Patent Publication Number: US-11644725-B2

Title: Driving circuit and display device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/931,401, filed May 13, 2020, which claims priority from Korean Patent Application No. 10-2019-0073354, filed on Jun. 20, 2019, which are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a driving circuit and a display device. 
     Description of the Background 
     The growth of the intelligent society leads to increased demand for image display devices and use of various types of display devices, such as liquid crystal displays, organic light emitting displays, etc. 
     The display device recognizes the user&#39;s touch on the display panel and performs input processing based on the recognized touch so as to provide more various functions to the user. 
     An example display device capable of touch recognition may apply touch driving signals to multiple touch electrodes arranged or embedded in the display panel, sense a variation in capacitance caused by the user&#39;s touch, and detect whether there is a touch and, if so, the coordinates of the touch. 
     The touch electrodes may be arranged on the display panel and have display driving voltages applied thereto. As a touch driving signal is applied to the display driving electrodes, display driving may be not enabled during the period of sensing the touch or image quality abnormality may occur. 
     SUMMARY 
     The present disclosure provides a driving circuit and display device, which use an electrode for display driving as a touch electrode and are capable of performing touch sensing simultaneously with display driving. 
     The present disclosure provides a driving circuit and display device, which may prevent image quality abnormality due to application of a signal for touch driving to the display driving electrode. 
     According to various aspects of the disclosure, a display device comprises a plurality of gate lines, a plurality of data lines, a plurality of pixel electrodes electrically connected with the data lines, a plurality of common electrodes corresponding to two or more pixel electrodes among the plurality of pixel electrodes, a data driving circuit outputting data voltages to the plurality of data lines, and a driving circuit outputting a first driving signal with a first voltage level to at least one common electrode of the plurality of common electrodes in a first driving period and a second driving signal with a second voltage level and a third voltage level to the at least one common electrode in a second driving period, the second driving signal being a pulse signal. The second voltage level and the third voltage level differ from the first voltage level. 
     Here, the first voltage level may be higher than the second voltage level and lower than the third voltage level. 
     Or, the first voltage level may be lower than the second voltage level, and the second voltage level may be lower than the third voltage level. 
     Thus, when the data voltage corresponding to the same grayscale in the first driving period and second driving period is supplied, the difference between the data voltage and the voltage applied to the common electrode in the first driving period may differ from the difference between the data voltage and the voltage applied to the common electrode in the second driving period. 
     According to various aspects of the disclosure, a driving circuit comprises an electrode driver outputting a first driving signal with a first voltage level to at least one common electrode of a plurality of common electrodes embedded in a panel in a first driving period and a second driving signal with a second voltage level and a third voltage level to the at least one common electrode in a second driving period, the second driving signal being a pulse signal, and the electrode driver receiving a sensing signal from at least one common electrode to which the second driving signal has been applied in the second driving period and a sensing signal converter outputting sensing data into which the sensing signal received in the second driving period has been converted. The second voltage level and the third voltage level differ from the first voltage level. 
     According to various aspects of the disclosure, touch sensing and display driving may simultaneously be performed by supplying the data voltage modulated based on the touch driving signal in the period during which the touch driving signal is applied to the common electrode. 
     According to various aspects of the disclosure, the level of the voltage applied to the common electrode in the period during which no touch driving signal is applied may be set to differ from the voltage level of the touch driving signal, thereby preventing an image quality abnormality from occurring in the touch driving signal-applied period. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and features, and advantages of the present disclosure will be more clearly understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a view schematically illustrating a configuration of a display device according to the present disclosure; 
         FIG.  2    is a view illustrating an example of timing of display driving and touch sensing of a display device according to the present disclosure; 
         FIG.  3    is a view illustrating another example of timing of display driving and touch sensing of a display device according to the present disclosure; 
         FIG.  4    is a view illustrating various examples of timing of finger sensing and pen sensing according to the display driving and touch sensing timings shown in  FIG.  3   ; 
         FIG.  5    is a view illustrating an example of image quality abnormality due to signals applied to a common electrode during a period when touch sensing is performed and a period when touch sensing is not performed in a display device according to the present disclosure; 
         FIG.  6    is a view illustrating example signals applied to a common electrode during a period when touch sensing is performed and a period when touch sensing is not performed in a display device according to the present disclosure; 
         FIG.  7    is a view illustrating other example signals applied to a common electrode during a period when touch sensing is performed and a period when touch sensing is not performed in a display device according to the present disclosure; 
         FIG.  8    is a view illustrating an example difference between common voltage and data voltage, caused by signals applied to a common electrode during a period when touch sensing is performed and a period when touch sensing is not performed in a display device according to the present disclosure; 
         FIG.  9    is a view illustrating an example in which image quality is enhanced when a signal is applied to a common electrode according to the examples shown in  FIGS.  6  to  8   ; and 
         FIG.  10    is a view illustrating an example configuration of a power circuit and a touch driving circuit for outputting signals to a common electrode in a display device according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples or aspects of the disclosure, reference will be made to the accompanying drawings in which it is shown by way of illustration specific examples or aspects that can be implemented, and in which the same reference numerals and signs can be used to designate the same or like components even when they are shown in different accompanying drawings from one another. Further, in the following description of examples or aspects of the disclosure, detailed descriptions of well-known functions and components incorporated herein will be omitted when it is determined that the description may make the subject matter in some aspects of the disclosure rather unclear. The terms such as “including”, “having”, “containing”, “constituting” “make up of”, and “formed of” used herein are generally intended to allow other components to be added unless the terms are used with the term “only”. As used herein, singular forms are intended to include plural forms unless the context clearly indicates otherwise. 
