Abstract:
A technology to sense a touch input by the alternate feedback connection of two feedback capacitors connected to a single operational amplifier is disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Korean Patent Application No. 10-2014-0195472 filed on Dec. 31, 2014 and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are incorporated by reference in their entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to a touch input sensing device, and more particularly, to a sensing device that may reduce a circuit area and uniformly maintain touch input sensitivity. 
         [0003]    A display device, such as a liquid crystal display (LCD), an organic light-emitting display (OLED), etc., a portable transmission device, other information processing devices, etc. perform functions by using various input devices. In recent, a touch screen device is being frequently used in a portable phone, a smart phone, a palm-size PC, an automated teller machine (ATM) device, etc. as such an input device. 
         [0004]    In recent, it is a trend that the touch screen is disposed on the screen, a character is written or a picture is painted by the contact of a finger or touch pen (stylus) with a touch panel, and a desired command is executed by the clicking of an icon. The touch screen device may discern whether the finger, touch pen, etc. is in contact with the screen and information on the contact position. 
         [0005]    Touch screens may be generally classified into a resistive type and a capacitive type according to a method of sensing a touch. 
         [0006]    The resistive type touch screen has a structure in which glass or a transparent plastic plate is coated with a resistive material on which a polyester film is covered. The resistive type touch screen senses a touch point by the detection of a change in resistance that appears when a screen is touched. The resistive type touch screen has a drawback in that the touch is not sensed when pressure is weak. 
         [0007]    On the contrary, the capacitive type touch screen forms electrodes on both or either of the surfaces of glass or transparent plastic, applies a voltage to between two electrodes, analyzes a change in capacitance between two electrodes appearing when a finger is in contact with the screen, and senses a touch point. 
         [0008]    In order for the capacitive type touch screen to sense the touch point, a circuit is needed which measures a capacitance that is formed by one electrode or between two electrodes. Such a capacitance measurement circuit has been mostly used in order to measure the capacitances of various circuits or devices, and as various portable devices provide touch input interfaces recently, a range to which the capacitance measurement circuit capable of sensing the contact and approach of a user is applied is being expanded. 
         [0009]    A typical capacitance measurement circuit may use two operational amplifiers (OA) for a single measurement channel in order to remove DC noise or low-frequency noise. However, since two OAs are used for the single measurement channel, there is a drawback in that the area of the circuit increases. Also, each OA may have a fabrication error. Due to such a fabrication error, a measurement value at the single measurement channel may appear differently from design intent. However, since such a fabrication error may vary according to a measurement channel, there is a drawback in that a measurement result at each measurement channel is non-uniform. 
       SUMMARY 
       [0010]    The present disclosure provides a touch input sensing device that may reduce an impact on input noise, though a single operational amplifier OA is used. 
         [0011]    A method for sensing a touch input using a touch input sensing device provided in accordance with an aspect of the present disclosure includes an operational amplifier, a sensing electrode connected to an inverting input terminal of the operational amplifier, and a driving electrode capacitively coupled to the sensing electrode. In this case, the method includes a first step of controlling a voltage of the driving electrode to become a first voltage, and connecting a first feedback capacitor to an output terminal of the operational amplifier to form a first feedback path, one terminal of the first feedback capacitor being connected to the inverting input terminal; and after the first step, a second step of controlling the voltage of the driving electrode to become a second voltage, and connecting a second feedback capacitor to the output terminal of the operational amplifier to form a second feedback path, one terminal of the second feedback capacitor being connected to the inverting input terminal. 
         [0012]    In addition, when the inverting input terminal of the operational amplifier is connected to the output terminal of the operational amplifier to form a feedback path, the feedback path is formed through only one of the first feedback capacitor and the second feedback capacitor. 
         [0013]    Also, the touch input sensing device further includes a first switch connecting the output terminal of the operational amplifier to the other terminal of the first feedback capacitor to form the first feedback path, the first switch being operated according to a first pulse train; and a second switch connecting the output terminal of the operational amplifier to the other terminal of the second feedback capacitor to form the second feedback path, the second switch being operated according to a second pulse train. 
         [0014]    A touch input sensing device provided in accordance with another aspect of the present disclosure includes an operational amplifier; a sensing electrode connected to an inverting input terminal of the operational amplifier; a driving electrode capacitively coupled to the sensing electrode; a first feedback capacitor configured to be connected to the inverting input terminal; a second feedback capacitor configured to be connected to the inverting input terminal; a switching part comprising a plurality of switches connected to the driving electrode, the first feedback capacitor, the second capacitor, and an output terminal of the operational amplifier; and a control part. In this case, the control part is configured to perform: a first step of controlling the switching part in order that a voltage of the driving electrode to become a first voltage, and in order that the first feedback capacitor is connected to the output terminal of the operational amplifier to form a first feedback path; and after the first step, a second step of controlling the switching part in order that the voltage of the driving electrode to become a second voltage, and in order that the second feedback capacitor is connected to the output terminal of the operational amplifier to form a second feedback path. 
