Abstract:
A liquid crystal display device with a touch panel includes: pixel electrodes which are disposed in each pixel disposed in a display region and to which a potential is applied depending on a gradation value; common electrodes which extend in one direction across the display region; detection electrodes which extend in a direction different from the one direction across the display region, form an electric capacitance with driving electrodes that are a part of the common electrodes , and detect a contact position on a panel; a liquid crystal layer that is formed by a liquid crystal composition in which an orientation is changed by an electric field formed by the pixel electrodes and the common electrodes; and a driving pulse output section that applies a driving pulse once to the driving electrodes for detecting contact within two successive horizontal synchronizing periods that are periods of display.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese application JP2013-207142 filed on Oct. 2, 2013, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a liquid crystal display device with a touch panel. 
         [0004]    2. Description of the Related Art 
         [0005]    A display device having, as an input device, a touch panel that is disposed so as to be overlapped on a display screen of an information communication terminal such as a computer is widely used. Liquid crystal display devices that are generally used as the display device are devices displaying an image by changing an orientation of a liquid crystal composition that is sealed between two substrates of a thin film transistor substrate (hereinafter, referred to as a TFT substrate) and a color filter substrate depending on a change in an electric field and by controlling a degree of transmission of light passing through the liquid crystal composition. Among them, in an In Plane Switching (IPS) system in which both a pixel electrode and a common electrode are disposed on the TFT substrate side, the electrodes forma so-called horizontal electric field and a display having a wide viewing angle is realized. 
         [0006]    The touch panel is an input device that causes a processing device to perform a process by recognizing coordinates on a panel that is touched with the fingers of a user and the like. In the touch panel, a resistance film system that detects a change in a resistance value of a portion that is touched, an optical sensor system that detects a change in light intensity of a portion that is blocked by a touch, an electrostatic capacitive coupling system that detects a change in capacitance, and the like are known. The electrostatic capacitive coupling system is widely used because transmittance of the panel is high, display quality is not reduced, and durability thereof is high without coming into contact with other electrodes. 
         [0007]    In the related art, a liquid crystal display device with a touch panel of a further thin type is required for satisfying a demand of a miniaturization and a thinning of an information communication terminal. In the liquid crystal display device of the IPS system in JP 2009-244958 A, a liquid crystal display device with a touch panel is disclosed, which is further thinned by using a common electrode of the liquid crystal display device as a driving electrode of the touch panel. 
       SUMMARY OF THE INVENTION 
       [0008]    In the touch panel in the liquid crystal display device with a touch panel, in order to avoid an influence of electromagnetic waves generated in a display operation, scanning of the electrode of the touch panel is performed by avoiding the electromagnetic waves of the display operation with reference to a timing of a horizontal synchronizing signal that is used for display. Thus, a driving frequency of the touch panel is a period of the horizontal synchronizing signal and, for example, if a frequency of an external noise such as a so-called alternate current (AC) charge noise generated during charging is an integer multiple of the frequency of the horizontal synchronizing signal, there is a concern that a false detection occurs in touch detection. 
         [0009]    The present invention is made in view of the above circumstances and an object of the invention is to provide a liquid crystal display device with a touch panel in which a false detection is suppressed and accuracy of an operation thereof is improved. 
         [0010]    A liquid crystal display device with a touchpanel of the present invention includes: pixel electrodes that are a plurality of electrodes which are disposed in each pixel disposed in a display region and to which a potential is applied depending on a gradation value; common electrodes that are a plurality of electrodes which extend in one direction across the display region; detection electrodes that are a plurality of electrodes which extend in a direction different from an electric capacitance with the one direction across the display region, form driving electrodes that are a part of the common electrodes, and detect a contact position on a panel; a liquid crystal layer that is formed by a liquid crystal composition in which an orientation is changed by an electric field formed by the pixel electrodes and the common electrodes; and a driving pulse output section that applies a driving pulse once to the driving electrodes for detecting contact within two successive horizontal synchronizing periods that are periods of display. 
         [0011]    Furthermore, the liquid crystal display device with a touch panel of the present invention may further include: a detection circuit that detects a touch by integrating a change in the potential of the detection electrodes on both of a rising and a falling of the driving pulse applied to the driving electrodes. 
         [0012]    Furthermore, in the liquid crystal display device with a touch panel of the present invention, the detection circuit may have a rising detection circuit that detects an electrical response in the detection electrodes on the rising of the driving pulse and a falling detection circuit that detects the electrical response in the detection electrodes on the falling of the driving pulse, and each of the rising detection circuit and the falling detection circuit may have a comparator and a capacitance that is connected in parallel with the comparator. 
