Abstract:
A noise reducing device for a capacitive touch panel and a method of reducing noise for a capacitive touch panel are disclosed to solve problems related to noise generated by a conventional filter circuit and an integrating circuit or external noise. In the invention, at least one switch circuit is used so that the conventional filter circuit and integrating circuit used in the prior are omitted. Signals output from a current measurement circuit are transmitting to a control unit to calculate the location of a touch point, reducing any noise.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention generally relates to a control unit, sensing device and a method, and particularly to a control unit, sensing device for a capacitive touch panel and a method therefor. 
         [0003]    2. Description of Related Art 
         [0004]    For a long time, the main means of input for electronic devices have been keyboard and mouse. Touch panels which receive the input information by using user&#39;s hands or touch pens to touch sensing areas on their panels have drawn attention and have been put into practice already. There are sensing devices underneath the touch panels corresponding to the sensing areas. Touch panels are categorized by the ways touch input is recognized, including resistive touch panels, capacitive touch panels, sound-wave touch panels, optical touch panels, and electromagnetic touch panels 
         [0005]    In capacitive touch panels having capacitive point-to-touch sensing means for example, all currents passing through a particular touch input location are sensed to determine the location of the touch point by means of their correlation. 
         [0006]      FIG. 1  is a perspective view of a conventional capacitive touch panel. As shown in  FIG. 1 , a capacitive touch panel  10  consists of a transparent substrate  11 , an electric conductive film  12 , an electrode pattern  13  and an insulating hard layer  14 . The transparent substrate  11  can be made of glass, for example. The electrode pattern  13  is formed along the periphery of the touch panel  10  for compensating curve distribution of an electric field for the conductive film  12  at work. 
         [0007]      FIG. 2  is a schematic view of a location determining circuit for a conventional capacitive touch panel. 
         [0008]    Four corners of the touch panel  10  are respectively connected to external wires A, B, C and D, and respectively receive alternative sensing signals AC 1 , AC 2 , AC 3  and A 4  to provide location data for a touch point P on the touch panel  10 . 
         [0009]    In operation, the alternative sensing signals AC 1 , AC 2 , AC 3  and AC 4  are alternative square waves or sinusoidal wave voltage signals. Currents I 1 , I 2 , I 3  and I 4  respectively pass through the corresponding external wires A, B, C and D. The coordinates of the touch point P can be calculated based on the following formula by respectively measuring the current changes ΔI 1 , ΔI 2 , ΔI 3  and ΔI 4  for the corresponding external wire A, B, C and D before and after the touch point appears: 
         [0000]        x =(Δ I 3+Δ I 4−Δ I 1−Δ I 2)/(Δ I 1+Δ I 2+Δ I 3+Δ I 4)   (1)
 
         [0000]        y =(Δ I 1+Δ I 4−Δ I 3−Δ I 2)/(Δ I 1+Δ I 2+Δ I 3+Δ I 4)   (2).
 
         [0010]    The current change ΔI 1 , ΔI 2 , ΔI 3  and ΔI 4  can be obtained in the manner as shown in  FIG. 2 . The current change ΔI 1  is obtained by measuring the current I 1  by using a current measuring circuit  15 , transmitting the current I 1  to a filter circuit  16 , reducing noise, integrating the noise-reduced current I 1  by using an integrating circuit  17 , transmitting the integrated current I 1  to a controller  18 , converting the analogue current signal into a digital signal by using an analogue/digital conversion circuit  180  in the controller  18 , and calculating the current change by using a location determining unit  182  in the controller  18 . Similarly, ΔI 2 , ΔI 3  and ΔI 4  can be obtained in turns. The current change ΔI 1 , ΔI 2 , ΔI 3  and ΔI 4  are processed in turns with the same analogue/digital conversion circuit  180  and calculated based on the above formula to obtain the X and Y coordinates of the touch point. 
         [0011]    However, there can be a time difference between the calculated coordinate and the real coordinate of the touch point. Additionally, noise generated by the filter circuit  16  and the integrating circuit  17  or external noise can cause errors in the determined coordinates. Furthermore, the configuration as shown in  FIG. 2  increases production costs. For example, it requires a large amount of current measurement circuits  15 , filter circuits  16  and integrating circuits. 
       SUMMARY OF THE INVENTION 
       [0012]    In order to solve the prior problem, it is an object of the invention to provide a sensing device for a capacitive touch panel and a method of reducing noise for a capacitive touch panel. In the invention, at least one switch circuit is placed on the X and Y axes of the touch panel, thereby reducing the use of the same circuits at backside. Current signals measured by the switch circuit are calculated by a control unit to obtain corresponding coordinate, thereby overcoming problems of time difference and external noise. 
         [0013]    In order to achieve the above and other objectives, in a sensing device for capacitive touch panel according to the invention, the capacitive touch panel is rectangular and has a transparent substrate and a sensing layer on the transparent substrate, the sensing layer being transparent and electrically conductive. The capacitive touch panel further has a first X side, a second X side, a first Y side and a second Y side. The sensing device includes at least one X side switch circuit, at least one Y side switch circuit, a sensing source and a control circuit. 