     Terms, such as “first”, “second”, “A”, “B”, “(A)”, or “(B)” may be used herein to describe elements of the disclosure. Each of these terms is not used to define essence, order, sequence, or number of elements etc., but is used merely to distinguish the corresponding element from other elements. 
     When it is mentioned that a first element “is connected or coupled to”, “contacts or overlaps” etc. a second element, it should be interpreted that, not only can the first element “be directly connected or coupled to” or “directly contact or overlap” the second element, but a third element can also be “interposed” between the first and second elements, or the first and second elements can “be connected or coupled to”, “contact or overlap”, etc. each other via a fourth element. Here, the second element may be included in at least one of two or more elements that “are connected or coupled to”, “contact or overlap”, etc. each other. 
     When time relative terms, such as “after,” “subsequent to,” “next,” “before,” and the like, are used to describe processes or operations of elements or configurations, or flows or steps in operating, processing, manufacturing methods, these terms may be used to describe non-consecutive or non-sequential processes or operations unless the term “directly” or “immediately” is used together. 
     In addition, when any dimensions, relative sizes etc. are mentioned, it should be considered that numerical values for an elements or features, or corresponding information (e.g., level, range, etc.) include a tolerance or error range that may be caused by various factors (e.g., process factors, internal or external impact, noise, etc.) even when a relevant description is not specified. Further, the term “may” fully encompasses all the meanings of the term “can”. 
       FIG.  1    is a view schematically illustrating a configuration of a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  1   , according to various aspects of the disclosure, a display device  100  may include a display panel  110 , a gate driving circuit  120 , a data driving circuit  130 , and a controller  140 . The display device  100  may include a touch driving circuit  150  for sensing a touch on the display panel  110  and a touch controller  160 . 
     The display panel  110  may include a plurality of gate lines GL, a plurality of data lines DL, and multiple subpixels SP at the crossings of the gate lines GL and the data lines DL. A pixel electrode PXL may be disposed in each subpixel SP. 
     Multiple touch electrodes TE may be arranged or embedded in the display panel  110 , and multiple touch lines TL for electrically connecting the touch electrodes TE with the touch driving circuit  150  may be arranged on the display panel  110 . 
     A configuration for display driving in the display device  100  is described first. The gate driving circuit  120  controls the driving timing of the subpixels SP arranged in the display panel  110 . The data driving circuit  130  supplies data voltage Vdata corresponding to image data to the subpixels SP to allow the subpixels SP to represent a brightness corresponding to the grayscale of the image data, thereby displaying an image. 
     Specifically, the gate driving circuit  120  may be controlled by the controller  140  to sequentially output scan signals to the plurality of gate lines GL disposed in the display panel  110 , controlling the driving timing of the subpixels SP. 
     The gate driving circuit  120  may include one or more gate driver integrated circuits (GDICs). Depending on driving schemes, the gate driving circuit  120  may be positioned on only one side, or each of two opposite sides, of the display panel  110 . 
     Each gate driver integrated circuit (GDIC) may be connected to the bonding pad of the display panel  110  in a tape automated bonding (TAB) or chip-on-glass (COG) scheme or may be implemented in a gate-in-panel (GIP) type to be directly disposed in the display panel  110  or, in some cases, may be integrated in the display panel  110 . Each gate driver integrated circuit (GDIC) may also be implemented in a chip-on-film (COF) scheme to be mounted on a film connected to the display panel  110 . 
     The data driving circuit  130  receives image data (or input data) from the controller  140  and converts the image data into an analog data voltage. The data driving circuit  130  outputs a data voltage to each data line DL according to the timing of applying a scan signal via the gate line GL, allowing each subpixel SP to represent a brightness according to the image data. 
     The data driving circuit  130  may include one or more source driver integrated circuits (SDICs). 
     Each source driver integrated circuit (SDIC) may include, e.g., shift registers, latch circuits, digital-analog converters, and output buffers. 
     Each source driver integrated circuit (SDIC) may be connected to the bonding pad of the display panel  110  in a TAB or COG scheme or may be directly disposed in the display panel  110  or, in some cases, may be integrated in the display panel  110 . Each source driver integrated circuit (SDIC) may be implemented in a COF scheme in which case each source driver integrated circuit (SDIC) may be mounted on a film connected to the display panel  110  and be electrically connected with the display panel  110  via wires on the film. 
     The controller  140  supplies various control signals to the gate driving circuit  120  and the data driving circuit  130  and controls the operation of the gate driving circuit  120  and the data driving circuit  130 . 
     The controller  140  enables the gate driving circuit  120  to output scan signals according to the timing of implementing each frame, converts image data received from the outside to meet the data signal format used by the data driving circuit  130 , and outputs the resultant image data to the data driving circuit  130 . 