         [0013]    Furthermore, in the liquid crystal display device with a touch panel of the present invention, the driving pulse output section may generate the change in the potential of one of the rising and the falling of the driving pulse, after writing of the potential is completed with respect to the pixel electrodes depending on the gradation value. 
         [0014]    Furthermore, in the liquid crystal display device with a touch panel of the present invention, the driving pulse output section may generate the change in the potential of one of the rising and the falling of the driving pulse, before writing of a potential depending on the gradation value is completed with respect to the pixel electrodes while the potential depending on the gradation value is applied to the pixel electrodes. 
         [0015]    Furthermore, the liquid crystal display device with a touch panel of the present invention may further include: a dummy electrode that detects noise; a noise frequency detection section that detects a frequency of the noise detected by the dummy electrode; and a frame frequency control section that sets a frame frequency based on the frequency detected by the noise frequency detection section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a view illustrating a liquid crystal display device with a touch panel according to a first embodiment of the present invention. 
           [0017]      FIG. 2  is a diagram schematically illustrating a circuit of a pixel formed in a TFT substrate. 
           [0018]      FIG. 3  is a plan view illustrating an arrangement of electrodes that are used for detection of a touch of a touch panel. 
           [0019]      FIG. 4  is a view schematically illustrating a cross section taken along line IV-IV of  FIG. 3 . 
           [0020]      FIG. 5  is a schematic diagram for describing an operation of the detection of the touch. 
           [0021]      FIG. 6  is a diagram illustrating a configuration of a detection circuit. 
           [0022]      FIG. 7  is a timing chart for describing a driving pulse applied to a driving electrode. 
           [0023]      FIG. 8  is a timing chart of a driving pulse in a modification example of the embodiment. 
           [0024]      FIG. 9  is a block diagram for describing display driving control of a liquid crystal display device with a touch panel according to a second embodiment of the invention. 
           [0025]      FIG. 10  is a timing chart illustrating an example of a display control signal applying the display driving control of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Moreover, in the drawings, the same reference characters are given to the same or equivalent elements and redundant descriptions will be omitted. 
       First Embodiment 
       [0027]      FIG. 1  is a view illustrating a liquid crystal display device  100  with a touch panel according to a first embodiment of the present invention. As illustrated in the view, the liquid crystal display device  100  with the touch panel is configured of a liquid crystal display panel  200  with the touch panel, and an upper frame  101  and a lower frame  102  that fix the liquid crystal display panel  200  with the touch panel so as to sandwich the liquid crystal display panel  200  with the touch panel. 
         [0028]    Next, a basic circuit of a liquid crystal display of an IPS system will be schematically described. The liquid crystal display panel  200  with the touch panel has a TFT substrate  210  (see  FIG. 4 ) in which a thin film transistor (TFT) is formed, and  FIG. 2  is a diagram schematically illustrating a circuit of a pixel  400  formed in the TFT substrate  210 . Each pixel  400  has a pixel electrode  212  to which a gradation voltage corresponding to a gradation value is applied, a common electrode  280  that forms an electric field between the pixel electrode  212  and the common electrode  280 , a pixel transistor  401  which has a gate, a source and a drain, and a common electrode wiring  405  that is connected to the common electrode  280  and that is kept to a common potential. With respect to the pixel transistor  401 , a scanning signal line G[N] is connected to the gate and one of the source and the drain is connected to a data signal line D[M] and the other is connected to the pixel electrode  212 . Moreover,  FIG. 2  schematically indicates a representative circuit in the liquid crystal display device of the IPS system in which both the pixel electrode  212  and the common electrode  280  are formed in the TFT substrate  210 , but other circuits may be used. 
         [0029]      FIG. 3  is a plan view illustrating an arrangement of electrodes that are used for the detection of a touch of a touch panel. The common electrode  280  used in the liquid crystal display has a driving electrode  281  which has a rectangular shape extending in a direction of a short side of a display region and to which a voltage is applied from a touch panel control section  260 , and rectangular-shaped non-driving electrodes  282  which are electrodes other than the driving electrode  281  and extend in the direction of the short side of the display region. The display region is lined with these electrodes. 
