Abstract:
A touch sensing circuit is configured to supply touch drive signals to electrodes of a touch sensitive display device and detect corresponding touch sense signals from the electrodes in response to the supplied touch drive signals, a touch sense signal indicating a change in self-capacitance of a driven electrode in response to a touch input on the driven electrode. The touch sensing circuit is further configured to integrate, for a first predetermined duration of time, a measure of each of the touch sense signals, to generate a first integrated signal corresponding to each touch sense signal; integrate, for a second predetermined duration of time, the first integrated signal, to generate a second integrated signal corresponding to each touch sense signal; and determine presence of one or more touch inputs on one or more of the electrodes based on the second integrated signal.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korea Patent Application No. 10-2015-0093289 filed on Jun. 30, 2015, the entire contents of which are incorporated herein by reference for all purposes as if fully set forth herein. 
       BACKGROUND 
       [0002]    Technical Field 
         [0003]    The present disclosure relates to a touch sensing apparatus. 
         [0004]    Discussion of the Related Art 
         [0005]    User interfaces (UIs), enabling communication between human beings (users) and various electric or electronic devices, allow users to easily control devices as they like. Typical examples of such user interfaces include keypads, keyboards, mouse, on-screen displays (OSDs), and remote controllers having an infrared or radio frequency (RF) communication function. User interface techniques have steadily advanced toward enhancing user emotions and operation convenience. Recently, user interfaces have evolved into touch UIs, voice recognition UIs, and 3D UIs, and thereamong, the touch UIs tend to be predominantly installed in portable information devices. Applications of touch UIs include a touch sensing apparatuses installed in display devices of home appliances or in portable information devices. 
         [0006]    A capacitive touch sensing apparatus has high durability and spatial precision and enables multi-touch recognition and proximity touch recognition. Capacitive touch sensors can be used in various applications, more so than existing resistive touch sensing schemes. In the capacitive touch sensing apparatus, a touch sensor maybe bonded to a display device or maybe installed in a display panel of the display device, and thus, the touch sensor is electrically coupled with the display pixels of the display device. 
         [0007]    The touch sensing apparatus determines whether a touch has been applied to the touch sensor upon sensing a change in capacitance of the touch sensor; but in some cases, an amount of a change in capacitance of the touch sensor due to an external touch is so small that it is not easy to determine whether a touch has been applied. 
         [0008]    In order to more accurately determine whether a touch has been applied, a longer touch driving period is needed. However, the touch panel coupled to the display panel is driven with the display panel in a time-division multiplexed manner within one frame period, making it difficult to secure a sufficiently long touch screen driving period. 
       SUMMARY 
       [0009]    According to one or more embodiments, a touch sensitive display device comprises a display panel comprising a plurality of display pixels defined at intersections of gate lines and data lines; a plurality of electrodes; and a touch sensing circuit. The touch sensing circuit is configured to supply touch drive signals to the electrodes and detect corresponding touch sense signals from the electrodes in response to the supplied touch drive signals, a touch sense signal indicating a change in self-capacitance of a driven electrode in response to a touch input on the driven electrode. The touch sensing circuit is further configured to integrate, for a first predetermined duration of time, a measure of each of the touch sense signals, to generate a first integrated signal corresponding to each touch sense signal; integrate, for a second predetermined duration of time, the first integrated signal, to generate a second integrated signal corresponding to each touch sense signal; and determine presence of one or more touch inputs on one or more of the electrodes based on the second integrated signal. 
         [0010]    In one or more embodiments, the touch sensitive display device is an in-cell touch sensitive display device where each of the electrodes operates as a common electrode for one or more of the display pixels during display driving mode, and operates as a touch electrode during touch driving mode. 
         [0011]    In one or more embodiments, the touch sensing circuit is configured to determine presence of touch inputs on the electrodes based on the second integrated signal by comparing the second integrated signal with a predefined threshold value, and determining a presence of a touch input on a respective electrode if the corresponding second integrated signal for the respective electrode exceeds the predefined threshold value. 