         [0015]    In this case, the switching part includes a first switch connecting the output terminal of the operational amplifier to the other terminal of the first feedback capacitor to form the first feedback path, the first switch being operated according to a first pulse train; and a second switch connecting the output terminal of the operational amplifier to the other terminal of the second feedback capacitor to form the second feedback path, the second switch being operated according to a second pulse train. 
         [0016]    A touch input sensing device provided in accordance with another aspect of the present disclosure includes an operational amplifier; a first feedback capacitor connected to an inverting input terminal of the operational amplifier through one terminal of the first feedback capacitor; a second feedback capacitor connected to the inverting input terminal of the operational amplifier through one terminal of the second feedback capacitor; a first switch connecting an output terminal of the operational amplifier to the other terminal of the first feedback capacitor to form a first feedback path, the first switch being operated according to a first pulse train; a second switch connecting the output terminal of the operational amplifier to the other terminal of the second feedback capacitor to form a second feedback path, the second switch being operated according to a second pulse train; a sensing electrode connected to the inverting input terminal of the operational amplifier; and a driving electrode capacitively coupled to the sensing electrode. In this case, the first pulse train and the second pulse train have time-domain shapes such that the first switch and the second switch is not simultaneously in a closed state. 
         [0017]    Also, the touch input sensing device further includes a driving part controlling a voltage of the driving electrode, wherein, the driving part is configured to control the voltage of the driving electrode so that the voltage of the driving electrode switches between a first voltage and a second voltage by being synchronized with the first pulse train or the second pulse train. 
         [0018]    Also, the operational amplifier comprises an operational transconductance amplifier, a first output driver, and a second output driver, the other terminal of the first feedback capacitor is connected to an output terminal of the first output driver, the other terminal of the second feedback capacitor is connected to an output terminal of the second output driver, the first switch connects between an output terminal of the operational transconductance amplifier and an input terminal of the first output driver, and the second switch connects between the output terminal of the operational transconductance amplifier and an input terminal of the second output driver. 
         [0019]    In this case, the inverting input terminal of the operational amplifier is an inverting input terminal of the operational transconductance amplifier, and the non-inverting input terminal of the operational amplifier is a non-inverting input terminal of the operational transconductance amplifier. 
         [0020]    A touch IC for a touch input sensing device provided in accordance with another aspect of the present disclosure includes a sensing electrode, a driving electrode capacitively coupled to the sensing electrode, a sensing signal driving part, and a control part. The touch IC includes an operational amplifier; a first feedback capacitor configured to be connected to an inverting terminal of the operational amplifier; a second feedback capacitor configured to be connected to the inverting terminal of the operational amplifier; and a feedback path selection switch part, 
         [0021]    In this case, the feedback path selection switch part is configured to connect an output terminal of the operational amplifier selectively to one of the first feedback capacitor and the second feedback capacitor. 
         [0022]    In this case, the touch IC further includes the control part, wherein, the feedback path selection switch part is configured to be connected to the control part, and the control part is configure to perform: a first step for controlling the sensing signal driving part and the feedback path selection switch part in order that a voltage of the driving electrode becomes a first voltage, and the first feedback capacitor is connected to the output terminal of the operational amplifier to form a first feedback path; and a second step for controlling the sensing signal driving part and the feedback path selection switch part in order that the voltage of the driving electrode becomes a second voltage, and the second feedback capacitor is connected to the output terminal of the operational amplifier to form a second feedback path. 
         [0023]    Also, the feedback path selection switch part includes a first switch configured to connect the output terminal of the operational amplifier to the first feedback capacitor, and a second switch configured to connect the output terminal of the operational amplifier to the second feedback capacitor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which: 
           [0025]      FIG. 1A  represents the fundamental structure of a sensing device  100  that uses a single operational amplifier (OA) in order to measure whether there is a touch input to a capacitive type touch panel in accordance with a first embodiment. 
           [0026]      FIG. 1B  represents the equivalent circuit of a touch screen panel (TSP). 
           [0027]      FIGS. 2A to 2F  are timing diagrams that represent, according to a time, states at switches Ø R , Ø 1 , and Ø 2  and terminals TX, RX, VOUT 1 , and VOUT 2  of the sensing device  100  in  FIG. 1A . 
           [0028]      FIGS. 3A to 3C  represent circuits that apply the ON and OFF states of each switch at each time section in  FIG. 2  to the sensing device  100  in  FIG. 1A . 
           [0029]      FIG. 4  represents the fundamental structure of a sensing device  200  that uses a single operational transconductance amplifier (OTA) and two output drivers in order to measure whether there is a touch input to a capacitive type touch panel in accordance with a second embodiment. 
           [0030]      FIGS. 5A to 5F  are timing diagrams that represent, according to a time, states at switches Ø R , Ø 1 , and Ø 2  and terminals TX, RX, VOUT 1 , and VOUT 2  of the sensing device  200  in  FIG. 4 . 