         [0030]    On the other hand, in a layer other than the layer in which the common electrode  280  is disposed, a plurality of detection electrodes  230  that extend in a longitudinal direction of the display region and are arranged in the direction of the short side of the display region, and a plurality of dummy electrodes  240  that are disposed between the detection electrodes  230  and arranged to extend in the same direction as the detection electrodes  230  are formed. Signals detected by the detection electrodes  230  are input to the touch panel control section  260  for each detection electrode  230  and touch coordinates are calculated. The dummy electrodes  240  may be electrically floated or may be grounded. When being floated, a function of auxiliary capacity is provided when detecting the touch. Moreover, each of the driving electrode  281 , the non-driving electrode  282 , the detection electrode  230 , and the dummy electrode  240  is formed using a transparent conductive material such as Indium Tin Oxide (ITO). Furthermore, each electrode may be configured as a bundle of conductive lines in which a plurality of conductive lines are disposed at predetermined intervals. 
         [0031]    Furthermore, the touch panel control section  260  has a driving pulse output section  261  that applies driving pulses in order with respect to each driving electrode  281 , a detection circuit  270  that integrates the signals detected in the detection electrode  230 , a register  264  in which parameters of controlling such as output timing of the driving pulse are stored, and a calculation processing section (not illustrated) that calculates the presence or absence of a touch and the position of the touch on a display surface based on an output of the detection circuit  270 . 
         [0032]      FIG. 4  schematically illustrates a cross section taken along line IV-IV of  FIG. 3 . As illustrated in the view, the liquid crystal display panel  200  with the touch panel is configured of the TFT substrate  210 , a counter substrate  220  that emits filtered incident light as light having a wavelength of each color of RGB for each pixel by a color filter (not illustrated), and a liquid crystal layer  227  that is formed by the liquid crystal composition sealed between the substrates. Here, as illustrated in  FIG. 4 , the pixel electrode  212  and the common electrode  280  in the liquid crystal display are formed on a glass substrate  211  in the TFT substrate  210 , and the detection electrode  230  and the dummy electrode  240  are formed on a glass substrate  221  in the counter substrate  220 . 
         [0033]      FIG. 5  is a schematic diagram for describing an operation of the detection of the touch. As illustrated in the diagram, the driving pulse output section  261  applies a plurality of driving pulses in order to each driving electrode  281  and cumulates a response detected in the detection electrode  230  in the detection circuit  270 , and determines the presence or absence of a touch. 
         [0034]      FIG. 6  is a diagram illustrating a configuration of the detection circuit  270 . As illustrated in the diagram, the detection circuit  270  is configured of a rising detection circuit  271 , a falling detection circuit  272 , and a sample hold circuit  273 . The rising detection circuit  271  is configured of a first detection switch RxSw 1  that is turned ON when a driving pulse of a drive signal Tx rises, a first comparator Cmp 1 , and a first integral capacitance Cint_A. In the circuit, responses in the detection electrode  230  with respect to a plurality of times of driving pulses applied to the driving electrode  281  are accumulated in the first integral capacitance Cint_A, the responses are compared to a first reference voltage Vref_A in the comparator Cmp 1 , and the responses are output to the sample hold circuit  273 . Thereafter, in the calculation processing section, the signal output from the sample hold circuit  273  is calculated and the presence or absence of a touch, and the position of the touch in the display surface is calculated. The falling detection circuit  272  is configured of a second detection switch RxSw 2  that is turned ON when the pulse of the drive signal Tx falls, a second comparator Cmp 2 , and a second integral capacitance Cint_B, andperforms the same operation as that of the rising detection circuit  271 . Here, in  FIG. 6 , a symbol Cxy represents a capacitance between the driving electrode  281  and the detection electrode  230 . 
         [0035]      FIG. 7  is a timing chart for describing the driving pulse applied to a driving electrode  281 . In the timing chart, a change in each signal is represented for a horizontal synchronizing signal Hsync in the liquid crystal display, scanning signals Gn and Gn+1 applied to adjacent scanning signal lines G of the display device, a video signal S applied to a signal line D, the drive signal Tx applied to the driving electrode  281 , control signals of the first detection switch RxSW 1  and the second detection switch RxSW 2 , and a display noise N. 
         [0036]    As illustrated in the timing chart, in the display control, a scanning signal line driving pulse is sequentially applied to the scanning signals Gn and Gn+1 and the video signal S is applied corresponding thereto, synchronized with the horizontal synchronizing signal Hsync. The display noise N is generated according to the timing of the change in the scanning signals Gn and Gn+1, and the video signal S. The drive signal Tx is output such that there is one change in a stable period α in which the display noise N is relatively small until the output of the video signal S is stopped and the next video signal S is output. In the drive signal Tx, that is, one of the rising and the falling is generated once in the stable period α and one pulse is output in two horizontal synchronizing periods (2H). The control signal of the first detection switch RxSW 1  is a High potential according to the drive signal Tx of the rising so that the response thereof can be obtained from the detection electrode  230 , and the first detection switch RxSW 1  is turned ON. A second control signal of the second detection switch RxSW 2  is a High potential according to the drive signal Tx of the falling so that the response thereof can be obtained from the detection electrode  230 , and the second detection switch RxSW 2  is turned ON. 