         [0012]    In one or more embodiments, the touch sensing circuit comprises an integrator circuit including a plurality of integrators connected in series. The plurality of integrators includes a first integrator to sample and accumulate the measure of the touch sense signal, based on a first control signal and a second control signal, respectively, to generate the first integrated signal; and a second integrator to sample and accumulate the first integrated signal, based on the first control signal and the second control signal, respectively, to generate the second integrated signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the principles of the invention. In the drawings: 
           [0014]      FIG. 1  is a block diagram illustrating a display device according to an embodiment. 
           [0015]      FIG. 2  is an equivalent circuit diagram of a liquid crystal cell. 
           [0016]      FIG. 3  is a plan view illustrating an interconnection structure of a touch screen according to an embodiment. 
           [0017]      FIG. 4  is a waveform view illustrating touch driving signals for sensing touch in the touch screen of  FIG. 3 . 
           [0018]      FIG. 5  is a block diagram illustrating a configuration of a touch sensing circuit, according to one or more embodiments. 
           [0019]      FIG. 6  is an equivalent circuit diagram of a touch screen according to an embodiment. 
           [0020]      FIG. 7  is a graphical illustration of principles of calculating a sensing voltage by a reception unit. 
           [0021]      FIG. 8  is a circuit diagram illustrating a multi-integrator according to an embodiment. 
           [0022]      FIG. 9  illustrates an equivalent model of the multi-integrator of  FIG. 8 . 
           [0023]      FIG. 10  illustrates calculation (e.g., detection) of the presence of touch input coordinates by an algorithm executing unit, according to one or more embodiments. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0024]    Hereinafter, embodiments of the present embodiments will be described in detail with reference to the accompanying drawings. Like reference numerals refer to like elements throughout. 
         [0025]    A display device according to an embodiment of the present disclosure may be implemented on the basis of a flat panel display device such as a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display (OLED), or an electrophoresist (EPD) display. Hereinafter, a liquid crystal display (LCD) device will be described as an example of a flat panel display device, but the display device of the present invention is not limited thereto. 
         [0026]      FIG. 1  is a block diagram illustrating a display device including a touch panel according to a first embodiment of the present disclosure. 
         [0027]    Referring to  FIG. 1 , the display device according to the first embodiment of the present invention includes a display panel driving circuit, a timing controller  22 , and a touch sensing circuit  100 . 
         [0028]    The display panel  10  includes two substrates and a liquid crystal layer formed between the two substrates. The substrates may be formed as glass substrates, plastic substrates, or film substrates. A pixel array formed on a lower substrate of the display panel  10  includes data lines DL, gate lines GL intersecting the data lines DL, and pixels disposed in a matrix form. The pixel array further includes a plurality of thin film transistors (TFTs) formed in the intersections of the data lines DL and the gate lines GL, pixel electrodes  1  for charging a data voltage in the pixels, and storage capacitors Cst connected to the pixel electrodes to maintain a pixel voltage. 
         [0029]    The pixels of the display panel  10  are disposed in the form of a matrix defined by the data lines DL and the gate lines GL. A liquid crystal cell of each of the pixels is driven by an electric field applied according to a difference between a data voltage applied to the pixel electrode  1  and a common voltage applied to a common electrode  2  to adjust a transmission amount of incident light. The TFT is turned on in response to a gate pulse from the gate line GL to supply a voltage from the data line DL to the pixel electrode  1  of the liquid crystal cell. The common electrode  2  may be formed on the lower substrate or an upper substrate. 
         [0030]    The upper substrate of the display panel  10  may include a black matrix, color filters, and the like. Polarizers are attached to the upper substrate and the lower substrate, and alignments layers are formed on inner surfaces of the substrates in contact with the liquid crystal to set a pre-tilt angle of the liquid crystal angle. A spacer maintaining a cell gap of the liquid crystal cell is formed between the upper substrate and the lower substrate of the display panel  10 . 