           [0031]      FIG. 6  represents the fundamental structure of a sensing device  300  that uses two OAs in order to measure whether there is a touch input to a capacitive type touch panel 
           [0032]      FIGS. 7A to 7F  are timing diagrams that represents, according to a time, states at switches Ø R , Ø 1 , and Ø 2  and terminals TX, RX, VOUT 1 , and VOUT 2  of the sensing device  300  in  FIG. 6 . 
           [0033]      FIG. 8  represents an example of an electronic device that utilizes the TSP as described in  FIG. 1A . 
           [0034]      FIG. 9  represents an example of the structure of the TSP as described in  FIG. 1A . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0035]    In the following, embodiments of the present disclosure are described with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments described in the specification and may be implemented in other forms. The terms used herein are to help the understanding of the embodiments and are not intended to define the scope of the present disclosure. Also, singular forms used below also include plural forms unless stated to the contrary. 
       Embodiment 1 
       [0036]      FIG. 1A  represents the fundamental structure of a sensing device  100  that uses a single operational OA in order to measure whether there is a touch input to a capacitive type touch panel in accordance with a first embodiment. 
         [0037]    The sensing device  100  may include a sensing signal reception device  30 , a TSP  10 , a sensing signal driving device  61 , a switch part  6 , and a control part  5 . In the present disclosure, the TSP may also be referred to as a ‘touch panel’. 
         [0038]    The TSP  10  may include a driving electrode TX and a sensing electrode RX, and further include a capacitor C M  that is formed by the driving electrode TX and the sensing electrode RX. The driving electrode TX may be referred to as a ‘TX terminal’, and the sensing electrode RX may be referred to as an ‘RX terminal’. Although the equivalent circuit of the TSP  10  may also be represented by a single capacitor C M  as represented in  FIG. 1A , it may also be represented by a pi model that includes resistors RTX and RRX, capacitors CP 1  and CP 2 , and a capacitor C M  as represented in  FIG. 1B . 
         [0039]    The sensing signal reception device  30  may include a single OPERATIONAL AMPLIFIER OA, two feedback capacitors C S1  and C S2 , a reset switch Ø R , and a feedback path selection switch part  62 . The inverting input terminal of the OPERATIONAL AMPLIFIER OA is connected to the sensing electrode that acts as one terminal of the capacitor C M . In addition, the inverting input terminal—and an output part VOUT of the operational amplifier OA may be connected to each other through a first feedback capacitor C S1  or a second feedback capacitor C S2 . In addition, a first switch Ø 1  and a second switch Ø 2  are connected to between feedback capacitors C S1  and C S2  and the output part VOUT. The output part VOUT is selectively connected to output terminals VOUT 1  and VOUT 2  through the first switch Ø 1  and the second switch Ø 2  That is, when only the first switch Ø 1  is in an on state, the output part VOUT is the same as the output terminal VOUT 1 , and when only the second switch Ø 2  is in an on state, the output part VOUT is the same as the output terminal VOUT 2 . In addition, reset switches OR may be connected in parallel with the first feedback capacitor C S1  and the second feedback capacitor C S2 , respectively. The non-inverting input terminal of the operational amplifier OA may be connected to a voltage VCM. In this case, the voltage VCM may be ground GND or have a certain voltage value. The operational amplifier OA may include a single operational transconductance amplifier OTA (not shown) and a single output driver (not shown). The sensing signal reception device  30  may be provided as a packaged chip that is separated from the TSP  10 . 
         [0040]    The sensing signal driving device  61  may include a third switch Ø H  and a fourth switch Ø L . The sensing signal driving device  61  may use the third switch Ø H  and the fourth switch Ø L  to selectively connect the driving electrode TX to a first voltage (e.g., VDD) and a second voltage (e.g., GND). 
         [0041]    In the present disclosure, a chip that includes the sensing signal reception device  30  and the sensing signal driving device  61  may also be referred to as a touch IC. The TSP  10  may be provided as a device independent of the touch IC. 
         [0042]    The feedback path selection switch part  62  and the sensing signal driving device  61  may be collectively referred to as the switching part  6 . 
         [0043]      FIG. 2A to 2F  are timing diagrams that represent, according to a time, states at switches Ø R , Ø 1 , and Ø 2  and terminals TX, RX, VOUT 1 , and VOUT 2  of the sensing device  100  in  FIG. 1A . 
         [0044]      FIG. 2A  is a graph that represents, according to a time, the voltage V VOUT1  of the output terminal VOUT 1 , the voltage V VOUT2  of the output terminal VOUT 2 , and the voltage V RX  of the RX terminal. 
         [0045]      FIG. 2B  is a graph that represents, according to a time, the voltage difference between the output terminal VOUT 1  and the RX terminal, and the voltage difference between the output terminal VOUT 2  and the RX terminal. 
         [0046]      FIGS. 2C to 2E  represent, according to a time, the ON and OFF states of the reset switch Ø R ), the first switch Ø 1 , and the second switch Ø 2 , respectively. 
         [0047]    In addition,  FIG. 2F  represents the voltage of the driving electrode TX according to a time. The voltage of the driving electrode TX may be controlled according to the ON/OFF state of the switches Ø H  and Ø L . In this case, the switches Ø H  and Ø L  do not simultaneously have ON states. 
