A part 56 of the scanning electrode is opposed to the pixel electrode 23 through the interlayer insulating film 63 to form an auxiliary capacitance. A part of the pixel electrode 23 overlaps the signal line 20 and the scanning line 21, and light transmitted from a part other than the pixel electrode is shielded by the signal line 20 and the scanning line 21. Under the pixel electrode 23, there are red, green, and blue color filters 57R, 57G, and 57B, which enable color display.
[0034]
As the switch element 22, a poly-Si TFT is used. The active layer of the poly-Si TFT was produced by depositing an a-Si film by a plasma CVD method using silane gas, irradiating the a-Si film with an excimer laser, melting and recrystallizing. The thickness of the active layer is 500 angstroms. As a method for forming a poly-Si film, in addition to the above method, a method for directly forming a poly-Si film using a low pressure CVD method, a method for solid-phase growth of an a-Si film in an annealing furnace at around 600 ° C., etc. Can be used.
[0035]
A silicon oxide film 62 formed by a plasma CVD method was used as the gate insulating film. The gate electrode is made of a low resistance molybdenum / tungsten alloy so that the image quality is not affected by the signal delay of the scanning line 21 even in a large panel. Molybdenum / tungsten alloy was formed by sputtering. The source / drain regions were formed by implanting phosphorus by ion doping using the gate electrode as a mask. A silicon oxide film formed by a plasma CVD method was used as the interlayer insulating film 63, contact holes were formed by a dry etching method, and source / drain electrodes formed by a Mo / Al film were formed by a sputtering method. The molybdenum film was inserted to make ohmic contact with the pixel electrode made of ITO.
[0036]
Since the polysilicon thin film transistor has a mobility about two orders of magnitude higher than that of the a-Si thin film transistor, the peripheral driver circuit can be formed on the glass substrate at the same time. The peripheral circuit preferably has a CMOS configuration in order to increase speed and reduce power consumption. In this case, the impurity doping process is performed in two steps using a resist mask, a P-type impurity process and an N-type impurity doping process.
[0037]
In order to use the polysilicon thin film transistor as a switching element, it is necessary to reduce the leakage current to the pA level or lower. In order to realize this, an LDD structure was formed with a sidewall or a resist mask to prevent a tunnel current due to a drain electric field.
[0038]
When light source light is incident from the first electrode substrate side in the cross-sectional configuration of FIG. 7B, the light source light is directly incident on the active layer of the poly-Si TFT. When the surface brightness of the liquid crystal display device with an aperture ratio of 80% is set to 70 nit which is a standard for OA applications, the light leakage current does not affect the image quality under the standard driving conditions. A decrease in contrast was observed due to leakage current. Although a method of suppressing the influence of the light leakage current by forming a light shielding layer under the TFT is conceivable, there is no appropriate light shielding film because the maximum process temperature is 600 ° C. in the activation process. Therefore, the influence of the light leakage current was canceled by using a driving method that suppresses the influence of the light leakage current.
[0039]
In the embodiment, as shown in FIG. 4, the switching period of the potential applied to the signal line 20 at the time of still image display is set to 1/60 seconds. For this purpose, the X driver is driven by one line every 1/120 seconds. This is a method that takes into account the characteristic that human eyes do not feel flicker when the luminance modulation period is 1/60 seconds or less. On the other hand, the direction of luminance modulation is reversed between adjacent pixels (one is set to the black side). By shifting one side to the white side) and keeping the average luminance constant, flicker can be eliminated. In particular, this method is effective in the case of a high-definition display whose pixel pitch is about the same as the resolution of the human viewing angle.
[0040]
In order to reverse the luminance modulation direction between the adjacent pixels, the timing of applying the white level and the black level between the adjacent signal lines may be reversed. FIG. 8 shows the drive circuit. As shown in FIG. 8, this is provided with a plurality of video buses, the black and white level timing applied to the video buses 27d and 27e is reversed, and the adjacent signal lines are connected to different video buses via analog switches. Connect to. FIG. 9 shows a circuit configuration for generating the adjacent signal of the opposite phase. In this case, since the video signal is divided and driven, there is an advantage that the X driver driving frequency can be lowered.
[0041]
In the above embodiment, the potential applied to the signal line 20 at the time of displaying a still image is set to the black level and the white level. However, one signal is output after one vertical scanning period, for example, when driving using the H line inversion. When the potential of the pixel connected to the line 20 has both positive and negative polarities, positive and negative black levels (in the case of normally white mode) may be used as the two DC levels.
[0042]
The above embodiment is an example of a liquid crystal display device of a dot sequential driving method, but the same effect can be obtained for a liquid crystal display device of a line sequential driving method by using the present invention. FIG. 10 shows an equivalent circuit diagram of an embodiment of a line sequential drive type liquid crystal display device. In the figure, the same components as those in FIG. 1 are indicated by the same numbers.
[0043]
In this embodiment, a shift register 71, a digital latch 72, a D / A conversion circuit 73, and a polarity inversion circuit 74 for transferring a digital video signal are installed in the X driver 70 corresponding to each signal line 20. . The video signal transferred by the shift register 71 during one horizontal period is held by the digital latch 72, converted to an AC analog signal by the D / A conversion circuit 73 and the polarity inversion circuit 74, and output to the signal line 20.
[0044]
As the external input, in addition to the digital video signal 27, a horizontal synchronizing signal 32, a vertical synchronizing signal 33, and an M / S signal 34 are prepared, and a driving method according to whether the display image changes between frames or not changes. Switching is performed by a control circuit 75 inserted in the input stage. The M / S signal is a control signal for identifying whether the transmitted video signal is a moving image or a still image. For example, in the case of a personal computer, the M / S signal is generated by detecting whether or not the frame buffer is rewritten.
[0045]
In the case of still image display in which the display image does not change between frames, the Y driver 30 is stopped, and the X driver 70 also stops the digital video signal 27 and the input signals 78, 79, 80 to the shift register 71, and the control signal 76. , 77 only. The DC level conversion cycle by the control signal is preferably 1/60 second or less. Alternatively, it is also possible to use a method in which the average luminance is made constant by reversing the direction of luminance change in adjacent pixels by reversing the connection on the DC signal side of the switch elements 81 and 82 between adjacent signal lines.
[0046]
【The invention's effect】
As described above, by using the liquid crystal display device according to the present invention, it is possible to provide a high-performance and low-power consumption liquid crystal display device to which a driving method for greatly reducing power consumption is applied even in the case of still image display including halftone.
[Brief description of the drawings]
FIG. 1 is an equivalent circuit diagram showing a first configuration of a liquid crystal display device according to the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration of a pixel switch.
FIG. 3 is a diagram for explaining the operating principle of the present invention.
4 is a timing chart illustrating the operation of the liquid crystal driving circuit of FIG.
FIG. 5 is a timing chart illustrating the operation of the liquid crystal driving circuit of FIG.
6 is a diagram showing a specific circuit configuration example of the polarity inversion circuit of FIG. 1;
7A is a plan view of a pixel portion of the liquid crystal cell, and FIG. 7B is a cross-sectional view showing the pixel portion of the liquid crystal cell.
FIG. 8 is a diagram illustrating a configuration of a circuit for reversing the direction of luminance modulation between adjacent pixels.
FIG. 9 is a diagram showing a configuration of a circuit for generating an adjacent signal of opposite phase.
FIG. 10 is an equivalent circuit diagram showing another embodiment of the liquid crystal display device according to the present invention.
FIG. 11 is an equivalent circuit diagram showing an embodiment of a conventional liquid crystal display device.
FIG. 12 is an equivalent circuit diagram showing an embodiment of a liquid crystal display device according to a conventional example.
[Explanation of symbols]
20 ... Signal line
21 ... Scanning line
22 ... Switch element
23. Pixel electrode
24 ... Liquid crystal cell
25 ... X driver
26 ... Analog switch
28 ... Digital-to-analog converter
29a, 29b ... polarity inversion circuit
30 ... Y driver
31 ... Control circuit
50, 51 ... operational amplifier
72. Latch circuit
90 ... Gate
91 ... Source region
92 ... Drain region
93 ... Depletion layer
94: Active layer
95 ... Diffusion length

