Patent Publication Number: US-11650685-B2

Title: Display panel with touch detection function, method of driving the same, driving circuit, and electronic unit

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This is a Continuation Application of the U.S. patent application Ser. No. 17/204,182, filed Mar. 17, 2021, which is a Continuation Application of the U.S. patent application Ser. No. 16/738,584, filed Jan. 9, 2020, now U.S. Pat. No. 10,983,623, issued on Apr. 20, 2021, which is a Continuation Application of the U.S. patent application Ser. No. 16/236,765, filed Dec. 31, 2018, now U.S. Pat. No. 10,572,090, issued on Feb. 25, 2020, which is a Continuation Application of the U.S. patent application Ser. No. 15/959,742, filed Apr. 23, 2018, now U.S. Pat. No. 10,203,829, issued on Feb. 12, 2019, which is a Continuation Application of the U.S. patent application Ser. No. 15/845,740, filed Dec. 18, 2017, now U.S. Pat. No. 10,013,131, issued on Jul. 3, 2018, which is a Continuation Application of the U.S. patent application Ser. No. 15/630,091, filed Jun. 22, 2017, now U.S. Pat. No. 9,864,473, issued on Jan. 9, 2018, which is a Continuation Application of the U.S. patent application Ser. No. 14/842,291, filed Sep. 1, 2015, now U.S. Pat. No. 9,715,318, issued on Jul. 25, 2017, which is a Continuation Application of the U.S. patent application Ser. No. 14/306,633, filed Jun. 17, 2014, now U.S. Pat. No. 9,141,247, issued on Sep. 22, 2015, which is a Continuation Application of the U.S. patent application Ser. No. 13/414,363, filed Mar. 7, 2012, now U.S. Pat. No. 8,791,916, issued on Jul. 29, 2014, which claims priority from Japanese Patent Application No.: 2011-089429, filed Apr. 13, 2011, and Japanese Patent Application No.: 2011-242797, filed Nov. 4, 2011, the entire contents of which being incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a display panel with a touch detection function of detecting a touch event due to an external proximity object, a method of driving the same, a driving circuit, and an electronic unit having the display panel with a touch detection function. 
     Recently, a display panel has been notified, where a touch detection device, a so-called touch panel, is mounted on a display unit such as a liquid crystal display unit, or the touch panel is integrated with the display unit, and various button images and the like are displayed on the display unit for inputting information, instead of typical mechanical buttons. Such a display panel having the touch panel needs not have an input device such as a keyboard, a mouse, and a keypad and therefore tends to be expansively used not only for computers but also for handheld information terminals such as mobile phones. 
     A type of the touch panel includes several types such as an optical type and a resistant type. In particular, a capacitance-type touch panel has been promising as a device allowing low power consumption with a relatively simple structure. For example, Japanese Unexamined Patent Application Publication No. 2009-244958 (JP-A-2009-244958) proposes a so-called in-cell-type display panel with a touch detection function, where a common-electrode originally provided for display of a display unit is used also as one of a pair of electrodes for a touch sensor, and the other electrode (touch detection electrode) is disposed to intersect the common electrode. In addition, several propositions have been made on a so-called on-cell-type display panel with a touch detection function, in which a touch panel is provided on a display surface of a display unit. 
     SUMMARY 
     In the display panel with a touch detection function, since a display function is integrated with the touch detection function, for example, display operation may be affected by operation for touch detection. However, JP-A-2009-244958 has no description on such influence and measures against the influence. 
     It is desirable to provide a display panel with a touch detection function, in which display operation is less affected by touch detection operation, a method of driving the display panel with a touch detection function, a driving circuit, and an electronic unit having the display panel with a touch detection function. 
     A display panel with a touch detection function according to an embodiment of the disclosure includes one or more display elements; one or more drive electrodes; one or more touch detection electrodes; and a drive section. The drive section selectively applies a DC drive signal or an AC drive signal to the drive electrodes. 
     A method of driving the display panel with a touch detection function according to an embodiment of the disclosure includes driving one or more display elements for display, and selectively applying a DC drive signal or an AC drive signal to the one or more drive electrodes. 
     A drive circuit according to an embodiment of the disclosure includes a display drive section and a touch detection drive section. The display drive section drives one or more display elements. The touch detection drive section selectively applies a DC drive signal or an AC drive signal to one or more drive electrodes. 
     An electronic unit according to an embodiment of the disclosure includes a display panel with a touch detection function, and a control section controlling operation using the display panel with a touch detection function. The display panel with a touch detection function includes one or more display elements, one or more drive electrodes, one or more touch detection electrodes, and a drive section selectively applying a DC drive signal or an AC drive signal to the drive electrodes. Such an electronic unit includes, for example, a television apparatus, a digital camera, a personal computer, a video camera, and a mobile terminal device such as a mobile phone. 
     In the display panel with a touch detection function and the method of driving the display panel with a touch detection function, the drive circuit, and the electronic unit according to the embodiments of the disclosure, the display elements are driven for display, a drive signal is applied to the drive electrodes, and the touch detection electrodes output a signal corresponding to the drive signal. At that time, one of the DC drive signal and the AC drive signal is selectively applied as the drive signal to the drive electrodes. 
     According to the display panel with a touch detection function and the method of driving the display panel with a touch detection function, the drive circuit, and the electronic unit according to the embodiments of the disclosure, since the DC drive signal or the AC drive signal is selectively applied to the drive electrodes, display operation is less affected by touch detection operation. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the technology as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the specification, serve to explain the principles of the technology. 
         FIG.  1    is a diagram for explaining a basic principle of a touch detection process of a display panel with a touch detection function according to embodiments of the disclosure, showing a state where a finger is not in contact with or not in proximity to the display panel. 
         FIG.  2    is a diagram for explaining the basic principle of the touch detection process of the display panel with a touch detection function according to the embodiments of the disclosure, showing a state where a finger is in contact with or in proximity to the display panel. 
         FIG.  3    is a diagram for explaining the basic principle of the touch detection process of the display panel with a touch detection function according to the embodiments of the disclosure, showing exemplary waveforms drawings of a drive signal and a touch detection signal. 
         FIG.  4    is a block diagram illustrating an exemplary configuration of a display panel with a touch detection function according to a first embodiment of the disclosure. 
         FIG.  5    is a block diagram illustrating an exemplary configuration of a selection switch section shown in  FIG.  4   . 
         FIG.  6    is a sectional diagram illustrating a schematic sectional structure of a display device with a touch detection function shown in  FIG.  4   . 
         FIG.  7    is a circuit diagram illustrating a pixel arrangement in the display device with a touch detection function shown in  FIG.  4   . 
         FIG.  8    is a perspective diagram illustrating exemplary configurations of drive electrodes and touch detection electrodes of the display device with a touch detection function shown in  FIG.  4   . 
         FIGS.  9 A to  9 C  are schematic diagrams illustrating an exemplary operation of touch detection scan of the display panel with a touch detection function shown in  FIG.  4   . 
         FIG.  10    is a schematic diagram illustrating exemplary operations of display scan and touch detection scan of the display panel with a touch detection function shown in  FIG.  4   . 
         FIG.  11    is a block diagram illustrating an exemplary configuration of a drive signal generation section shown in  FIG.  4   . 
         FIG.  12    is a block diagram illustrating an exemplary configuration of a drive electrode driver according to the first embodiment. 
         FIG.  13    is a timing waveform chart illustrating an exemplary operation of the display panel with a touch detection function according to the first embodiment. 
         FIG.  14    is a timing waveform chart illustrating an exemplary touch detection operation of the display panel with a touch detection function according to the first embodiment. 
         FIG.  15    is a block diagram illustrating an exemplary configuration of a drive signal generation section according to a comparative example. 
         FIG.  16    is a block diagram illustrating an exemplary configuration of a drive electrode driver according to the comparative example. 
         FIG.  17    is a timing waveform chart illustrating an exemplary operation of a display panel with a touch detection function according to the comparative example. 
         FIG.  18    is a block diagram illustrating an exemplary configuration of a drive signal generation section according to a modification of the embodiment. 
         FIG.  19    is a block diagram illustrating an exemplary configuration of a drive electrode driver according to another modification of the embodiment. 
         FIGS.  20 A to  20 C  are schematic diagrams illustrating an exemplary operation of touch detection scan according to a still another modification of the embodiment. 
         FIG.  21    is a timing waveform chart illustrating an exemplary operation of a display panel with a touch detection function according to a still another modification of the embodiment. 
         FIG.  22    is a block diagram illustrating an exemplary configuration of a drive electrode driver according to a second embodiment. 
         FIG.  23    is a timing waveform chart illustrating an exemplary operation of the display panel with a touch detection function according to the second embodiment. 
         FIG.  24    is a timing waveform chart illustrating an exemplary touch detection operation of the display panel with a touch detection function according to the second embodiment. 