         [0014]    The X side switch circuit is respectively electronically connected to the first X side and the second X side. The Y side switch circuit is respectively electrically connected to the first Y side and the second Y side. The sensing source includes a first sensing signal source and a second sensing signal source. The control circuit receives at least one first sensing signal generated by the first sensing signal source and at least one second sensing signal generated by the second sensing signal source. The X side switch circuits or the Y side switch circuits is connected according to the received first sensing signals or the second sensing signals, after the X side current signal generated by the X side switch circuits or Y side current signal generated by the Y side switch circuits are received, some calculations are carried out to determine the X and the Y coordinates of a touch point. 
         [0015]    In another embodiment, a sensing device for a capacitive touch panel is the same as above except that a first sample and hold circuit and second sample and hold circuit are added. The first sample and hold circuit is arranged between the first current measurement circuit and the first analogue/digital conversion circuit to receive the first X side current signal or the first Y side current signal for signal sampling, thereby reducing any noise generated by the first X side switch circuit or the first Y side switch circuit. The second sample and hold circuit is arranged between the second current measurement circuit and the second analogue/digital conversion circuit to receive the second X side current signal or the second Y side current signal for signal sampling, thereby reducing any noise generated the second X side switch or the second Y side switch circuit. 
         [0016]    In still another embodiment of the invention, the sensing device for a capacitive touch panel is the same as above, except that the control unit uses only one analogue/digital conversion circuit, and an electronic switch is added to reduce any noise generated by the circuits or externally. 
         [0017]    In order to achieve the above objectives, the method of reducing noise for a capacitive touch panel includes providing a first sensing signal source and a second sensing signal source; respectively transmitting the first sensing signal and the second sensing signal to the first X side, the first Y side, the second X side and the second Y side; obtaining a first X side analogue current signal, a first Y side analogue current signal, a second X side analogue current signal and a second Y side analogue current signal; respectively converting the first X side analogue current signal, the first Y side analogue current signal, the second X side analogue current signal and the second Y side analogue current signal into a first side digital current signal, a first Y side analogue signal, a second X side digital current signal and a second Y side digital signal; and transmitting the first X side digital current signal, the first Y side digital current, the second X side digital current signal and the second Y side digital current signal to a location determining unit for calculating the X and Y coordinates of a touch point. 
         [0018]    To provide a further understanding of the invention, the following detailed description illustrates embodiments and examples of the invention, this detailed description being provided only for illustration of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a perspective view of a conventional capacitive touch panel. 
           [0020]      FIG. 2  is a schematic view of a location determining device for a conventional capacitive touch panel. 
           [0021]      FIG. 3  is a schematic view of a sensing device for a capacitive touch panel according to one embodiment of the invention. 
           [0022]      FIG. 4  is a schematic view of a sensing device for a capacitive touch panel according to a first embodiment of the invention. 
           [0023]      FIG. 5  is a schematic view of a sensing device for a capacitive touch panel according to a second embodiment of the invention. 
           [0024]      FIG. 6  is a schematic view of a sensing device for a capacitive touch panel according to a third embodiment of the invention. 
           [0025]      FIG. 7  is a flow chart of a method of reducing noise for a capacitive touch panel according to one embodiment of the invention. 
           [0026]      FIGS. 8A and 8B  is a schematic view of two layer capacitive touch panel of the invention. 
           [0027]      FIG. 9  is a schematic view of a function diagram of the digital integration circuit of the invention. 
           [0028]      FIG. 10  is a schematic view of a function diagram of the control unit of the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    Wherever possible in the following description, like reference numerals will refer to like elements and parts unless otherwise illustrated. 
         [0030]      FIG. 3  is a schematic view of a sensing device for a capacitive touch panel according to one embodiment of the invention. As shown in  FIG. 3 , the capacitive touch panel is rectangular, and has a transparent substrate and a sensing layer on the transparent substrate. The sensing layer is transparent and electrically conductive. The capacitive touch panel has a first X side, a second X side, a first Y side and a second Y side. The sensing device  20  of the invention includes a sensing source  21 , a capacitive touch panel  22 , at least one X side switch circuit  23 , at least one Y side switch circuit  24  and a control circuit  27 . 
         [0031]    The sensing source  21  includes a first sensing signal source and a second sensing signal source. The first sensing signal source and the second sensing signal source respectively generate at least one first sensing signal and at least one second sensing signal. The X side switch circuits  23  are respectively connected the first X side and the second X side. The Y side switch circuits  24  are respectively connected to the first Y side and the second Y side. The control circuit  27  receives the first sensing signal and the second sensing signal, and decides to connect to either the X side switch circuit  23  or the Y side switch circuit  24  according to the first sensing signal or the second sensing signal. Meanwhile, the control circuit  27  receives at least one X side current signal generated by the X side switch circuit  23  and at least one Y side current signal generated by the Y side switch circuit  24 . Then, some proper calculations are performed to determine the X/Y coordinate of a touch point. In a preferred embodiment, the X side switch circuit  23  and the Y side switch circuit  24  can be a short circuit. Alternatively, the first sensing signal source is the same as the second sensing signal source, and the first sensing signal is the same as the second sensing signal. 
