JP2009008869A - Liquid crystal display device, driving circuit and driving method thereof - Google Patents

Abstract

An object of the present invention is to provide a liquid crystal display device capable of preventing sound generation caused by a drive signal without requiring a member such as a vibration damping material.
In order to apply a voltage between each pixel formation portion via a liquid crystal layer, each of the common electrodes is divided into k pieces corresponding to one or more scanning signal lines. k). Each common electrode is paired with one of the other common electrodes arranged adjacent to each other, and each of the two adjacent common electrodes constituting the pair of common electrodes has a common electrode drive signal having opposite polarities. Is provided by the common electrode drive circuit 24.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device, and more particularly to a technique for preventing vibration in a small liquid crystal display device employed in a mobile phone or the like.

  2. Description of the Related Art Conventionally, an active matrix type liquid crystal display device including a TFT (Thin Film Transistor) as a switching element is known. This liquid crystal display device includes a liquid crystal panel composed of two insulating substrates facing each other. On one substrate of the liquid crystal panel, a plurality of scanning signal lines (gate bus lines) and a plurality of video signal lines (source bus lines) are arranged in a lattice pattern, and the plurality of scanning signal lines and the plurality of video signal lines are arranged. There are provided a plurality of pixel forming portions arranged in a matrix corresponding to the intersections. FIG. 14 is a circuit diagram showing an equivalent circuit of a pixel formation portion for 2 rows × 2 columns. As shown in FIG. 14, a TFT 11 is provided in the vicinity of the intersection between the scanning signal line GL and the video signal line SL. The TFT 11 includes a gate electrode connected to the scanning signal line GL, a source electrode connected to the video signal line SL, and a drain electrode. The drain electrode is connected to the pixel electrodes 12 arranged in a matrix on the substrate in order to form an image. On the other substrate of the liquid crystal panel, an electrode (hereinafter referred to as a “common electrode”) 14 for applying a voltage to the pixel electrode 12 through the liquid crystal layer 13 is commonly provided in a plurality of pixel formation portions. It has been. A liquid crystal capacitor is formed by the pixel electrode 12, the liquid crystal layer 13, and the common electrode 14. Further, an auxiliary capacitor (not shown) is added in parallel with the liquid crystal capacitor as necessary. In such a configuration, when the gate electrode of each TFT 11 receives an active scanning signal (gate signal) from the scanning signal line GL, the video signal (source signal) received by the source electrode of the TFT 11 from the video signal line SL; A voltage is applied to the liquid crystal layer 13 of each pixel formation portion based on the common electrode drive signal applied to the common electrode 14. As a result, the liquid crystal is driven and a desired image is displayed on the screen.

  By the way, the liquid crystal has a property of deteriorating when a DC voltage is continuously applied. For this reason, in the liquid crystal display device, an AC voltage is applied to the liquid crystal layer 13. This will be described with reference to FIGS. 15 and 16.

  FIG. 15 is a diagram schematically showing a cross section of a liquid crystal panel of an active matrix liquid crystal display device. As shown in FIG. 15, the liquid crystal panel includes a TFT glass substrate 15, a pixel electrode 12, a liquid crystal layer 13, a common electrode 14, and a CF (Color Filter) glass substrate 16. The application of the AC voltage to the liquid crystal layer 13 is realized, for example, by inverting the polarity of the voltage applied to the liquid crystal layer 13 in each pixel forming unit described above for each frame period. Specifically, the liquid crystal display device is driven so that the polarity of the source electrode voltage (video signal voltage) with respect to the potential of the common electrode 14 is inverted every frame period. Note that one frame period is a period required for applying a voltage to the liquid crystal layer 13 in all the pixel formation portions of the liquid crystal display device and displaying an image for one screen on the screen.

  As a technique for realizing driving of the liquid crystal display device as described above, for example, a driving method called line inversion driving is known. FIG. 16 is a signal waveform diagram in a liquid crystal display device in which line inversion driving is adopted as a driving method. In FIG. 16, symbol THn (TH1, TH2, TH3,...) Indicates a period in which the n-th scanning signal line is selected, and symbol TF indicates one frame period. As shown in FIG. 16, the polarity of the video signal Vs is inverted every horizontal scanning period, and the polarity is inverted every frame period. Similarly, the polarity of the common electrode drive signal Vcom for driving the common electrode is inverted every horizontal scanning period, and further, the polarity is inverted every frame period. As a result, the polarity of the voltage applied to the liquid crystal layer 13 is reversed every horizontal scanning period, and AC driving of the liquid crystal display device is realized.

  In recent years, liquid crystal display devices such as those described above are often used as main screens for electronic devices such as mobile phones. For example, as one of such liquid crystal display devices, there is a standard called QVGA (Quarter Video Graphics Array) having a resolution of 320 × 240. In the liquid crystal display device having such QVGA class resolution, the CF glass substrate 16 shown in FIG. 15 vibrates due to the AC drive as described above, and the vibration may be felt as annoying sound. It has been pointed out. The following are known as conventional techniques for preventing the generation of annoying sounds (hereinafter referred to as “sounds”) due to such vibrations. Note that the squealing occurs when the frequency representing the frequency of reversal of the potential of the common electrode 14 (hereinafter referred to as “common electrode potential reversal frequency”) is in the human audible frequency band. It is known that it becomes prominent at 15 KHz.