Claims (8)

A plurality of signal lines and scanning lines wired in a matrix, signal line and scanning line driving circuits for driving the signal lines and scanning lines, and switching elements at intersections of the signal lines and scanning lines Between the first electrode substrate having the formed pixel electrode, the second electrode substrate having the counter electrode formed to face the pixel electrode, and the first electrode substrate and the second electrode substrate In a liquid crystal display device having a liquid crystal layer sandwiched between
Have a control means for switching the driving method of the signal line and the scan line driver circuit in the case where the display image between the image frame does not change when changed, the control unit, when the display image does not change between the frame a liquid crystal display device, characterized in that said scanning lines the switching element is held at a potential which turns off to have a means for switching a potential of the signal line at fixed intervals. 2. The liquid crystal display device according to claim 1, wherein the potential of the signal line is a white and black display potential. 2. The liquid crystal display device according to claim 1, wherein a switching cycle of the signal line potential is 1/60 second or less. 2. The liquid crystal display device according to claim 1, wherein the phase of the potential of the signal line switched every predetermined period is opposite between adjacent signal lines. A plurality of signal lines and scanning lines wired in a matrix, signal line and scanning line driving circuits for driving the signal lines and scanning lines, and switching elements at intersections of the signal lines and scanning lines Between the first electrode substrate having the formed pixel electrode, the second electrode substrate having the counter electrode formed to face the pixel electrode, and the first electrode substrate and the second electrode substrate In a liquid crystal display device having a liquid crystal layer sandwiched between, a driving method is switched between a case where a display image changes between image frames and a case where a display image does not change, and driving when the display image does not change between the frames The method includes a driving method of holding a scanning line at a potential at which the switch element is turned off, and switching the potential of the signal line at regular intervals. 6. The method of driving a liquid crystal display device according to claim 5, wherein the signal lines have white and black display potentials. 6. The method of driving a liquid crystal display device according to claim 5, wherein a switching cycle of the signal line potential is 1/60 second or less. 6. The method for driving a liquid crystal display device according to claim 5, wherein the phase of the potential of the signal line switched every predetermined period is opposite between adjacent signal lines.

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