     The controller  140  receives, from the outside (e.g., a host system), various timing signals including a vertical synchronization signal VSYNC, a horizontal synchronization signal HSYNC, an input data enable signal DE, and a clock signal, along with the image data. 
     The controller  140  may generate a diversity of control signals using the timing signals received from the outside and output the control signals to the gate driving circuit  120  and the data driving circuit  130 . 
     As an example, to control the gate driving circuit  120 , the controller  140  outputs various gate control signals GCS including a gate start pulse GSP, a gate shift clock GSC, and a gate output enable signal GOE. 
     The gate start pulse GSP controls the operation start timing of one or more gate driver integrated circuits GDICs constituting the gate driving circuit  120 . The gate shift clock GSC is a clock signal commonly input to one or more gate driver integrated circuits GDICs and controls the shift timing of the scan signals. The gate output enable signal GOE designates timing information about one or more gate driver integrated circuits GDICs. 
     To control the data driving circuit  130 , the controller  140  outputs various data control signals DCS including, e.g., a source start pulse SSP, a source sampling clock SSC, and a source output enable signal SOE. 
     The source start pulse SSP controls the data sampling start timing of one or more source driver integrated circuits SDICs constituting the data driving circuit  130 . The source sampling clock SSC is a clock signal for controlling the sampling timing of data in each source driver integrated circuit (SDIC). The source output enable signal SOE controls the output timing of the data driving circuit  130 . 
     The display device  100  may further include a power management integrated circuit (not shown) that supplies various voltages or currents to, e.g., the display panel  110 , the gate driving circuit  120 , the data driving circuit  150 , and the touch driving circuit  150  or controls various voltages or currents to be supplied. 
     Each subpixel SP may be defined by the crossing of the gate line GL and the data line DL, and liquid crystals or a light emitting element may be disposed in each subpixel SP depending on the type of the display device  100 . 
     As an example, when the display device  100  is a liquid crystal display device, the display device  100  may include a light source device, such as a backlight unit, to emit light to the display panel  110 . Liquid crystals are disposed in the subpixel SP of the display panel  110 . The alignment of liquid crystals may be adjusted by an electric field created as data voltage (Vdata) is applied to each subpixel SP, thereby representing a brightness per image data and displaying an image. 
     As an example, when the display device  100  is an organic light emitting display device, an organic light emitting diode (OLED) is disposed in each subpixel SP, and the current flowing to the OLED per data voltage supplied to the subpixel SP may be controlled to represent a brightness per image data supplied to the subpixel SP. 
     Or, in some cases, a light emitting diode (LED) may be disposed in each subpixel SP to display images. 
     Meanwhile, according to various aspects of the disclosure, the display device  100  may detect the user&#39;s touch on the display panel  110  using the touch driving circuit  150  and the touch electrodes TE included in the display panel  110 . 
     As an example, the display panel  110  may include the plurality of touch electrodes (TE) and a plurality of touch lines (TL) to connect the touch electrodes TE with the touch driving circuit  150 . 
     The touch electrodes TE may be disposed on, or embedded in, the display panel  110 . 
     The touch electrodes TE may be electrodes used for display driving or be separate electrodes provided for touch sensing. The touch electrode TE may be a whole transparent electrode with no open area or an opaque mesh-shaped electrode. The touch electrode TE may be a transparent electrode partially having an open area. 
     As an example, when the display device  100  is a liquid crystal display device, the touch electrode TE may be a common electrode COM embedded in the display panel  110  and, upon display driving, having a common voltage Vcom applied thereto. 
     In other words, separate common electrodes COM may be arranged on the display panel  110  to be used as touch electrodes TE for touch sensing. Thus, each touch electrode TE may be disposed to overlap multiple subpixels SP. 
     According to various aspects of the disclosure, although the display device  100  is a liquid crystal display device, as an example, for ease of description, aspects of the disclosure are not limited thereto. 
     The touch electrodes TE may be electrically connected with the touch driving circuit  150  via the touch lines TL arranged on the display panel  110 . 
     The touch driving circuit  150  may include an amplifier that outputs a touch driving signal TDS to the touch electrode TE and receives a touch sensing signal TSS from the touch electrode TE, an integrator that integrates output signals from the amplifier, and an analog-digital converter that converts the output signal from the integrator into a digital signal. 
     In some cases, the touch driving circuit  150  may be integrated with the data driving circuit  130 . 
     The touch driving circuit  150  may be connected with the touch electrodes TE in a one-to-one manner to receive the touch sensing signal TSS. In other words, the touch driving circuit  150  may output the touch driving signal TDS to the touch electrode TE via the touch line TL, receive the touch sensing signal TSS, and sense a variation in self capacitance due to a touch. 
     The touch electrodes TE may be divided into driving electrodes and sensing electrodes, and the touch driving circuit  150  may connect to each of the driving electrodes and the sensing electrodes. In such a case, the touch driving circuit  150  may output the touch driving signal TDS to the driving electrode, receive the touch sensing signal TSS from the sensing electrode, and sense a variation in mutual capacitance between the driving electrode and sensing electrode due to a touch. 
     The touch driving circuit  150  converts the received touch sensing signal TSS into digital sensing data and transmits the digital sensing data to the touch controller  160 . 