         [0048]    The vertical axes of the graphs in  FIGS. 2A and 2B  represent the size of a voltage and the horizontal axes thereof represent the time. 
         [0049]      FIGS. 3A to 3C  represent the ON and OFF states of each switch of the sensing device  100  in  FIG. 1A  at each time section in  FIGS. 2A to 2F . 
         [0050]    In the following, the operations of a sensing device circuit are described with reference to  FIGS. 2A to 3C . In the following, it is assumed that the first feedback capacitor C S1  and the second feedback capacitor C S2  are the same (C S1 =C S2 =C S ) in size, for the convenience of description. 
         [0051]      FIG. 3A  represents the sensing device circuit at the time sections RESET and TR 1  in  FIGS. 2 a  to 2 f    In this case, the first feedback capacitor C S1  and the second feedback capacitor C S2  are discharged by means of the reset switch ØR, and voltages across the first feedback capacitor C S1  and the second feedback capacitor C S2  are the same. 
         [0052]    In the RESET section, the fourth switch Ø L  is closed (ON) and the third switch Ø H  is opened (OFF), so the voltage of the TX terminal has e.g., ground GND and a voltage of—VCM is charged across the capacitor C M . If the voltage VCM is the same as ground GND, a voltage across the capacitor C M  becomes zero. 
         [0053]      FIG. 3B  represents the sensing device circuit at the time section TA. In this case, the time section TA may be divided into time sections T1 and T11. In the time section T1, the third switch Ø H  is closed (ON) and the fourth switch Ø L  is opened (OFF), so the voltage of the TX terminal is changed from GND to VDD. In this case, since the voltage—VCM is charged across the capacitor C M , the voltage of the RX terminal attempts to rise from the reference voltage VCM of the operational amplifier OA to voltage VCM+VDD as the voltage of the TX terminal is changed from GND to VDD. However, the operational amplifier OA performs discharging through an output from the operational amplifier OA in order to adjust the voltage of the RX terminal to the reference voltage VCM. Thus, since discharging is performed simultaneously with the rise of the voltage of the RX terminal, the voltage of the RX terminal rises to a certain voltage V T  and then returns to voltage VCM. 
         [0054]    Since during the time section T1, the first switch Ø 1  is ON, the discharging current of the operational amplifier OA for restoring the voltage of the RX terminal to voltage VCM flows through the first feedback capacitor C S1  and the total charge of the discharging current is the same as the total charge for charging a charging voltage across the capacitor C M  to change it from −VCM to VDD−VCM. Accordingly, it is possible to calculate a voltage that is charged across the first feedback capacitor C S1 . That is, it is possible to calculate a voltage ΔVOUT that is charged across the first feedback capacitor C S1 , by using the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0055]    Thus, |ΔVOUT|=VDD×(C M /C S1 ). During the time section T1, a voltage of ΔVOUT is charged across the first feedback capacitor C S1  by means of the discharging charge, thus the voltage V of the output terminal VOUT 1  is lower than the voltage VCM by ΔVOUT. That is, V VOUT1(end of T1) =VCM−ΔVOUT=VCM−(VDD×(C M /C S1 )). The above state is maintained during the time section T11 after the time section T1. 
         [0056]      FIG. 3C  represents the sensing device circuit at a time section TB. In this case, the time section TB may be divided into time sections T2 and T21. In the time section T2, the second switch Ø 2  is closed and the first switch Ø 1  is opened, so the voltage of the output terminal VOUT 2  starts from the voltage VCM−ΔVOUT of the output terminal VOUT 1 . In addition, the initial voltage of the RX terminal also starts from the same voltage VCM−ΔVOUT as the voltage of the output terminal VOUT 2 , because there is no charged voltage at the second feedback capacitor C S2 . 
         [0057]    In this case, the fourth switch Ø L  is closed the third switch Ø H  is opened, so the voltage of the TX terminal is changed from VDD to GND. Since voltage VDD−VCM is charged across the capacitor C M , the voltage of the RX terminal attempts to fall to a voltage lower than the start voltage VCM−ΔVOUT by VDD as the TX voltage is changed from VDD to GND. However, the operational amplifier OA performs charging through an output from the operational amplifier OA in order to adjust the voltage of the RX terminal to the reference voltage VCM. Thus, since charging is performed simultaneously with the fall of the voltage of the RX terminal, the voltage of the RX terminal returns to VCM from VCM−ΔVOUT−V T  that is obtained by subtracting a certain voltage V T . 
