Abstract:
The present invention introduces a touch sensing apparatus capable of adjusting an Rx frequency band, and the touch sensing apparatus can adjust the width of the Rx frequency band of a driving signal which is applied from a driving electrode of a touch screen panel and transferred to a receiving electrode of the touch screen panel, using a high pass filter and a low pass filter which are implemented with a differentiator and an integrator, respectively. The touch sensing apparatus can adjusting the resistances of a plurality of resistors and the capacitance of a capacitor, thereby selectively receiving a driving signal at each frequency and amplifying the received driving signal to a predetermined magnitude. Thus, since the touch sensing apparatus does not requires a separate filter for removing noise contained in the driving signal, the system can be simplified.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part application of U.S. patent application Ser. No. 14/369,225, filed Jun. 27, 2014 (now pending), the disclosure of which is herein incorporated by reference in its entirety. The U.S. patent application Ser. No. 14/369,225 is a national entry of International Application No. PCT/KR2012/011697, filed on Dec. 28, 2012, which claims priority to Korean Application No. 10-2011-0144722 filed on Dec. 28, 2011, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a touch sensing apparatus, and more particularly, to a touch sensing apparatus capable of improving the efficiency of a process of determining a touch sensing signal of a touch screen panel. 
         [0004]    2. Related Art 
         [0005]    A touch screen panel may be configured to sense a touch in a capacitive manner. 
         [0006]    The capacitive touch screen panel includes driving electrodes for receiving a driving signal and sensing electrodes for outputting a touch sensing signal, and senses a touch using coupling capacitors formed between the respective driving electrodes and the sensing electrodes. 
         [0007]    For example, when the driving electrodes and the sensing electrodes of the touch screen panel are configured to cross each other, the coupling capacitors are formed at the respective nodes where the driving electrodes and the sensing electrodes cross each other. The capacitance of the coupling capacitor is changed when the corresponding node of the touch screen panel is touched. 
         [0008]    The driving electrodes receive driving signals with the same magnitude and frequency. When there is no touch on the nodes at which the coupling capacitors are formed, the same touch sensing signals are outputted from the sensing electrodes. When there is a touch on a specific node, the capacitance of the coupling capacitor of the corresponding node is changed, and a touch sensing signal outputted from the sensing electrode of the corresponding node is changed according to the change of the capacitance. A touch sensing apparatus senses the touch of the corresponding node by determining the change of the touch sensing signal. 
         [0009]    The touch sensing signal may contain various frequencies of noise while being influenced by noise caused by a parasitic capacitor and parasitic resistor of the touch screen panel. Thus, the touch sensing apparatus must be able to accurately determine the touch sensing signal while distinguishing between the touch sensing signal and noise. 
         [0010]    The touch sensing signal is also influenced by a load of the touch screen panel. Although touch sensing signals are generated from the same sensing electrode, the touch sensing signals may have a difference therebetween depending on the touch positions. That is, a touch sensing signal generated through a touch on a node close to an output terminal of a sensing line is different from a touch sensing signal generated through a touch on a node away from the output terminal of the sensing line. Therefore, in order for the touch sensing apparatus to accurately determine a touch sensing signal, the influence of the load on the touch sensing signal must be reduced. 
       SUMMARY 
       [0011]    Various embodiments are directed to a touch sensing apparatus capable of adjusting a receive (Rx) frequency band to accurately determine a touch sensing signal while distinguishing between the touch sensing signal and noise. 
         [0012]    Also, various embodiments are directed to a touch sensing apparatus capable of accurately determining a touch sensing signal by reducing the influence of a load on the touch sensing signal. 