     The touch controller  160  may control the driving of the touch driving circuit  150 , receive sensing data from the touch driving circuit  150 , and detect the user&#39;s touch on the display panel  110  based on the received sensing data. 
     In other words, the touch controller  160  may detect a variation in self capacitance or mutual capacitance from the sensing data and detect, e.g., the presence or absence of a touch or the coordinates of a touch based on the detected capacitance variation. 
     According to various aspects of the disclosure, the display device  100  may perform touch sensing simultaneously with display driving, using the common electrodes COM as touch electrodes TE. In other words, touch sensing may be performed during the whole or part of the period when display driving is performed. 
       FIG.  2    is a view illustrating an example of timing of display driving and touch sensing of a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  2   , according to various aspects of the disclosure, the display device  100  may perform touch sensing simultaneously with display driving. 
     Here, the touch sensing period may be identical to the display driving period or may be a blank period within the display driving period. In other words, touch sensing may be independently performed regardless of display driving and, thus, touch sensing may be performed simultaneously with display driving. 
     When touch sensing is performed simultaneously with display driving, the touch driving signal TDS is applied to the touch electrode TE. Here, the touch driving signal TDS may be a pulse signal whose voltage varies over time. For display driving, data voltage Vdata may be supplied to the data line DL, and a scan signal generated using a gate high voltage VGH and a gate low voltage VGL may be output to the gate line GL. 
     At this time, when the common electrode COM of the display panel  110  is used as the touch electrode TE, the touch driving signal TDS is applied to the touch electrode TE. Thus, no voltage difference corresponding to image data may be formed between the common electrode COM and the pixel electrode PXL to which the data voltage Vdata is applied. 
     In other words, since the touch driving signal TDS is varied over time, no voltage difference corresponding to the image data is formed between the pixel electrode PXL and the common electrode COM to which the touch driving signal TDS is applied, so that the subpixel SP may not represent the brightness corresponding to the image data. 
     Thus, a voltage difference corresponding to the image data may be formed between the pixel electrode PXL and the touch driving signal (TDS)-applied common electrode COM by supplying modulated data voltage Vdata to the data line DL based on the touch driving signal TDS. 
     As an example, the data voltage Vdata may be modulated based on the pulse width modulation signal PWM used for generating the touch driving signal TDS. 
     The modulation of the data voltage Vdata may be performed, e.g., in such a manner as to modulate the gamma voltage used for generating the data voltage Vdata in the data driving circuit  130 . Or, the ground voltage of the display panel  110  may be modulated so that the modulated data voltage Vdata may be supplied to the data line DL. 
     The gate low voltage VGL may be modulated based on the touch driving signal TDS, so that the modulated scan signal may be applied to the gate line GL, allowing the gate line GL to be normally driven. 
     As such, the data voltage Vdata applied to the data line DL and the scan signal applied to the gate line GL may be modulated based on the touch driving signal TDS, allowing display driving and touch sensing to be performed simultaneously. 
     According to various aspects of the disclosure, the display device  100  may perform touch sensing simultaneously with display driving or may perform touch sensing only during a portion of the display driving period. 
       FIG.  3    is a view illustrating another example of timing of display driving and touch sensing of a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  3   , touch sensing may be performed within the display driving period. 
     Within the period during which display driving and touch sensing are simultaneously performed, a touch driving signal TDS for touch sensing may be applied to the common electrode COM, and data voltage Vdata modulated based on the touch driving signal TDS may be supplied to the data line DL. The scan signal modulated based on the touch driving signal TDS may be applied to the gate line GL. 
     This means that display driving and touch sensing are performed temporally within the same time period but not that the display driving area and touch sensing area are the same. In other words, although the modulated common voltage Vcom is supplied to the overall display panel  110  within the period during which display driving and touch sensing are simultaneously performed in one frame, the area where the data voltage Vdata is supplied and the area where the sensing signal is detected may not overlap each other. 
     As such, the display device  100  may supply the modulated voltage to, e.g., the common electrode COM and data line DL, displaying an image on the display panel  110  and performing touch sensing. 
     The display device  100  may perform display driving alone during some period within one frame. 
     In the period during which display driving only is performed, a predetermined level (e.g., 0V or 5.5V) of constant voltage, rather than the modulated voltage, may be applied to the common electrode COM. Further, non-modulated data voltage Vdata may be applied to the data line DL, and a non-modulated scan signal may be applied to the gate line GL. In other words, during the period when display driving alone is performed, the data voltage Vdata for display driving alone may be applied to the data line DL, and the gate voltage Vgate for display driving alone may be applied to the gate line GL. 
     Thus, even when touch sensing is performed simultaneously with display driving, a non-modulated constant voltage may be applied to the common electrode COM, and there may exist a period during which only display driving is performed. Further, in some cases, display driving and pen touch sensing may be performed within the period during which the constant voltage is applied to the common electrode COM. 
       FIG.  4    is a view illustrating various example schemes of performing finger sensing or pen sensing according to the timing of display driving and touch sensing as shown in  FIGS.  2  and  3   . 