Japanese Patent Laying-Open No. 2005-156633 discloses an invention of a liquid crystal display device that prevents sound generation by making the common electrode potential inversion frequency higher than the human audible frequency band. Japanese Patent Application Laid-Open No. 8-179285 discloses an invention of a liquid crystal display device in which noise associated with liquid crystal vibration is reduced by attaching a damping material to the liquid crystal display element. Japanese Patent Application Laid-Open No. 6-149174 discloses a liquid crystal display device that prevents noise by making the common electrode potential inversion frequency lower than the human audible frequency band, for example, by inverting the polarity of the common electrode potential every frame period. The invention is disclosed. There is also known a technique for preventing sound due to polarity inversion of the common electrode potential by inverting the polarity of the video signal potential with respect to the common electrode potential while keeping the common electrode potential constant.
JP 2005-156633 A JP-A-8-179285 JP-A-6-149174

  However, according to the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 2005-156633, power consumption increases by increasing the common electrode potential inversion frequency. According to the liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 8-179285, it is necessary to provide a vibration damping material, which increases costs and obstructs miniaturization and weight reduction. According to the liquid crystal display device disclosed in Japanese Patent Laid-Open No. 6-149174, flicker is conspicuous and the display quality is lowered. In addition, according to the driving method in which the common electrode potential is constant, the video signal line driving circuit having a large output range (driving voltage) is required because the amplitude of the video signal is large, which leads to increase in power consumption and cost. become.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device that can prevent a noise caused by a drive signal without using a member such as a damping material. Another object of the liquid crystal display device is to reduce power consumption.

According to a first aspect of the present invention, a plurality of video signal lines for respectively transmitting a plurality of video signals representing images to be displayed, a plurality of scanning signal lines intersecting with the plurality of video signal lines, and the plurality of video signals A plurality of pixel electrodes provided in a plurality of pixel forming portions arranged in a matrix corresponding to intersections of the lines and the plurality of scanning signal lines, and the plurality of video signals to the plurality of video signal lines. An active matrix type liquid crystal display device comprising a video signal line driving circuit to be supplied and a scanning signal line driving circuit for selectively driving the plurality of scanning signal lines,
A plurality of common electrodes provided so as to correspond to one or more scanning signal lines in order to apply a voltage between the plurality of pixel electrodes;
A common electrode drive circuit for applying a positive voltage and a negative voltage to each of the plurality of common electrodes as a common electrode drive signal with a predetermined voltage level as a reference,
The common electrode driving circuit has a common voltage applied to each common electrode such that electrical vibrations caused by alternately applying a positive voltage and a negative voltage to each common electrode cancel each other. The polarity of the electrode drive signal is changed.

According to a second invention, in the first invention,
Each common electrode is paired with one of the other common electrodes arranged adjacent to it,
The common electrode driving circuit may supply the common electrode driving signal to each of the plurality of common electrodes so that voltages having different polarities are applied to one and the other of the pair of common electrodes.

According to a third invention, in the second invention,
The common electrode driving circuit is configured such that a cycle in which the polarity of a common electrode driving signal applied to a common electrode other than a pair of common electrodes including a common electrode provided corresponding to a scanning signal line in a selected state is changed Each of the plurality of common electrodes so as to be longer than a period in which the polarity of the common electrode drive signal applied to the pair of common electrodes including the common electrode provided corresponding to the scanning signal line in the state is longer. A common electrode driving signal is supplied.

According to a fourth invention, in any one of the first to third inventions,
The number of scanning signal lines corresponding to each common electrode is the same for all of the plurality of common electrodes.

According to a fifth aspect of the invention, a plurality of video signal lines for transmitting a plurality of video signals representing images to be displayed, a plurality of scanning signal lines intersecting with the plurality of video signal lines, and the plurality of video signals A voltage is applied between a plurality of pixel electrodes provided in a plurality of pixel formation portions arranged in a matrix corresponding to intersections of a line and the plurality of scanning signal lines, and the plurality of pixel electrodes. For this purpose, there is provided a drive circuit for an active matrix type liquid crystal display device comprising a plurality of common electrodes each corresponding to one or more scanning signal lines,
A video signal line driving circuit for supplying the plurality of video signals to the plurality of video signal lines;
A scanning signal line driving circuit for selectively driving the plurality of scanning signal lines;
A common electrode drive circuit for applying a positive voltage and a negative voltage to each of the plurality of common electrodes as a common electrode drive signal with a predetermined voltage level as a reference,
The common electrode driving circuit has a common voltage applied to each common electrode such that electrical vibrations caused by alternately applying a positive voltage and a negative voltage to each common electrode cancel each other. The polarity of the electrode drive signal is changed.

  Moreover, the modification grasped | ascertained by referring embodiment and drawing in 5th invention is considered as a means for solving a subject.