         FIG.  25    is a perspective diagram illustrating an appearance configuration of an application example 1, among display panels with a touch detection function applied with the embodiments. 
         FIGS.  26 A and  26 B  are perspective diagrams illustrating an appearance configuration of an application example 2. 
         FIG.  27    is a perspective diagram illustrating an appearance configuration of an application example 3. 
         FIG.  28    is a perspective diagram illustrating an appearance configuration of an application example 4. 
         FIGS.  29 A to  29 G  are front diagrams, side diagrams, a top diagram, and a bottom diagram illustrating an appearance configuration of an application example 5. 
         FIG.  30    is a sectional diagram illustrating a schematic sectional structure of a display device with a touch detection function according to a modification. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. It is to be noted that description is made in the following order. 
     1. Basic Principle of Capacitance-Type Touch Detection 
     2. First Embodiment 
     3. Second Embodiment 
     4. Application Examples 
     1. BASIC PRINCIPLE OF CAPACITANCE-TYPE TOUCH DETECTION 
     First, a basic principle of touch detection of a display panel with a touch detection function according to embodiments of the disclosure is described with reference to  FIGS.  1  to  3   . This touch detection process is embodied as a capacitance-type touch sensor. In the capacitance-type touch sensor, for example, a pair of electrodes (drive electrode E 1  and touch detection electrode E 2 ) disposed to face each other with a dielectric body D in between are used to configure a capacitance element, as illustrated in (A) of  FIG.  1   . Such a structure is expressed as an equivalent circuit illustrated in (B) of  FIG.  1   . The drive electrode E 1 , the touch detection electrode E 2 , and the dielectric body D define a capacitance element C 1 . One end of the capacitance element C 1  is connected to an AC signal source (drive signal source) S, and the other end P is grounded through a resistor R and connected to a voltage detector (a touch detection circuit) DET. After an AC rectangular wave Sg ((B) of  FIG.  3   ) having a predetermined frequency (for example, approximately several kilohertz to several tens kilohertz) is applied from the AC signal source S to the drive electrode E 1  (a first end of the capacitance element C 1 ), an output waveform (a touch detection signal) Vdet, as illustrated in (A) of  FIG.  3    is shown at the touch detection electrode E 2  (a second end P of the capacitance element C 1 ). It is to be noted that the AC rectangular wave Sg corresponds to an AC drive signal VcomAC described below. 
     In a state where a finger is not in contact with (or not in proximity to) the display panel, current I 0  corresponding to a capacitance value of the capacitance element C 1  flows in response to charge and discharge with respect to the capacitance element C 1  as illustrated in  FIG.  1   . Here, a potential waveform at the second end P of the capacitance element C 1  is, for example, as shown by a waveform V 0  in (A) of  FIG.  3   , which is detected by the voltage detector DET. 
     On the other hand, in a state where a finger is in contact with (or in proximity to) the display panel, a capacitance element C 2  is formed by a finger and is added in series to the capacitance element C 1  as illustrated in  FIG.  2   . In this state, a current I 1  and a current I 2  flow in response to charge and discharge of the capacitance elements C 1  and C 2 , respectively. Here, a potential waveform at the second end P of the capacitance element C 1  is, for example, as shown by a waveform V 1  in (A) of  FIG.  3   , which is detected by the voltage detector DET. Here, electric potential of the point P corresponds to a divided potential determined by the values of the currents I 1  and I 2  flowing through the respective capacitance elements C 1  and C 2 . The waveform V 1 , therefore, has a small value compared with the waveform V 0  in the non-contact state. The voltage detector DET compares a detected voltage with a predetermined threshold voltage Vth. If the detected voltage is equal to or higher than the threshold voltage, the voltage detector DET determines that no contact occurs. If the detected voltage is lower than the threshold voltage, the voltage detector DET determines that some contact occurs. In this way, touch detection is performed. 
     2. FIRST EMBODIMENT 
     Exemplary Configuration 
     Exemplary Overall Configuration 
       FIG.  4    illustrates an exemplary configuration of a display panel with a touch detection function  1  according to a first embodiment. The display panel includes liquid crystal display elements as display elements, and is a so-called in-cell type display panel, in which a liquid crystal display device configured of the liquid crystal display elements is integrated with a capacitance-type touch detection device. 
     The display panel with a touch detection function  1  includes a control section  11 , a gate driver  12 , a source driver  13 , a selection switch section  14 , a drive signal generation section  15 , a drive electrode driver  16 , a display device with a touch detection function  10 , and a touch detection section  40 . 
     The control section  11  is a circuit that supplies a control signal to each of the gate driver  12 , the source driver  13 , the drive signal generation section  15 , the drive electrode driver  16 , and the touch detection section  40  based on a video signal Vdisp supplied from the outside, and controls the components to operate in synchronization with one another. 
     The gate driver  12  has a function of sequentially selecting one horizontal line as a display drive object in the display device with a touch detection function  10  based on the control signal supplied from the control section  11 . In detail, the gate driver  12  generates a scan signal Vscan based on the control signal supplied from the control section  11 , and applies the scan signal Vscan to a gate of a TFT element Tr of each pixel Pix through a scan signal line GCL to sequentially select one row (one horizontal line) as a display drive object of pixels Pix provided in a matrix in a liquid crystal display device  20  of the display device with a touch detection function  10 . 
     The source driver  13  generates and outputs a pixel signal Vsig based on a video signal and a source driver control signal supplied from the control section  11 . In detail, the source driver  13  generates the pixel signal Vsig, in which pixel signals Vpix for a plurality of (here, three) sub-pixels SPix of the liquid crystal display device  20  of the display device with a touch detection function  10  are time-divisionally multiplexed, from a video signal corresponding to one horizontal line, and supplies the pixel signal Vsig to the selection switch section  14 , as described below. In addition, the source driver  13  generates a switching control signal Vsel (VselR, VselG, and VselB) necessary for demultiplexing the pixel signals Vpix multiplexed into the pixel signal Vsig, and supplies the switching control signal Vsel together with the pixel signal Vsig to the selection switch section  14 . It is to be noted that such multiplexing is performed to reduce the number of wirings between the source driver  13  and the selection switch section  14 . 
     The selection switch section  14  demultiplexes the pixel signals Vpix, which have been time-divisionally multiplexed into the pixel signal Vsig, based on the pixel signal Vsig and the switching control signal Vsel supplied from the source driver  13 , and supplies the pixel signals Vpix to the liquid crystal display device  20  of the display device with a touch detection function  10 . 
       FIG.  5    illustrates an exemplary configuration of the selection switch section  14 . The selection switch section  14  has a plurality of switch groups  17 . Each switch group  17  includes three switches SWR, SWG, and SWB herein, where respective first ends of the switches are connected to one another and supplied with a pixel signal Vsig from the source driver  13 , and respective second ends thereof are connected to three sub-pixels SPix (R, G, and B) relevant to a pixel Pix through pixel signal lines SGL of the liquid crystal display device  20  of the display device with a touch detection function  10 . The respective three switches SWR, SWG, and SWB are controlled to be on or off by the switching control signal Vsel (VselR, VselG, and VselB) supplied from the source driver  13 . According to such a configuration, the selection switch section  14  sequentially changes the three switches SWR, SWG, and SWB in a time-divisional manner to be on in response to the switching control signal Vsel, thereby demultiplexing the pixel signals Vpix (VpixR, VpixG, and VpixB) from the multiplexed pixel signal Vsig. In addition, the selection switch section  14  supplies the respective pixel signals Vpix to the three sub-pixels SPix (R, G, and B). 
     The drive signal generation section  15  generates a drive signal Vcom based on a control signal supplied from the control section  11 . In detail, the drive signal generation section  15  generates a DC drive signal VcomDC and generates an AC drive signal VcomAC based on a Vcom control signal EXVCOM (described below) supplied from the control section  11 , and supplies the signals to the drive electrode driver  16 , as described below. The DC drive signal VcomDC is a DC signal having a voltage of 0 V. The AC drive signal VcomAC has a pulse waveform having a low-level voltage of 0 V and a high-level voltage of VH. 
     The drive electrode driver  16  is a circuit that supplies the drive signal Vcom to drive electrodes COML (described below) of the display device with a touch detection function  10  based on a control signal supplied from the control section  11 . In detail, the drive electrode driver  16  applies the AC drive signal VcomAC to the relevant drive electrodes COML in touch detection operation. At that time, the drive electrode driver  16  drives the drive electrodes COML by one block (drive electrode block B described below) including a predetermined number of drive electrodes COML at a time. In addition, the drive electrode driver  16  applies the DC drive signal VcomDC to the drive electrodes COML other than the drive electrodes COML relevant to the touch detection operation. 