     Referring to  FIG.  4   , according to various aspects of the disclosure, the display device  100  may perform display driving only and may perform touch sensing simultaneously with display driving. The display device  100  may perform touch sensing only during a portion of the display driving period and may perform finger sensing (F/S) and pen sensing (P/S) during the same or different periods. 
     As an example, the display device  100  may perform only display driving without touch sensing, e.g., finger sensing (F/S) and pen sensing (P/S), in one frame, e.g., the pth frame. 
     Or, the display device  100  may perform touch sensing, such as finger sensing (F/S) or pen sensing (P/S), during a portion, when touch sensing is needed, of the period when display driving is performed, e.g., the qth frame. Here, finger sensing (F/S) and pen sensing (P/S) may be performed during non-overlapping periods. 
     Or, the display device  100  may perform touch sensing during the display driving period, e.g., the rth frame, and may perform finger sensing (F/S) and pen sensing (P/S) during overlapping periods. In such a case, the respective results of the finger sensing (F/S) and pen sensing (P/S) may be differentiated by signal analysis per sensing positions or an algorithm determined by the touch controller. 
     Without limitations thereto, display driving and touch sensing (finger sensing or pen sensing) may independently be performed at various timings. 
     As touch sensing is performed independently from display driving, a sufficient touch sensing period may be secured, and the performance of touch sensing may be enhanced. 
     In some cases, touch sensing may be performed during a portion of the display driving period but not during another portion of the display driving period. In other words, touch sensing may be performed within a required period regardless of display driving. 
     At this time, different signals may be applied to the common electrode COM, which is used as the touch electrode TE, in the period during which touch sensing is performed and the period during which no touch sensing is performed. Thus, a difference in image quality may occur between the period during which the touch driving signal TDS, a modulated signal, is applied to the common electrode COM and the period during which a non-modulated common voltage Vcom is applied to the common electrode COM. 
       FIG.  5    is a view illustrating an example of image quality abnormality due to signals applied to a common electrode COM during a period when touch sensing is performed and a period when touch sensing is not performed in a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  5   , the first driving period P 1  denotes a period during which display driving is performed, but touch sensing is not, and the second driving period P 2  denotes a period during which display driving and touch sensing are performed simultaneously. 
     Since no touch sensing is performed in the first driving period P 1 , a non-modulated common voltage Vcom is applied to the common electrode COM. In the second driving period P 2 , a modulated touch driving signal TDS for touch sensing is applied to the common electrode COM. Further, in the second driving period P 2 , a modulated data voltage Vdata may be supplied to the pixel electrode PXL. 
     Here, as the voltage modulated based on the pulse width modulation signal PWM is applied to the common electrode COM and pixel electrode PXL in the second driving period P 2 , the difference between the common voltage Vcom and the data voltage Vdata may be uneven. 
     As an example, although the common voltage Vcom and data voltage Vdata are modulated by the same pulse width modulation signal PWM, the difference between the modulated common voltage Vcom and the modulated data voltage Vdata may be uneven due to the difference in the supply source of the pulse width modulation signal PWM. Further, the difference between the two voltages may be uneven due to a difference between the load according to an aspect the path of supplying the modulated common voltage Vcom and the load according to the path of supplying the modulated data voltage Vdata. 
     In such a case, an image quality abnormality may arise due to the uneven difference between the common voltage Vcom and data voltage Vdata supplied for image displaying. 
     As an example, as shown in  FIG.  5   , when a start signal Vst indicating the start of one frame is applied, scan signals are sequentially supplied to the gate lines GL arranged on the display panel  110 , and display driving commences. 
     At this time, in the period, e.g., the first driving period P 1 , during which no touch sensing is performed, a common voltage Vcom, which is a non-modulated constant voltage, is applied to the common electrode COM. In the period, e.g., the second driving period P 2 , during which touch sensing is performed, a touchscreen display TDS, which is a modulated common voltage Vcom, may be applied to the common electrode COM. Further, a data voltage Vdata reflecting a variation in voltage due to the voltage variation in the touch driving signal TDS applied to the common electrode COM is applied to the data line DL, and a scan signal reflecting a variation in voltage due to the voltage variation in the touch driving signal TDS applied to the common electrode COM may be applied to the gate line GL. 
     Here, as the modulated common voltage Vcom is applied, an image quality abnormality may occur in the area where display driving is performed in the period of applying the modulated common voltage Vcom. 
     Thus, in the period during which display driving is performed in area D 1  or D 3  of the display panel  110 , the constant common voltage Vcom may be applied to the common electrode COM, preventing an image quality abnormality from occurring. In contrast, as the modulated common voltage Vcom and modulated data voltage Vdata are supplied in the period during which display driving is performed in area D 2 , an image quality abnormality may occur in area D 2 . 
     According to various aspects of the disclosure, there is provided a way for preventing a difference in image quality that arises in the period during which a modulated touch driving signal TDS is applied and in the period during which a non-modulated common voltage Vcom is applied in a case where touch sensing is performed during at least a portion of the display driving period. 
       FIG.  6    is a view illustrating example signals applied to a common electrode COM during a period when touch sensing is performed and a period when touch sensing is not performed in a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  6   , the display device  100  may refrain from touch sensing like in the first driving period P 1  among the periods during which display driving is performed and may perform touch sensing like in the second driving period P 2 . 