According to an eighth aspect of the present invention, a plurality of video signal lines for respectively transmitting a plurality of video signals representing images to be displayed, a plurality of scanning signal lines intersecting with the plurality of video signal lines, and the plurality of video signals A voltage is applied between a plurality of pixel electrodes provided in a plurality of pixel formation portions arranged in a matrix corresponding to intersections of a line and the plurality of scanning signal lines, and the plurality of pixel electrodes. Therefore, there is provided a driving method of an active matrix type liquid crystal display device including a plurality of common electrodes each corresponding to one or more scanning signal lines,
A video signal line driving step of supplying the plurality of video signals to the plurality of video signal lines;
A scanning signal line driving step of selectively driving the plurality of scanning signal lines;
A common electrode driving step for applying a positive voltage and a negative voltage to each of the plurality of common electrodes as a common electrode driving signal with a predetermined voltage level as a reference,
In the common electrode driving step, a common voltage applied to each common electrode is canceled so that electrical vibrations caused by alternately applying a positive voltage and a negative voltage to each common electrode are canceled. The polarity of the electrode driving signal is changed.

  Moreover, the modification grasped | ascertained by referring embodiment and drawing in 8th invention is considered as a means for solving a subject.

  According to the first aspect, the common electrode provided for applying a voltage between the pixel electrode is divided into a plurality of parts. A common electrode drive signal is given to each of the divided common electrodes by the common electrode drive circuit. The common electrode drive circuit is configured to drive the common electrodes so that electrical vibrations generated in the common electrodes are canceled out. Change the polarity of the signal. For this reason, generation | occurrence | production of the sound resulting from the polarity reversal of a common electrode potential is suppressed, without providing members, such as a damping material.

  According to the second aspect, when attention is paid to a pair of adjacent common electrodes, common electrode drive signals having different polarities are applied to one common electrode and the other common electrode. For this reason, since electrical vibration is mutually canceled between adjacent common electrodes, generation | occurrence | production of a sound is suppressed effectively.

  According to the third aspect, when any pair of common electrodes is focused on, during the period in which one of the scanning signal lines corresponding to the pair of common electrodes is in a selected state, the pair The common electrode potential inversion frequency for the common electrodes other than the common electrode is set lower than the common electrode potential inversion frequency for the pair of common electrodes. For this reason, power consumption is reduced compared to a configuration in which the common electrode potential inversion frequency for each common electrode is constant throughout one frame period.

  According to the fourth aspect, since the number of scanning signal lines associated with each common electrode is set to a fixed number, the same effect as in the first aspect can be obtained with a simple configuration.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

<1. Overall configuration and operation>
FIG. 2 is a block diagram showing the overall configuration of the liquid crystal display device according to one embodiment of the present invention. This liquid crystal display device includes a display unit 100, a display control circuit 200, a scanning signal line driving circuit 300, and a video signal line driving circuit 400. The display control circuit 200 includes a control circuit 21, an analog output circuit 22, a timing signal generation circuit 23, and a common electrode drive circuit 24.

  The display unit 100 includes a plurality (n) of video signal lines (source bus lines) SL1 to SLn, a plurality (m) of scanning signal lines (gate bus lines) GL1 to GLm, and a plurality of these. A plurality of (n × m) pixel forming portions provided corresponding to the intersections of the video signal lines SL1 to SLn and the plurality of scanning signal lines GL1 to GLm are included. For example, this liquid crystal display device conforms to a standard called QVGA, and is provided with 240 video signal lines and 320 scanning signal lines.

  The display unit 100 has a cross-sectional structure as shown in FIG. 15, and the TFT glass substrate 15 is provided with the scanning signal lines and the video signal lines in a lattice shape as described above, and the scanning signal lines and the video signals are provided. A TFT is provided in the vicinity of the intersection with the signal line. Then, based on the video signal that the source electrode of the TFT receives from the video signal line when the gate electrode of each TFT receives the active scanning signal from the scanning signal line, and the common electrode drive signal applied to the common electrode 14 A voltage is applied to the liquid crystal layer 13 of each pixel formation portion. As a result, the liquid crystal is driven and a desired image is displayed on the screen.

  The display control circuit 200 receives (narrowly defined) image data representing an image to be displayed on the display unit 100 and data (hereinafter referred to as “display control data”) that determines the timing of the display operation from an external signal source. Received (hereinafter, these data Dw sent from the outside are referred to as “broadly defined image data”, (narrowly defined) image data is denoted by reference symbol Dv, and display control data is denoted by reference symbol Dc). Broadly defined image data Dw including narrowly defined image data Dv and display control data Dc is input to the control circuit 21 in the display control circuit 200.

  The control circuit 21 receives image data Dw in a broad sense including narrowly defined image data Dv and display control data Dc, and controls internal image data Dm based on the narrowly defined image data Dv and the operation of the timing signal generation circuit 23. Control signal group S and polarity inversion signals POL (1) to POL (k) for controlling the operation of the common electrode drive circuit 24 are output.