         [0058]    Since during the time section T2, the second switch Ø 2  is ON, the charging current of the operational amplifier OA for restoring the voltage of the RX terminal to voltage VCM flows through the second feedback capacitor C S2  and the total charge of the charging current is the same as the total charge for discharging a charging voltage across the capacitor C M  to change it from VDD−VCM to −VCM. Accordingly, it is possible to calculate a voltage that is charged across the second feedback capacitor C S2  at the T2 section. That is, it is possible to calculate a voltage ΔVOUT that is charged across the second feedback capacitor C S2 , by using the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
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         [0059]    Thus, |ΔVOUT|=VDD×(C M /C S2 ). During the time section T2, a voltage of ΔVOUT is charged across the second feedback capacitor C S2  by means of the charging charge. Thus, the voltage V VOUT2  of the output terminal VOUT 2  rises by ΔVOUT from VCM. That is, V VOUT2(end of T2) =VCM+ΔVOUT=VCM+VDD×(C M /C S2 ). Then, the above state is maintained during the time section T21. 
         [0060]    During the time section T2, the voltage that is charged across the first feedback capacitor C S1  maintains ΔVOUT as it is. Thus, the voltage of the output terminal VOUT 1  is shifted by a certain value from the voltage of the RX terminal during the time section T2. Even during the time section T21, the voltage that is charged across the first feedback capacitor C S1  maintains ΔVOUT as it is. Thus, during the time section T21, V VOUT1 =VCM−ΔVOUT. 
         [0061]    The sensing device circuit at a time section TC in  FIGS. 2A to 2F  may correspond to  FIG. 3B . In this case, the time section TC may be divided into time sections T3 and T31. In the time section T3, the first switch Ø 1  is closed and the second switch Ø 2  is opened as in the time section T1, so the voltage of the output terminal VOUT 1  starts from the voltage VCM+ΔVOUT of the previous output terminal VOUT 2 . Also, the initial voltage of the RX terminal starts from a voltage of VCM+2 ΔVOUT that is higher than the voltage of the output terminal VOUT 1  by a voltage of ΔVOUT that is charged across the first feedback capacitor C S1 . 
         [0062]    In this case, the third switch Ø H  is closed (ON) and the fourth switch Ø L  is opened (OFF) as in the time section T1, so the voltage of the TX terminal is changed from GND to VDD. 
         [0063]    Since a voltage of −VCM is charged across the capacitor C M , the voltage of the RX terminal attempts to rise to a voltage higher than the start voltage VCM+2ΔVOUT by VDD as the TX voltage is changed from GND to VDD. However, since discharging through an output from the operational amplifier OA is performed simultaneously with the rise of the voltage of the RX terminal, the voltage returns to VCM from VCM+2ΔVOUT+V T  that includes a certain rise voltage V T . 
         [0064]    Since during the time section T3, the first switch Ø 1  is ON, the discharging current of the operational amplifier OA for restoring the voltage of the RX terminal to voltage VCM flows through the first feedback capacitor C S1  and the total charge of the discharging current is the same as the total charge for changing a charging voltage across the capacitor C M  to change it from −VCM to VDD−VCM. Accordingly, it is possible to calculate a voltage that is additionally charged across the first feedback capacitor C S1 . The additional charging voltage is the same as the voltage that is charged across the first feedback capacitor C S1  at the time section T1. 
         [0065]    Due to the discharged charge, the same voltage as ΔVOUT is additionally charged in the first feedback capacitor C S1  in addition to existing ΔVOUT. Thus, the voltage of the output terminal VOUT 1  is lower than VCM by 2×ΔVOUT, and a voltage of VDD−VCM is charged across the capacitor C M . That is, V VOUT1(end of T3) =VCM−2ΔVOUT=VCM−2×VDD×(C M /C S1 ). 
         [0066]    In this case, since the voltage charged across the second feedback capacitor C S2  is maintained as ΔVOUT as it is, the voltage of the output terminal VOUT 2  varies to follow the temporary change of the voltage of the RX terminal. In addition, during the time section T31, the above state is maintained. 
         [0067]    Until the output voltages of the output terminal are accumulated, the sections after the time section TC may repetitively perform operations in the same way as the time sections TA and TB. 
         [0068]    In Embodiment 1, it may be seen that the lengths of the time sections T1, T2, T3, . . . become longer gradually for the following reason. When discussion is performed based on the voltage of the RX terminal, in the time section T1, the voltage starts from VCM, in the time section T2, the voltage starts from VCM−ΔVOUT, in the time section T3, the voltage starts from VCM+2ΔVOUT, and in the time section T4, the voltage starts from VCM−3ΔVOUT. In this case, since the voltage of the RX terminal rises or falls by a certain voltage V T  and then returns to VCM from whatever the voltage starts, the larger an absolute value of a difference value between the start voltage of each of time sections T1 to T4 and VCM is, a time when the voltage returns to VCM increases. Thus, time until the voltage returns to VCM becomes longer. That is, T1&lt;T2&lt;T3&lt;T4. 
         [0069]    In this case, the lengths of the time sections TA, TB, TC . . . are the same, so the lengths of the time sections T11, T21, T31, . . . decrease gradually. 
         [0070]    After reset by the rest switch Ø R  in  FIG. 1A , the relative voltage difference between voltage V VOUT1  and voltage V VOUT2  increases when the ON/OFF operations of the switches Ø 1 , Ø 2 , Ø L , and Ø H  are repeated. In this case, the relative voltage difference may be input to an analog to digital converter (ADC) so that it is possible to obtain the voltage difference as a digital value. It is possible to estimate the value of the capacitance C M  formed by the driving electrode TX and the sensing electrode RX according to a value of the voltage difference and as a result, it is possible to discern whether there is a touch input on a region where the driving electrode TX and the sensing electrode RX intersect each other, and the intensity of the touch input. 