     Whether to perform touch sensing may be controlled by a touch sync signal Tsync which may be a signal output from the touch controller  160 . The touch sync signal Tsync may be a signal generated and output from the controller  140  which controls the timing of display driving and touch sensing. Although  FIG.  6    illustrates an example in which touch sensing is performed in a period during which the touch sync signal Tsync is at a low level, touch sensing may be, in some case, performed in a period during which the touch sync signal Tsync is at a high level. 
     In the first driving period P 1 , a non-modulated constant common voltage Vcom is applied to the common electrode COM. The data voltage Vdata supplied to the data line DL and the scan signal supplied to the gate line GL may also be in a non-modulated form. Thus, the subpixel SP may be charged with the data voltage Vdata, and display driving may be performed. 
     In the second driving period P 2 , a touch driving signal TDS modulated based on a pulse width modulation signal is applied to the common electrode COM. Further, a data voltage Vdata modulated to correspond to the touch driving signal TDS may be applied to the data line DL, and a scan signal modulated to correspond to the touch driving signal TDS may be applied to the gate line GL. 
     Here, the voltage level of the common voltage Vcom applied to the common electrode COM in the first driving period P 1  may be a first voltage level L 1 . The touch driving signal TDS applied to the common electrode COM in the second driving period P 2  may be a pulse signal with a second voltage level L 2  and a third voltage level L 3 . 
     At this time, the first voltage level L 1  may differ from the second voltage level L 2  and the third voltage level L 3 . 
     As an example, the first voltage level L 1  may be lower than the second voltage level L 2  and the third voltage level L 3 . 
     When the modulated voltage is applied to the common electrode COM and the pixel electrode PXL, in the first driving period P 1 , the difference between the common voltage Vcom and the data voltage Vdata may be even whereas in the second driving period P 2 , the difference between the common voltage Vcom and the data voltage Vdata applied to the pixel electrode PXL may be uneven due to application of the modulated voltage to the common electrode COM and the pixel electrode PXL. 
     In some cases, the peak where the difference between the common voltage Vcom and the data voltage Vdata is positive (+) may be larger than the peak where the difference between the common voltage Vcom and the data voltage Vdata is negative (−). 
     In such a case, the voltage level of the common voltage Vcom applied to the common electrode COM in the second driving period P 2  may be allowed to be relatively higher than the voltage level of the common voltage Vcom applied to the common electrode COM in the first driving period P 1 . 
     This may be regarded as raising the second voltage level L 2  of the touch driving signal TDS supplied in the second driving period P 2  or as lowering the first voltage level L 1  of the common voltage Vcom supplied in the first driving period P 1 . 
     Raising the second voltage level  12  of the touch driving signal TDS supplied in the second driving period P 2  may render the root mean square (RMS) value of the differences between the common voltage Vcom and the data voltage Vdata in the first driving period P 1  and second driving period P 2  constant. 
     In other words, the difference between the common voltage Vcom and data voltage Vdata in the first driving period P 1  and the difference between the common voltage Vcom and data voltage Vdata in the second driving period P 2  may be varied by altering the minimum voltage of the touch driving signal TDS to the second voltage level L 2  which is higher than the first voltage level L 1  of the common voltage Vcom supplied in the first driving period P 1  and driving the common electrode COM. The RMS value of the differences between the common voltage Vcom and data voltage Vdata in the first driving period P 1  and the RMS value of the differences between the common voltage Vcom and data voltage Vdata in the second driving period P 2  may be allowed to remain the same. 
     By so doing, the RMS value of the differences between the common voltage Vcom and data voltage Vdata in the first driving period P 1  and second driving period P 2  may be adjusted to be even. 
     Further, when the grayscale represented by the data voltage Vdata supplied in the first driving period P 1  and second driving period P 2  is constant, the RMS value of the differences between the common voltage Vcom and data voltage Vdata in the first driving period P 1  and the RMS value of the differences between the common voltage Vcom and data voltage Vdata in the second driving period P 2  may be identical or be rendered to fall within a predetermined range. Here, as the level of the common voltage Vcom supplied in the first driving period P 1  and second driving period P 2  is varied, the difference between the common voltage Vcom and data voltage Vdata may be altered although the data voltage Vdata representing the same grayscale is supplied in the first driving period P 1  and second driving period P 2 . In other words, even when the difference between the common voltage Vcom and data voltage Vdata is varied in the first driving period P 1  and second driving period P 2 , image quality abnormality may be prevented by adjusting the RMS value of the differences between the common voltage Vcom and data voltage Vdata in each of the periods. 
     As such, a difference in image quality between the first driving period P 1  and second driving period P 2  or an image quality abnormality in the second driving period P 2  may be prevented from arising by setting different levels of voltage applied to the common electrode COM in the first driving period P 1  and second driving period P 2 . 
     In other words, the voltage level of the touch driving signal TDS may be set so that no image quality abnormality occurs in the second driving period P 2  during which the touch driving signal TDS modulated based on the pulse width modulation signal PWM is applied to the common electrode COM. The set voltage level of the touch driving signal TDS may differ from the voltage level of the common voltage Vcom applied to the common electrode COM in the first driving period P 1 . 
