Abstract:
A panel sensing device and a positioning location searching method of the same are disclosed. A control unit serves to provide at least one reference voltage and at least one reference voltage with opposite phase. Thereby, a plurality of position blocks are defined by the electric field distributions produced by the reference voltages. A sensing pen is used to touch the sensing plate for sensing the object voltage of a touch position. The control unit searches the touch position according to the phase and level of the object voltage and the reference voltages.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to panel sensing device and a positioning location searching method of the same, in which phase difference is used to determine a touch position of a sensing pen on a sensing plate. 
   2. Description of the Related Art 
   In general, an electronic book has a sensing pen and a plurality of sensing pages. The sensing pen is used to touch the sensing pages for selecting desired items.  FIG. 1  schematically illustrates a sensing plate of a conventional electronic book  11 , wherein two ends A 1  and B 1  are inputted with driving waveforms for getting the row position of the sensing pen  12 . The other two ends C 1  and D 1  are applied with driving waveforms for getting the column position of the sensing pen  12 . 
     FIG. 2  shows the driving waveforms applied to the four ends A 1 , B 1 , C 1  and D 1 . At Initial time, for example 10 to 20 micro seconds, the four ends are applied with identical reference voltage waveforms. Then, at about 6˜9 seconds, an addressing voltage waveform (row) is applied to the A 1  end so that the sensing pen  12  can sense an electric field waveform, as shown in  FIG. 3 , by sensing the electric field. 
   Because the distribution of the electric field is linear, it is able to determine the current touching position of the sensing pen  12  via comparing the voltage that the sensing pen  12  detected in the addressing voltage waveform period (i.e., 6˜9 seconds) with the voltage that the sensing pen  12  detected in the reference voltage waveform period (i.e., 0˜3 seconds). 
   However, the sensing pen  12  needs to use a high precision analog to digital converter to sense the strength of amplitude. If a high resolution is required, a highly precise analog to digital converter is required, resulting in the increase of the manufacturing cost. Moreover, the amplitude and energy caused by sensing voltage are difficult to control to get a good precision and to match the specification in mass production. 
   SUMMARY OF THE INVENTION 
   Accordingly, the primary object of the present invention is to provide a panel sensing device and a positioning location searching method of the same, wherein phase difference is used to determine a touch position of a sensing pen, and thus no precise analog to digital converter is required. 
   Another object of the present invention is to provide a panel sensing device and a positioning location searching method of the same, wherein the resolution can be improved by a simple digital to analog converter. 
   In accordance with one aspect of the present invention, there is provided a panel sensing device, which comprises: a sensing plate having a first side, a second side opposite to the first side, a third side and a fourth side opposite to the third side; a control unit for providing an adjustable first reference voltage, an adjustable second reference voltage, an adjustable third reference voltage, and an adjustable fourth reference voltage to the first side, second side, third side and fourth side, respectively, wherein the first reference voltage has a phase opposite to that of the second reference voltage, and the third reference voltage has a phase opposite to that of the fourth reference voltage, whereby the first to fourth reference voltages generate electric fields for distributing on the sensing plate to define a plurality of position blocks; and a sensing pen for touching the sensing plate to sense an object voltage on a touch position, whereby the control unit searches the touch position according to the phases and levels of the object voltage and the first to fourth reference voltages. 
   In accordance with another aspect of the present invention, there is provided a positioning location searching method for searching a touch position of a sensing pen on a sensing plate. The sensing plate has a first side, a second side opposite to the first side, a third side and a fourth side opposite to the third side. The method comprises the steps of: (A) providing an adjustable first reference voltage, an adjustable second reference voltage, an adjustable third reference voltage, and an adjustable fourth reference voltage to the first side, second side, third side and fourth side, respectively, wherein the first reference voltage has a phase opposite to that of the second reference voltage, and the third reference voltage has a phase opposite to that of the fourth reference voltage, whereby the first to fourth reference voltages generate electric fields for distributing on the sensing plate to define a plurality of position blocks; (B) using a sensing pen to touch the sensing plate in order to sense an object voltage at a touch position; (C) comparing the phase of the object voltage with the phases of the first to fourth reference voltages for determining a position block where the touch position is located; (D) adjusting the level of at least one of the first to fourth reference voltages to change the defined position blocks; and (E) comparing the phase of the object voltage with the first to fourth reference voltages again for determining the position block where the touch position is located so as to determine the touch position. 
   The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a prior art electronic book. 
       FIG. 2  is a schematic view of a sensed input driving wave of the prior art electronic book. 
       FIG. 3  is a schematic view about the sensing waveform of a prior art electronic book. 
       FIG. 4  is a schematic view showing the panel sensing device of the present invention. 
       FIG. 5  is a schematic view showing one embodiment of the present invention. 