         [0013]    In an embodiment, a touch sensing apparatus may include: a high pass filter configured to decide a second cut-off frequency by varying the resistance of at least one of a first resistor which transfers a touch sensing signal outputted from a sensing electrode to a first amplifier and is implemented with a variable resistor and a second resistor which forms a first feedback loop for the first amplifier and is implemented with the variable resistor, and output a first output signal obtained by filtering a frequency component equal to or lower than the second cut-off frequency in the touch sensing signal, and a low pass filter comprising a sampling switch which switches transfer of the first output signal, a third resistor which transfers the first output signal having passed through the sampling switch to a second amplifier and is implemented with the variable resistor, and a feedback capacitor which forms a second feedback loop for the second amplifier and is implemented with a variable capacitor, and configured to sample the first output signal during a sampling period, decide a third cut-off frequency by varying at least one of the resistance of the third resistor and the capacitance of the feedback capacitor, and output a second output signal obtained by filtering a frequency component equal to or higher than the third cut-off frequency in the first output signal. The sampling period may be maintained for a second time from a time point delayed by a first time based on a transition time point of a driving signal applied to the driving electrode. 
         [0014]    In another embodiment, a touch sensing apparatus may include: a differentiator configured to output a first output signal obtained by differentiating a touch sensing signal outputted from a sensing electrode, using a coupling capacitor between a driving electrode and the sensing electrode of a touch screen pad and a sheet resistor formed by the sensing electrode; and an integrator configured to sample the first output signal during a sampling period, and output a second output signal obtained by integrating the first output signal transferred during the sampling period. The sampling period may be maintained for a second time from a time point delayed by a first time based on a transition time of a driving signal applied to the driving electrode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a block diagram illustrating a touch sensing apparatus according to an embodiment of the present invention. 
           [0016]      FIG. 2  is a circuit diagram equivalently illustrating the touch sensing apparatus of  FIG. 1 . 
           [0017]      FIG. 3  illustrates a pre-stage of  FIG. 2  and a transfer characteristic graph thereof. 
           [0018]      FIG. 4  illustrates a differentiator of  FIG. 2  and a transfer characteristic graph thereof. 
           [0019]      FIG. 5  illustrates an integrator of  FIG. 2  and a transfer characteristic graph thereof. 
           [0020]      FIG. 6  is a waveform diagram for describing an operation of the touch sensing apparatus according to the embodiment of the present invention, depending on an operation of a sampling switch SW 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In order to promote understanding of the advantages in operation of the present invention and the purpose achieved by exemplary embodiments of the present invention, the accompanying drawings for describing the exemplary embodiments of the present invention and the contents described in the drawings should be referred to. 
         [0022]    Hereafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals denote the same components. 
         [0023]      FIG. 1  illustrates a touch sensing apparatus  100  according to an embodiment of the present invention. 
         [0024]    The touch sensing apparatus  100  includes a touch screen panel  110  and a driving and sensing module  120 . The driving and sensing module  120  includes a driving unit  122  for providing driving signals Txa to Txn and a sensing unit  124  for receiving touch sensing signals Rxa to Rxm. Each of the driving unit  122  and the sensing unit  124  may be prepared in the form of an integrated circuit. 
         [0025]    The touch screen panel  110  may include a plurality of driving electrodes  111   a  to  111   n  and a plurality of sensing electrodes  113   a  to  113   m , and the driving electrodes  111   a  to  111   n  and the sensing electrodes  113   a  to  113   m  may be arranged adjacent to each other. For example, the driving electrodes  111   a  to  111   n  and the sensing electrodes  113   a  to  113   m  may be arranged to cross each other. At each of the nodes between the driving electrodes  111   a  to  111   n  and the sensing electrodes  113   a  to  113   m , a coupling capacitor Cc of  FIG. 2  is formed. That is, the touch screen panel  110  is configured to sense a touch in a capacitive manner. 
         [0026]    The driving unit  122  provides the driving signals Txa to Txn with the same magnitude and frequency to the driving electrodes  111   a  to  111   n , and the sensing unit  124  receives the touch sensing signals Rxa to Rxm outputted from the sensing electrodes  113   a  to  113   n . Hereafter, the driving signals Txa to Txn are collectively referred to as a driving signal Tx, and the touch sensing signals Rxa to Rxm are collectively referred to as a touch sensing signal Rx. 
         [0027]    The capacitance of the coupling capacitor Cc is changed when a user touches the corresponding node of the touch screen panel  110 . The touch sensing signal Rx is changed according to the change in capacitance of the coupling capacitor Cc. Thus, the touch sensing signal Rx differs depending on whether there is a touch. 
