Abstract:
A touch panel device includes an excitation transducer for exciting a surface acoustic wave upon application of a burst wave and a reception transducer for receiving the surface acoustic wave and converting the same into a reception signal that are arranged at a peripheral portion of a detection area so that a position of an object touching the detection area is detected in accordance with a change in the reception signal. A control method for eliminating noises in the touch panel device includes the steps of detecting a differential between a reception signal due to a burst wave and another reception signal due to another burst wave, deciding that there is a noise if the detected differential exceeds a preset threshold value, and performing a control operation so that the detection of an object based on the reception signal is not performed in accordance with the decision.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a touch panel device for detecting a touch position of an object such as a finger by detecting a position where a surface acoustic wave is attenuated due to a touch of the object, and a control method and a control device for eliminating noises in the detection.  
         [0003]     2. Description of the Prior Art  
         [0004]     Such a touch panel device is often used as an input device of a personal computer, a mobile computer or a portable information terminal (or a personal digital assistant, PDA). A user of the touch panel device can enter information by touching a display screen of a display device with a finger or a pen.  
         [0005]     There is one type of the touch panel device, which utilizes a surface acoustic wave (SAW). This includes transducers arranged at sides of a touch area for exciting a surface acoustic wave or receiving the same. When a finger or the like touches the touch area, the touch position is detected based on a position where the surface acoustic wave is attenuated. The applicant has proposed one type of such touch panel devices in Japanese unexamined patent publication No. 2004-171213. This touch panel device uses transducers having an electrode structure in which a piezo-electric thin film is sandwiched between a comb electrode and a plate electrode so that only one electrode is arranged on one face (a single phase transducer, SPT) and has a chevron-shaped electrode structure in which plural V-shaped comb electrodes are arranged successively.  
         [0006]     The touch panel device includes a rectangular transparent substrate and four transducers disposed on the substrate. Two of the four transducers are for excitation arranged at the upper and the lower sides of the substrate, and the other two are transducers for reception arranged at the right and the left sides of the same. The portion surrounded by the four transducers is the touch area.  
         [0007]     An excitation voltage of a burst wave is alternately applied to the transducers arranged at the upper and the lower sides so as to generate a surface acoustic wave. The generated surface acoustic wave propagates on the substrate in a diagonal direction so that the transducers arranged at the right and the left sides can receive the same. The surface acoustic wave propagates in parallel with the diagonal line. Therefore, the closer to the diagonal line, the longer a propagation distance as well as a time period until arrival is. Accordingly, the transducer for reception produces a sequential reception signal (time domain waveform) due to one burst wave.  
         [0008]     When a finger, a pen or the like touches a position in the touch area, the surface acoustic wave is attenuated at the touched position. Responding to it a level of the reception signal drops, so the position touched by the finger or the like can be detected base on the position where the level drops.  
         [0009]     In order to detect the drop of the level of the reception signal (the time domain waveform), a difference between the signal and a time domain waveform (slice data) stored in a memory in advance is determined. If there is a drop of the level due to a touch of a finger or the like, the difference increases. When this difference exceeds a threshold value (a slice level), it is decided that a finger or the like touched. If the slice level is set to a smaller value, a small value of the difference can be detected. In other words, detection sensitivity (touch sensitivity) increases.  
         [0010]     A pressure (weight) of contact with a finger or the like is substantially proportional to an attenuation level of the surface acoustic wave. It is preferable to use a slice level as small as possible in order to detect a small pressure applied by a finger or the like.  
         [0011]     As described above, it is preferable to set the slice level as small as possible for improving detection sensitivity. However, it is found that there is a possibility of fluctuation generated by a dirty surface of the touch area or noises of incoming radio wave, and the fluctuation is not negligible to the detection sensitivity of the received time domain waveform. In other words, if the detection sensitivity is increased, the difference generated by the fluctuation due to the noises or the like may exceed the threshold value, resulting in an error of detection.  