     The display device with a touch detection function  10  is a display device in which a touch detection function is embedded. The display device with a touch detection function  10  includes the liquid crystal display device  20  and a touch detection device  30 . The liquid crystal display device  20  performs sequential scan by one horizontal line basis for performing display in response to scan signals Vscan supplied from the gate driver  12 , as described below. The touch detection device  30  operates on the basis of the above-described basic principle of the capacitance-type touch detection and outputs a touch detection signal Vdet. The touch detection device  30  performs sequential scan in response to the AC drive signal VcomAC supplied from the drive electrode driver  16  to perform touch detection, as described below. 
     The touch detection section  40  detects presence of a touch event in the touch detection device  30  based on a touch detection control signal supplied from the control section  11  and the touch detection signal Vdet supplied from the touch detection device  30  of the display device with a touch detection function  10 , and obtains the coordinates of a touch event in a touch detection region if the touch event is detected. The touch detection section  40  includes a low pass filter (LPF) section  42 , an A/D conversion section  43 , a signal processing section  44 , a coordinate extraction section  45 , and a detection timing control section  46 . The LPF section  42  is a low-pass analog filter that removes the high-frequency components (noise components) contained in the touch detection signal Vdet supplied from the touch detection device  30 , and thus extracts and outputs the touch components. A resistance R for providing a DC potential (0 V) is connected between each of input terminals of the LPF section  42  and ground. It is to be noted that, for example, a switch may be provided in place of the resistance R such that the switch is turned on at a predetermined timing so as to provide the DC potential (0 V). The A/D conversion section  43  is a circuit that samples each of the analog signals output from the LPF section  42  at a timing in synchronization with the AC drive signal VcomAC, and converts the analog signals to digital signals. The signal processing section  44  is a logical circuit that detects presence of a touch event in the touch detection device  30  based on signals output from the A/D conversion section  43 . The coordinate extraction section  45  is a logical circuit that determines touch-panel coordinates of a touch event if signal processing section  44  detects a touch event. The detection timing control section  46  controls these circuits to operate in synchronization with one another. 
     (Display Device with Touch Detection Function  10 ) 
     An exemplary configuration of the display device with a touch detection function  10  is now described in detail. 
       FIG.  6    illustrates an exemplary sectional structure of a major part of the display device with a touch detection function  10 . The display device with a touch detection function  10  includes a pixel substrate  2 , a counter substrate  3  disposed to face the pixel substrate  2 , and a liquid crystal layer  6  interposed between the pixel substrate  2  and the counter substrate  3 . 
     The pixel substrate  2  includes a TFT substrate  21  as a circuit substrate, the drive electrodes COML, and pixel electrodes  22 . The TFT substrate  21  functions as a circuit substrate on which various kinds of electrodes, wirings, thin film transistors (TFTs), and the like are provided. The TFT substrate  21  is configured of, for example, glass. The drive electrodes COML are provided on the TFT substrate  21 . The drive electrodes COML are electrodes for supplying the common voltage to a plurality of pixels Pix (described below). The drive electrodes COML function as a common drive electrode for liquid crystal display operation, and also function as the drive electrodes for touch detection operation. An insulating layer  23  is provided on the drive electrodes COML, and the pixel electrodes  22  are provided on the insulating layer  23 . The pixel electrodes  22  are translucent electrodes for supplying the pixel signals for performing display. The drive electrodes COML and the pixel electrodes  22  include, for example, indium tin oxide (ITO). 
     The counter substrate  3  includes a glass substrate  31 , a color filter  32 , and touch detection electrodes TDL. The color filter  32  is provided on a first surface of the glass substrate  31 . The color filter  32  is configured of, for example, color filter layers of three colors of red (R), green (G), and blue (B) arranged periodically, where a set of three colors R, G, and B is associated with each display pixel. The touch detection electrodes TDL are provided on a second surface of the glass substrate  31 . The touch detection electrodes TDL, which are translucent, include for example, ITO. A polarizing plate  35  is disposed on the touch detection electrodes TDL 
     The liquid crystal layer  6  acts as a display function layer that modulates light passing through the liquid crystal layer  6  depending on a state of an electric field. The electric field is formed by a difference in electric potential between the voltage of the drive electrode COML and the voltage of the pixel electrode  22 . A transverse-mode liquid crystal, such as fringe field switching (FFS) liquid crystal and in-plane switching (IPS) liquid crystal, is used for the liquid crystal layer  6 . 
     It is to be noted that an alignment film is provided between the liquid crystal layer  6  and the pixel substrate  2  and between the liquid crystal layer  6  and the counter substrate  3 , and an incidence-side polarizing plate is disposed on a bottom of the pixel substrate  2 , which are omitted to be shown herein. 
       FIG.  7    illustrates an exemplary configuration of a pixel structure of the liquid crystal display device  20 . The liquid crystal display device  20  has a plurality of pixels Pix arranged in a matrix. Each pixel Pix is configured of three sub-pixels SPix. The respective, three sub-pixels SPix are disposed in correspondence to the three colors (RGB) of the color filter  32  shown in  FIG.  6   . Each sub-pixel SPix includes a TFT element Tr and a liquid crystal element LC. The TFT element Tr is configured of a thin film transistor which is an n-channel metal oxide semiconductor (MOS) TFT herein. A source of the TFT element Tr is connected to the pixel signal line SGL, a gate thereof is connected to the scan signal line GCL, and a drain thereof is connected to a first end of the liquid crystal element LC. A first end of the liquid crystal element LC is connected to the drain of the TFT element Tr, and the second end thereof is connected to the drive electrode COML. 
     The sub-pixel SPix is connected mutually with other sub-pixels SPix on the same row of the liquid crystal display device  20  through the scan signal line GCL. The scan signal line GCL is connected to the gate driver  12  and is supplied with the scan signal Vscan from the gate driver  12 . In addition, the sub-pixel SPix is connected mutually with other sub-pixels SPix on the same column of the liquid crystal display device  20  through the pixel signal line SGL. The pixel signal line SGL is connected to the selection switch section  14  and is supplied with the pixel signal Vpix from the selection switch section  14 . 
     Furthermore, the sub-pixel SPix is connected mutually with other sub-pixels SPix on the same row of the liquid crystal display device  20  through the drive electrode COML. The drive electrode COML is connected to the drive electrode driver  16  and is supplied with the drive signal Vcom (DC drive signal VcomDC) from the drive electrode driver  16 . 
     According to such a configuration, in the liquid crystal display device  20 , the gate driver  12  drives the scan signal lines GCL to be line-sequentially scanned in a time-divisional manner, thereby one horizontal line is sequentially selected, and the source driver  13  and the selection switch section  14  supply the pixel signals Vpix to pixels Pix along the one horizontal line, so that display is performed by one horizontal line basis. 
       FIG.  8    perspectively illustrates an exemplary configuration of the touch detection device  30 . The touch detection device  30  is configured of the drive electrodes COML provided on the pixel substrate  2  and the touch detection electrodes TDL provided on the counter substrate  3 . The drive electrodes COML are configured as a plurality of stripe-shaped electrode patterns extending in a horizontal direction in the figure. In the touch detection operation, the AC drive signal VcomAC is sequentially supplied to each of the electrode patterns by the drive electrode driver  16  so that the electrode patterns are driven to be sequentially scanned in a time-divisional manner as described below. The touch detection electrodes TDL are configured of stripe-shaped electrode patterns extending in a direction orthogonal to the extending direction of the electrode patterns of the drive electrodes COML. The electrode pattern of each of the touch detection electrode TDL is connected to input parts of the LPF section  42  of the touch detection section  40 . The electrode patterns of the drive electrode COML intersect the electrode patterns of the touch detection electrode TDL, resulting in formation of capacitance at respective intersections. 
     According to such a configuration, in the touch detection device  30 , the drive electrode driver  16  applies the AC drive signal VcomAC to the drive electrodes COML, so that the touch detection electrodes TDL output the touch detection signal Vdet for touch detection. Specifically, the drive electrodes COML correspond to the drive electrode E 1  in the basic principle of touch detection illustrated in  FIGS.  1  to  3   , and the touch detection electrodes TDL correspond to the touch detection electrode E 2 . The touch detection device  30  detects a touch event in accordance with the basic principle. As illustrated in  FIG.  8   , a capacitance-type touch sensor is formed in a matrix by the electrode patterns intersecting each other. Accordingly, a position of contact or proximity of an external proximity object is detected by scanning the entire touch detection surface of the touch detection device  30 . 
       FIGS.  9 A to  9 C  schematically illustrate touch detection scan.  FIGS.  9 A to  9 C  show application operation of the AC drive signal VcomAC to each of twenty drive electrode blocks B 1  to B 20  which define a display screen/touch detection surface herein. A drive-signal-applied block BAC indicates a drive electrode block B to which the AC drive signal VcomAC is applied, while the DC drive signal VcomDC is applied to other drive electrode blocks B. The drive electrode driver  16  sequentially selects a drive electrode block B as an object of touch detection operation and applies the AC drive signal VcomAC to the selected drive electrode block B so as to scan all the drive electrode blocks B, as shown in  FIGS.  9 A to  9 C . During such operation, the drive electrode driver  16  applies the AC drive signal VcomAC to each drive electrode block B over a plurality of predetermined horizontal periods as described below. While the number of the drive electrode blocks B is twenty for convenience of description herein, this is not limitative. 