         [0028]    The touch sensing signal Rx may not only contain the change in capacitance of the coupling capacitor Cc, but also contain noise caused by a parasitic capacitor and parasitic resistor of the touch screen panel  110 . 
         [0029]    The touch sensing signal Rx is influenced by a position of the touch screen panel  110 , at which a touch occurs, that is, a load. In  FIG. 1 , a touch sensing signal Rx outputted from the sensing electrode  113   a  differs depending on touches at positions A, B and C of the sensing electrode  113   a . That is, the touch sensing signal Rx has such a waveform that is attenuated as a touch position is away from an output terminal of the sensing electrode  113   a . Therefore, in order for the touch sensing apparatus  100  to accurately determine a touch sensing signal Rx, the touch sensing signal Rx needs to be insensitive to the influence of a load depending on a difference in distance to the output terminal of the sensing electrode  113   a  between touch positions, that is, a difference between touch positions. 
         [0030]      FIG. 2  is a circuit diagram equivalently illustrating the touch sensing apparatus  100  of  FIG. 1 , in order to describe the generation and determination of the touch sensing signal Rx corresponding to the driving signal Tx. As illustrated in  FIG. 2 , the touch sensing apparatus according to the present embodiment may adjust a receive (Rx) frequency band to accurately determine a touch sensing signal while distinguishing between the touch sensing signal and noise. 
         [0031]    The touch sensing apparatus  100  of  FIG. 2  is divided into a pre-stage  210 , a differentiator  220  and an integrator  230  on a circuit basis.  FIG. 2  exemplifies one driving electrode  111   a  and one sensing electrode  113   a . The circuits are formed across the driving unit  122 , the touch screen panel  110  and the sensing unit  124 . According to the above-described configuration, the touch sensing apparatus  100  may adjust the Rx frequency band of the touch sensing signal Rx and acquire a touch sensing signal from which noise is filtered. 
         [0032]    The touch screen panel  110  includes a coupling capacitor Cc formed at the node between the driving electrode  111   a  and the sensing electrode  113   a . The driving electrode  111   a  serves as an equivalent model of a first sheet resistor Rp 1 , and the sensing electrode  113   a  serves as an equivalent model of a second sheet resistor Rp 2 . A capacitive load component applied to the driving electrode  111   a  of the touch screen panel  110  serves as an equivalent model of a first sheet capacitor Cp 1 , and a capacitive load component applied to the sensing electrode  113   a  serves as an equivalent model of a second sheet capacitor Cp 2 . The first and second sheet capacitors Cp 1  and Cp 2  may be understood as parasitic components. 
         [0033]    The pre-stage  210  includes the first sheet resistor Rp 1  and the first sheet capacitor Cp 1  which are operated in the driving electrode  111   a  to which the driving signal Tx is applied. One end of the first sheet capacitor Cp 1  is grounded, and the first sheet resistor Rp 1  and the first sheet capacitor Cp 1  are connected in parallel to each other. In the pre-stage  210 , Vin represents an equivalent model of the driving unit  122  for providing a driving signal Tx. The pre-stage  210  includes the first sheet resistor Rp 1  and the first sheet capacitor Cp 1  of the touch screen panel  110 . 
         [0034]    The differentiator  220  includes the coupling capacitor Cc, the second sheet resistor Rp 2  and the second sheet capacitor Cp 2 , which are operated in the sensing electrode  113   a  that outputs a touch sensing signal Rx. One end of the second sheet capacitor Cp 2  is grounded, and the second sheet resistor Rp 2  and the second sheet capacitor Cp 2  are connected in parallel to each other. 
         [0035]    The differentiator  220  further includes a first resistor R 1 , a second resistor R 2  and a first amplifier  221 . The first and second resistors R 1  and R 2  may be embodied by variable resistors. The first resistor R 1  transfers a touch sensing signal Rx outputted through the sensing electrode  113   a , that is, the second sheet resistor Rp 2  to a negative input terminal (−) of the first amplifier  221 . The second resistor R 2  is disposed between an output terminal and the negative input terminal of the first amplifier  221 , while forming a feedback loop. The positive input terminal (+) of the first amplifier is grounded. 
         [0036]    The differentiator  220  includes the second sheet resistor Rp 2  and the second sheet capacitor Cp 2  of the touch screen panel  110  and the first resistor R 1 , the second resistor R 2  and the first amplifier  221  of the sensing unit  124 . 
         [0037]    As the driving signal Tx of the pre-stage  210  is applied to the coupling capacitor Cc, the differentiator  220  differentiates the touch sensing signal Rx outputted from the sensing electrode  113   a , that is, the second sheet resistor Rp 2 , and outputs the differentiated signal as a first output signal Vout 1 . The first output signal Vout 1  may be understood as the differentiated touch sensing signal Rx. 