         [0012]     As a countermeasure against this problem, it is possible to add a smoothing process on the received time domain waveform so as to reduce the fluctuation. Thus, the influence of the noises or the like can be reduced substantially. However, once a noise like a spike noise having a large variation is picked up, it is very difficult to eliminate such a noise, which may cause an error of detection.  
         [0013]     In particular, as cellular phones have become widespread recent years, influences of noises due to microwave radio waves emitted by the cellular phones have become non-negligible.  
       SUMMARY OF THE INVENTION  
       [0014]     An object of the present invention is to improve detection sensitivity of a touch panel device and prevent an error of detection due to an influence of noises generated by a cellular phone or the like.  
         [0015]     A control method according to the present invention is used for eliminating noises in a touch panel device including an excitation transducer for exciting a surface acoustic wave upon application of a burst wave and a reception transducer for receiving the surface acoustic wave and converting the same into a reception signal that are arranged at a peripheral portion of a detection area so that a position of an object touching the detection area is detected in accordance with a change in the reception signal. The control method includes the steps of detecting a differential between a reception signal due to a burst wave and another reception signal due to another burst wave, deciding that there is a noise if the detected differential exceeds a preset threshold value, performing a control operation so that the detection of an object based on the reception signal is not performed in accordance with the decision.  
         [0016]     Preferably, the differential detecting step includes detecting a differential between a reception signal at a time and a reception signal at a previous time. In addition, the control method further includes the steps of stopping an application of the burst wave until a preset wait time passes if the detected differential exceeds the preset threshold value, and restarting the application of the burst wave after the wait time has passed.  
         [0017]     In addition, the control method further includes the steps of deciding that there is a noise if a level of a noise floor exceeds a preset second threshold value in a period other than a period in which a reception signal due to the burst wave is obtained, and performing a control operation so that the detection of an object based on the reception signal is not performed in accordance with the decision.  
         [0018]     In addition, the control method further includes the steps of stopping an application of the burst wave if a level of a noise floor exceeds a preset second threshold value until a preset wait time passes, and restarting the application of the burst wave after the wait time has passed.  
         [0019]     A control device according to the present invention includes a differential detecting portion for detecting a differential between a reception signal due to a burst wave and another reception signal due to another burst wave, a noise detecting portion for detecting a noise when the detected differential exceeds a preset threshold value, and a control portion for performing a control operation so that the detection of an object based on the reception signal is not performed when a noise is detected.  
         [0020]     In addition, the control device further includes a count portion for counting the number of times when the detected differential exceeds the preset threshold value and a threshold change portion for changing the threshold value when a count value of the count portion exceeds a predetermined value.  
         [0021]     A touch panel device according to the present invention includes an oscillation portion for producing the burst wave plural times, an A/D converter for converting the reception signal into digital reception data, an object detecting portion for detecting a position of an object that touches the detection area by comparing the reception data with reference data that are stored in advance, a differential detecting portion for detecting a differential between reception data due to a burst wave and another reception data due to another burst wave, a noise detecting portion for detecting a noise when the detected differential exceeds a preset threshold value, and a control portion for performing a control operation so that the detection of the object based on the reception data is not performed when a noise is detected.  
         [0022]     According to the present invention, it is possible to improve detection sensitivity of a touch panel device and to prevent an error of detection due to an influence of noises generated by a cellular phone or the like. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a front view of a touch panel device according to an embodiment of the present invention.  
         [0024]      FIG. 2  is a block diagram showing an example of a functional structure of a drive control portion of the touch panel device.  
         [0025]      FIG. 3  is a diagram showing an example of a circuit of the drive control portion.  
         [0026]      FIG. 4  is a diagram showing examples of an excitation signal and a reception signal.  
         [0027]      FIG. 5  is a diagram showing the excitation signal for one burst wave.  
         [0028]      FIG. 6  is a diagram showing an example of the reception signal.  