         [0071]    In  FIG. 3A  of Embodiment 1 as described above, the voltage of the TX terminal in the reset section has been set to be e.g., GND. However, in an embodiment modified therefrom, it is possible to set the voltage of the TX terminal to e.g., VDD in the reset section, in which case a voltage of +VCM may be charged across a capacitor. Then, the operation of the device  100  may be performed by the same principle as the above-described embodiment. That is, the present disclosure is not limited to the voltage of the TX terminal in the reset section. 
       Embodiment 2 
       [0072]      FIG. 4  represents the fundamental structure of a sensing device  200  that uses a single operational transconductance amplifier (OTA) and two output drivers in order to measure whether there is a touch input to a capacitive type touch panel in accordance with a second embodiment. 
         [0073]      FIGS. 5A to 5F  are timing diagrams that represent states according to a time at switches Ø R , Ø 1 , and Ø 2  and terminals TX, RX, VOUT 1 , and VOUT 2  of the sensing device  200  in  FIG. 4 . 
         [0074]      FIG. 5A  is a graph that represents, according to a time, the voltage V VOUT1  of the output terminal VOUT 1 , the voltage V VOUT2  of the output terminal VOUT 2 , and the voltage V RX  of the RX terminal. 
         [0075]      FIG. 5B  is a graph that represents, according to a time, the voltage difference between the output terminal VOUT 1  and the RX terminal, and the voltage difference between the output terminal VOUT 2  and the RX terminal. 
         [0076]      FIGS. 5C to 5E  represent, according to a time, the ON and OFF states of the reset switch Ø R ), the first switch Ø 1 , and the second switch Ø 2 , respectively. 
         [0077]    In addition,  FIG. 5F  represents the voltage of the driving electrode TX according to a time. The voltage of the driving electrode TX may be controlled according to the ON/OFF state of the third and fourth switches Ø H  and Ø L . In this case, the third and fourth switches Ø H  and Ø L  do not simultaneously have ON states. 
         [0078]    When comparing  FIG. 1A  with  FIG. 4 , the single operational amplifier OA in the sensing device in  FIG. 1A  includes a single operational transconductance amplifier OTA (not shown) and a single output driver (not shown) but the single operational amplifier OA 2  in the sensing device in  FIG. 4  includes a single operational transconductance amplifier OTA and two output drivers  311  and  312 . 
         [0079]    In the first embodiment, since the output terminal of the operational transconductance amplifier OTA in the operational amplifier OA is connected directly to any one of the output terminals VOUT 1  and VOUT 2  at all times, the output voltage value of the output terminal of any time section (e.g., time section T11) may affect the start voltage value of the output terminal of the current time section (e.g., time section T2). 
         [0080]    However, in the configuration of the second embodiment, since respective output drivers  311  and  312  connect the output part VOUT to respective output terminals VOUT 1  and VOUT 2  and the inputs of respective output drivers are electrically separated from each other by means of the first switch Ø 1  and the second switch Ø 2 , the voltage value of the output terminal VOUT 1  and the voltage value of the output terminal VOUT 2  do not affect each other. Thus, when the two output drivers are used for the single operational transconductance amplifier, the voltage starts from voltages charged in the feedback capacitors C S1  and C S2  that are connected to the output terminals VOUT 1  and VOUT 2 , respectively, unlike when a single operational amplifier OA is used. That is, the voltage starts from the output voltages of the output terminals VOUT 1  and VOUT 2  in time sections T11′, T21′, T31′, . . . . 
         [0081]    For example, the start voltage of the output terminal VOUT 2  in the time section T2′ is not the voltage VCM−ΔVOUT of the output terminal VOUT 1  in the time section T11′ but the voltage VCM of the output terminal VOUT 2  in the time section T11′. Also, the start voltage of the output terminal VOUT 1  in the time section T3′ is not the same as the voltage VCM+ΔVOUT in the output terminal VOUT 2  in the time section T21′ but is the same as the voltage VCM−ΔVOUT of the output terminal VOUT 1  in the time section T21′. 
         [0082]    The start voltage of the RX terminal starts from a voltage higher (or lower) by a voltage charged in the feedback capacitor connected to the output terminal, than the start voltage of the output terminal in a corresponding time section. 
         [0083]    For example, the start voltage of the RX terminal in the time section T2′ starts from a voltage lower than the start voltage VCM of the output terminal VOUT 2  by a voltage charged across the feedback capacitor (e.g., C S2 ), in which case since there is no voltage charged across the feedback capacitor (e.g., C S2 ), the start voltage of the RX terminal starts from the start voltage VCM of the output terminal VOUT 2 . 