         [0038]    The integrator  230  integrates the first output signal Vout 1  outputted from the differentiator  220 , and outputs the integrated signal as a second output signal Vout 2 . For this operation, the integrator  230  includes a sampling switch SW 1 , a reset switch SW 2 , a third resistor R 3 , a feedback capacitor Cf and a second amplifier  231 , which are included in the sensing unit  124 . The third resistor R 3  may be embodied by a variable resistor, and the feedback capacitor Cf may be embodied by a variable capacitor Cf while forming a feedback loop for the second amplifier  231 . 
         [0039]    The sampling switch SW 1  is switched by the sampling signal CK. When the sampling switch SW 1  is turned on, the sampling switch SW 1  transfers the first output signal Vout 1  of the differentiator  220  to the third resistor R 3 . 
         [0040]    The third resistor R 3  is positioned between the sampling switch SW 1  and the negative input terminal (−) of the second amplifier  231 . The feedback capacitor Cf is positioned between an output terminal and the negative input terminal of the second amplifier  231 , while forming a feedback loop. The positive input terminal (+) of the second amplifier  231  is grounded. 
         [0041]    The reset switch SW 2  is switched by a reset signal RST, and connected in parallel to the feedback capacitor Cf. When the reset switch SW 2  is turned off, the reset switch SW 2  guarantees charging of the feedback capacitor Cf, and when the reset switch SW 2  is tuned on, the reset switch SW 2  resets the charge stored in the feedback capacitor Cf. 
         [0042]    The integrator  230  integrates the first output signal Vout 1  outputted from the differentiator  220  and outputs the integrated signal as the second output signal Vout 2 , in response to the state in which the sampling switch SW 1  is turned on and the reset switch SW 2  is turned off. Furthermore, when the reset switch SW 2  is turned on, the integrator  230  initializes the second output signal Vout 2  by resetting the charge stored in the feedback capacitor Cf. The second output signal Vout 2  may be understood as a touch sensing signal Rx obtained by integrating the differentiated touch sensing signal Rx through the integrator  230 . 
         [0043]    According to the above-described configuration, the driving unit  122  periodically provides the driving signal Tx. 
         [0044]    The sensing unit  124  periodically receives the touch sensing signal Rx in response to the periodically provided driving signal Tx. That is, the differentiator  220  differentiates the touch sensing signal Rx which is periodically generated, and provides the differentiated signal as the first output signal Vout. The differentiator  220  provides the first output signal Vout 1  including a positive differentiated signal formed at a rising edge of the driving signal Tx and a negative differentiated signal formed at a falling edge of the driving signal Tx. The existence of the positive differentiated signal and the negative differentiated signal in the first output signal Vout 1  is based on the characteristic of a differentiating operation of the differentiator  220  which senses the direction of change in a signal. 
         [0045]    The integrator  230  samples the positive differentiated signal of the first output signal Vout, and samples the negative differentiated signal of the first output signal Vout. Here, the sampling indicates integration, and is performed in response to a turn-on of the sampling switch SW 1 . That is, the integrator  230  provides the second output signal Vout 2  which is reset after the positive differentiated signal is sampled, and reset after the negative differentiated signal is sampled, in response to a one-cycle driving signal Tx. 
         [0046]    The operation of the touch sensing apparatus according to the embodiment of  FIGS. 1 and 2  has been described on a time basis. Thus, the terms such as differentiator and integrator have been used. On the other hand, the operation of the touch sensing apparatus according to the embodiment of  FIGS. 1 and 2  may be described on a frequency basis. Referring to  FIGS. 3 to 5 , the operations of the pre-stage  210 , the differentiator  220  and the integrator  230  in  FIGS. 1 and 2  will be described on a basis of operation frequency. 
         [0047]      FIG. 3  illustrates the pre-stage  210  of  FIG. 2  and a transfer characteristic graph of the pre-stage  210 . The pre-stage  210  has a low pass characteristic, and is embodied by a gain circuit including the first resistor R 1 , the second resistor R 2  and the first amplifier  221 . Here, the gain may indicate the ratio of the first resistor R 1  to the second resistor R 2 , and the values of the first and second resistors R 1  and R 2  embodied by variable resistors may be adjusted to control the gain. 
         [0048]    The pre-stage  210  of  FIG. 3  has an operation characteristic of a low pass filter as indicated by the transfer characteristic graph. The pre-stage  210  has a transfer function H(ω 1 ) expressed as Equation 1 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     H 
                      