         [0029]      FIG. 7  is a diagram showing A/D conversion of the reception signal into reception data.  
         [0030]      FIG. 8  is a diagram showing an example of the reception signal containing a noise due to a cellular phone.  
         [0031]      FIG. 9  is a diagram showing an example of a differential of the reception signal containing a noise.  
         [0032]      FIG. 10  is a diagram for explaining a principle of noise detection by the differential of the reception signal.  
         [0033]      FIG. 11  is a diagram showing the noise detection on a noise floor.  
         [0034]      FIG. 12  is a flowchart showing a general process operation of the touch panel device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]     Hereinafter, the present invention will be explained more in detail with reference to embodiments and drawings.  
         [0036]      FIG. 1  is a front view of a touch panel device  1  according to an embodiment of the present invention.  
         [0037]     As shown in  FIG. 1 , the touch panel device  1  includes a rectangular transparent glass substrate  11 , four transducers  20   a - 20   d  arranged at the peripheral portion of the glass substrate  11  and wiring electrodes  30   a - 30   d  and  31   a - 31   d  along the perimeter of the transducers  20   a - 20   d . The middle portion of the touch panel device  1 , i.e., a rectangular portion surrounded by the transducers  20   a - 20   d  is a touch area TE.  
         [0038]     Two transducers  20   a  and  20   b  arranged at the upper side portion and the lower side portion are for excitation, while two transducers  20   c  and  20   d  arranged at the left side portion and the right side portion are for reception. The transducers  20   a  and  20   b  for excitation are supplied with an excitation voltage (or an excitation signal as shown in  FIG. 4 ) that is a burst wave so that a surface acoustic wave is generated. The generated surface acoustic wave propagates on the glass substrate  11  in a diagonal direction and is received by the transducers  20   c  and  20   d  for reception.  
         [0039]     More specifically, the surface acoustic wave from the transducer  20   a  at the upper side portion propagates diagonally toward the lower right direction (channel  1 ) as well as toward the lower left direction (channel  2 ), which are received by the transducers  20   c  and  20   d  at the right side portion and the left side portion, respectively. In the same way, the surface acoustic wave from the transducer  20   b  at the lower side portion propagates diagonally toward the upper right direction (channel  3 ) as well as toward the upper left direction (channel  4 ), which are received by the transducers  20   c  and  20   d  at the right side portion and the left side portion. Note that the excitation voltage is applied to the transducers  20   a  and  20   b  for excitation alternatively at different timings.  
         [0040]     A time period necessary for the surface acoustic wave to propagate is proportional to a length of the propagation path. Therefore, the time when the surface acoustic wave reaches the transducers  20   c  and  20   d  for reception is delayed more at the end portion farther from the transducers  20   a  and  20   b  for transmission. Accordingly, a reception signal of each of the transducers  20   c  and  20   d  for reception continues while diminishing gradually during a period from first arrival to last arrival of the surface acoustic wave (see  FIGS. 4 and 6 ). When a finger, a pen or the like touches a part in the touch area TE, the surface acoustic wave is attenuated at the touched part. As a result, a level of the reception signal decreases. Therefore, the touch position is detected in accordance with the position where the level of the reception signal decreases.  
         [0041]      FIG. 2  is a block diagram showing an example of a functional structure of a drive control portion  3  of the touch panel device  1 ,  FIG. 3  is a diagram showing an example of a circuit of the drive control portion  3 ,  FIG. 4  is a diagram showing examples of an excitation signal and a reception signal,  FIG. 5  is a diagram showing the excitation signal for one burst wave,  FIG. 6  is a diagram showing an example of the reception signal,  FIG. 7  is a diagram showing A/D conversion of the reception signal into reception data,  FIG. 8  is a diagram showing an example of the reception signal containing a noise due to a cellular phone,  FIG. 9  is a diagram showing an example of a differential of the reception signal containing a noise,  FIG. 10  is a diagram for explaining a principle of noise detection by the differential of the reception signal, and  FIG. 11  is a diagram showing the noise detection on a noise floor.  