  The timing signal generation circuit 23 controls the analog output control signal Sa for controlling the operation of the analog output circuit 22 and the operation of the scanning signal line driving circuit 300 based on the control signal group S output from the control circuit 21. A signal group A for controlling the video signal line driving circuit 400 and a signal group B for controlling the operation of the video signal line driving circuit 400 are output. The analog output circuit 22 outputs an analog image signal Av based on the internal image data Dm and the analog output control signal Sa.

  Based on the polarity inversion signals POL (1) to POL (k) output from the control circuit 21, the common electrode drive circuit 24 drives common electrode drive signals COM (1) to COM (k) for driving the common electrode. Is output. In the present embodiment, since the common electrode is divided into k pieces as will be described later, k common electrode drive signals COM (1) to COM (k) are output from the common electrode drive circuit 24 as described above. The The common electrode drive signal gives the common electrode a positive voltage and a negative voltage with reference to a predetermined voltage level. The common electrode drive circuit 24 drives the output buffer to supply the counter electrode potential (common electrode potential) and the liquid crystal storage capacitor potential, and the polarity inversion signal POL (1) ˜POL output from the control circuit 21. This is a circuit that switches the polarity at various periods and phases based on POL (K).

  The scanning signal line drive circuit 300 receives a signal group A output from the timing signal generation circuit 23 in the display control circuit 200, for example, a scanning signal line control signal such as a gate start pulse signal GSP and a gate clock signal GCK, and is active. The application of a simple scanning signal to each of the scanning signal lines GL1 to GLm is repeated with one vertical scanning period as a cycle.

  The video signal line driving circuit 400 includes an analog image signal Av output from the analog output circuit 22 in the display control circuit 200 and a signal group B output from the timing signal generation circuit 23, such as a source start pulse signal SSP, a source clock, and the like. A video signal line control signal such as the signal SCK is received, and a video signal (hereinafter referred to as “driving video signal”) for displaying an image on the display unit 100 is applied to each of the video signal lines SL1 to SLn.

  As described above, the scanning signal line driving circuit 300 outputs the scanning signal, the video signal line driving circuit 400 outputs the driving video signal, and the common electrode driving circuit 24 outputs the common electrode driving signals COM (1) to COM. By outputting (k), a voltage corresponding to the potential difference between the pixel electrode and the common electrode is applied to the liquid crystal layer of each pixel formation portion, and a desired image is displayed.

<2. Configuration of common electrode>
Next, the configuration of the common electrode 14 in the present embodiment will be described with reference to FIGS. 1 and 3. FIG. 3 is a schematic diagram showing the configuration of the common electrode 14 in the present embodiment. As shown in FIG. 3, the common electrode 14 is divided into k pieces on the CF glass substrate 16. The divided common electrodes 14 (1) to 14 (k) are each connected to a common electrode driving circuit 24. A common electrode drive signal is applied to each of the common electrodes 14 (1) to 14 (k). Hereinafter, the i-th common electrode from the top in FIG. 3 among the k common electrodes 14 (1) to 14 (k) is referred to as “i-th common electrode 14 (i)”. The common electrode drive signal applied to the i-th common electrode is referred to as “i-th common electrode drive signal COM (i)”. That is, the first common electrode 14 (1) has the first common electrode drive signal COM (1), the second common electrode 14 (2) has the second common electrode drive signal COM (2), ..., the kth common electrode 14 (k) is supplied with the kth common electrode drive signal COM (k) by the common electrode drive circuit 24, respectively. As described above, the common electrodes 14 (1) to 14 (k) are independently driven by the common electrode driving circuit 24.

  FIG. 1 is a schematic diagram showing the relationship between scanning signal lines and common electrodes. In the present embodiment, as shown in FIG. 1, each common electrode is provided so as to be associated with four scanning signal lines. For example, in the case of a liquid crystal display device including 320 scanning signal lines GL1 to GL320, the first common electrode 14 (1) is provided corresponding to the first to fourth scanning signal lines GL1 to GL4, and the fifth to eighth lines. The second common electrode 14 (2) is provided corresponding to the scanning signal lines GL5 to GL8, and the 80th common electrode 14 (corresponding to the 317th to 320th scanning signal lines GL317 to GL320). 80).

<3. Driving method>
Next, a driving method in the present embodiment will be described. FIG. 4 is a signal waveform diagram for explaining the driving method in the present embodiment. The scanning signal line driving circuit 300 takes in the gate start pulse signal GSP shown in FIG. 4A at the timing when the gate clock signal GCK shown in FIG. At a timing when the gate clock signal GCK changes from the high level to the low level, the pulse included in the gate start pulse signal GSP is transferred from the input end to the output end of the shift register provided in the scanning signal line driver circuit 300. Are transferred sequentially. In response to this, as shown in FIGS. 4C to 4E, active scanning signals are sequentially output from each stage of the shift register in the scanning signal line driving circuit 300.

  As described above, the first to kth common electrodes 14 (1) to 14 (k) are supplied with the first to kth common electrode drive signals COM (1) to COM (k). As shown in f) to (i), the polarity of each common electrode drive signal is inverted every horizontal scanning period within one frame period.