                     
                       ( 
                       
                         ω 
                         1 
                       
                       ) 
                     
                   
                   = 
                   
                     1 
                     
                       1 
                       + 
                       
                         Rp 
                          
                         
                             
                         
                          
                         
                           1 
                           · 
                           j 
                         
                          
                         
                             
                         
                          
                         
                           ω 
                           1 
                         
                          
                         Cp 
                          
                         
                             
                         
                          
                         1 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0049]    In Equation 1, Rp 1  denotes the resistance of the first sheet resistor, Cp 1  denotes the capacitance of the first sheet capacitor, and ω 1  denotes a first cut-off frequency of the low pass filter. 
         [0050]    The pre-stage  210  removes a frequency component higher than the first cut-off frequency ω 1  and passes only a frequency component lower than the first cut-off frequency ω 1 , among frequency components included in the pulse-type driving signal Tx. 
         [0051]      FIG. 4  illustrates the differentiator  220  and a transfer characteristic graph of the differentiator  220 . The differentiator  220  has a high pass characteristic. 
         [0052]    The differentiator  220  of  FIG. 4  has an operation characteristic of a high pass filter as indicated by the transfer characteristic graph. The differentiator  220  has a transfer function H(ω 2 ) expressed as Equation 2 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     H 
                      
                     
                       ( 
                       
                         ω 
                         2 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         R 
                          
                         
                             
                         
                          
                         2 
                       
                       
                         
                           R 
                            
                           
                               
                           
                            
                           1 
                         
                         + 
                         
                           Rp 
                            
                           
                               
                           
                            
                           2 
                         
                         + 
                         
                           1 
                           
                             j 
                              
                             
                                 
                             
                              
                             
                               ω 
                               2 
                             
                              
                             Cc 
                           
                         
                       
                     
                     = 
                     
                       - 
                       
                         
                           j 
                            
                           
                               
                           
                            
                           
                             ω 
                             2 
                           
                            
                           
                             Cc 
                             · 
                             R 
                           
                            
                           
                               
                           
                            
                           2 
                         
                         
                           1 
                           + 
                           
                             
                               jω 
                               2 
                             
                              
                             
                               Cc 
                                
                               
                                 ( 
                                 
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                   + 
                                   
                                     Rp 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
         [0053]    In Equation 2, R 1  denotes the resistance of the first resistor, R 2  denotes the resistance of the second resistor value, Rp 2  denotes the resistance of the second sheet resistor, and Cc denotes the capacitance of the coupling capacitor. 
         [0054]    The differentiator  220  passes a frequency component which is lower than the first cut-off frequency ω 1  of the pre-stage  210  and higher than a second cut-off frequency ω 2 , among the frequency components included in the touch sensing signal Rx. That is, the differentiator  220  has the operation characteristic of the high pass filter which removes a frequency component lower than the second cut-off frequency ω 2 . When the values of the first and second resistors R 1  and R 2  in the differentiator  220  are changed, the second cut-off frequency ω 2  may be changed as indicated by an arrow illustrated in the transfer characteristic graph of  FIG. 4 . That is, the differentiator  220  may filter noise from the touch sensing signal Rx, the noise being distributed in frequency components equal to or less than a desired level. 
         [0055]    The differentiator  220  amplifies the touch sensing signal Rx by a gain of Equation 3 which can be expressed by the resistances of the first resistor R 1 , the second resistor R 2  and the second sheet resistor Rp 2 . In Equation 3, a minus symbol (−) represents that the first amplifier  221  is used in the form of a negative feedback. 
         [0000]    
       
         
           
             
               
                 
                   Gain 
                   = 
                   
                     
                       R 
                        
                       
                           
                       
                        
                       2 
                     
                     
                       
                         R 
                          
                         
                             
                         
                          
                         1 
                       
                       + 
                       
                         Rp 
                          
                         
                             
                         
                          
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
             
           
         
       
     
         [0056]      FIG. 5  illustrates the integrator  230  and a transfer characteristic graph of the integrator  230 . 
         [0057]    The integrator  230  of  FIG. 5  has an operation characteristic of a low pass filter as indicated by the transfer characteristic graph. The integrator  230  has a transfer function H(ω 3 ) expressed as Equation 4 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     H 
                      