         [0032]    The control circuit  27  further includes at least one current measurement circuit  270  and a control unit  272 . The current measurement circuit  270  receives the X side current signal or the Y side current signal. The control unit  270  further includes at least one analogue/digital conversion circuit  2720  and a location determining unit  2722 . The analogue/digital conversion circuit  2720  converts the X side analogue signal generated by the X side current signal into at least one X side digital signal, or converts at least one Y side analogue signal generated by the Y side current signal into at least one Y side digital signal. The location determining unit  2722  carries out proper calculations on the X side digital signal and the Y side digital signal respectively to obtain the X/Y coordinate. 
         [0033]      FIG. 4  is a schematic view of a sensing device for a capacitive touch panel according to a first embodiment of the invention. As shown in  FIG. 4 , the capacitive touch panel  22  is rectangular, and has a transparent substrate and a sensing layer on the transparent substrate. The sensing layer is transparent and electrically conductive. The capacitive touch panel has a first X side, a second X side, a first Y side and a second Y side. On the sensing layer of the capacitive touch panel  22  has a work area  220 , and a touch point P within the work area  220 . The sensing device  20  of the invention includes a sensing source  21 , a first X side switch circuit  28 , a second X side switch circuit  25 , a first Y side switch circuit  29 , a second Y side switch circuit  26  and a control circuit  27 . 
         [0034]    The sensing source  21  includes a first sensing signal source  210  and a second sensing signal source  212 . The first sensing signal source  210  generates a first sensing signal VS 1 , a second sensing signal source  212  generates a second sensing signal VS 2 . When a specific location of the capacitive touch panel  22  is pressed down by an user, four corners of the capacitive touch panel  22  respectively receive the first sensing signal VS 1  and the second sensing signal VS 2  to measure the location of the touch point P. In  FIG. 4 , in practice, the first sensing signal VS 1  has I 2  and I 3  flowing over the first X side, and I 1  and I 4  flowing over the second X side. The second sensing signal VS 2  has I 3  and I 4  flowing over the first Y side, and I 1  and I 2  flowing over the second Y side. 
         [0035]    The first X side switch circuit  28  is electrically connected to the first X side. The second X side switch circuit  25  is electrically connected to the second X side. The first Y side switch circuit  29  is electrically connected to the first Y side. The second Y side switch circuit  26  is electrically connected to the second Y side. 
         [0036]    The control circuit  27  includes a first current measurement circuit  275 , a second current measurement circuit  276  and a control unit  274 . The control unit  274  further includes a first analogue/digital conversion circuit  2740 , a second analogue/digital conversion circuit  2742  and a location determining unit  2744 . The location determining unit  2744  further includes an X coordinate determining device  27440  and a Y coordinate determining device  27442 . 
         [0037]    The first current measurement circuit  275  receives either a first X side current signal generated by the first X side switch circuit  28  or a first Y side current signal generated by the first Y side switch circuit  29 . The second current measurement circuit  276  receives either a second X side current signal generated by the second X side switch circuit  25  or a second Y side current signal generated by the second Y side switch circuit  26 . The first analogue/digital conversion circuit  2740  either converts a first X side analogue signal generated by the first X side current signal into a first X side digital signal, or converts a first Y side analogue signal generated by the firs Y side current signal into a first Y side digital signal. The second analogue/digital conversion circuit  2742  either converts a second X side analogue signal generated by the second X side current signal generated by the second X side current signal into a second X side digital signal or converts a second Y side analogue signal generated by the second Y side current signal into a second Y side digital signal. 
         [0038]    The location determining unit  2744  is electrically connected to the first analogue/digital conversion circuit  2740  and the second analogue/digital conversion circuit  2742 . The X coordinate determining device  27440  decides to connect to the first X side switch circuit  28  and the second X side switch circuit  25  according to the received first sensing signal. Meanwhile, the X coordinate determining device  27440  receives the first X side digital current signal and the second X side digital current signal. After proper calculations respectively on the first X side digital current signal and the second X side digital current signal, the X coordinate of the touch point P is defined. The Y coordinate determining device  27442  decides to connect to the first Y side switch circuit  29  and the second Y side switch circuit  26  according to the received second sensing signal. Meanwhile, the Y coordinate determining device  27442  receives the first Y side digital current signal and the second Y side digital current signal. After proper calculations respectively on the first Y side digital current signal and the second Y side digital current signal, the Y coordinate of the touch point P is defined. The X coordinate and the Y coordinate of the touch point P are respectively obtained by the following formula: 
         [0000]        X =(( I 2+ I 3)−( I 1+ I 4))/ I 1+ I 2+ I 3+ I 4   (3), and
 
         [0000]        Y =(( I 3+ I 4)−( I 1+ I 2))/ I 1+ I 2+ I 3+ I 4   (4).
 
         [0039]    In the above formula, (I 2 +I 3 ) is obtained after the first X side switch circuit  28  is connected. (I 1 +I 4 ) is obtained after the second X side switch circuit  25  is connected. (I 3 +I 4 ) is obtained after the first Y side switch circuit  29  is connected. (I 1 +I 2 ) is obtained after the second Y side switch circuit  26  is connected. 