         [0084]    Also, the start voltage of the RX terminal in the time section T3′ starts from a voltage VCM higher than the start voltage VCM−ΔVOUT of the output terminal VOUT 1  by the voltage ΔVOUT charged across the feedback capacitor (e.g., CO connected to the output terminal. 
         [0085]    Also, the start voltage of the RX terminal in the time section T4′ starts from a voltage VCM lower than the start voltage VCM+ΔVOUT of the output terminal VOUT 2  by the voltage ΔVOUT charged across the feedback capacitor (e.g., C S2 ) connected to the output terminal. 
         [0086]    The start voltages of the RX terminals in the following time sections are determined in the same way and as a result, the start voltages of the RX terminals may be the same as VCM. 
         [0087]    In this case, since as in the first embodiment, the start voltage of the RX terminal attempts to rise (or fall) to a voltage higher (or lower) than the start voltage VCM by VDD but at the same time, discharging (or charging) is performed through an output through the operational transconductance amplifier OTA and the output drivers, the voltage rises (or falls) by a certain voltage (e.g., V T ′) from the start voltage and then returns to VCM. In this case, the voltages of the output terminals VOUT 1  and VOUT 2  that are connected to closed switches Ø 1  and Ø 2  in corresponding time sections T1′, T2′, T3′, T4′, . . . also rise (or fall) by a certain voltage (e.g., V T ′) from the start voltage. In addition, a voltage corresponding to ΔVOUT is additionally charged across the feedback capacitors C S1  and C S2  by means of the discharged (or charged) charge, and the output terminal has a lower (or higher) voltage by the charged voltage. 
         [0088]    In summary, it is different from the first embodiment in that in the second embodiment, the start voltages of the output terminals VOUT 1  and VOUT 2  are charged voltages in all time sections and the start voltage of the RX terminal is VCM at all times, because the start voltages of the output terminals VOUT 1  and VOUT 2  and the RX terminal in time sections T1′, T2′, T3′, T4′, . . . do not affect each other. 
         [0089]    The operation method of remaining time sections T1′, T2′, T3′, T4′, . . . in the second embodiment may be the same as that of the first embodiment. 
         [0090]    In this case, since the start voltage of the RX terminal is the same as VCM at all times, it may be seen that the lengths of time sections T1′, T2′, T3′, T4′, . . . may be the same. Also, the lengths of time sections TA′, TB′, TC′ . . . are the same one another, so the lengths of time sections T11′, T21′, T31′ . . . are also the same one another. 
       Comparative Embodiment 
       [0091]      FIG. 6  represents the fundamental structure of a sensing device  300  that uses two operational amplifiers OA in order to measure whether there is a touch input to a capacitive type touch panel. 
         [0092]    The sensing device  300  may include a first operational amplifier OA 1 , a second operational amplifier OA 2 , and a capacitor C M . The inverting input terminals—of the first operational amplifier OA 1  and the second operational amplifier OA 2  are connected to the sensing electrode RX that acts as one terminal of the capacitor C M , through the first switch Ø 1  and the second switch Ø 2 , respectively. In addition, the driving electrode TX that acts as the other terminal of the capacitor C M  is selectively connected to the first voltage (e.g., VDD) and the second voltage (e.g., GND) through the third switch Ø H  and the fourth switch Ø L . 
         [0093]    The inverting input terminal—and output terminal VOUT 1  of the first operational amplifier OA 1  are connected to each other through the first feedback capacitor C S1 , and the inverting input terminal—and output terminal VOUT 2  of the second operational amplifier OA 2  are connected to each other through the second feedback capacitor C S2 . In addition, the non-inverting input terminals+of the first operational amplifier OA 1  and the second operational amplifier OA 2  may all be connected to VCM. In this case, the voltage VCM may be ground GND or have a certain voltage value. In addition, the reset switches Ø R  may connect the inverting input terminals—and output terminals of the first operational amplifier OA 1  and the second operational amplifier OA 2 . 
         [0094]      FIGS. 7A to 7F  are timing diagrams that represent, according to a time, states at switches Ø R , Ø 1 , and Ø 2  and terminals TX, RX, VOUT 1 , and VOUT 2  of the sensing device  300  in  FIG. 6 . 
         [0095]      FIGS. 7A to 7C  represent, according to a time, the ON and OFF states of the reset switch Ø R ), the first switch Ø 1 , and the second switch Ø 2 , respectively. 
         [0096]      FIGS. 7D and 7E  represent, according to a time, the voltages of the driving electrode TX and the sensing electrode RX, respectively. The voltage of the driving electrode TX may be controlled according to the ON/OFF state of the switches Ø H  and Ø L . In this case, the switches Ø H  and Ø L  do not simultaneously have ON states. 
         [0097]    In addition,  FIG. 7F  is a graph that represents, according to a time, the voltage difference between the output terminal VOUT 1  and the RX terminal, and the voltage difference between the output terminal VOUT 2  and the RX terminal. 