                     
                       ( 
                       
                         ω 
                         3 
                       
                       ) 
                     
                   
                   = 
                   
                     - 
                     
                       1 
                       
                         R 
                          
                         
                             
                         
                          
                         
                           3 
                           · 
                           j 
                         
                          
                         
                             
                         
                          
                         
                           ω 
                           3 
                         
                          
                         Cf 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ] 
                 
               
             
           
         
       
     
         [0058]    In Equation 4, R 3  denotes the resistance of the third resistor, Cf denotes the capacitance of the feedback capacitor, and ω 3  denotes the third cut-off frequency of the low pass filter. 
         [0059]    The integrator  230  removes a frequency component higher than the third cut-off frequency ω 3  among the frequency components included in the touch sensing signal Rx having passed through the differentiator  220  serving as a high pass filter. More specifically, the second amplifier  231  of the integrator  230  charges the feedback capacitor Cf by integrating the first output signal Vout 1  transferred through the third resistor R 3  in response to a turn-on of the sampling switch SW 1  during a sampling period, and outputs the second output signal Vout 2  obtained by filtering frequency components equal to or higher than the third cut-off frequency ω 3 . The second integrator  231  of the integrator  230  outputs the reset second output signal Vout 2  as the feedback capacitor Cf is discharged in response to a turn-on of the reset switch SW 2  after the sampling period. 
         [0060]    The transfer function H(ω) of the touch sensing apparatus  100  including the pre-stage  210 , the differentiator  220  and the integrator  230  of  FIGS. 3 to 5  may be expressed as Equation 5. 
         [0061]    When the integrator  230  changes the value of the third resistor R 3  and the capacitance of the feedback capacitor Cf, the third cut-off frequency ω 3  may be changed as indicated by an arrow illustrated in the transfer characteristic graph of  FIG. 5 . That is, the integrator  230  may filter noise from the touch sensing signal Rx, the noise being distributed in frequency components equal to or less than a desired level. 
         [0000]    
       
         
           
             
               
                 
                   
                     H 
                      
                     
                       ( 
                       ω 
                       ) 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         1 
                         
                           1 
                           + 
                           
                             Rp 
                              
                             
                                 
                             
                              
                             
                               1 
                               · 
                               j 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             Cp 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       ) 
                     
                     · 
                     
                       ( 
                       
                         - 
                         
                           
                             j 
                              
                             
                                 
                             
                              
                             
                               ω 
                               2 
                             
                              
                             
                               Cc 
                               · 
                               R 
                             
                              
                             
                                 
                             
                              
                             2 
                           
                           
                             1 
                             + 
                             
                               jω 
                                
                               
                                   
                               
                                
                               
                                 Cc 
                                  
                                 
                                   ( 
                                   
                                     
                                       R 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                     + 
                                     
                                       Rp 
                                        
                                       
                                           
                                       
                                        
                                       2 
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                         
                       
                       ) 
                     
                     · 
                     
                       ( 
                       
                         - 
                         
                           1 
                           
                             R 
                              
                             
                                 
                             
                              
                             
                               3 
                               · 
                               j 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             Cf 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     5 
                   
                   ] 
                 
               
             
           
         
       
     
         [0062]    In Equation 5, the resistance of the first sheet resistor Rp 1  and the capacitance of the first sheet capacitor Cp 1  may be defined as constants which are considerably small. Referring to Equations 1 and 5, the resistance of the first sheet resistor Rp 1  and the capacitance of the first sheet capacitor Cp 1  are considerably low. Thus, the first cut-off frequency ω 1  has a considerably high value. In reality, the first cut-off frequency ω 1  is considerably higher than the third cut-off frequency ω 3 . Therefore, the characteristic of the low pass filter of the pre-stage  210  may be omitted in the following descriptions. 
         [0063]    Referring to Equation 5, the relation between the driving signal Tx of the pre-stage  210  and the output signal Vout 2  of the integrator  230  may be expressed as Equation 6 below. In Equations 6 and 7, the driving signal Tx is denoted by ‘Vin’. 
         [0000]    
       
         
           
             
               
                 
                   Vout 
                   = 
                   
                     
                       - 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           
                             2 
                             · 
                             Cc 
                           