         [0031]    The display panel  10  may be implemented in any known liquid crystal mode such as a twisted nematic (TN) mode, a vertical alignment (VA) mode, an in-plane switching (IPS) mode, or a fringe field switching (FFS) mode. A backlight unit may be disposed on a rear surface of the display panel  10 . The backlight unit may be implemented as an edge type or direct type backlight unit and irradiate light to the display panel  10 . 
         [0032]    The display panel driving circuit may write data of an input image to the pixels of the display panel  10  by using a data driving circuit  24  and gate driving circuits  26  and  30 . 
         [0033]    The data driving circuit  24  converts digital video data RGB into a positive polarity/negative polarity gamma compensation voltage to generate a data voltage. The data driving circuit  24  supplies the data voltage to the data lines DL and reverses polarity of the data voltage under the control of the timing controller  22 . 
         [0034]    The gate driving circuits  26  and  30  sequentially supply a gate pulse (or a scan pulse) synchronized with a data voltage to the gate lines GL to select a line of the display panel  10  to which a data voltage is written. The gate driving circuits  26  and  30  include a level shifter  26  and a shift register  30 . The shift register  30  may be formed directly on the substrate of the display panel  10  in a gate-in-panel (GIP) manner. 
         [0035]    The level shifter  26  may be formed on a printed circuit board (PCB)  20  electrically connected to the lower substrate of the display panel  10 . The level shifter  26  outputs a start pulse (VST) and a clock signal CLK swung between a gate high voltage VGH and a gate low voltage VGL under the control of the timing controller  22 . The gate high voltage VGH is set to a voltage equal to or higher than a threshold voltage of the TFTs formed in the pixel array of the display panel  10 . The gate low voltage VGL is set to a voltage lower than the threshold voltage of the TFTs formed in the pixel array of the display panel  10 . In response to a start pulse ST, a first clock GCLK, and a second clock MCLK input from the timing controller  22 , the level shifter  26  outputs the start pulse VST and the clock signal CLK swung between the gate high voltage VGH and the gate low voltage VGL. The clock signals CLK output from the level shifter  26  are sequentially shifted in phase and transmitted to a shift register  30  formed in the display panel  10 . 
         [0036]    The shift register  30  is formed on the edge of the lower substrate of the display panel  10  in which the pixel array is formed, such that the shift register  30  is connected to the gate lines  12  of the pixel array. The shift register  30  includes a plurality of dependently connected stages. The shift register  30  starts to operate in response to the start pulse VST input from the level shifter  26 , and shifts an output in response to the clock signals CLK to sequentially supply a gate pulse to the gate lines of the display panel  10 . 
         [0037]    The timing controller  22  supplies digital video data input from an external host system to integrated circuits (ICs) of the data driving circuit  24 . Upon receiving a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal (Data Enable (DE)), a timing signal such as a clock, from the external host system, the timing controller  22  generates timing control signals for controlling an operation timing of the gate driving circuits  26  and  30 . The timing controller  22  or the host system generate a synchronization signal SYNC for controlling an operation timing of the display panel driving circuit and the touch sensing circuit  100 . 
         [0038]    The touch sensing circuit  100  applies a touch driving signal to sensing lines L 1  to L 4  connected to capacitive touch sensors COMs of the touch screen to count a change in a touch driving signal voltage before or after a touch or a rising or falling edge delay time of the touch driving signal to sense a change in capacitance before or after the touch (or a proximity touch) is input. The touch sensing circuit  100  converts a voltage received from capacitive sensors of the touch screen into digital data to generate touch raw data, and analyze the touch raw data by executing a preset touch recognition algorithm to detect the touch (or a proximity touch) input. The touch sensing circuit  100  transmits touch report data including coordinates of the touch (or the proximity touch) input position to the host system. 