         [0040]    The difference between the first embodiment and prior art is that the first X side switch circuit  28 , the second X side switch circuit  25 , the first Y side switch circuit  29  and the second Y side switch circuit  26  are used to reduce the number of same circuit used in the prior art, and the conventionally used filter circuits and integration circuits are omitted. The first X side analogue signal of the first current measurement circuit  275  and the second X side analogue signal of the second current measurement circuit  276  are respectively input to the first analogue/digital conversion circuit  2740  and the second analogue/digital conversion circuit  2742 . The X side digital current signal, the second X side digital current signal, the first Y side digital current signal and the second Y side digital current signal re input to the location determining device  2744  for calculation. Thereby, any noise generated by the circuit or externally can be reduced. 
         [0041]      FIG. 5  is a schematic view of a sensing device for a capacitive touch panel according to a second embodiment of the invention. The second embodiment is the same as the first embodiment, except that a first sample and hold circuit  277  and a second sample and hold circuit  278  are added. The first sample and hold circuit  277  is mounted between the first current measurement circuit  275  and the first analogue/digital conversion circuit  2740 , and receives the first X side current signal or the first Y side current signal to proceed the signal sampling, thereby reducing noise generated by the first X side switch circuit  28  or the first Y side switch circuit  29 . The second sample and hold circuit  278  is mounted between the second current measurement circuit  276  and the second analogue/digital conversion circuit  2742 , and receives the second X side current signal or the second Y side current signal to proceed the signal sampling, thereby reducing any noise generated by the second X side switch circuit  25  or the second Y side switch circuit  26 . 
         [0042]      FIG. 6  is a schematic view of a sensing device for a capacitive touch panel according to a third embodiment of the invention. The third embodiment of the invention is the same as the second embodiment, except that the control unit  274  has only one analogue/digital conversion circuit  2746 , and electronic switches  279  is added among the sample and hold circuit  277 , the &#39;second sample and hold circuit  278  and the analogue/digital conversion circuit  2746 . One of the first sample and hold circuit  277  and the second sample and hold circuit  278  is selected to operate according to if the first sensing signal or the second sensing signal is received, so that the first X side current signal and the first Y side current signal or the second X side current signal and the second Y side current signal are obtained. The electronic switch  279  can be any types of electronic switches. 
         [0043]    The analogue/digital conversion circuit  2746  receives the first X side analogue signal generated by the first X side current signal, the first Y side analogue signal generated by the first Y side current signal, the second X side analogue signal generated by the second X side current signal and the second Y side analogue signal generated by the second Y side current signal, and respectively converts into a first X side digital signal, a second X side digital signal, a first Y side digital signal and a second Y side digital signal. Meanwhile, the first X side digital current signal, the second X side digital current signal, the first Y side digital current signal and the second Y side digital current signal are input into the location determining device  2744  for calculation, thereby, any noise generated by circuits or externally can be reduced. 
         [0044]      FIG. 7  is a flow chart of a method of reducing noise for a capacitive touch panel according to one embodiment of the invention. A first sensing signal source  210  and a second sensing signal source  212  are provided to generate at least one first sensing signal VS 1  and at least one second sensing signal VS 2  (S 100 ). The first sensing signal VS 1  is transmitted to the first X side and the first Y side of the capacitive touch panel  22 , and the second sensing signal VS 2  is transmitted to the second X side and the second Y side of the capacitive touch panel (S 102 ). A first X side analogue current signal is obtained from the sum of I 2  and I 3  of the first X side via the first X side switch circuit  28 . A first Y side analogue current signal is obtained from the sum of I 3  and I 4  of the first Y side via the first Y side switch circuit  29 . A second X side analogue current signal is obtained from the sum of I 1  and I 4  of the second X side via the second X side switch circuit  25 . A second Y side analogue current signal is obtained from the sum of I 1  and I 2  of the second Y side via the second Y side switch circuit  26  (S 104 ). The first X side analogue current signal and the first Y side analogue current signal are input to the first current measurement circuit  275 , and the second X side analogue current signal and the second Y side analogue current signal are input to the second current measurement circuit  276  (S 106 ). The first X side analogue current signal and the first Y side analogue current signal from the first current measurement circuit  275  are transmitted to the first analogue/digital conversion circuit  2740 , and the second X side analogue current signal and the second Y side analogue current signal from the second current measurement circuit  276  are transmitted to the second analogue/digital conversion circuit  2742  (S 108 ). 
         [0045]    The first X side analogue current signal, the first Y side analogue current signal, the second X side analogue current signal and the second Y side analogue current signal are respectively converted into the first X side digital current signal, the first Y side digital current signal, the second X side digital current signal and the second Y side digital current signal (S 110 ). Finally, the first X side digital current signal, the first Y side digital current signal, the second X side digital current signal and the second Y side digital current signal are transmitted at the same time to the location determining unit  2744  for calculation in order to obtain the x and y coordinates of the touch point P (S 112 ). 
         [0046]    In the prior art, the analog signal of the different corner of the touch panel has different errors in time domain because the errors may change depending on the estimated current time. So, the present invention provides a sensing method and device of a capacitive touch panel to ensure all current signals received simultaneously. 