                         
                         
                           
                             R 
                              
                             
                                 
                             
                              
                             1 
                           
                           + 
                           
                             Rp 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                       
                     
                     × 
                     
                       
                          
                         Vin 
                       
                       
                          
                         t 
                       
                     
                     × 
                     
                       1 
                       
                         
                           Cf 
                           · 
                           R 
                         
                          
                         
                             
                         
                          
                         3 
                       
                     
                     × 
                     
                       ∫ 
                       
                         Vin 
                          
                         
                            
                           t 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     6 
                   
                   ] 
                 
               
             
           
         
       
     
         [0064]    Equation 6 may be simply summarized as expressed by Equation 7 below. 
         [0000]    
       
         
           
             
               
                 
                   Vout 
                   = 
                   
                     
                       
                         R 
                          
                         
                             
                         
                          
                         2 
                       
                       
                         
                           
                             ( 
                             
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               + 
                               
                                 Rp 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                             ) 
                           
                           · 
                           R 
                         
                          
                         
                             
                         
                          
                         3 
                       
                     
                     × 
                     
                       Cc 
                       Cf 
                     
                     × 
                     Vin 
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     7 
                   
                   ] 
                 
               
             
           
         
       
     
         [0065]    Referring to  FIG. 7 , the resistance of the second sheet resistance Rp 2  is lower than the resistances of the other three resistors R 1 , R 2  and R 3 , and defined as a constant value which is decided by the material of the sensing electrode  113   a , and the capacitance of the coupling capacitor Cc is also defined as a constant value which is decided by the material of the touch screen panel  110 . On the other hand, since the first to third resistors R 1  to R 3  and the feedback capacitor Cf are embodied by variable resistors and a variable capacitor, the values of the first to third resistors R 1  to R 3  and the feedback capacitor Cf may be adjusted. 
         [0066]    Equation 5 expresses the transfer function of the touch sensing apparatus  100  according to the present embodiment in the frequency domain, and Equation 7 expresses the transfer function of the touch sensing apparatus  100  according to the present embodiment in the time domain. Referring to Equations 5 and 7, the touch sensing apparatus  100  according to the present embodiment may adjust the gain and filtering frequency of the touch sensing signal Rx by varying the resistances of the first to third resistors R 1  to R 3  and the capacitance of the feedback capacitor Cf. 
         [0067]    The touch sensing apparatus according to the embodiment of  FIGS. 1 and 2  have an operation characteristic of a band-pass filter through a combination of the differentiator  220  and the integrator  230 . For this configuration, the touch sensing apparatus needs to set the resistances of the first to third resistors R 1  to R 3  and the capacitance of the feedback capacitor Cf such that the second cut-off frequency ω 2  is lower than the first cut-off frequency ω 1  and the third cut-off frequency ω 3 . That is, the touch sensing signal Rx is filtered by the touch sensing apparatus  100  according to the present embodiment, and thus has a frequency component higher than the second cut-off frequency ω 2  and lower than the first and third cut-off frequencies ω 1  and ω 3 . 
         [0068]    The touch sensing apparatus according to the present embodiment described with reference to  FIGS. 1 to 5  may adjust the Rx frequency band of the touch sensing signal Rx by changing the resistances of the first to third resistors R 1  to R 3  and the capacitance of the feedback capacitor Cf, and accurately determine the touch sensing signal Rx while distinguishing between the touch sensing signal Rx and noise. 