       FIG. 6  shows one flow diagram of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 4 to 6 , a schematic view of the panel sensing device and positioning location searching method of the same in accordance with the present invention is illustrated. The present invention includes a sensing plate  2 , a sensing pen  3  and a control unit  4 . The control unit  4  further includes a digital to analog converter  41  for converting digital values into analog reference voltages which are provided to the sensing plate  2 . In this embodiment, the digital to analog converter  41  has preferably a seven-bit resolution, i.e., the digital to analog converter is a 7-bit digital to analog converter capable of converting a 7-bit digital value into an analog reference voltage thereby providing a resolution of 128 levels because 2 to the power of 7 is 128 (2 7 =128. The sensing pen  3  is connected to the control unit  4  through a filtering unit, a shaping unit and a signal amplifying unit so that the control unit  4  can process the voltage sensed by the sensing pen  3 . 
   The sensing plate  2  has four sides, denoted as A 2 , B 2 , C 2  and D 2 . The side A 2  is opposite to side B 2  and the side C 2  is opposite to side D 2 . The control unit  4  provides a reference voltage to the sides A 2 , B 2 , C 2  and D 2 . The amplitude of the reference voltage of the side A 2  is identical to that of the side B 2 , but have an opposite phase. The reference voltages inputted to the sides C 2  and D 2  are identical in amplitude but opposite to each other in phase, so that the phase differences of these reference voltages are used in area searching. 
   Next, an example is given by addressing the position of a row, i.e., the position in row of the sensing plate  2  where the sensing pen  3  touches. Referring to  FIGS. 5 and 6 , the control unit  4  serves for providing a reference voltage of positive phase to the side A 2 , where the reference voltage has an amplitude of 0 to 5V, and providing a reference voltage of negative phase to the side B 2 , where the reference voltage has an amplitude of 5 to 0 (step  601 ). The loop count for repeatedly adjusting the reference voltage level of the side A 2  or B 2  is set according to the precision degree of the electronic book and the searching algorithm used, so as to determine the touch position. In this embodiment, the precision degree of the electronic book is 128 bits and the searching algorithm is a binary search algorithm. The loop count is seven times (step  602 ). Then, the sensing pen  3  touches an α position of the sensing plate  2  for sensing the object voltage of the α position. For example, the object voltage is a positive phase voltage with an amplitude of 3V (step  603 ). 
   Next, the phase of the object voltage is compared with the phases of the reference voltages at sides A 2  and B 2  so as to determine the touch position of the sensing pen  3 . In this embodiment, the phase of the object voltage is identical to the phase of the reference voltage of the side A 2 . Therefore, it is determined that the touch position of the sensing pen  3  is near the side A 2  (step S 604 ). That is, the touch position of the sensing pen  3  is located in a block between the side A 2  and a cutting line L( 1 / 2 ) which equally divides the sensing plate  2 . Thus, the reference voltage level of the side A 2  is adjusted to have a smaller range (half range in this example) through the control unit  4 . In this embodiment, because the binary search algorithm is employed, the reference voltage level of the side A 2  is adjusted to be a positive reference voltage having an amplitude with a value between 5×1/2=2.5V to 5V. Then, the loop count is decreased (step S 605 ). When the loop count is not equal to zero, the steps S 603 , S 604  and S 605  are executed repeatedly. For example, the phase of the object voltage is compared with the adjusted phases of the sides A 2  and B 2 . Now, the phase of the object voltage is identical to the phase of side A 2 . Thereby, it is determined that touching position (α) of the sensing pen  3  is located in a block between the side A 2  and a cutting line L( 3 / 4 ) which equally divides the area between the side A 2  and the cutting line L( 1 / 2 ). The reference voltage level of the side A 2  is adjusted to be a positive reference voltage having an amplitude with a value between 5×3/4=3.75V to 5V. Next, the loop count is reduced by 1, and the phase of the object voltage is compared with the adjusted phases of the sides A 2  and B 2 . Now, the phase of the object voltage is identical to the phase of side B 2 . Thereby, it is determined that touching position (α) of the sensing pen  3  is located in a block between the cutting line ( 3 / 4 ) and a cutting line L( 7 / 8 ) which equally divides the area between the side A 2  and the cutting line L( 3 / 4 ). Again, the loop count of the reference voltage is then reduced by 1, and the process continues until the loop count is 0. Then the touch position (row address) is determined (step S 606 ). 
   The process for positioning the column address is identical to that for positioning the row address as described above, and thus a detailed description is deemed unnecessary. The above method for searching the touch point of the sensing pen  3  is determined by phase difference and binary searching algorithm. However, the panel sensing device of the present invention can also use other searching algorithm to position the touch position. 
   It is known from above description that the sensing plate of the present invention provides at least one reference voltage and at least one reverse phase reference voltage. The phase and level of the object voltage sensed by the sensing pen to touch the sensing plate is compared with the phase of the reference voltage so as to acquire the touch position of the sensing pen. Thereby, no analog to digital converter of high precision is required. Furthermore, a simple digital to analog converter can be used to increase the resolution. Thus, the circuit design is simple and the mass production can be done easily. 
   The present invention is thus described, and it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.