         [0042]     As shown in  FIG. 2 , the drive control portion  3  includes an oscillation portion  41 , a reception portion  42 , a smoothing portion  43 , a noise detection portion  44  and a control portion  45 .  
         [0043]     The oscillation portion  41  is provided for the purpose of applying a burst wave BW to the transducers  20   a  and  20   b  for excitation. The oscillation portion  41  includes a frequency controller  51 , an oscillator  52  and a frequency counter  53 . The oscillator  52  is a voltage controlled oscillator (VCO), and a phase locked loop (PLL) is made up of the oscillator  52  and the frequency controller  51  that uses a quartz resonator. Thus, the oscillator  52  produces an excitation signal S 1  that is a pulse train as shown in  FIG. 5 . Although the rectangular pulse train is used in this embodiment, a sine wave or other waveform signal can be used.  
         [0044]     In the frequency counter  53 , a value is set in accordance with an instruction by the control portion  45 . Depending on the set value, the number of pulses of the excitation signal S 1  produced by the oscillator  52  is determined. In other words, when a gate is opened by a reference signal S 0 , the pulse of the excitation signal S 1  is delivered from the oscillator  52  to the transducers  20   a  and  20   b . The frequency counter  53  counts the number of pulses of the excitation signal S 1  and closes the gate when the number has reached the set value. The excitation signal S 1  that is a pulse train of successively produced pulses constitutes the burst wave BW for one time. As shown in  FIG. 4 , plural burst waves BW are delivered successively at an appropriate interval for one detecting operation.  
         [0045]     Note that the pulse of the excitation signal S 1  has a frequency of 20 MHz, a period of 50 ns, a voltage of a few volts, for example. The number of pulses of one burst wave is approximately 10-20, for example. A detection time T 2  of the reception signal S 2  produced by the transducers  20   c  and  20   d  when the surface acoustic wave is received is approximately 50 μs. The number of burst waves BW during one detecting operation is approximately 30-40.  
         [0046]     The reception portion  42  is supplied with the reception signal S 2  that is delivered by the transducers  20   c  and  20   d . An example of the reception signal S 2  is shown in  FIG. 6 . In the reception signal S 2  shown in  FIG. 6 , there is a drop of the level that appears between the times t 1  and t 2  due to a touch of a finger or the like on the touch area TE.  
         [0047]     The reception portion  42  includes an amplifier  61  and an A/D converter  62 . The amplifier  61  amplifies the reception signal S 2 , and the A/D converter  62  samples the amplified signal at an appropriate period so as to convert it into digital reception data S 3 . The A/D converter  62  produces the reception data S 3  as a result of sampling of the reception signal S 2  containing a time domain waveform as shown in  FIG. 7 . Note that a sampling frequency of the A/D converter  62  is 10 MHz, for example.  
         [0048]     The smoothing portion  43  smoothes the reception data S 3  during a period T 3  (see  FIGS. 7, 10  and  11 ) corresponding to the time domain waveform in each time of the plural burst waves BW for one detecting operation so as to deliver reception data S 4  that correspond to an average time domain waveform.  
         [0049]     As shown in  FIG. 3 , the smoothing portion  43  includes an adding portion  71 , a memory  72 , a dividing portion  73  and a gate GT 3 . The gate GT 3  is controlled so as to open only during the period T 3 , and the reception data S 3  are permitted to pass during this period T 3 . Note that the period T 3  corresponds to the time domain waveform with end portions of the waveform cut off.  
         [0050]     The adding portion  71  adds each data vale of each sampling position for the reception data S 3  that correspond to plural time domain waveforms to be obtained on one detecting operation.  