         [0069]    Furthermore, the touch sensing apparatus according to the present embodiment may adjust the turn-on time of the sampling switch SW 1  as illustrated in  FIG. 6 , in order to accurately determine the touch sensing signal Rx while reducing the influence of a load on the touch sensing signal Rx. The period during which a turn-on of the sampling switch SW 1  is maintained after the sampling switch SW 1  is turned on may be defined as the sampling period, and the sampling period may be decided in consideration of a load having an influence on the touch sensing signal Rx. The sampling period may be set to be maintained for a preset time CK Width from a time point delayed by a preset time CK Delay based on a transition time point of the driving signal Tx applied to the driving electrode  111   a . For this setting, the sampling signal CK for controlling the switching operation of the sampling switch SW 1  transitions to a high level at the time point delayed by the preset time CK Delay based on the transition time point of the driving signal Tx, and retains a high level for the preset time CK Width. 
         [0070]    The touch sensing signal Rx may have a different waveform due to the influence of a load depending on a difference in distance to the output terminal of the sensing electrode  113   a  between touch positions, that is, a difference between the positions of touched nodes. 
         [0071]    In the first output signal Vout 1  of  FIG. 6 , a waveform A indicates the first output signal Vout 1  of the differentiator  220  for the touch sensing signal Rx corresponding to the position A of  FIG. 1 , a waveform B indicates the first output signal Vout 1  of the differentiator  220  for the touch sensing signal Rx corresponding to the position B of  FIG. 1 , and a waveform C indicates the first output signal Vout 1  of the differentiator  220  for the touch sensing signal Rx corresponding to the position C of  FIG. 1 . 
         [0072]    Referring to  FIG. 1 , the position A is the most remote from the output terminal of the sensing electrode  113   a , and the position C is the closest to the output terminal of the sensing electrode  113   a . That is, the resistance of the second sheet resistor Rp 2  and the capacitance of the second sheet capacitor Cp 2  which are applied to the touch sensing signal Rx corresponding to a touch on the position A are the largest, and the resistance of the second sheet resistor Rp 2  and the capacitance of the second sheet capacitor Cp 2  which are applied to the touch sensing signal Rx corresponding to a touch on the position C are the smallest. Thus, since the touch sensing signal Rx corresponding to the touch on the position A is influenced by the largest load, the waveform of the touch sensing signal Rx is most attenuated. Furthermore, since the touch sensing signal Rx corresponding to the touch on the position C is influenced by the smallest load, the waveform of the touch sensing signal Rx is least attenuated. 
         [0073]    Therefore, as illustrated in  FIG. 6 , the first output signal Vout 1  obtained by differentiating the touch sensing signal Rx is significantly attenuated by the influence of a load, as a touch position is away from the output terminal of the sensing electrode  113   a.    
         [0074]    The first output signal Vout is sampled by the integrator  230 . 
         [0075]    The integrator  230  starts sampling the first output signal Vout 1  according to the sampling signal CK which transitions to a high level at a time point delayed by the preset time CK Delay based on the transition time of the driving signal Tx, and samples the first output signal Vout 1  for the preset time CK Delay. 
         [0076]    The feedback capacitor Cf is charged with the integrated voltage of the first output signal Vout 1  which is transferred through the third resistor R 3  in response to a turn-on of the sampling switch SW 1  during the sampling period, and the amplifier  231  outputs the second output signal Vout 2  corresponding to the voltage stored in the feedback capacitor Cf until the feedback capacitor Cf is reset by the reset switch SW 2 . The second output signal Vout 2  may be reset by the reset switch SW 2  before the next sampling period. 
         [0077]    The integrator  230  receives the first output signal Vout 1  having a difference depending on the position of a touched node. When the sampling switch SW 1  is controlled to be turned on for a predetermined time from the same time point as a rising edge of the driving signal Tx, the integrator  230  outputs the second output signal Vout having a difference depending on the position of a touched node. 
         [0078]    In the present embodiment, however, the sampling period may be set to be maintained for the preset time CK Width from a time point delayed by the preset time CK Delay based on a transition time point of the driving signal Tx applied to the driving electrode  111   a . The sampling period may be set in such a manner that values obtained by sampling the first output signals Vout 1  corresponding to the nodes formed in the sensing electrode  113   a  have the smallest difference therebetween. 
         [0079]    The initial sampling period may be preset by a value obtained during a test process, and periodically changed with reference to the second output signal Vout 2  while the operation is performed. The start point of the sampling period and the duration of the sampling period may be set in various manners through a method of adjusting the start point, a method of adjusting the duration, and a method of adjusting the start point and the duration. The sampling period may be periodically changed according to a period set by a designer, or changed in synchronization with a signal set by a designer. 
         [0080]    The touch sensing apparatus according to the present embodiment may set the sample period such that the values obtained by sampling the first output signals Vout 1  have the smallest difference, as illustrated in  FIG. 6 . Thus, the touch sensing apparatus can reduce the influence of a load on the touch sensing signal Rx, thereby accurately determining the touch sensing signal Rx. 
         [0081]    While various embodiments have been described above, it will be understood to those skilled in the art that the embodiments described are by way of example only. Accordingly, the disclosure described herein should not be limited based on the described embodiments.