  In FIG. 4, during a period from time t11 to time t12, active scanning signals G (1) to G (4) are sequentially applied to the first to fourth scanning signal lines GL1 to GL4 for each horizontal scanning period. The During this period, (1 horizontal) of the first common electrode drive signal COM (1) applied to the first common electrode 14 (1) provided corresponding to the first to fourth scanning signal lines GL1 to GL4. The polarity (for each scanning period) is “negative, positive, negative, positive”. Further, the polarity (for each horizontal scanning period) of the second common electrode drive signal COM (2) in the period from the time point t11 to the time point t12 is “positive, negative, positive, negative”.

  In FIG. 4, during the period from time t12 to time t13, the active scanning signals G (5) to G (8) are sequentially applied to the fifth to eighth scanning signal lines GL5 to GL8 by one horizontal scanning period. The During this period, the second common electrode drive signal COM (2) (1 horizontal) applied to the second common electrode 14 (2) provided corresponding to the fifth to eighth scanning signal lines GL5 to GL8. The polarity (for each scanning period) is “positive, negative, positive, negative”. Further, the polarity (for each horizontal scanning period) of the first common electrode drive signal COM (1) in the period from the time point t12 to the time point t13 is “negative, positive, negative, positive”.

  In FIG. 4, in the period from time t13 to time t21 when the next frame period starts, the same operation as in the period from time t11 to time t13 is repeated. In the next frame period (time t21), the polarities appearing in each horizontal scanning period for the first to k-th common electrode drive signals COM (1) to COM (k) are from time t11 to time t21. This is opposite to the polarity in the frame period. For example, the polarity (for each horizontal scanning period) of the first common electrode drive signal COM (1) in the frame period starting from time t11 is “negative, positive, negative, positive”, but starts from time t21. The polarity (for each horizontal scanning period) of the first common electrode drive signal COM (1) in the frame period is “positive, negative, positive, negative”.

  Here, focusing on FIGS. 4F and 4G, the polarity of the first common electrode drive signal COM (1) and the polarity of the second common electrode drive signal COM (2) are mutually different at each time point. It is reversed. 4 (h) and 4 (i), the polarity of the third common electrode drive signal COM (3) and the polarity of the fourth common electrode drive signal COM (4) are opposite to each other at each time point. It has become. As described above, in this embodiment, the j-th (j is an odd number) common electrode 14 (j) and the (j + 1) -th common electrode 14 (j + 1) are paired. One and the other are supplied with common electrode drive signals having different polarities at each time point.

<4. Effect>
As described above, according to the present embodiment, the common electrode 14 for applying a voltage to the pixel electrode 12 of each pixel formation portion via the liquid crystal layer 13 is divided into k pieces. The k-th divided first to k-th common electrodes 14 (1) to 14 (k) are independently driven by the common electrode driving circuit 24 and are adjacent to each other constituting a pair of common electrodes. Each of the two common electrodes is supplied with a common electrode drive signal having opposite polarities. For this reason, electrical vibrations caused by polarity inversion of the common electrode potential are canceled out between adjacent common electrodes. As a result, the generation of noise due to the polarity inversion of the common electrode potential is suppressed. Moreover, according to this embodiment, since it is not necessary to provide members, such as a damping material, a raise of cost can be suppressed.

<5. Modification>
Hereinafter, modifications of the embodiment will be described.

<5.1 First Modification>
In the above embodiment, an example in which one common electrode is provided for every four scanning signal lines has been described, but the present invention is not limited to this. The number of divisions of the common electrode is not particularly limited. For example, as shown in FIG. 5, when the common electrode is divided into only four pieces, that is, when 320 scanning signal lines are provided, 80 scans are performed. The configuration may be such that one common electrode is provided for each signal line. However, if the common electrode is divided more finely, the electric vibration generated in each common electrode is reduced, so that the effect of suppressing the generation of noise can be obtained. Therefore, it is preferable that the number of divisions of the common electrode is determined in consideration of the balance between the cost and the noise reduction effect.

<5.2 Second Modification>
In the above embodiment, as shown in FIG. 4, the polarities of the common electrode driving signals given to the two common electrodes adjacent to each other are opposite to each other for the two common electrodes according to any combination. Yes. That is, in the above embodiment, the common electrodes 14 (1) to 14 (k) sequentially arranged in the display unit 100 are alternately supplied with the common electrode drive signals having different polarities. However, the present invention is not limited to this. For example, as shown in FIG. 6, the first common electrode drive signal COM (1) and the fourth common electrode drive signal COM (4) have the same polarity, and their signals COM (1), COM ( 4), the second common electrode drive signal COM (2), and the third common electrode drive signal COM (3) may have opposite polarities. Further, as shown in FIG. 7, the first common electrode drive signal COM (1) and the second common electrode drive signal COM (2) have the same polarity, and their signals COM (1), COM ( 2), the third common electrode drive signal COM (3), and the fourth common electrode drive signal COM (4) may have opposite polarities.