     In some cases, the first voltage level L 1  of the common voltage Vcom applied to the common electrode COM in the first driving period P 1  may be rendered to be higher than the second voltage level L 2  of the touch driving signal TDS applied to the common electrode COM in the second driving period P 2 . 
       FIG.  7    is a view illustrating other example signals applied to a common electrode COM during a period when touch sensing is performed and a period when touch sensing is not performed in a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  7   , a non-modulated common voltage Vcom may be applied to the common electrode COM in a first driving period P 1  among periods during which display driving is performed. Thus, non-modulated voltages or signals may be applied to the data line DL and gate line GL. 
     In a second driving period P 2 , a touch driving signal TDS modulated based on a pulse width modulation signal PWM may be applied to the common electrode COM. Thus, a data voltage Vdata modulated to correspond to the touch driving signal TDS may be supplied to the data line DL. A scan signal modulated to correspond to the touch driving signal may be applied to the gate line GL. 
     Here, the common voltage Vcom applied to the common electrode COM in the first driving period P 1  may have a first voltage level L 1 . The touch driving signal TDS applied to the common electrode COM in the second driving period P 2  may be a pulse signal with a second voltage level L 2  and a third voltage level L 3 . 
     In this case, the first voltage level L 1  may be higher than the second voltage level L 2  and lower than the third voltage level L 3 . 
     As an example, in the difference between the data voltage Vdata applied to the pixel electrode PXL via the data line DL and the touch driving signal TDS, i.e., the common voltage Vcom, applied to the common electrode COM in the second driving period P 2 , the positive (+) peak may be larger than the negative (−) peak as shown in  FIG.  7   . 
     In such a case, the difference between the data voltage Vdata and common voltage Vcom in the second driving period P 2  may be varied by lowering the second voltage level L 2  of the touch driving signal TDS applied to the common electrode COM in the second driving period P 2 . This may be regarded as raising the first voltage level L 1  of the common voltage Vcom applied to the common electrode COM in the first driving period P 1 . 
     As the voltage level of the touch driving signal TDS applied to the common electrode COM in the second driving period P 2  is adjusted, the RMS value of the differences between the data voltage Vdata and the common voltage Vcom in the second driving period P 2  may be adjusted to be identical to the RMS value of the differences between the data voltage Vdata and the common voltage Vcom in the first driving period P 1 . 
     In other words, the RMS value of the differences between the data voltage Vdata applied to the pixel electrode PXL and the common voltage Vcom applied to the common electrode COM in the first driving period P 1  and second driving period P 2  may be adjusted to a predetermined level. Hence, an image quality abnormality may be prevented from occurring due to application of a modulated voltage to, e.g., the common electrode COM and pixel electrode PXL in the second driving period P 2 . Also possible is it to prevent a significant image quality difference from the first driving period P 1  when a non-modulated voltage is applied to, e.g., the common electrode COM. 
     Further, in some cases, the period of performing touch sensing within one frame may be varied, preventing an image quality abnormality due to application of the modulated common voltage Vcom. As an example, in a case where each frame is divided into 20 periods, the modulated common voltage Vcom may be applied in the fourth, eighth, twelfth, and sixteenth periods of the first frame and in the fifth, ninth, thirteenth, and seventeenth periods of the second frame. In other words, the image quality abnormality (e.g., horizontal dimming) which occurs only in fixed areas may be dispersed and mitigated by varying, over time, the area where display driving is performed in the period during which the modulated common voltage Vcom is applied. 
       FIG.  8    is a view illustrating an example difference between common voltage Vcom and data voltage Vdata, caused by signals applied to a common electrode COM during a period when touch sensing is performed and a period when touch sensing is not performed in a display device  100  according to various aspects of the disclosure.  FIG.  9    is a view illustrating an example in which image quality is enhanced when a signal is applied to a common electrode COM according to the examples shown in  FIGS.  6  to  8   . 
     Referring to  FIG.  8   , a non-modulated common voltage Vcom is applied to the common electrode COM in a first driving period P 1 . In the first driving period P 1 , the first voltage level L 1  of the common voltage Vcom applied to the common electrode COM may be, e.g., 4.56V. 
     In a second driving period P 2 , a touch driving signal TDS modulated based on a pulse width modulation signal PWM is applied to the common electrode COM. The touch driving signal TDS may be a pulse signal with the second voltage level L 2  and the third voltage level L 3 . As an example, the second voltage level L 2  may be 4.60V, and the third voltage level L 3  may be 5.60V. 
     In other words,  FIG.  8    illustrates an example in which the first voltage level L 1  of the common voltage Vcom applied to the common electrode COM in the first driving period P 1  is lower than the second voltage level L 2  of the touch driving signal TDS applied to the common electrode COM in the second driving period P 2 . 
     The RMS value of the differences between the data voltage Vdata applied to the pixel electrode PXL and the common voltage Vcom applied to the common electrode COM in the first driving period P 1  and second driving period P 2  may be rendered to be even by setting the first voltage level L 1  to be lower than the second voltage level L 2  of the touch driving signal TDS applied to the common electrode COM in the second driving period P 2 . 