         [0039]    The host system may be implemented as any one of a navigation system, a set-top box (STB), a DVD player, a Blu-ray player, a personal computer (PC), a home theater system, a broadcast receiver, and a phone system. The host system converts digital video signal of an input image into a format fitting to resolution of the display panel  10  by using a scaler, and transmits a timing signal together with the corresponding data to the timing controller  22 . Also, in response to the touch report data input from the touch sensing circuit  100 , the host system executes an application program associated with the touch (or the proximity touch) input. 
         [0040]      FIG. 3  is a plan view illustrating an interconnection structure of a self-capacitive touch screen (TSP).  FIG. 4  is a waveform view illustrating touch driving signals for sensing the touch screen (TSP) of  FIG. 3 . 
         [0041]    Referring to  FIGS. 3 and 4 , the self-capacitive touch screen (TSP) includes touch sensors COM. Each of the touch sensors (COM) is formed of a transparent conductive material larger than pixels. Each of the touch sensors (COM) overlaps a plurality of pixels. Each of the touch sensors (COM) is connected to self-capacitance so as to be used as an electrode of the self-capacitance during a touch screen driving period Tt 1 ,Tt 2 . 
         [0042]    The touch sensing circuit  100  may be connected to the touch sensors C 1  to C 4  through the sensing lines L 1  to L 4  in a one-to-one manner. A common voltage source (not shown) supplies a common voltage Vcom to the touch sensors COM through the sensing lines L 1  to L 4  during a display panel driving period Td 1 ,Td 2 . Thus, the touch sensors COM operate as the common electrode  2  during the display panel driving period Td 1 ,Td 2 . 
         [0043]    The touch sensing circuit  100  is disabled during the display panel driving period Td 1 ,Td 2  and enabled during the touch screen driving period Tt 1 ,Tt 2  to simultaneously supply touch driving signals (Vac) illustrated in  FIG. 4  to the sensing lines L 1  to L 4 . 
         [0044]      FIG. 5  is a view illustrating connections between the touch sensing circuit  100  and the touch sensors COM. In the self-capacitive touch screen (TSP), in order to reduce the number of input/output pins of the touch sensor circuit  100 , a multiplexer  150  may be installed between the touch sensing circuit  100  and the sensing lines L 1  to L 4  as illustrated in  FIG. 5 . When the multiplexer  150  is implemented as a 1:N (N is a positive integer equal to or greater than 2 and smaller than n) multiplexer, n/N number of input/output pins from which a touch driving signal is output in the touch sensing circuit  100  are connected to input terminals of the multiplexer  150 . The n number of output terminals of the multiplexer  150  are connected to the sensing lines L 1  to L 4  in a one-to-one manner. Thus, in the present invention, the number of pins of the touch sensing circuit  100  may be reduced by 1/N by using the multiplexer  150 . 
         [0045]    When the sensing lines L 1  to L 4  are divided into three groups, the multiplexer  150  connects n/3 number of input/output pins P 1  to Pn/3 to the sensing lines of the first group to simultaneously supply a touch driving signal to capacitive sensors connected to the sensing lines of the first group. Subsequently, the multiplexer  150  connects n/3 number of input/output pins P 1  to Pn/3 to the sensing lines of the second group to simultaneously supply a touch driving signal to capacitive sensors connected to the sensing lines of the second group. Subsequently, the multiplexer  150  connects n/3 number of input/output pins P 1  to Pn/3 to the sensing lines of the third group to simultaneously supply a touch driving signal to capacitive sensors connected to the sensing lines of the third group. Thus, the touch sensing circuit  100  may supply the touch driving signal to n number of transparent conductive block patterns COM 1  to COMn through the n/3 number of pins by using the multiplexer  150 . 