<5.3 Third Modification>
In the above embodiment, the common electrodes are divided so that the same number of scanning signal lines is associated with each common electrode. However, the present invention is not limited to this, and is associated with each common electrode. The number of scanning signal lines may be different. For example, as shown in FIG. 8, “20 scanning signal lines GL1 to GL20 are associated with the first common electrode 14 (1), and 80 scans are associated with the second common electrode 14 (2). The signal lines GL21 to GL100 are associated with each other, and the 60 scanning signal lines GL101 to GL160 are associated with the third common electrode 14 (3). In this case, for example, as shown in FIG. 9, the first common electrode drive signal COM (1) and the third common electrode drive signal COM (3) have the same polarity, and their signals COM (1), COM ( By making the polarity of 3) and the second common electrode drive signal COM (2) opposite in polarity, the generation of sound is suppressed relatively effectively.

<5.4 Fourth Modification>
FIG. 10 is a schematic diagram showing the configuration of the common electrode in the fourth modification of the embodiment. In the above embodiment, the common electrode is divided into k pieces, and the first to kth common electrodes 14 (1) to 14 (k) are driven independently. On the other hand, in this modified example, as shown in FIG. 10, two comb-shaped common electrodes 14a and 14b are provided on the CF glass substrate 16, and the comb-tooth portions are arranged so as to mesh with each other and face each other. ing. Regarding the two common electrodes 14a and 14b, for example, one common electrode 14a corresponds to the first to fourth, 9th to 12th, 17th to 20th,... Scanning signal lines, and the other common electrode 14b. Corresponds to the 5th to 8th scanning signal lines, the 13th to 16th scanning lines, the 21st to 24th scanning lines, and so on. One common electrode 14a is supplied with a common electrode drive signal COMa having a waveform similar to the waveform shown in FIGS. 4F and 4H, and the other common electrode 14b is supplied with FIGS. A common electrode drive signal COMb having a waveform similar to the waveform shown in i) is provided.

  According to this modification, only two types of common electrode drive signals COMa and COMb need be generated in the common electrode drive circuit 24, so that the internal configuration of the common electrode drive circuit 24 can be simplified.

<5.5 Fifth Modification>
FIG. 11 is a signal waveform diagram for explaining a driving method in the fifth modification of the embodiment. In this modification, the cycle in which the polarity of the common electrode drive signal applied to the common electrode other than the pair of common electrodes including the common electrode provided corresponding to the scanning signal line in the selected state is the selected state. The first to k-th common electrodes 14 (so as to be longer than the period in which the polarity of the common electrode drive signal applied to the pair of common electrodes including the common electrode provided corresponding to the scanning signal line is changed. The first to kth common electrode drive signals COM (1) to COM (k) are given to 1) to 14 (k), respectively.

  For example, in FIG. 11, during the period from time t11 to time t12, active scanning signals G (1) to G (4) are sequentially applied to the first to fourth scanning signal lines GL1 to GL4 by one horizontal scanning period. Applied. During this period, the first common electrode drive signal COM (1) applied to the first common electrode 14 (1) provided corresponding to the first to fourth scanning signal lines GL1 to GL4, and the first The polarity of the second common electrode drive signal COM (2) given to the second common electrode 14 (2) paired with one common electrode 14 (1) changes every horizontal scanning period. To do. On the other hand, the polarity does not change for the common electrode drive signal applied to the common electrodes other than the first and second common electrodes 14 (1) and (2).

  In the period from time t12 to time t13, the active scanning signals G (5) to G (8) are sequentially applied to the fifth to eighth scanning signal lines GL5 to GL8 by one horizontal scanning period. During this period, the second common electrode drive signal COM (2) applied to the second common electrode 14 (2) provided corresponding to the fifth to eighth scanning signal lines GL5 to GL8, and the second The polarity of the first common electrode drive signal COM (1) applied to the first common electrode 14 (1) paired with the two common electrodes 14 (2) changes every horizontal scanning period. To do. On the other hand, the polarity does not change for the common electrode drive signal applied to the common electrodes other than the first and second common electrodes 14 (1) and (2).

  Further, during the period from time t13 to time t14, the active scanning signals G (9) to G (12) are sequentially applied to the ninth to twelfth scanning signal lines GL9 to GL12 for each horizontal scanning period. During this period, the third common electrode drive signal COM (3) provided to the third common electrode 14 (3) provided corresponding to the ninth to twelfth scanning signal lines GL9 to GL12, and the first The polarity of the fourth common electrode drive signal COM (4) applied to the fourth common electrode 14 (4) paired with the three common electrodes 14 (3) changes every horizontal scanning period. To do. On the other hand, the polarity does not change for the common electrode drive signal applied to the common electrodes other than the third and fourth common electrodes 14 (3) and (4).

  Furthermore, during the period from time t14 to time t15, the active scanning signals G (13) to G (16) are sequentially applied to the 13th to 16th scanning signal lines GL13 to GL16 for each horizontal scanning period. . During this period, the fourth common electrode drive signal COM (4) applied to the fourth common electrode 14 (4) provided corresponding to the 13th to 16th scanning signal lines GL13 to GL16, and the fourth The polarity of the third common electrode drive signal COM (3) given to the third common electrode 14 (3) paired with the four common electrodes 14 (4) changes every horizontal scanning period. To do. On the other hand, the polarity does not change for the common electrode drive signal applied to the common electrodes other than the third and fourth common electrodes 14 (3) and (4).