         [0047]    The sensing device of capacitive touch panel of fourth embodiment of the invention comprises a sensing signal source, a plurality of connection circuits, a plurality of digital synchronization circuits and a location determining unit. 
         [0048]    The capacitive touch panel connects with a plurality of contacts and the type of capacitive touch panel may be a rectangle, a circular or a polygon. In the present embodiment, the capacitive touch panel is a rectangle and each corner connects with the contacts. In the other embodiment, the capacitive touch panel may be a rectangle and each side connects with the contacts such as  FIG. 4  to  FIG. 6 . In addition, each side of the capacitive touch panel may connect to a plurality of contacts. 
         [0049]    Each connection circuit connects with at least one contact to generate an analogue signal respectively. The connection circuit may be a circuit or simply a conducting wire. For example, the connection circuit can be a current detection circuit, a filtering circuit, or integration circuit. Furthermore, the contacts of the same connection circuit may use the conducting wire connects with the same side or two corners of the same side. In the best mode embodiment, the conducting wire may be a short circuit on the contacts. In the other embodiment, the connection circuit connects with a side or a corner through the contact. The present invention comprises a switch or a multiplexer. The switch sets up between the connection circuit and the contacts for selecting a contact connects with the connection circuit. 
         [0050]    The digital synchronization circuits receive a plurality of analogue signals for generating a digital signal simultaneously. Each digital synchronization circuit connects with a connection circuit respectively. The digital synchronization circuit and the connection circuits use the switch or the multiplexer for selectively connect with the connection circuit of digital synchronization circuit. The digital synchronization circuit receives a group of analogue signals in a time period and receives other group of analogue signals in a next time period simultaneously. All of the digital synchronization circuits are controlled by a clock signal to ensure that the analogue signals are received simultaneously. 
         [0051]    In the best mode embodiment, each whole analogue signal receives one part of each the digital synchronization circuit respectively. In other words, a whole analogue signal divides a plurality of parts in the time domain and each part received by a digital synchronization circuit respectively. Each whole analogue signal has the same ratio noise. The digital synchronization circuit receives noise when analogues signal converts to digital signal. In other words, A current value response to the analogue signal is generated from response to the digital signal of the analogue signal summary. In the same way, the analogue signal of the contact also receives partially for each the connection circuit. In other words, the analogue signal of the contact cuts off a plurality of parts and each the parts is received by a connection circuit. 
         [0052]    The location determining unit obtains a current value of each contact in before touch of the capacitive touch panel via the contact, the connection circuit and the digital synchronization circuit. The current value of each the contact is changed when the capacitive touch panel is touch. Comparing the current of before touch with present touch of the capacitive touch panel, and the location determining unit obtains a current difference of each contact. The location determining unit calculates a coordinate according to the above manner. The current of both opposing sides is detected in a first time period, and the current of other both opposing sides are detected in a second time period. A first one dimensional coordinate and a second one dimensional coordinate of a two dimensional coordinate are calculated through above manner. The first one dimensional coordinate and the second one dimensional coordinates are X coordinates and Y coordinates respectively, and the X coordinates and the Y coordinates are obtained by following formula: 
         [0000]        X =( IΔX 2− IΔX 1)/( IΔX 1+ IΔX 2)   (5); and
 
         [0000]        Y =( IΔY 2− IΔY 1)/( IΔY 1+ IΔY 2)   (6)
 
         [0053]    The location determining unit obtains a difference IΔX 1  and IΔX 2  of IX 1  and IX 2  current value of the two contacts between the first time period and the third time period according to the capacitive touch panel receives the analogue signal on the first time period of before touch and on the third time period of the present touch simultaneously. The location determining unit obtains a difference IΔY 1  and IΔY 2  of IY 1  and IY 2  current value of the two contacts between the second time period and the fourth time period according to the capacitive touch panel receives the analogue signal on the second time period of before touch and on the fourth time period of the present touch simultaneously. The first time period and the second time period are continuous two time period in time domain and the third time period and the fourth time period are other continuous two time period. In other words, the analogue signal converts into IX 1 , IX 2 , IY 1  and IY 2  current value in before touch and present touch of the capacitive touch panel. The location determining unit calculates the first one dimensional coordinate X of two dimensional coordinate according to the current difference IΔX 1  and IΔX 2  of the IX 1  and IX 2 , and calculates the second one dimensional coordinate Y of two dimensional coordinate according to the current difference IΔY 1  and IΔY 2  of IY 1  and IY 2 . The current of each side received from a contact of the side. The other best mode embodiment, the current of each side received from at least two contact of the side, for example, the contacts of the two corners. 
         [0054]    The sensing signal source provides a sensing signal to contact and the connection circuit receives current from the contact. In a best mode embodiment, the sensing signal source provides the sensing signal to a pair of opposing sides in the first time period, and provides the sensing signal to other pair of opposing sides in the second time period. The current of contact is received according to the sensing signal selectively. For example, at least one switch sets up between each contact and the sensing signal source. The contact connects with the sensing signal source through an independent switch respectively, or a plurality of contacts connect with the sensing signal source through the same switch. Therefore, the sensing signal source provides the sensing signal through the switch crisscross. 