     The RMS value of the differences between the common voltage Vcom and data voltage Vdata in the first driving period P 1  and the RMS value of the differences between the common voltage Vcom and data voltage Vdata in the second driving period P 2  may be adjusted to a predetermined level by allowing the difference between the common voltage Vcom and data voltage Vdata in the first driving period P 1  and second driving period P 2  to be varied. 
     In other words, since the common voltage Vcom is 4.56V in the first driving period P 1  and, in the second driving period P 2 , the low level of the common voltage Vcom is 4.60V, the difference between the common voltage Vcom and data voltage Vdata may not be identical although the same level of data voltage Vdata is supplied in the first driving period P 1  and second driving period P 2 . 
     As an example, the difference between the common voltage Vcom and data voltage Vdata in the second driving period P 2  may be 0.04V larger than the difference between the common voltage Vcom and data voltage Vdata n the first driving period P 1 . This involves an example in which the data voltage Vdata is subtracted from the common voltage Vcom. In some cases, the difference between the common voltage Vcom and data voltage Vdata in the second driving period P 2  may also be regarded as being 0.04V smaller than in the first driving period P 1 . 
     As such, although the difference between the common voltage Vcom and data voltage Vdata is varied, the RMS value of the differences between the common voltage Vcom and data voltage Vdata may be allowed to fall within a predetermined range by setting different levels for the voltage applied to the common electrode COM in the first driving period P 1  and second driving period P 2 , thereby preventing an image quality abnormality from occurring in the period during which the modulated common voltage Vcom is applied. 
     Thus, even when there are a period during which a modulated signal is applied to the common electrode COM and a period during which a non-modulated signal is applied to the common electrode COM as shown in  FIG.  9   , it may be possible to prevent an image quality abnormality in the period during which the modulated signal is applied or a difference in image quality from that in the period during which the non-modulated signal is applied. 
       FIG.  10    is a view illustrating an example configuration of a power circuit and a touch driving circuit  150  for outputting signals to a common electrode COM in a display device  100  according to various aspects of the disclosure. 
     Referring to  FIG.  10   , a touch driving circuit  150  for driving a common electrode COM disposed on a display panel  110  may include an electrode driver  151  and a sensing signal converter  152 . 
     The electrode driver  151  may output a non-modulated common voltage Vcom or a modulated touch driving signal TDS to the common electrode COM under the control of the touch controller  160 . Upon outputting the touch driving signal TDS to the common electrode COM, the electrode driver  151  may receive a touch sensing signal TSS from the common electrode COM. 
     Upon receiving the touch sensing signal TSS from the touch driving signal (TDS)-applied common electrode COM, the sensing signal converter  152  may convert the touch sensing signal TSS into digital sensing data and transmit the digital sensing data to the touch controller  160 . 
     The electrode driver  151  may output the voltage from a first power circuit  200  or second power circuit  300  to the common electrode COM. 
     The first power circuit  200  may generate and output a first voltage V 1  with a first voltage level L 1 . The first power circuit  200  may be a power circuit included in the display device  100  to generate various voltages for display driving. 
     The first voltage V 1  generated from the first power circuit  200  may be transferred to the second power circuit  300 . 
     The second power circuit  300  may generate and output a second voltage V 2  with a second voltage level L 2  and a third voltage V 3  with a third voltage level L 3 . The second voltage level L 2  and the third voltage level L 3  may differ from the first voltage level L 1  as described above. 
     The second power circuit  300  may include a multiplexer  310 . The multiplexer  310  may be controlled by a touch sync signal Tsync output from the touch controller  160  and may receive a pulse width modulation signal PWM. 
     For example, the multiplexer  310  of the second power circuit  300  may output a first voltage V 1 , which is received from the first power circuit  200  in a period during which the touch sync signal Tsync is at a high level, to the electrode driver  151  of the touch driving circuit  150 . 
     The multiplexer  310  of the second power circuit  300  may output a second voltage V 2  and third voltage V 3 , which are generated from the second power circuit  300  in a period during which the touch sync signal Tsync is at a low level, to the electrode driver  151  of the touch driving circuit  150  based on the pulse width modulation signal PWM. 
     Thus, the electrode driver  151  of the touch driving circuit  150  may output the first voltage V 1  from the second power circuit  300  to the common electrode COM or a pulse signal of the second voltage V 2  and third voltage V 3  to the common electrode COM. 
     An image quality abnormality may be prevented from occurring due to application of the modulated common voltage Vcom to the common electrode COM by setting the first voltage V 1 , second voltage V 2 , and third voltage V 3  so that the RMS value of the differences between the common voltage Vcom applied to the common electrode COM and the data voltage Vdata applied to the pixel electrode PXL falls within a predetermined range. 
     The above description has been presented to enable any person skilled in the art to make and use the technical idea of the disclosure, and has been provided in the context of a particular application and its requirements. Various modifications, additions and substitutions to the described aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects and applications without departing from the spirit and scope of the disclosure. The above description and the accompanying drawings provide an example of the technical idea of the disclosure for illustrative purposes only. That is, the disclosed aspects are intended to illustrate the scope of the technical idea of the disclosure. Thus, the scope of the disclosure is not limited to the aspects shown, but is to be accorded the widest scope consistent with the claims. The scope of protection of the disclosure should be construed based on the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included within the scope of the disclosure.