  According to this modification, when paying attention to an arbitrary pair of common electrodes, only during a period in which an active scanning signal is applied to one of the scanning signal lines corresponding to the pair of common electrodes, A common electrode drive signal that is inverted every horizontal scanning period is given, and the common electrode potential inversion frequency is reduced during other periods. For this reason, the power consumption is greatly reduced as compared with the configuration in which the polarity of the common electrode drive signal applied to each common electrode is inverted every horizontal scanning period through one frame period.

  Note that the common electrode potential inversion frequency for the second common electrode drive signal COM (2) and the third common electrode drive signal COM (3) cannot be reduced, or the first common electrode In the case where the drive signal COM (1) and the fourth common electrode drive signal COM (4) can be driven with the frequency of the display area reduced as compared with other areas, for example, as shown in FIG. The power consumption can be reduced by always setting the common electrode potential inversion frequency for the first common electrode drive signal COM (1) and the fourth common electrode drive signal COM (4) to a low state.

<5.6 Sixth Modification>
In the above embodiment, k common electrode drive signals COM (1) to COM (k) are generated based on the k polarity inversion signals POL (1) to POL (k). It is not limited to this. As shown in FIG. 4, the waveforms of the common electrode drive signals given to the odd-numbered common electrodes are all the same waveform, and the waveforms of the common electrode drive signals given to the even-numbered common electrodes are all the same waveform. It has become. Further, the common electrode drive signal given to the odd-numbered common electrode and the common electrode drive signal given to the even-numbered common electrode have the same timing of polarity inversion. Therefore, for example, as shown in FIG. 13, the first drive unit 246 that generates a common electrode drive signal applied to the odd-numbered common electrode and the second drive unit that generates the common electrode drive signal applied to the even-numbered common electrode. 247, and the first drive unit 246 may be provided with the polarity inversion signal POL as it is, and the second drive unit 247 may be provided with a signal obtained by inverting the polarity of the polarity inversion signal POL by the inverter 245. Thereby, the number of polarity inversion signals POL to be supplied from the control circuit 21 to the common electrode driving circuit 24 is reduced, and the internal configuration of the common electrode driving circuit 24 is simplified.

In the liquid crystal display device which concerns on one Embodiment of this invention, it is the schematic which shows the relationship between a scanning signal line and a common electrode. It is a block diagram which shows the whole structure of the liquid crystal display device which concerns on the said embodiment. In the said embodiment, it is the schematic which shows the structure of a common electrode. It is a signal waveform diagram for demonstrating the drive method in the said embodiment. FIG. 10 is a schematic diagram illustrating a relationship between a scanning signal line and a common electrode in a first modification example of the embodiment. It is a signal waveform diagram for demonstrating the drive method in the 2nd modification of the said embodiment. It is a signal waveform diagram for demonstrating the drive method of another example in the 2nd modification of the said embodiment. It is the schematic which shows the relationship between a scanning signal line and a common electrode in the 3rd modification in the said embodiment. It is a signal waveform diagram for demonstrating the drive method in the 3rd modification of the said embodiment. In the 4th modification of the said embodiment, it is the schematic which shows the structure of a common electrode. It is a signal waveform diagram for demonstrating the drive method in the 5th modification of the said embodiment. It is a signal waveform diagram for demonstrating the drive method of another example in the 5th modification of the said embodiment. FIG. 20 is a block diagram showing an internal configuration of a common electrode drive circuit in a sixth modification example of the embodiment. . It is a circuit diagram which shows the equivalent circuit of a pixel formation part. It is the figure which showed typically the cross section of the liquid crystal panel of an active matrix type liquid crystal display device. FIG. 11 is a signal waveform diagram in a liquid crystal display device in which line inversion driving is employed as a driving method in a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... Pixel electrode 13 ... Liquid crystal layer 14 (1)-(k) ... Common electrode 15 ... TFT glass substrate 16 ... CF glass substrate 21 ... Control circuit 24 ... Common electrode drive circuit 100 ... Display part 200 ... Display control circuit 300 ... Scanning signal line drive circuit (gate driver)
400 ... Video signal line drive circuit (source driver)
COM (1) to (k) ... Common electrode drive signals GL1 to GLm ... Scanning signal lines (gate bus lines)
POL (1) to (k): polarity inversion signals SL1 to SLn: video signal lines (source bus lines)

Claims (10)