         [0055]    In the fifth embodiment of the present invention, the number of the contacts, the connection circuits and the digital synchronization circuits is four, respectively. Each connection circuit connects with a contact and each the digital synchronization circuit receives the analogue signal from the connection circuit respectively. 
         [0056]    In the sixth embodiment of the present invention, the number of contacts, the connection circuit and the digital synchronization circuit is four, four (two pairs) and two. Each connection circuit connects with at least one contact respectively and two digital synchronization circuits receive the analogue signal from a pair of the two pairs connection circuit crisscross simultaneously. For example, the contacts comprise a first contact, a second contact, a third contact and a fourth contact. The connection circuits comprise a first connection circuit connects the first contact with the second contact, a second connection circuit connects the third contact with the fourth contact, a third connection circuit connects the first contact with the fourth contact and a fourth connection circuit connects the second contact with the third contact, the first connection circuit and the second connection circuit are one of two pair connection circuit, and the third connection circuit and the fourth connection circuit are other of two pair connection circuit. For example, the contacts comprise a first contact, a second contact, a third contact and a fourth contact, the connection circuits comprise a first connection circuit connects with the first contact, a second connection circuit connects with the second contact, a third connection circuit connects with the third contact, and a fourth connection circuit connects with the fourth contact, the first connection circuit and the third connection circuit is a first pair connection circuit and the second connection circuit and the fourth connection circuit is a second pair connection circuit. 
         [0057]    In the seventh embodiment of the present invention, the number of the contacts, the connection circuits and the digital synchronization circuits is four, two and two respectively, each connection circuit connect to at least one of contacts respectively, and each digital synchronization circuit receives the analogue signal from one of the connection circuit of two connection circuit simultaneously. For example, the contacts comprise a first contact, a second contact, a third contact and a fourth contact, the connection circuits comprise a first connection circuit and a second connection circuit, the first connection circuit and the second connection circuit connects with two contacts respectively, the second connection circuit connect the third contact with the fourth contact when the first connection circuit connect the first contact with the second contact, the second connection circuit connect the second contact with the third contact when the first connection circuit connect the first contact with the fourth contact. 
         [0058]    In additional, the between of contact and the capacitive touch panel or the contact and the connection circuit comprise at least one passive element, such as a resistor or an electrostatic discharge circuit. 
         [0059]    In additional, the sensing signal may be an alternating current voltage and comprises a carrier waveform. The carrier waveform may be a sine wave or a square wave. In a whole cycle of alternating current, the carrier wave comprises a positive-half cycle and a negative-half cycle response to the alternating current. The analogue signal of the contact formed on the positive-half cycle and the negative-half cycle. The summary of current value is generated by subtract negative-half cycle from the positive-half cycle as a result of the current direction of the positive-half cycle carrier wave and the positive-half cycle carrier wave are opposite to each other. 
         [0060]    In the prior art, the carrier wave may comprise many kinds of noise. Thus, the current signal of positive-half cycle and the negative-half cycle do not have a symmetrical distribution. 
         [0061]    In the eighth embodiment of the present invention, a sensing method of a capacitive touch panel comprising: providing a sensing signal to a plurality of contacts of the capacitive touch panel; selectively connecting a plurality of connection circuits with at least one part of the contacts; selectively connecting a plurality of digital synchronization circuits with at least one part of the contacts; separately generating an analog signal according to the contact of each connection circuit; separately generating a digital signal according to each digital synchronization circuit received the analogue signal from one of connection circuit simultaneously; and calculating a coordinate according to a plurality of digital signals. 
         [0062]    In the ninth embodiment of the present invention shown as  FIG. 8 , a two-layer capacitive touch panel comprises an upper layer touch panel  101  and a bottom layer touch panel  102 . The upper layer touch panel  101  and the bottom layer touch panel  102  have two pairs of opposing sides  103 , respectively. Each side  103  connects with a plurality of contacts  104 . In another best mode embodiment, each side  103  connects with above three contacts  104 . In the other best embodiment, the contacts  104  of the two opposing sides  103  are connected one-by-one correspondingly. The two opposing sides form a parallel electric field  105  when the sensing signal source provides a sensing signal to the contact  104  of the a pair of opposing sides  103 . 
         [0063]    Referring to  FIG. 9 , each digital synchronization circuit comprises a digital integration circuit  110 . The digital integration circuit  110  comprises an analog/digital converter  111  and an adder  112 . The analog/digital converter  111  generates a plurality of digital sub-current values  1111  continuously by repeated sampling of the analogue signal and executing analogue signal to digital signal conversion. The adder  112  summarizes the digital sub-current values  1111 . The adder  112  receives and summarizes the digital sub-current values  1111  for generating a summation output  1121  in an added cycle. The cycle of the alternating current voltage is a multiple of the added cycle. 
         [0064]    The analogue signal received from an analog/digital converter  111 , or the analogue signal cuts off a plurality of parts for received from a plurality of analog/digital converters  111  respectively. The summation output  1121  response to the analogue signal generated by each of adder  112  stores in a storage unit. 