         [0051]     In other words, it is supposed that the reception data S 3  is obtained corresponding to 32 time domain waveforms in one detecting operation, for example. The reception data S 3  of the first time, the second time, the third time, the m-th time, . . . the 32nd time are represented by D1, D2, D3, Dm, . . . D32, respectively. Then, the following relationships are satisfied. 
 
 D 1 =R 1(0)+ R 1(1)+ R 1(2)+ . . . + R 1(255) 
 
 D 2 =R 2(0)+ R 2(1)+ R 2(2)+ . . . + R 2(255) 
 
. . . 
 
 Dm=Rm (0)+ Rm (1)+ Rm (2)+ . . . + Rm (255) 
 
. . . 
 
 D 32 =R 32(0)+ R 32(1)+ R 32(2)+ . . . + R 32(255) 
 
         [0052]     Here, Rm(n) indicates n-th sampling data of m-th reception data S 3 . In this example, it is supposed that 256 sampling data are obtained from one reception signal S 2 .  
         [0053]     The adding portion  71  calculates a sum value ΣR(n) of sampling data from the first through the 32nd times (m=1-32) for each value of n (=0, 1, 2, . . . ) of each sampling position. The memory  72  stores sampling data for each sampling position. As a result, the sum value ΣR(n) of 32 times for each sampling position added by the adding portion  71  is stored in the memory  72 .  
         [0054]     The dividing portion  73  divides the sum value ΣR(n) for each sampling position stored in the memory  72  by 32 each that is the number of total times. The dividing portion  73  delivers the reception data S 4  that are an average value of 32 reception data S 3  in one detecting operation.  
         [0055]     Therefore, even if some noises are contained in the 32 reception data S 3 , the noises are averaged and are not conspicuous in the reception data S 4 . In this way, one-shot noises that are generated impulsively can be eliminated effectively. Note that the timing of the sampling position can be determined in accordance with the timing of the reference signal S 0  described above.  
         [0056]     A touch position is detected by the control portion  45  in accordance with the reception data S 4  delivered from the smoothing portion  43 . In other words, the control portion  45  includes a memory  65 , an operational portion  66  and a counter  67 . In addition, it includes an operation input portion and a display portion, if necessary.  
         [0057]     The memory  65  stores a reference time domain waveform DR that is obtained when no object touches the panel, a slice time domain waveform DS that is obtained by subtracting a predetermined slice value (threshold) thd from the reference time domain waveform DR, and the slice value thd. The reference time domain waveform DR is, for example, digital data in the same sampling period as that of the reception data S 3  and is obtained by an initialization process when the touch panel device  1  is powered on. After that the reference time domain waveform DR is updated regularly. The threshold thd can also be changed.  
         [0058]     Although the operational portion  66  is structured by using hardware logic, it is possible to constitute the same using an MPU, a ROM and a RAM so as to realize the function by executing a program. It is also possible to structure the same by combining the hardware and the software.  
         [0059]     The operational portion  66  compares the time domain waveform of the reception data S 4  with the slice time domain waveform DS that is read out of the memory  65 . In other words, time points t 1  and t 2  at intersections of the reception data S 4  and the slice time domain waveform DS are detected as shown in  FIG. 6 . A touch position in the touch area TE is calculated in accordance with the detected time points t 1  and t 2 , the slice value thd and the like. Note that the aforementioned patent document may be referred to for more detailed description of the method for determining a touch position.  
         [0060]     Next, the noise detection portion  44  detects noises contained in the reception data S 2  (reception signal S 3 ). As described above in the prior art, the reception signal S 2  often contains noises due to radio waves emitted by cellular phones for example. If a cellular phone is used near the touch panel device  1 , various levels of noises enter the touch panel device  1  depending on a distance between the touch panel device  1  and the cellular phone. If the reception signal S 2  contains a large level of noise, the reception signal S 4  will be distorted so that a touch position cannot be detected correctly.  