       FIG.  10    schematically illustrates display scan and touch detection scan. In the display panel with a touch detection function  1 , the gate driver  12  drives the scan signal lines GCL to be line-sequentially scanned in a time-divisional manner so as to perform display scan Scand, and the drive electrode driver  16  sequentially selects the drive electrode block B to be driven so as to perform touch detection scan Scant. Here, the touch detection scan Scant is performed at a scan speed two times as high as the display scan Scand. In this way, in the display panel with a touch detection function  1 , the scan speed of touch detection is higher than that of display scan, allowing a prompt response to a touch event due to an external proximity object, and leading to an improvement in response characteristics for touch detection. It is to be noted that the above scan is not limitative, and, for example, the touch detection scan Scant may be performed at a scan speed two times or more as high as the display scan Scand, or may be performed at a scan speed two times or less as high as the display scan Scand. 
     (Drive Signal Generation Section  15  and Drive Electrode Driver  16 ) 
       FIG.  11    illustrates an exemplary configuration of the drive signal generation section  15 . The drive signal generation section  15  includes a high-level-voltage generation sub-section  61 , a low-level-voltage generation sub-section  62 , buffers  63  to  65 , and a switching circuit  66 . 
     The high-level-voltage generation sub-section  61  generates a high-level voltage of the AC drive signal VcomAC. The low-level-voltage generation sub-section  62  generates a DC voltage of the DC drive signal VcomDC. The voltage generated by the low-level-voltage generation sub-section  62  is also used as a low-level voltage of the AC drive signal VcomAC. The buffer  63  outputs the voltage supplied from the high-level-voltage generation sub-section  61  to the switching circuit  66  while performing impedance conversion of the voltage. The buffer  64  outputs the voltage supplied from the low-level-voltage generation sub-section  62  to the switching circuit  66  while performing impedance conversion of the voltage. The switching circuit  66  generates the AC drive signal VcomAC based on the Vcom control signal EXVCOM. In detail, if the Vcom control signal EXVCOM is high, the switching circuit  66  outputs the voltage supplied from the buffer  63 , and if the Vcom control signal EXVCOM is low, it outputs the voltage supplied from the buffer  64 . The buffer  65  outputs the voltage supplied from the low-level-voltage generation sub-section  62  as the DC drive signal VcomDC while performing impedance conversion of the voltage. The buffers  63  to  65  are each configured of a voltage follower, for example. 
       FIG.  12    illustrates an exemplary configuration of the drive electrode driver  16 . The drive electrode driver  16  includes a scan control section  51 , a touch detection scan section  52 , and a drive section  530 . The drive section  530  includes twenty drive sub-sections  53 ( 1 ) to  53 ( 20 ). Hereinafter, any one of the twenty drive sub-sections  53 ( 1 ) to  53 ( 20 ) is simply referred to as drive sub-section  53 . 
     The scan control section  51  supplies a control signal to the touch detection scan section  52  based on a control signal supplied from the control section  11 . In addition, the scan control section  51  has a function of supplying a Vcom selection signal VCOMSEL to the drive section  530 . The Vcom selection signal VCOMSEL indicates appropriate one of the DC drive signal VcomDC and the AC drive signal VcomAC to be supplied to the drive electrodes COML. 
     The touch detection scan section  52  includes a shift register, and generates scan signals St for selecting the drive electrodes COML to which the AC drive signal VcomAC is applied. In detail, the touch detection scan section  52  generates a plurality of scan signals St corresponding to the drive electrode blocks B based on the control signal supplied from the scan control section  51 , as described below. In the case where the touch detection scan section  52  supplies a high-level signal to a kth drive sub-section  53 ( k ) as a kth scan signal St(k), for example, the drive sub-section  53 ( k ) applies the AC drive signal VcomAC to a plurality of drive electrodes COML in a kth drive electrode block B(k). 
     The drive section  530  applies the DC drive signal VcomDC or the AC drive signal VcomAC supplied from the drive signal generation section  15  to the drive electrodes COML based on the scan signal St supplied from the touch detection scan section  52  and the Vcom selection signal VCOMSEL supplied from the scan control section  51 . The drive sub-section  53  is provided by one in correspondence to each of the signals output from the touch detection scan section  52  so as to apply the drive signal Vcom to a corresponding drive electrode block B. 
     The drive sub-section  53  includes an AND gate  54 , an inverter  55 , buffers  56  and  57 , and switches SW 1  and SW 2 . The AND gate  54  generates a logical product (AND) of the scan signal St supplied from the touch detection scan section  52  and the Vcom selection signal VCOMSEL supplied from the scan control section  51 , and outputs the logical product. The inverter  55  generates an inverting logic of the signal output from the AND gate  54  and outputs the inverting logic. The buffer  56  has a function of amplifying the signal supplied from the AND gate  54  to an amplitude level allowing on/off control of the switch SW 1 . The switch SW 1  is controlled to be on or off based on the signal supplied from the buffer  56 , and has a first end to which the AC drive signal VcomAC is supplied, and a second end connected to the plurality of drive electrodes COML defining the drive electrode block B. The buffer  57  has a function of amplifying the signal supplied from the inverter  55  to an amplitude level allowing on/off control of the switch SW 2 . The switch SW 2  is controlled to be on or off based on the signal supplied from the buffer  57 , and has a first end to which the DC drive signal VcomDC is supplied, and a second end connected to the second end of the switch SW 1 . 
     According to such a configuration, if the scan signal St is high, the drive sub-section  53  outputs the AC drive signal VcomAC as the drive signal Vcom while the Vcom selection signal VCOMSEL is high, and outputs the DC drive signal VcomDC as the drive signal Vcom while the Vcom selection signal VCOMSEL is low. If the scan signal St is low, the drive sub-section  53  outputs the DC drive signal VcomDC as the drive signal Vcom. The drive signal Vcom output from the drive sub-section  53  in this way is supplied to a plurality of drive electrodes COML defining the drive electrode block B corresponding to the drive sub-section  53 . 
     The liquid crystal element LC corresponds to a specific example of “display element” of the disclosure. The drive electrode driver  16  corresponds to a specific example of “drive section” of the disclosure. The high-level-voltage generation sub-section  61  and the buffer  63  correspond to a specific example of “first voltage generation sub-section” of the disclosure. The low-level-voltage generation sub-section  62  corresponds to a specific example of “second voltage generation sub-section” of the disclosure. The buffer  64  corresponds to a specific example of “buffer circuit” of the disclosure. 
     [Operations and Functions] 
     Operations and functions of the display panel with a touch detection function  1  according to the embodiment are now described. 
     (Summary of General Operation) 
     Summary of general operation of the display panel with a touch detection function  1  is described with reference to  FIG.  4   . The control section  11  supplies the control signal to each of the gate driver  12 , the source driver  13 , the drive signal generation section  15 , the drive electrode driver  16 , and the touch detection section  40  based on a video signal Vdisp supplied from the outside, and thus controls those to operate in synchronization with one another. The gate driver  12  supplies the scan signals Vscan to the liquid crystal display device  20  to sequentially select one horizontal line as a display drive object. The source driver  13  generates the pixel signal Vsig with the pixel signals Vpix multiplexed and the switching control signal Vsel corresponding to the pixel signal Vsig, and supplies the generated signals to the selection switch section  14 . The selection switch section  14  demultiplexes the pixel signals Vpix based on the pixel signal Vsig and the switching control signal Vsel, and supplies the pixel signals Vpix to the respective pixels Pix defining the one horizontal line. The drive signal generation section  15  generates the DC drive signal VcomDC and the AC drive signal VcomAC. The drive electrode driver  16  sequentially applies the AC drive signal VcomAC to the drive electrode blocks B while applying the DC drive signal VcomDC to the drive electrodes COML to which the AC drive signal VcomAC is not applied. The display device with a touch detection function  10  performs display operation while performing touch detection operation so that the touch detection electrodes TDL output the touch detection signal Vdet. The LPF section  42  removes high frequency components (noise components) contained in the touch detection signal Vdet to extract touch components for output. The A/D conversion section  43  converts the analog signals output from the LPF section  42  into digital signals. The signal processing section  44  detects presence of a touch event to the display device with a touch detection function  10  based on the signals output from the A/D conversion section  43 . Upon detection of a touch event by the signal processing section  44 , the coordinate extraction section  45  determines the touch-panel coordinates of the touch event. The detection timing control section  46  controls the LPF section  42 , the A/D conversion section  43 , the signal processing section  44 , and the coordinate extraction section  45  to operate in synchronization with one another. 
     (Detailed Operation) 
     Detailed operation of the display panel with a touch detection function  1  is now described. 