         [0065]    The control unit  274  provides two embodiments. First embodiment, the control unit  274  comprises a first analog/digital converter  2740 , a second analog/digital converter  2742  and a location determining unit  2744 . Second embodiment, the control unit  274  comprises an analog/digital converter  2476  and the location determining unit  2744 . 
         [0066]    The control unit  274  also provides other embodiment besides above two embodiments, shown as  FIG. 10 . The control unit  274  comprises a plurality of digital integration units  2748 , at least one switch circuit  2750 , a storage circuit  2752  and a coordinate calculation unit  2754 . 
         [0067]    Each digital integration unit  2748  comprises an analog/digital converter  27480  and an adder  27482 . The analog/digital converter  27480  converts a plurality of sampled analogue signals into a plurality of digital signals continuously when the analogue signal come from a signal source in an added cycle. The adder  27482  generates an integration value according to the summary of the digital signals in the added cycle. The storage circuit  2752  stores the integration values. The coordinate calculation unit  2754  calculates a coordinate according to the integration value. 
         [0068]    The digital integration unit  2748  comprises a first and a second digital integration unit  2748 . The switch circuits  2750  receives the analogue signal from a first pair of opposing side and a second pair of opposing side of the capacitive touch panel in a first and a second cycle respectively. The first pair of opposing side crisscrosses with the second pair of opposing sides. The first cycle and the second cycle comprises at least one added cycle respectively. In other words, the first cycle and the second cycle may comprise the added cycle or continuous a plurality of added cycles. The time length of the cycle may be a clock cycle, a ½ clock cycle, a ¼ clock cycle or another fractional clock cycle. 
         [0069]    The coordinate calculation unit  2754  calculates a coordinate according to a whole (such as a whole clock cycle) or partially (such as ½ or ¼ clock cycle) analogue signal. Besides, the analogue signal may be received from a single or a plurality of different digital integration units  2748  in cycle duration. For example, the analogue signals of each source signal received by different digital integration unit  2748  in different added cycle at the same cycle duration respectively. The integration values may be stored on the storage circuit  2752 . The coordinate calculation unit  2754  generates a summary value of the source signal according to the integration values from the same signal source in the same cycle duration. Then, the coordinate calculation unit  2754  calculates the coordinate according to the summary value. The analogue signal is only received by a digital integration circuit  2748  when a cycle includes an added cycle. The summary value (integration value) of each analogue signal has different digital integration circuit  2748  noise. The summary value of each analogue signal has all of digital integration unit  2748  noise when the analogue signal of each signal source received by all of digital integration unit  2748  respectively. 
         [0070]    The digital integration unit  2748  has at least three embodiments. In the first embodiment, the coordinate calculation unit  2754  generates a summary value (may be the current value or parts of current value) according to at least one integration value of the same source signal in a cycle duration. The cycle comprises at least one added cycle and every integration value corresponding an added cycle respectively. The coordinate calculation unit  2754  generates a first and a second summary value from a plurality of signal sources in a first and a second cycle respectively. The coordinate calculation unit  2754  generate a difference from subtract the first summary value from the second summary value of the same signal source. The coordinate calculation unit  2754  calculates the coordinate according to the difference. The difference may be a one dimensional coordinates or a two dimensional coordinate. The difference comprises a first and a second difference when the coordinate is one dimensional coordinate. The one dimensional coordinate calculated by (the first difference−the second difference)/(the first difference+the second difference). 
         [0071]    The difference comprises a first, a second, a third and a fourth difference, a first one dimension of the two dimension is calculated from ((the first difference+the second difference)−(the third difference+the fourth difference))/(the first difference+the second difference+the third difference+the fourth difference), a second one dimensional coordinate of the two dimensional coordinates is calculated from ((the first difference+the fourth difference)−(the second difference+the third difference))/(the first difference+the second difference+the third difference+the fourth difference) when the coordinate is a two dimensional coordinate. 
         [0072]    In the second embodiment, he digital integration unit  2748  generates a plurality of first, second, third and fourth summary values from a first, second, third and fourth cycle respectively, the coordinate calculation unit  2754  generates a first difference by subtract the first summary value and the third summary value, and a second difference by subtract the second summary value and the fourth summary value from the same signal source, the coordinate calculation unit  2484  calculates a first one dimensional coordinate of a two dimensional coordinate according to the first difference, and a second one dimensional coordinate of the two dimensional coordinate according to the second difference. 
         [0073]    In the third embodiment, the digital integration unit  2748  generates a plurality of first, second, third, fourth, fifth and sixth summary values according to a first, second, third, fourth, fifth and sixth cycle respectively, the coordinate calculation unit  2754  generating a first difference and a second difference by subtract the third summary value and the fifth summary value from the first summary value of the same signal source respectively, the coordinate calculation unit generating a third difference and a fourth difference by subtract the fourth summary value and the sixth summary value from the second summary value of the same signal source respectively, the coordinate calculation unit calculates a first one dimensional coordinate of a first and a second two dimensional coordinate according to the first difference and the second difference respectively, the coordinate calculation unit  2754  calculates a second one dimensional coordinate of the first and the second two dimensional coordinate according to the second difference and t he fourth difference. 