A plurality of video signal lines for respectively transmitting a plurality of video signals representing an image to be displayed, a plurality of scanning signal lines intersecting with the plurality of video signal lines, the plurality of video signal lines and the plurality of scannings A plurality of pixel electrodes provided in a plurality of pixel formation portions arranged in a matrix corresponding to intersections with the signal lines, and a video signal line drive for supplying the plurality of video signals to the plurality of video signal lines An active matrix liquid crystal display device comprising a circuit and a scanning signal line driving circuit for selectively driving the plurality of scanning signal lines,
A plurality of common electrodes provided so as to correspond to one or more scanning signal lines in order to apply a voltage between the plurality of pixel electrodes;
A common electrode drive circuit for applying a positive voltage and a negative voltage to each of the plurality of common electrodes as a common electrode drive signal with a predetermined voltage level as a reference,
The common electrode driving circuit has a common voltage applied to each common electrode such that electrical vibrations caused by alternately applying a positive voltage and a negative voltage to each common electrode cancel each other. A liquid crystal display device characterized by changing the polarity of an electrode drive signal. Each common electrode is paired with one of the other common electrodes arranged adjacent to it,
The common electrode driving circuit provides the common electrode driving signal to each of the plurality of common electrodes so that voltages having different polarities are applied to one and the other of the pair of common electrodes, respectively. Item 2. A liquid crystal display device according to item 1.   The common electrode driving circuit is configured such that a cycle in which the polarity of a common electrode driving signal applied to a common electrode other than a pair of common electrodes including a common electrode provided corresponding to a scanning signal line in a selected state is changed Each of the plurality of common electrodes so as to be longer than a period in which the polarity of the common electrode drive signal applied to the pair of common electrodes including the common electrode provided corresponding to the scanning signal line in the state is longer. The liquid crystal display device according to claim 2, wherein a common electrode driving signal is supplied.   4. The liquid crystal display device according to claim 1, wherein the number of scanning signal lines corresponding to each common electrode is the same for all of the plurality of common electrodes. 5. A plurality of video signal lines for respectively transmitting a plurality of video signals representing an image to be displayed, a plurality of scanning signal lines intersecting with the plurality of video signal lines, the plurality of video signal lines and the plurality of scannings In order to apply a voltage between the plurality of pixel electrodes provided in the plurality of pixel formation portions arranged in a matrix corresponding to the intersections with the signal lines and the plurality of pixel electrodes, respectively. A drive circuit of an active matrix type liquid crystal display device comprising a plurality of common electrodes provided to correspond to the scanning signal lines,
A video signal line driving circuit for supplying the plurality of video signals to the plurality of video signal lines;
A scanning signal line driving circuit for selectively driving the plurality of scanning signal lines;
A common electrode drive circuit for applying a positive voltage and a negative voltage to each of the plurality of common electrodes as a common electrode drive signal with a predetermined voltage level as a reference,
The common electrode driving circuit has a common voltage applied to each common electrode such that electrical vibrations caused by alternately applying a positive voltage and a negative voltage to each common electrode cancel each other. A drive circuit, wherein the polarity of an electrode drive signal is changed.   The common electrode driving circuit applies the common electrode driving signal to each of the plurality of common electrodes so that voltages having different polarities are applied to one and the other of a pair of common electrodes arranged adjacent to each other. The drive circuit according to claim 5, wherein the drive circuit is provided.   The common electrode driving circuit is configured such that a cycle in which the polarity of a common electrode driving signal applied to a common electrode other than a pair of common electrodes including a common electrode provided corresponding to a scanning signal line in a selected state is changed Each of the plurality of common electrodes so as to be longer than a period in which the polarity of the common electrode drive signal applied to the pair of common electrodes including the common electrode provided corresponding to the scanning signal line in the state is longer. The drive circuit according to claim 6, wherein a common electrode drive signal is provided. A plurality of video signal lines for respectively transmitting a plurality of video signals representing an image to be displayed, a plurality of scanning signal lines intersecting with the plurality of video signal lines, the plurality of video signal lines and the plurality of scannings In order to apply a voltage between the plurality of pixel electrodes provided in the plurality of pixel formation portions arranged in a matrix corresponding to the intersections with the signal lines and the plurality of pixel electrodes, respectively. A driving method of an active matrix type liquid crystal display device comprising a plurality of common electrodes provided so as to correspond to the scanning signal lines,
A video signal line driving step of supplying the plurality of video signals to the plurality of video signal lines;
A scanning signal line driving step of selectively driving the plurality of scanning signal lines;
A common electrode driving step for applying a positive voltage and a negative voltage to each of the plurality of common electrodes as a common electrode drive signal with a predetermined voltage level as a reference,
In the common electrode driving step, a common voltage applied to each common electrode is canceled so that electrical vibrations caused by alternately applying a positive voltage and a negative voltage to each common electrode are canceled. A driving method characterized in that the polarity of an electrode driving signal changes.   In the common electrode driving step, the common electrode driving signal is applied to each of the plurality of common electrodes so that voltages having different polarities are applied to one and the other of the pair of common electrodes disposed adjacent to each other. The driving method according to claim 8, wherein the driving method is provided.   In the common electrode driving step, the cycle in which the polarity of the common electrode driving signal applied to the common electrode other than the pair of common electrodes including the common electrode provided corresponding to the scanning signal line in the selected state is changed to the selected one. Each of the plurality of common electrodes so as to be longer than a period in which the polarity of the common electrode drive signal applied to the pair of common electrodes including the common electrode provided corresponding to the scanning signal line in the state is longer. The driving method according to claim 9, wherein a common electrode driving signal is supplied.

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