       FIG.  13    illustrates an exemplary timing waveform of the display panel with a touch detection function  1 , where (A) illustrates a waveform of the AC drive signal VcomAC, (B) illustrates a waveform of the DC drive signal VcomDC, (C) illustrates waveforms of the scan signal Vscan, (D) illustrates a waveform of the pixel signal Vsig, (E) illustrates waveforms of the switching control signal Vsel, (F) illustrates waveforms of the pixel signal Vpix, (G) illustrates a waveform of the Vcom selection signal VCOMSEL, (H) illustrates waveforms of the drive signal Vcom, and (I) illustrates a waveform of the touch detection signal Vdet. 
     The display panel with a touch detection function  1  performs the display operation and the touch detection operation during each horizontal period (1H). In the display operation, the gate driver  12  sequentially applies the scan signal Vscan to the scan signal lines GCL to perform display scan. In the touch detection operation, the drive electrode driver  16  sequentially applies the AC drive signal VcomAC to the drive electrode blocks B by one at a time to perform touch detection scan, and the touch detection section  40  detects a touch event based on the touch detection signal Vdet output from the touch detection electrodes TDL. These are described in detail below. 
     After start of one horizontal period (1H) at timing t 0 , the scan control section  51  of the drive electrode driver  16  changes the voltage of the Vcom selection signal VCOMSEL from the low level to the high level at timing t 1  ((G) of  FIG.  13   ). As a result, in the drive electrode driver  16 , the switch SW 1  is turned on while the switch SW 2  is turned off in a kth drive sub-section  53 ( k ) relevant to the touch detection operation, so that the AC drive signal VcomAC ((A) of  FIG.  13   ) generated by the drive signal generation section  15  is applied as a drive signal Vcom(B(k)) to the drive electrodes COML defining the corresponding kth drive electrode block B(k) through the switch SW 1  ((H) of  FIG.  13   ). In each of the drive sub-sections  53  other than the kth drive sub-section  53 ( k ), the switch SW 1  is turned off while the switch SW 2  is turned on, so that the DC drive signal VcomDC ((B) of  FIG.  13   ) generated by the drive signal generation section  15  is applied to the drive electrodes COML defining the corresponding drive electrode block B through the switch SW 2  ((H) of  FIG.  13   ). 
     The drive signal generation section  15  then changes the voltage of the AC drive signal VcomAC from the low level to the high level at timing t 2  ((A) of  FIG.  13   ). In detail, in the drive signal generation section  15 , the buffer  63  supplies a current through the switching circuit  66  based on the Vcom control signal EXVCOM, so that the voltage of the AC drive signal VcomAC is changed from the low level to the high level. Along with this, the drive signal Vcom (B(k)) applied to the kth drive electrode block B(k) is also changed from the low level to the high level ((H) of  FIG.  13   ). The drive signal Vcom (B(k)) is transmitted to the touch detection electrodes TDL through capacitance, so that the voltage of the touch detection signal Vdet is changed ((I) of  FIG.  13   ). 
     The A/D conversion section  43  of the touch detection section  40  then performs A/D conversion of the signals output from the LPF section  42  which has received the touch detection signal Vdet, at a sampling timing ts ((I) of  FIG.  13   ). The signal processing section  44  of the touch detection section  40  detects a touch event based on the A/D conversion results collected over a plurality of horizontal periods as described below. 
     The drive signal generation section  15  then changes the voltage of the AC drive signal VcomAC from the high level to the low level at timing t 3  ((A) of  FIG.  13   ). In detail, in the drive signal generation section  15 , the buffer  64  sinks the current through the switching circuit  66  based on the Vcom control signal EXVCOM, so that the voltage of the AC drive signal VcomAC is changed from the high level to the low level. Along with this, the drive signal Vcom (B(k)) applied to the kth drive electrode block B(k) is also changed from the high level to the low level ((H) of  FIG.  13   ), so that the voltage of the touch detection signal Vdet is changed ((I) of  FIG.  13   ). 
     Subsequently, the scan control section  51  of the drive electrode driver  16  changes the voltage of the Vcom selection signal VCOMSEL from the high level to the low level at timing t 4  ((G) of  FIG.  13   ). As a result, in the drive electrode driver  16 , the switch SW 1  is turned off while the switch SW 2  is turned on in the drive sub-section  53 ( k ), so that the DC drive signal VcomDC ((B) of  FIG.  13   ) generated by the drive signal generation section  15  is applied as the drive signal Vcom(B(k)) to the drive electrodes COML defining the corresponding drive electrode block B(k) through the switch SW 2  ((H) of  FIG.  13   ). 
     The gate driver  12  applies the scan signal Vscan to an nth scan signal line GCL(n) relevant to display operation at timing t 5 , so that the voltage of the scan signal Vscan is changed from the low level to the high level ((C) of  FIG.  13   ). In addition, the source driver  13  and the selection switch section  14  apply the pixel signals Vpix to the pixel signal lines SGL ((F) of  FIG.  13   ) for display of pixels Pix on one horizontal line corresponding to the nth scan signal line GCL(n). 
     In detail, the gate driver  12  changes the scan signal Vscan from the low level to the high level at timing t 5  to select one horizontal line relevant to the display operation. In addition, the source driver  13  supplies a pixel voltage VR for a red sub-pixel SPix as a pixel signal Vsig to the selection switch section  14  ((D) of  FIG.  13   ), and generates a switching control signal VselR that is high during a period of supplying the pixel voltage VR, and supplies the switching control signal VselR to the selection switch section  14  ((E) of  FIG.  13   ). The selection switch section  14  allows a switch SWR to be on in a period where the switching control signal VselR is high (write period PW) to separate the pixel voltage VR supplied from the source driver  13  from the pixel signal Vsig, and supplies the pixel voltage VR as a pixel signal VpixR to the red sub-pixels SPix on one horizontal line through the pixel signal line SGL ((F) of  FIG.  13   ). It is to be noted that after the switch SWR is turned off, the pixel signal line SGL is floated and thus the voltage of the pixel signal line SGL is maintained ((F) of  FIG.  13   ). Similarly, the source driver  13  supplies a pixel voltage VG for a green sub-pixel SPix together with a corresponding switching control signal VselG to the selection switch section  14  ((D) and (E) of  FIG.  13   ). The selection switch section  14  demultiplexes the pixel voltage VG from the pixel signal Vsig based on the switching control signal VselG, and supplies the pixel voltage VG as a pixel signal VpixG to the green sub-pixels SPix on one horizontal line through the pixel signal line SGL ((F) of  FIG.  13   ). Similarly, the source driver  13  then supplies a pixel voltage VB for a blue sub-pixel SPix together with a corresponding switching control signal VselB to the selection switch section  14  ((D) and (E) of  FIG.  13   ). The selection switch section  14  demultiplexes the pixel voltage VB from the pixel signal Vsig based on the switching control signal VselB, and supplies the pixel voltage VB as a pixel signal VpixB to the blue sub-pixels SPix on one horizontal line through the pixel signal line SGL ((F) of  FIG.  13   ). 
     Next, the gate driver  12  changes the scan signal Vscan(n) of the scan signal line GCL (n) in the nth row from the high level to the low level at timing t 6  ((C) of  FIG.  13   ). As a result, the sub-pixels SPix on the one horizontal line relevant to display operation are electrically separated from the pixel signal lines SGL. 
     Then, one horizontal period is finished and a subsequent horizontal period is started at timing t 10 . 
     After that, the above operation is repeated, thereby the display panel with a touch detection function  1  performs display operation over the entire display surface through line-sequential scan, and performs touch detection operation over the entire touch-detection surface through scanning the drive electrode blocks B by one at a time. 
       FIG.  14    illustrates an exemplary operation of the touch detection scan, where (A) illustrates a waveform of the AC drive signal VcomAC, (B) illustrates a waveform of the DC drive signal VcomDC, (C) illustrates a waveform of the Vcom selection signal VCOMSEL, (D) illustrates waveforms of the scan signal St, (E) illustrates waveforms of the drive signal Vcom, and (F) illustrates a waveform of the touch detection signal Vdet. 
     As shown in  FIG.  14   , the drive electrode driver  16  sequentially applies the AC drive signal VcomAC to the corresponding drive electrode block B ((E) of  FIG.  14   ) based on the scan signal St ((D) of  FIG.  14   ) generated by the touch detection scan section  52  to perform touch detection scan. During this, the drive electrode driver  16  applies the AC drive signal VcomAC to each of the drive electrode blocks B over a plurality of predetermined horizontal periods ((E) of  FIG.  14   ). The touch detection section  40  samples the touch detection signal Vdet based on the AC drive signal VcomAC during each one horizontal period. After such sampling is finished in the last horizontal period among the plurality of predetermined horizontal periods, the signal processing section  44  detects presence of a touch event in a region corresponding to the relevant drive electrode block B based on the plurality of sampling results. In this way, touch detection is performed based on the plurality of sampling results. As a result, the sampling results are statistically analyzed. This suppresses a reduction in an S/N ratio due to variations in the sampling results, leading to an improvement in accuracy of touch detection. 