         [0061]     As shown in  FIG. 2 , the noise detection portion  44  includes a first noise detection portion  63  and a second noise detection portion  64 . As shown in  FIG. 3 , the first noise detection portion  63  includes a delay portion  74 , a differential operational portion  75 , a comparing portion  76 , a decision portion  77 , a threshold storage portion  78  and a gate GT 1 . The second noise detection portion  64  includes a threshold storage portion  79 , a comparing portion  80 , a decision portion  81  and a gate GT 2 .  
         [0062]     In the first noise detection portion  63 , the gate GT 1  is controlled to open only during a predetermined period T 3  so as to allow the reception data S 3  to pass during the period T 3 . The delay portion  74  stores reception data S 3  that correspond to one reception time domain waveform delivered from the A/D converter  62 . In this way, the reception data S 3  are delayed by the time corresponding to one time domain waveform. The differential operational portion  75  performs an operation for determining the differential SBm between the reception data S 3  corresponding to the present reception time domain waveform delivered from the A/D converter  62  and the reception data S 3  corresponding to the previous reception time domain waveform stored in the delay portion  74 . The comparing portion  76  compares the differential SBm delivered from the differential operational portion  75  with the threshold value th 1  of the threshold storage portion  78  so as to deliver a comparison result. The comparing portion  76  delivers the comparison result for each of the sampling data. The decision portion  77  decides whether noises are contained or not in accordance with the comparison result from the comparing portion  76 .  
         [0063]     In the second noise detection portion  64 , the gate GT 2  is controlled to open only during a predetermined period T 4  (see  FIG. 11 ) so as to allow the noise floor NF to pass during the period T 4 . The comparing portion  80  compares a level of the noise floor NF with a threshold value th 2  of the threshold storage portion  79  so as to deliver a comparison result. The decision portion  81  decides whether noises are contained or not in accordance with the comparison result from the comparing portion  80 .  
         [0064]     Note that a signal that is given to the gates GT 1 -GT 3  for determining the periods T 3  and T 4  are delivered from the control portion  45  for example.  
         [0065]     Hereinafter, the operation of the noise detection portion  44  will be described more in detail.  
         [0066]     As shown in  FIG. 8 , noises from a cellular phone may disturb the reception signal. In the example shown in  FIG. 8 , the time domain waveform is disturbed by the noises, and the noise floor is raised between the time domain waveform and the time domain waveform. If the time domain waveform is disturbed to the extent shown in  FIG. 8 , it is difficult to detect a touch position correctly.  
         [0067]     Therefore, the first noise detection portion  63  and the second noise detection portion  64  perform the following two types of noise detection processes according to this embodiment.  
         [0068]     (1) The first noise detection portion  63  detects the differential SBm between the present time domain waveform and the previous time domain waveform in the burst wave BW, and it is decided that noises are contained if the differential SBm exceeds the first threshold value th 1 .  
         [0069]     (2) The second noise detection portion  64  monitors the noise floor and decide that noises are contained if a level of the noise floor exceeds the second threshold value th 2 .  
         [0070]     In  FIG. 9  there are shown the differential between the time domain waveform at a certain time point and the previous time domain waveform as noise  1  and noise  2 . The noise  1  shows the case where a cellular phone approaches very closely to the touch panel device  1 , and the noise  2  shows the case where the cellular phone is apart from the touch panel device  1  by approximately 1 meter. Note that there is a differential that is indicated as “fluctuation” in  FIG. 9  even if there is no noise. Therefore, the threshold value th 1  is set to a value that is larger than a normal fluctuation component so that the fluctuation component is not detected but the noises  1  and  2  having larger levels can be detected.  
         [0071]     In other words, the differential SBm is obtained when Dm−1 that is the previous reception data S 4  is subtracted from Dm that is the present reception data S 4  as shown in  FIG. 10 . The differential SBm is obtained for each of the sampling data of the time domain waveform. The differential SBm is small in the normal state without noises as shown in (A) of  FIG. 10 , while the differential SBm is large in the state with noises as shown in (B) of  FIG. 10 . The threshold value th 1  is set to an appropriate value so that the above two cases can be distinguished from each other.  