         [0046]    The touch sensing circuit  100  includes a reception unit  110 , a multi-integrator  120 , and a sampling holder unit  130 . The reception unit  110  receives a voltage of the touch driving signal changing according to capacitance of the touch sensors COM. The multi-integrator  120  accumulates the sensing voltage transferred from the reception unit  110  two or more times. Hereinafter, an embodiment will be described mainly with the multi-integrator  120  including a first integrator  121  and a second integrator  122  (illustrated in  FIG. 8 ). The sampling holder unit  130  holds an output from the multi-integrator  120  and subsequently transfers the output to the ADC  170 . 
         [0047]    Upon receiving the output from the multi-integrator  120 , the ADC converts the output into touch data, binary data, and transfers the touch data to an algorithm executing unit  180 . 
         [0048]    The algorithm executing unit  180  receives the touch data from the ADC  170  and calculates touch coordinates. 
         [0049]      FIG. 6  is an equivalent circuit diagram of a touch sensor according to an embodiment of the present invention, and  FIG. 7  is a view illustrating a principle of calculating a sensing voltage by the reception unit. 
         [0050]    Referring to  FIGS. 6 and 7 , the equivalent circuit of the touch sensor according to an embodiment of the present invention includes a resistor R and capacitors Cg, Cd, and Co. The resistor R includes lead resistance and parasitic resistance of the display panel  10  and the touch sensor COM. Cg denotes a capacitor between the sensing lines L 1  to L 4  and a gate line, and Cd is a capacitor between the sensing lines L 1  to L 4  and a data line. Co is a capacitor formed between components other than the data line DL and the gate line GL in the display panel  10 , and the sensing lines L 1  to L 4 . 
         [0051]    When a touch driving signal Vo is applied to the sensing lines L 1  to L 4 , a rising edge and a falling edge of the touch driving signal Vo are delayed by an RC delay value determined by the resistor R and the capacitors Cg, Cd, and Co. When a conductor or a finger comes into contact with the touch sensors COM, capacitance is increased by Cf (e.g., corresponding to a change in self-capacitance of a driven touch electrode due to a touch input) to increase the RC delay. For example, in  FIG. 7 , the solid line represents a falling edge of a touch driving signal when a touch input is not present, and the dotted line represents a falling edge of a touch driving signal when a touch input is present. 
         [0052]    The reception unit  110  receives a falling edge voltage V 2  of the touch driving signal for a unit time (Δt) and compares the received falling edge voltage of the touch driving signal with a reference voltage V 1 . The reference voltage V 1  indicates a falling edge voltage of the touch driving signal for the unit time (Δt) when a touch input is not present. The reception unit  110  calculates a difference (ΔV) between the reference voltage V 1  and the falling edge voltage V 2  of the touch driving signal, and outputs the calculated difference as a sensing voltage Vsen. 
         [0053]      FIG. 8  is a view illustrating the multi-integrator  120 , and  FIG. 9  is a view illustrating modeling of the multi-integrator  120 . 
         [0054]    Referring to  FIG. 8 , the multi-integrator  120  includes a first integrator  121  and a second integrator  122 . The first integrator  121  receives (e.g., samples via the first capacitor C 1 ) the sensing voltage Vsen from the reception unit  110  and accumulates it (e.g., via the second capacitor C 2 ) n times. The second integrator  122  receives (e.g., samples via the third capacitor C 3 ) an output from the first integrator  121  and accumulates it (e.g., via the fourth capacitor C 4 ) n times. 
         [0055]    The first integrator  121  accumulates the sensing voltage Vsen through operations of first switch S 1  to fourth switch S 4 . The first switch S 1  and the third switch S 3  are turned on by a first control signal CS 1  during a first period to accumulate an electric charge corresponding to the sensing voltage Vsen to a first capacitor C 1 . The operation of the first integrator  121  by the first control signal CS 1  is expressed by Equation 1 and a first transfer function (H[z]1) as follows. 