     COMPARATIVE EXAMPLE 
     The functions of the display panel with a touch detection function  1  according to the embodiment are now described in comparison with a display panel with a touch detection function according to a comparative example. In the comparative example, a drive signal generation section generates high and low, two kinds of DC drive signals, and a drive electrode driver selects one of the two DC drive signals and applies the selected DC drive signal to drive electrodes COML. Other configurations are the same as in the embodiment ( FIG.  4    and others). 
       FIG.  15    illustrates an exemplary configuration of a drive signal generation section  15 R according to the comparative example. The drive signal generation section  15 R generates two kinds of DC drive signals VcomH and VcomDC. The DC drive signal VcomH is generated by a high-level-voltage generation sub-section  61  and output through a buffer  63 . The DC drive signal VcomDC is generated by a low-level-voltage generation sub-section  62  and output through a buffer  65 . 
       FIG.  16    illustrates an exemplary configuration of a drive electrode driver  16 R according to the comparative example. The drive electrode driver  16 R includes a scan control section  51 R. The scan control section  51 R supplies a Vcom selection signal VCOMSELR to a drive section  530 . The Vcom selection signal VCOMSELR indicates appropriate one of the two kinds of DC drive signals VcomH and VcomDC to be supplied to the drive electrodes COML. 
     The drive electrode driver  16 R has switches SW 1  each having one end to which the DC drive signal VcomH is supplied, as shown in  FIG.  16   . According to such a configuration, if a scan signal St is high, the drive sub-section  53  outputs the DC drive signal VcomH as a drive signal Vcom while the Vcom selection signal VCOMSELR is high, and outputs the DC drive signal VcomDC as the drive signal Vcom while the Vcom selection signal VCOMSELR is low. 
       FIG.  17    illustrates an exemplary timing waveform of the display panel with a touch detection function according to the comparative example, where (A) illustrates a waveform of the DC drive signal VcomH, (B) illustrates a waveform of the DC drive signal VcomDC, (C) illustrates waveforms of a scan signal Vscan, (D) illustrates a waveform of a pixel signal Vsig, (E) illustrates waveforms of a switching control signal Vsel, (F) illustrates waveforms of a pixel signal Vpix, (G) illustrates a waveform of the Vcom selection signal VCOMSELR, (H) illustrates waveforms of a drive signal Vcom, and (I) illustrates a waveform of a touch detection signal Vdet. 
     The scan control section  51 R of the drive electrode driver  16 R changes the voltage of the Vcom selection signal VCOMSELR from the low level to the high level at timing t 11  ((G) of  FIG.  17   ). As a result, in the drive electrode driver  16 , the switch SW 1  is turned on while a switch SW 2  is turned off in a kth drive sub-section  53 ( k ) relevant to the touch detection operation, so that the DC drive signal VcomH ((A) of  FIG.  17   ) generated by the drive signal generation section  15 R is applied as a drive signal Vcom(B(k)) to the drive electrodes COML defining the corresponding kth drive electrode block B(k) through the switch SW 1  ((H) of  FIG.  17   ). In detail, the buffer  63  of the drive signal generation section  15 R supplies a current to the drive electrodes COML, so that the drive signal Vcom(B(k)) is changed from the low level to the high level. In each of the drive sub-sections  53  other than the drive sub-section  53 ( k ), the switch SW 1  is turned off while the switch SW 2  is turned on, so that the DC drive signal VcomDC ((B) of  FIG.  17   ) generated by the drive signal generation section  15 R is applied to the drive electrodes COML defining the corresponding drive electrode block B through the switch SW 2  ((H) of  FIG.  17   ). An A/D conversion section  43  of a touch detection section  40  then performs A/D conversion of the signals output from an LPF section  42  which has received the touch detection signal Vdet, at a sampling timing ts ((I) of FIG.  17 ). 
     The scan control section  51 R of the drive electrode driver  16 R changes the voltage of the Vcom selection signal VCOMSELR from the high level to the low level at timing t 12  ((G) of  FIG.  17   ). As a result, in the drive electrode driver  16 R, the switch SW 1  is turned off while the switch SW 2  is turned on in the kth drive sub-section  53 ( k ), so that the DC drive signal VcomDC ((B) of  FIG.  17   ) generated by the drive signal generation section  15 R is applied as the drive signal Vcom(B(k)) to the drive electrodes COML defining the corresponding drive electrode block B(k) through the switch SW 2  ((H) of  FIG.  17   ). In detail, the buffer  65  of the drive signal generation section  15 R sinks the current from the drive electrodes COML, so that the voltage of the drive signal Vcom(B(k)) is changed from the high level to the low level. 
     At that time, the buffer  65  of the drive signal generation section  15 R drives all the drive electrodes COML through the switches SW 2  of the drive section  530  of the drive electrode driver  16 R. Thus, the buffer  65  may not sufficiently drive the drive electrodes COML due to a large load. In such a case, at and after timing t 2 , electric charge, which has been accumulated in the drive electrodes COML of the drive electrode block B(k) during application of the DC drive signal VcomH, moves to other drive electrode blocks B through the switch SW 2  of the drive sub-section  53 ( k ), resulting in rising of the voltage of the drive signal Vcom (Vcom(B(k−1), Vcom(B(k), Vcom(B(k+1) and others) applied to the drive electrode blocks B (wavy portions WR). The buffer  65  sinks such electric charge, so that the voltage of the drive signal Vcom gradually converges to the voltage level of the DC drive signal VcomDC. If such converging time is long, nearly the write period PW, the pixel signal Vpix is insufficiently written into the pixels during the relevant write period PW, leading to a possibility of a reduction in image quality. 
     Contrarily, in the display panel with a touch detection function according to the embodiment, as shown in (H) of  FIG.  13   , the AC drive signal VcomAC is changed from the high level to the low level at timing t 3 , and then the switch SW 1  is turned off while the switch SW 2  is turned on at timing t 4  in the drive sub-section  53 ( k ), so that the drive signal supplied to the drive electrodes COML is switched from the AC drive signal VcomAC to the DC drive signal VcomDC. 
     As a result, in the drive signal generation section  15 , the buffer  64 , which is different from the buffer  65  generating the DC drive signal VcomDC, sinks the current at the timing when the AC drive signal VcomAC is changed from the high level to the low level at timing t 3 , and therefore the DC drive signal VcomDC is less affected by the AC drive signal VcomAC. Specifically, noise in the DC drive signal VcomDC, which is supplied to the horizontal line to which display operation is performed, is suppressed, thereby suppressing a reduction in image quality. 
     In addition, since the electric potential of the drive electrode block B(k) (the low-level voltage of the AC drive signal VcomAC) is substantially equal to the electric potential of other drive electrode blocks B(k) (the DC voltage of the DC drive signal VcomDC) immediately before the timing t 4 , substantially no electric charge moves after the switch SW 2  is turned on at the timing t 4 . This reduces rising of the voltage of the drive signal Vcom (B(k)) as shown in the wavy portions WR in the comparative example, thereby suppressing a reduction in image quality. 
     [Effect] 
     As described before, in the embodiment, the AC drive signal and the DC drive signal are selectively applied to the drive electrodes to be driven, and the DC drive signal is switched from the AC drive signal after the AC drive signal is changed from the high level to the low level, thereby suppressing a reduction in image quality. 
     In addition, in the embodiment, the buffer for supplying the low level of the AC drive signal and the buffer for supplying the DC drive signal are separately provided, thereby suppressing a reduction in image quality. 
     [Modification 1-1] 
     While the drive signal generation section  15  is configured as shown in  FIG.  11    in the first embodiment, this is not limitative. For example, a buffer  64 A for generating the low level of the AC drive signal may receive the DC drive signal VcomDC, as shown in  FIG.  18   . The low-level-voltage generation sub-section  62  and the buffer  65  correspond to a specific example of “second voltage generation section” of the disclosure. The buffer  64 A corresponds to a specific example of “buffer circuit” of the disclosure. In this case, the DC drive signal VcomDC is also less affected by the noise due to the AC drive signal VcomAC, thereby suppressing a reduction in image quality. 
     [Modification 1-2] 
     While the drive electrode driver  16  drives the drive electrode blocks B, each including the predetermined number of drive electrodes COML, by one at a time in the first embodiment, this is not limitative. Instead, the drive electrode driver  16  may directly drive the drive electrodes COML by one at a time, for example, as shown in  FIG.  19   . In such a case, a drive section  530 B includes the same number of drive sub-sections  53  as the total number of the drive electrodes COML, and a touch detection scan section  52 B supplies the scan signals St to the drive section  530 B. 
     [Modification 1-3] 
     While the drive electrodes COML are scanned to be driven by one drive-electrode-block B, which includes the predetermined number of drive electrodes COML, at a time, this is not limitative. Instead, for example, a predetermined number of drive electrodes COML may be simultaneously driven while the drive electrodes COML to be driven are shifted one by one to scan the drive electrodes COML. This is described in detail below. 