         [0072]     In addition, the threshold value th 2  is set to an appropriate value so that the case where the noise floor NF is raised as shown in  FIG. 11  can be distinguished from the case without noises. Note that a period T 4  for detecting the noise floor NF is a period other than the period while the reception signal due to the burst wave BW can be obtained.  
         [0073]     Such threshold values th 1  and th 2  may be set in accordance with a design value of the touch panel device  1 . In addition, they may be set by a real operation of the device in a factory or in accordance with a situation of a site where the device is installed. It is also possible to set them every time when the drive control portion  3  is activated. In addition, the setting may be updated in accordance with a change in the situation of the site or an aged deterioration thereof.  
         [0074]     For example, it is possible to provide a counter for counting the number of times when the differential SBm exceeds the threshold value th 1  and to change the threshold value th 1  when a value of the counter reaches a predetermined value. It can be applied to the threshold value th 2  in the same way. Such a process of updating the threshold values can be performed under control of the control portion  45 , for example.  
         [0075]     Note that the decision portions  77  and  81  decide that a noise is contained if the sampling data exceed the threshold values th 1  and th 2  even once, for example. Alternatively, they decide that a noise is contained if a predetermined number of sampling data exceed the threshold values th 1  and th 2  for one burst wave BW. Still alternatively, they decide that a noise is contained if a predetermined number of sampling data exceed the threshold values th 1  and th 2  successively. Any of the methods can be adopted in accordance with a situation of noises on the site or the like.  
         [0076]     If a noise is detected by the above-mentioned method, it is controlled so that the detection process of an object (a detection process of a touch position) is not performed in accordance with the reception signal S 2 . In other words, decision signals S 5  and S 6  delivered from the decision portions  77  and  81  are supplied to the control portion  45 . The control portion  45  controls the detection process of a touch position in the control portion  45  and operations of the oscillation portion  41  and the like in accordance with the decision signals S 5  and S 6 .  
         [0077]     In other words, when a noise is detected, the reception data S 4  with the noise are abandoned for example. Then, after a predetermined time (a wait time TW 1 ) has passed, the detecting operation is restarted. If a noise at the noise floor NF is detected, the detection process and the detecting operation are stopped at the time point when the noise is detected. The oscillation portion  41  stops excitation of the burst wave BW during this period. Then, after a predetermined time (a wait time TW 2 ) has passed, the detecting operation is restarted.  
         [0078]     As the wait times TW 1  and TW 2 , appropriate values are set in accordance with a situation of noise generation or the like. For example, a value within the range of few milliseconds to a few tens of milliseconds is set. Concerning noises due to a cellular phone, it often emits an intermittent radio wave that is turned on and off every 20-30 milliseconds. In this case, a value within the range of 10-20 milliseconds is set to the wait times TW 1  and TW 2 , for example. Then, the next detecting operation will be performed without noises at high probability. Note that the same value or different values may be set to the wait times TW 1  and TW 2 .  
         [0079]     Next, a general operation of the touch panel device  1  will be described with reference to flowcharts.  
         [0080]      FIG. 12  is a flowchart showing a general process operation of the touch panel device  1 .  
         [0081]     As shown in  FIG. 12 , the noise floor NF is checked (# 11 ), and it is decided whether or not a level of the noise floor NF exceeds the threshold value th 2  (# 12 ). If the noise floor NF exceeds the threshold value th 2  (Yes in # 12 ), the process is halted for a predetermined wait time TW (# 13 ). In other words, the burst wave BW is not delivered from the oscillation portion  41  for this time period, for example. When the wait time TW passes, the process is restarted from the first step in the flowchart.  