         [0037]    Here, in order to avoid including the display noise N in the detection signal, the control signal of the first detection switch RxSW 1  and the second detection switch RxSW 2  is necessary to be a Low potential (OFF) before the video signal S is output and the timing of the change in the drive signal Tx should be earlier by an amount of a pulse width wrx of the control signal from the start of the video signal S. The stable period α is determined considering the pulse width wrx of the control signal. 
         [0038]    Therefore, since the touch panel control section  260  can output the driving pulse which has a period different from the period of the display, even if an external noise which has an integral multiple of the period of the display exists, it is possible to suppress false detection. Furthermore, since only one of the rising and the falling are disposed in the stable period α, it is easy to avoid display noise, accuracy of an operation is improved by suppressing the false detection, and accuracy of detection coordinates can be improved. Furthermore, since only one of the rising and the falling is disposed, the arrangement is easily performed and it is possible to correspond to high resolution of the display device even if the stable period α is short. 
         [0039]      FIG. 8  is a timing chart of a driving pulse in a modification example of the embodiment. In the modification example, a stable period β is defined rather than the stable period α represented in  FIG. 7  and one of the rising and falling of the driving pulse is disposed in each stable period β. The stable period β is set as a period before the falling of a scanning signal Gn occurs after display noise N is stable by applying a video signal S to a video signal line. Moreover, in the timing chart, description of a pulse width wrx of the control signal is omitted, but the pulse width wrx is also considered in the definition of stable period β. It is possible to obtain the same effects as those of the above embodiment even if one of the rising and falling of the driving pulse of the touch panel is disposed in such a stable period β. Specifically, in the display device in which a time (writing time) when the video signal S is applied is long, it is effective that the rising and falling of the drive pulse is disposed in the stable period β. Here, in the modification example, the rising and falling of the driving pulse is disposed only in the stable period β, but the rising or falling of the driving pulse may be set by combining the stable periods α and β. In this case, it is possible to further freely change the period of the driving pulse. 
       Second Embodiment 
       [0040]      FIG. 9  is a block diagram for describing display driving control of a liquid crystal display device with a touch panel according to a second embodiment of the present invention. Since an entire configuration of liquid crystal display device with the touch panel and the touch detection operation are the same as those in  FIGS. 1 to 4  and of the first embodiment indicated in the description thereof, the description will be omitted. As illustrated in  FIG. 9 , the display driving control according to the embodiment is performed by using a timing control section  300 , a dummy driving electrode  303  disposed on a glass substrate  221 , and a display driving circuit  304 . External noise such as AC charge noise detected in the dummy driving electrode  303  is input to a noise frequency detection circuit  302  in the timing control section  300  and the frequency of the external noise is calculated. The calculated frequency is notified to a frame frequency control section  301  and, the frame frequency which does not raises false detection and in which, for example, the horizontal synchronizing signal is not to be integer multiples of the noise frequency or the noise frequency divided by an integral number is selected based on the calculated frequency, and the display driving circuit is operated with the frame frequency. The display driving circuit outputs the scanning signal and the video signal so that the display operation is performed with a designated frame frequency. Moreover, the detection of the noise frequency and the control of the frame frequency may be periodically performed and may be performed only when a mobile terminal including the liquid crystal display device with the touch panel of the embodiment is connected to a charger, for example, as an object to suppress the false detection due to AC charge noise. The selected frame frequency may be, for example, selected from candidates of a plurality of frame frequencies stored in a register and the like. 
         [0041]      FIG. 10  is a timing chart illustrating an example of a display control signal applying the display driving control of  FIG. 9 . As shown, 3-Mux represents a case of RGB three switches and 2-Mux represents a case of RG switch terminals of RGB two switches. A range in which the frame frequency is controlled is a range of 55 Hz to 65 Hz and corresponds to 8.0 μs to 9.4 μs in one horizontal synchronizing period. As described above, it is possible to suppress the false detection in the detection circuit  270  due to the frequency of the external noise by changing the frame frequency based on the frequency of the external noise. 
         [0042]    While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.