         [0098]    When comparing  FIG. 6  with  FIG. 4 , the circuit in  FIG. 4  uses a single operational transconductance amplifier OTA and two output drivers  311  and  312  so that the voltages of the output terminals VOUT 1  and VOUT 2  may not affect each other, and the circuit in  FIG. 6  uses two operational amplifiers OA to separate the output terminals VOUT 1  and VOUT 2  so that the voltages of the output terminals VOUT 1  and VOUT 2  may not affect each other. Thus, as represented in  FIG. 5A  and  FIG. 7E , it may be seen that the start voltage of the RX terminal in each time section is the same as VCM. Thus, as the lengths of time sections T1′, T2′, T3′, T4′, . . . in  FIGS. 5A to 5F  are the same, so the lengths of time sections T1“, T2”, T3″, T4″, . . . in  FIGS. 7A to 7F  may also be the same. 
         [0099]    When comparing  FIGS. 2A to 2F, 5A to 5F and 7A to 7F ,  FIG. 2B ,  FIG. 5B , and  FIG. 7F  are all graphs that represent the voltage difference between the output terminals VOUT 1  and VOUT 2  and the RX terminal and it may be seen that it is possible to obtain similar results when a single operational amplifier OA is used, when a single operational transconductance amplifier OTA capable of functioning as a single operational amplifier OA and two output drivers are together used, and when two operational amplifiers OA are used. 
         [0100]      FIG. 8  represents an example of an electronic device that utilizes the TSP as described in  FIG. 1A . 
         [0101]    An electronic device  101  may receive a user input signal through a TSP  10 . The TSP  10  may include a substrate on which an electrode pattern is formed in the form of a matrix. The electronic device  101  may include the TSP  10  configured to be capable of transmitting a touch input signal, a touch panel control device  3  outputting a signal for driving the TSP  10  and receiving an input signal from the TSP  10 , a voltage driver  2  receiving a touch panel driving signal from the touch panel control device  3  to generate a touch panel driving voltage, a main processor  4  receiving a touch input signal from the touch panel control device  3  to execute a program stored in a storage device  51 , the storage device  51  storing one or more programs executed according to the touch input signal, and a display device  91  displaying a result processed by the main processor  4 . The display device  91  and the TSP  10  may overlap each other. 
         [0102]    The touch panel control device  3  may include a touch sensing part sensing a signal input from the TSP  10 , a panel driving part generating a touch panel driving signal to be transmitted to the TSP  10 , and a touch panel processor controlling them. The touch panel processor may be a re-programmable processor or a processor of a type operating by a dedicated logic, such as a state machine. 
         [0103]    Moreover, the electronic device  101  may include a RAM or storage devices of other types and may further include another device such as watchdog, though not shown. 
         [0104]    The TSP  10  may be conceptually divided into rows and columns. The intersection of each row and each column may be referred to as a ‘node’ or ‘touch node’. As a result, matrix type nodes may be defined, and when a touch input is performed, it is possible to identify on which node the touch input is performed. 
         [0105]    In order to implement the concept of the rows and columns, it is possible to use so-called a ‘self type’ touch panel or ‘mutual type’ touch panel.  FIG. 9  represents an example of a mutual type touch panel. 
         [0106]      FIG. 9  represents an example of the structure of the TSP as described in  FIG. 1A . 
         [0107]    In  FIG. 9 , first type electrodes (horizontally-extended rectangular electrodes) may be disposed on a first surface of a dielectric substrate and second type electrodes (vertically-extended, thick solid line-shaped electrodes) may be disposed on a second surface of the dielectric substrate. The first type electrodes may be electrically isolated from the second type electrodes by means of the dielectric substrate. 
         [0108]    The first type electrodes may spatially intersect with the second type electrodes. Each intersection may be defined as the node.  FIG. 9  represents an example of 24 rows and 20 columns, so 24*20 nodes may be defined. 
         [0109]    The example in  FIG. 9  is only an embodiment, and many literatures disclose embodiments in which the first type electrodes and the second type electrodes of the mutual type touch panel are disposed together on the first surface of the dielectric substrate. 
         [0110]    The capacitance measurement circuit according to the above comparative embodiment uses two operational amplifiers OA for a single measurement channel in order to remove DC noise or low-frequency noise. However, since two OAs are used for the single measurement channel, there is a drawback in that the area of the circuit increases. On the contrary, according to the first and second embodiments of the present disclosure and various embodiments that may be modified therefrom, it is possible to obtain an advantageous effect in that it is possible to decrease the area occupied by a touch input sensing circuit because only a single operational amplifier OA is required. 
         [0111]    According to the present disclosure, it is possible to provide a touch input sensing circuit that may provide the same or similar result as when two operational amplifiers OA are used, by using a single operational amplifier OA, and decrease the area of a sensing device. In this case, when the single operational amplifier OA is made up of a single operational transconductance amplifier OTA and two output drivers, it is possible to further enhance performance. 
         [0112]    A person skilled in the art to which the present disclosure pertains may easily implement various variations and modifications without departing from the essential characteristic of the present disclosure, by using the above-described embodiments of the present disclosure. The details of each claim in the following claims may be combined with other claims not dependent thereon as long as it is possible to understand through the specification.