         [0082]     If the noise floor NF is the threshold value th 2  or lower, the reference signal S 0  is delivered so as to produce the burst wave BW for example. The time domain waveform is obtained in accordance with the reception signal S 2  (# 14 ). Then, the differential SBm for each time is determined for the time domain waveform (# 15 ). If the differential SBm exceeds the threshold value th 1  (Yes in # 16 ), the process is halted during a predetermined wait time TW (# 17 ). After that, the process is restarted from the first step of the flowchart.  
         [0083]     If the differential SBm is the threshold value th 1  or lower (No in # 16 ), the reception data S 4  that is smoothed by the smoothing portion  43  is used for performing the detection process of a touch position (# 18  and # 19 ).  
         [0084]     It is possible to set a flag for example when a noise is detected, so that the detection process is restarted from the first step.  
         [0085]     Thus, the touch panel device  1  according to this embodiment includes two noise detection portions  63  and  64  as the noise detection portion  44  for checking noises in the reception data S 3 , and the detection result is fed back to the control portion  45 . Thus, the process of detecting a touch position is halted during a period when the noise is generated. Therefore, the process of detecting a touch position is performed only for the reception data S 3  without a noise, and a detection error due to a noise can be prevented. In addition, as an influence of a noise is reduced, the slice value thd can be decreased so that sensitivity in detection of a touch position can be enhanced. Thus, even a light touch on the panel can be detected.  
         [0086]     According to this embodiment, noises can be eliminated effectively by a simple structure in which the noise detection portion  44  is added to the drive control portion  3  and the control portion  45  performs a simple control. In addition, as the surface acoustic wave is not delivered during the period when a noise is detected and a weight is applied, power consumption during the period can be suppressed.  
         [0087]     Although 32 excitation signals S 1  are delivered as the burst wave BW in the embodiment described above, other number of times can be adopted. It is possible that the number of times is variable. It is possible that the number of pulses in one excitation signal S 1  can be changed by the control portion  45  if necessary. The periods T 1 -T 4  may be other appropriate values without limited to the above-exemplified values. The sampling period and the number of sampling data of the reception data S 3  can be changed to values other than the above-exemplified values.  
         [0088]     In the embodiment described above, the differential SBm is determined in accordance with the present reception data S 3  and the previous reception data S 3 . Instead, the differential SBm may be determined in accordance with the reception data S 3  and a reference waveform. For example, the reception data S 3  corresponding to the first time domain waveform is used as the reference waveform, and the reception data S 3  corresponding to the time domain waveform of each time is compared with the reference waveform so as to determine the differential SBm.  
         [0089]     In the embodiment described above, the decision signals S 5  and S 6  are delivered from the noise detection portions  63  and  64  to the control portion  45  so that the control portion  45  controls operations of the oscillation portion  41  and the like. Alternatively, the decision signals S 5  and S 6  may be delivered directly to the oscillation portion  41  so that an operation of the oscillation portion  41  is controlled directly. In this case, the circuit structure of the drive control portion  3  is simplified more. In other words, a detection error due to a noise can be prevented by a simple logic structure without using an MPU or a CPU in the control portion  45 , for example. In addition, although two noise detection portions  63  and  64  are provided in the embodiment described above, one of them can be eliminated so that only the other detects a noise.  
         [0090]     Furthermore, the structure of the whole or a part of the noise detection portions  63  and  64 , the smoothing portion  43 , the control portion  45 , the drive control portion  3  and the touch panel device  1 , and the circuit thereof, the shape, the dimensions, the number, the material and the value thereof, the contents and the order of the process and timings thereof can be modified, if necessary, in accordance with the spirit of the present invention.  
         [0091]     The touch panel device according to the present invention can be utilized as an input device of a personal computer, a mobile computer, a portable information terminal or other type of device.  
         [0092]     While example embodiments of the present invention have been shown and described, it will be understood that the present invention is not limited thereto, and that various changes and modifications may be made by those skilled in the art without departing from the scope of the invention as set forth in the appended claims and their equivalents.