         [0074]    The first, second, third, fourth, fifth and sixth cycle is a clock cycle respectively. In other embodiment, the first, second, third, fourth, fifth and sixth cycle is a part of clock cycle respectively such as ½ clock cycle or ¼ clock cycle. In other words, the one dimensional coordinate or two dimensions coordinate calculated by parts of clock cycle of the analogue signal. 
         [0075]    Besides, the switch circuit  2750  allows the analogue signal of one side to be received by different digital integration circuits, and generates a summary value for storing on the storage circuit  2752 . The switch circuit  2750  lets the first and second digital integration circuit to receive the analogue signal of a different side of the opposite side in before half cycle (such as first cycle) of a first clock cycle and after half cycle (such as second cycle) respectively. For example, the opposite side is a first side and a third side. In the first cycle, the switch circuit  2750  lets the first and the second digital integration circuit to receive the third side and the after half analogue signal of the first side. 
         [0076]    The switch circuit  2750  is achieved by a plurality of multipliers, the first X side switch circuit, the first Y side switch circuit, the second X side switch circuit and the second Y side switch circuit or consists of multiplier and the first X side switch circuit, the first Y side switch circuit, the second X side switch circuit and the second Y side switch circuit. 
         [0077]    The control unit  274  provides another embodiment, the function diagram control unit  274  is the same of  FIG. 10 . 
         [0078]    The each part of same analogue signal received from different digital integration circuit  2748  when the analogue/digital converter  27480  receives the analogue signal come from a part of an analogue signal. The analogue/digital converter  27480  converts a plurality of sampled analogue signals into a plurality of digital signals continuously when the analogue signal come from a part of an analogue signal, each digital integration circuit receives a part of different analogue signal respectively. The adder  27482  generates an integration value of the part of the analogue signal according to the summary of the digital signals. The coordinate calculation unit  2754  obtains a summary value of the analogue signal from every part of the same analogue signal summary respectively and for calculating a coordinate according to the summary values. The coordinate calculation unit  2754  calculates the coordinate according to the summary value. 
         [0079]    The digital integration unit  2748  comprises a first and a second digital integration unit  2748 . The switch circuits  2750  receives the analogue signal from a first pair of opposing side and a second pair of opposing side of the capacitive touch panel in a first and a second cycle respectively. The first pair of opposing side crisscrosses with the second pair of opposing side. The storage circuit  2752  stores the summary value. 
         [0080]    The digital integration unit  2748  has at least three embodiments. In the first embodiment, the coordinate calculation unit  2754  generates a first and a second summary value from a plurality of signal sources in a first and a second cycle respectively. The coordinate calculation unit  2754  generate a difference from subtract the first summary value from the second summary value of the same signal source. The coordinate calculation unit  2754  calculates the coordinate according to the difference. The difference may be a one dimensional coordinates or a two dimensional coordinate. The difference comprises a first and a second difference when the coordinate is one dimensional coordinate. The one dimensional coordinate calculated by (the first difference−the second difference)/(the first difference+the second difference). 
         [0081]    The difference comprises a first, a second, a third and a fourth difference, a first one dimension of the two dimension is calculated from ((the first difference+the second difference)−(the third difference+the fourth difference))/(the first difference+the second difference+the third difference+the fourth difference), a second one dimensional coordinate of the two dimensional coordinate is calculated from ((the first difference+the fourth difference)−(the second difference+the third difference))/(the first difference+the second difference+the third difference+the fourth difference) when the coordinate is a two dimensional coordinate. 
         [0082]    In the second embodiment, he digital integration unit  2748  generates a plurality of first, second, third and fourth summary values from a first, second, third and fourth cycle respectively, the coordinate calculation unit  2754  generates a first difference by subtract the first summary value and the third summary value, and a second difference by subtract the second summary value and the fourth summary value from the same signal source, the coordinate calculation unit  2484  calculates a first one dimensional coordinate of a two dimensional coordinate according to the first difference, and a second one dimensional coordinate of the two dimensional coordinate according to the second difference. 
         [0083]    In the third embodiment, the digital integration unit  2748  generates a plurality of first, second, third, fourth, fifth and sixth summary values according to a first, second, third, fourth, fifth and sixth cycle respectively, the coordinate calculation unit  2754  generating a first difference and a second difference by subtract the third summary value and the fifth summary value from the first summary value of the same signal source respectively, the coordinate calculation unit generating a third difference and a fourth difference by subtract the fourth summary value and the sixth summary value from the second summary value of the same signal source respectively, the coordinate calculation unit calculates a first one dimensional coordinate of a first and a second two dimensional coordinate according to the first difference and the second difference respectively, the coordinate calculation unit  2754  calculates a second one dimensional coordinate of the first and the second two dimensional coordinate according to the second difference and t he fourth difference. 
         [0084]    It should be apparent to those skilled in the art that the above description is only illustrative of specific embodiments and examples of the invention. The invention should therefore cover various modifications and variations made to the herein-described structure and operations of the invention, provided they fall within the scope of the invention as defined in the following appended claims. Furthermore, the X axis and the Y axis recited above can be exchanged and also in the scope of the invention.