       FIG.  20    schematically illustrates an exemplary operation of a drive electrode driver  16 C according to the modification. The drive electrode driver  16 C simultaneously applies the AC drive signal VcomAC to a predetermined number of drive electrodes COML. In detail, the drive electrode driver  16 C simultaneously applies the AC drive signal VcomAC to the predetermined number (here, five) of drive electrodes COML (drive-signal-applied electrodes LAC). Then, the drive electrode driver  16 C shifts the drive electrodes COML, to which the AC drive signal VcomAC is applied, one by one to perform touch detection scan. Such touch detection scan is achieved by, for example, using the drive electrode driver  16 B shown in  FIG.  19   , where a shift register in the touch detection scan section  52 B transmits a wide pulse. While the AC drive signal VcomAC is simultaneously applied to the five drive electrodes COML herein, this is not limitative. Instead, the AC drive signal VcomAC may be simultaneously applied to not more than four drive electrodes COML or not less than six drive electrodes COML. While the drive electrodes COML, to which the AC drive signal VcomAC is applied, are shifted one by one herein, this is not limitative. Instead, the drive electrodes COML may be shifted by two or more at a time. 
     [Modification 1-4] 
     While the voltage of the AC drive signal VcomAC is changed from the low level to the high level at timing t 2  after the voltage of the Vcom selection signal VCOMSEL is changed from the low level to the high level at timing t 1  as shown in  FIG.  13    in the first embodiment, this is not limitative. For example, the voltage of the Vcom selection signal VCOMSEL may be changed from the low level to the high level at timing t 22  after the voltage of the AC drive signal VcomAC is changed from the low level to the high level at timing t 21 , as shown in  FIG.  21   . 
     3. SECOND EMBODIMENT 
     A display panel with a touch detection function  7  according to a second embodiment is now described. The second embodiment is different from the first embodiment in a selection process of the drive signal in the case where one of the DC drive signal VcomDC and the AC drive signal VcomAC is selected to be supplied to the drive electrodes COML. It is to be noted that substantially the same components as those of the display panel with a touch detection function  1  according to the first embodiment are designated by the same numerals, and description of them is appropriately omitted. 
       FIG.  22    illustrates an exemplary configuration of a drive electrode driver  18  of the display panel with a touch detection function  7 . The drive electrode driver  18  includes a scan control section  71  and a drive section  730 . 
     The scan control section  71  supplies a control signal to a touch detection scan section  52  based on a control signal supplied from a control section  11 . 
     The drive section  730  applies a drive signal Vcom (a DC drive signal VcomDC or an AC drive signal VcomAC) to the drive electrodes COML based on a scan signal St supplied from the touch detection scan section  52 . Each drive sub-section  73  includes an inverter  55 , buffers  56  and  57 , and switches SW 1  and SW 2 . Specifically, the drive sub-section  73  does not include an AND gate  54  unlike the drive sub-section  53  in the first embodiment. According to such a configuration, the drive sub-section  73  outputs the AC drive signal VcomAC as the drive signal Vcom if the scan signal St is high, and outputs the DC drive signal VcomDC as the drive signal Vcom if the scan signal St is low. 
       FIG.  23    illustrates an exemplary timing waveform of the display panel with a touch detection function  7 , where (A) illustrates a waveform of the AC drive signal VcomAC, (B) illustrates a waveform of the DC drive signal VcomDC, (C) illustrates waveforms of the scan signal Vscan, (D) illustrates a waveform of a pixel signal Vsig, (E) illustrates waveforms of a switching control signal Vsel, (F) illustrates waveforms of a pixel signal Vpix, (G) illustrates waveforms of the drive signal Vcom, and (H) illustrates a waveform of a touch detection signal Vdet. 
     Upon start of one horizontal period (1H) at timing t 0 , the drive electrode driver  18  supplies the AC drive signal VcomAC to the drive electrodes COML relevant to touch detection ((G) of  FIG.  23   ). In detail, in the drive electrode driver  18 , the switch SW 1  is turned on while the switch SW 2  is turned off in a kth drive sub-section  73 ( k ) relevant to the touch detection operation, so that the AC drive signal VcomAC ((A) of  FIG.  23   ) generated by the drive signal generation section  15  is applied as a drive signal Vcom(B(k)) to the drive electrodes COML defining the corresponding kth drive electrode block B(k) through the switch SW 1  ((G) of  FIG.  23   ). 
     The drive signal generation section  15  then changes the voltage of the AC drive signal VcomAC from the low level to the high level at timing t 2  ((A) of  FIG.  23   ). Along with this, the drive signal Vcom (B(k)) applied to the kth drive electrode block B(k) is changed from the low level to the high level ((G) of  FIG.  23   ). The drive signal Vcom (B(k)) is transmitted to touch detection electrodes TDL through capacitance, so that the voltage of the touch detection signal Vdet is changed ((H) of  FIG.  23   ). An A/D conversion section  43  of a touch detection section  40  then performs A/D conversion of the signals output from an LPF section  42  which has received the touch detection signal Vdet, at a sampling timing ts ((H) of  FIG.  23   ). The drive signal generation section  15  then changes the voltage of the AC drive signal VcomAC from the high level to the low level at timing t 3  ((A) of  FIG.  23   ). 
     At and after timing t 5 , the display panel with a touch detection function  7  performs display operation as in the display panel with a touch detection function  1  according to the first embodiment. In the display panel with a touch detection function  7 , the drive electrode driver  18  still applies the AC drive signal VcomAC as the drive signal Vcom(B(k)) to the drive electrodes COML relevant to the touch detection during a period of the display operation ((G) of  FIG.  23   ). 
       FIG.  24    illustrates an exemplary operation of the touch detection scan of the display panel with a touch detection function  7 , where (A) illustrates a waveform of the AC drive signal VcomAC, (B) illustrates a waveform of the DC drive signal VcomDC, (C) illustrates waveforms of the scan signal St, (D) illustrates waveforms of the drive signal Vcom, and (E) illustrates a waveform of the touch detection signal Vdet. 
     As shown in  FIG.  24   , the drive electrode driver  18  sequentially applies the AC drive signal VcomAC to the relevant drive electrode block B based on the scan signal St ((C) of  FIG.  24   ) generated by the touch detection scan section  52  ((D) of  FIG.  24   ) to perform touch detection scan. In this operation, the drive electrode driver  18  continuously supplies the AC drive signal VcomAC to the corresponding kth drive electrode block B(k) during a period where the kth scan signal St(k) is high, for example. Specifically, in the first embodiment, the AC drive signal VcomAC is applied only while the Vcom selection signal VCOMSEL is high in the period where the kth scan signal St(k) is high, as shown in (E) of  FIG.  14   . Contrarily, in the second embodiment, the AC drive signal VcomAC is continuously applied in the period where the kth scan signal St(k) is high, as shown in (D) of  FIG.  24   . 
     The AC drive signal VcomAC or the DC drive signal VcomDC is applied to the drive electrode COML along one horizontal line relevant to the display operation. In detail, in the case where the drive electrode COML along one horizontal line relevant to the display operation is not included in the drive detection block B relevant to touch detection operation, the DC drive signal VcomDC is applied to the drive electrode COML. Contrarily, the drive electrode COML along one horizontal line relevant to the display operation is included in the drive detection block B relevant to the touch detection operation at the timing W 1  in  FIG.  10   . In such a case, the AC drive signal VcomAC is applied to the drive electrode COML. The DC voltage of the DC drive signal VcomDC and the low-level voltage of the AC drive signal VcomAC are generated by the low-level-voltage generation sub-section  62  of the drive signal generation section  15  as shown in  FIG.  11    and thus have substantially the same voltage level. In this way, since the voltage of the drive electrode COML along one horizontal line relevant to the display operation is substantially the same between the case where the one horizontal line corresponds to the drive detection block B relevant to the touch detection operation and another case, substantially the same pixel signal is written during the write period PW, thereby suppressing a reduction in image quality. 
     It is to be noted that in the case where the DC voltage of the DC drive signal VcomDC is slightly different from the low-level voltage of the AC drive signal VcomAC due to a difference in performance between the buffers  64  and  65  ( FIG.  11   ), the voltage is differently written into a pixel between the case where the DC drive signal VcomDC is supplied to the drive electrode COML along one horizontal line relevant to the display operation and the case where the AC drive signal VcomAC is supplied thereto, leading to a possibility of degradation in image quality. In such a case, the AC drive signal VcomAC is desirably applied to the drive electrode COML during periods other than the write period PW as in the display panel with a touch detection function  1  of the first embodiment. 
     As described above, in the second embodiment, the drive signal supplied to the drive electrode is selected only based on the scan signal St, which simplifies the configurations of the scan control section and the drive section. Other effects are the same as in the first embodiment. 