         [0000]        H ( z )1=−( C 1/ C 2)(1/(1− Z   −1 )  [Equation 1]
 
         [0056]    Here, −(C1/C2) is a gain value of the first transfer function, and Z denotes a Z domain determining stability of a system in discrete signal processing. 
         [0057]    The second switch S 2  and the fourth switch S 4  are turned on by a second control signal CS 2  during a second period and transfer the electric charges accumulated in the first capacitor C 1  to the second capacitor C 2 . 
         [0058]    As a result, the first integrator  121  accumulates the sensing voltage Vsen to a repetition number (n) of a switching signal including a pair of the first control signal and the second control signal and outputs a first integrated voltage Vout 1 . 
         [0059]    The second integrator  122  accumulates the first integrated voltage Vout 1  for a second time through operations of fifth switch S 5  through eighth switch S 8 . The fifth switch S 5  and the seventh switch S 7  are turned on by the first control signal to accumulate an electric charge corresponding to the first integrated voltage Vout 1  to a third capacitor C 3 . The operation of the second integrator  122  by the first control signal is expressed by Equation 2 and a second transfer function (H[z]2) as follows. 
         [0000]        H ( z )2=−( C 3/ C 4)(1/(1− Z   −1 )  [Equation 2]
 
         [0060]    Here, −(C3/C4) is a gain value of the third transfer function, and Z denotes a Z domain determining stability of a system in discrete signal processing. 
         [0061]    The sixth switch S 6  and the eighth switch S 8  are turned on by the second control signal and transfer electric charges accumulated in the third capacitor C 3  to the fourth capacitor C 4 . 
         [0062]    As a result, the second integrator  122  accumulates the first integrated voltage Vout 1  output from the first integrator  121  to a repetition number of a switching signal including a pair of the first control signal and the second control signal, and outputs a second integrated voltage Vout 2 . 
         [0063]    The multi-integrator  120  may be modeled as illustrated in  FIG. 9 . That is, since the multi-integrator  120  accumulates the sensing voltage Vsen for the second time and outputs the same, the sensing voltage having a magnitude proportional to the square of the accumulation number (n) is output. 
         [0064]      FIG. 10  is a view illustrating the second integrated voltage Vout 2  output by the multi-integrator  120 . In  FIG. 10 , the graph indicated by the dotted line represents an output (e.g., Vout 1 ) of a single integrator according to a comparative example. 
         [0065]    The algorithm executing unit  180  determines whether the second accumulated voltage of the multi-integrator  120  has reached a threshold voltage Vx, and when the second accumulated voltage Vout 2  is equal to or higher than the threshold voltage Vx, the algorithm executing unit  180  determines that a touch event has occurred. Here, as illustrated in  FIG. 10 , since the multi-integrator  1200  determines a touch event on the basis of the second accumulated voltage Vout 2 , the multi-integrator  120  may determine the touch event within a short period of time, compared with a comparative example indicated by the dotted line. For example, as illustrated in  FIG. 10 , the voltage obtained by accumulating a certain sensing voltage by the multi-integrator  120  for a second time has reached the threshold voltage Vx within a period of time t 3 , while an output voltage Vout 1  according to the comparative example has reached the threshold voltage Vx within a period of time t 8 . 
         [0066]    As described above, the touch sensing apparatus according to an embodiment of the present invention may determine whether a touch event has occurred within a short period of time. Thus, in the present invention, even though a touch sensing period is short, a touch event may be accurately sensed. 
         [0067]    A display panel driving period and a touch sensing period are driven in a time division manner within a first frame period. Thus, the touch sensing period may be reduced, and the display panel driving period and the touch sensing period may be driven two or more times in a time division multiplexed manner. That is, the touch sensing apparatus of the present invention may accurately sense a touch event even when a driving frequency increases so the touch sensing period is shortened. Thus, the touch sensing apparatus of the present embodiments may be advantageously applied to an LHB (Long Horizontal Blank) driving mode, and thus, a display panel may be driven at a high driving frequency. 
         [0068]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.