     [Modification 2] 
     In the second embodiment, the drive signal generation section  15  may be configured as shown in  FIG.  18   , for example, as in the modification 1-1 of the first embodiment. In addition, the drive electrode driver  18  may directly drive the drive electrodes COML by one at a time as in the modification 1-2 of the first embodiment. In addition, touch detection scan may be performed as shown in  FIG.  20    as in the modification 1-3 of the first embodiment. 
     3. APPLICATION EXAMPLES 
     Next, application examples of each display panel with a touch detection function in the above-described embodiments and modifications are now described with reference to  FIGS.  25  to  29 G . The display panel with a touch detection function described in the embodiments and others is applicable to electronic units in various fields, including a television apparatus, a digital camera, a notebook personal computer, a mobile terminal device such as a mobile phone, and a video camera. In other words, the display panel with a touch detection function in the embodiments and others is applicable to electronic units in various fields for displaying externally-input or internally-generated video signals as still or video images. 
     Application Example 1 
       FIG.  25    shows appearance of a television apparatus applied with the display panel with a touch detection function according to the embodiments and others. The television apparatus has, for example, an image display screen section  510  including a front panel  511  and a filter glass  512 . The image display screen section  510  is configured of the display panel with a touch detection function according to the embodiments and others. 
     Application Example 2 
       FIGS.  26 A and  26 B  show appearance of a digital camera applied with the display panel with a touch detection function according to the embodiments and others. The digital camera has, for example, a light emitting section for flash  521 , a display section  522 , a menu switch  523 , and a shutter button  524 . The display section  522  is configured of the display panel with a touch detection function according to the embodiments and others. 
     Application Example 3 
       FIG.  27    shows appearance of a notebook personal computer applied with the display panel with a touch detection function according to the embodiments and others. The notebook personal computer has, for example, a main body  531 , a keyboard  532  for input operation of letters and the like, and a display section  533  for displaying images. The display section  533  is configured of the display panel with a touch detection function according to the embodiments and others. 
     Application Example 4 
       FIG.  28    shows appearance of a video camera applied with the display panel with a touch detection function according to the embodiments and others. The video camera has, for example, a main body section  541 , an object-shooting lens  542  provided on a front side face of the main body section  541 , a start/stop switch  543  for shooting, and a display section  544 . The display section  544  is configured of the display panel with a touch detection function according to the embodiments and others. 
     Application Example 5 
       FIGS.  29 A to  29 G  show appearance of a mobile phone applied with the display panel with a touch detection function according to the embodiments and others. For example, the mobile phone is configured of an upper housing  710  and a lower housing  720  connected to each other by a hinge section  730 , and has a display  740 , a sub display  750 , a picture light  760 , and a camera  770 . The display  740  or the sub display  750  is configured of the display panel with a touch detection function according to the embodiments and others. 
     While the present technology has been described with the several embodiments, the modifications, and the application examples to electronic units hereinbefore, the technology is not limited to the embodiments and others, and various modifications or alterations may be made. 
     For example, while the drive electrodes COML are provided on the TFT substrate  21  and the pixel electrodes  22  are provided on the drive electrodes COML with the insulating film  23  therebetween as shown in  FIG.  6    in the embodiments and others, this is not limitative. Instead, for example, the pixel electrodes  22  may be provided on the TFT substrate  21 , and the drive electrodes COML may be provided on the pixel electrodes  22  with the insulating film  23  therebetween. 
     For example, while the touch detection device is integrated with the liquid crystal display device including liquid crystal of a transverse electric mode such as a FFS mode and an IPS mode in the embodiments and others, the touch detection device may be integrated with a liquid crystal display device including liquid crystal of various modes such as a twisted nematic (TN) mode, a vertical alignment (VA) mode, and an electrically controlled birefringence (ECB) mode instead. In the case where such liquid crystal is used, the display device with a touch detection function is configured as shown in  FIG.  30   .  FIG.  30    illustrates an exemplary sectional structure of a major part of a display device with a touch detection function  10 D, showing a configuration where a liquid crystal layer  6 B is sandwiched between a pixel substrate  2 B and a counter substrate  3 B. Since names and functions of other sections are similar to those shown in the case of  FIG.  6   , description of them is omitted. This example is different from the case of  FIG.  6    in that the drive electrodes COML used for both display and touch detection are provided on the counter substrate  3 B. 
     In addition, while, for example, a so-called in-cell type display device, where a liquid crystal display device is integrated with a capacitance-type touch detection device, is used in the above-described embodiments and others, this is not limitative. Instead, for example, a so-called on-cell type display device, where the capacitance-type touch detection device is mounted on the surface of the liquid crystal display device, may be used. In the on-cell type display device, for example, in the case where noise in touch detection drive is transmitted from the touch detection device to the liquid crystal display device, the noise is reduced through the driving as in the embodiments, leading to suppression of a reduction in image quality of the liquid crystal display device. 
     In addition, for example, while the liquid crystal elements are used for the display elements in the above-described embodiments and others, this is not limitative. Instead, electro luminescence (EL) elements may be used, for example. 
     It is possible to achieve at least the following configurations from the above-described exemplary embodiments and the modifications of the disclosure. 
     (1) A display panel with a touch detection function including: 
     one or more display elements; 
     one or more drive electrodes; 
     one or more touch detection electrodes; and 
     a drive section selectively applying a DC drive signal or an AC drive signal to the drive electrodes. 
     (2) The display panel according to (1), 
     wherein the display elements perform write operation for display during a write period, 
     the AC drive signal has a pulse waveform that transits from a first voltage to a second voltage corresponding to a DC voltage level of the DC drive signal at a transition timing in a period other than the write period, 
     the drive section applies the AC drive signal to the drive electrodes in an enable period including the transition timing, and applies the DC drive signal to the drive electrodes in a period other than the enable period to perform touch detection drive. 
     (3) The display panel according to (2), 
     wherein the AC drive signal has a pulse waveform that includes the first voltage in a pulse period different from the write period, and includes the second voltage in a period other than the pulse period, and 
     the transition timing corresponds to end timing of the pulse period. 
     (4) The display panel according to (3), wherein the enable period is in a period other than the write period. 
     (5) The display panel according to (3) or (4), wherein the enable period includes the pulse period. 
     (6) The display panel according to (3), 
     wherein the plurality of display elements are arranged in a matrix and line-sequentially scanned for display operation, and 
     the enable period corresponds to one horizontal period or consecutive, multiple horizontal periods. 
     (7) The display panel according to any one of (1) to (6), further including 
     a drive signal generation section generating the DC drive signal and the AC drive signal, 
     wherein the drive signal generation section includes 
     a first-voltage generation sub-section generating the first voltage, 
     a second-voltage generation sub-section generating a voltage corresponding to a DC voltage level of the DC drive signal, 
     a buffer circuit generating the second voltage based on the voltage output from the second voltage generation sub-section, and 
     a switching circuit generating the AC drive signal through switching the first voltage and the second voltage from each other. 
     (8) The display panel according to any one of (2) to (7), further including 
     a touch detection section, 
     wherein the drive electrodes are formed to extend in a predetermined direction, 
     the touch detection electrodes are formed to extend in a direction crossing the extending direction of the drive electrodes in a layer different from a layer of the drive electrodes, and 
     the drive section sequentially selects one or more drive electrodes among the drive electrodes as a drive object electrode, and drives the drive object electrode for touch detection while applying the DC drive signal to drive electrodes other than the drive object electrode, and 
     the touch detection section detects a touch event based on signals output from the touch detection electrodes. 
     (9) The display panel according to any one of (1) to (8), 
     wherein the display element includes 
     a liquid crystal layer, and 
     a pixel electrode provided between the liquid crystal layer and the drive electrodes, or disposed facing the liquid crystal layer with the drive electrodes therebetween. 
     (10) The display panel according to any one of (1) to (8), 
     wherein the display element includes 
     a liquid crystal layer, and 
     a pixel electrode disposed facing the drive electrodes with the liquid crystal layer therebetween. 
     (11) A method of driving a display panel with a touch detection function, including: 
     driving one or more display elements for display; and 
     selectively applying a DC drive signal or an AC drive signal to one or more drive electrodes. 
     (12) A drive circuit including: 
     a display drive section driving one or more display elements; and 
     a touch detection drive section selectively applying a DC drive signal or an AC drive signal to one or more drive electrodes. 
     (13) An electronic unit including: 
     a display panel with a touch detection function; and 
     a control section controlling operation using the display panel with a touch detection function, 
     wherein the display panel with a touch detection function includes 
     one or more display elements, 
     one or more drive electrodes, 
     one or more touch detection electrodes, and 
     a drive section selectively applying a DC drive signal or an AC drive signal to the drive electrodes. 
     The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2011-89429 filed in the Japan Patent Office on Apr. 13, 2011 and Japanese Priority Patent Application JP 2011-242797 filed in the Japan Patent Office on Nov. 4, 2011, the entire content of which is hereby incorporated by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.