Abstract:
The present invention relates to an information input panel using the light emitted diode (LED) matrix. The panel includes the LED matrix and a control circuit. The LED matrix includes N×M LEDs. The control circuit includes N first terminals and M second terminals, wherein the i th  first terminal thereof is coupled to first terminals of the LEDs in the i th  row and the j th  second terminal thereof is coupled to second terminals of the LEDs in the j th  column. In the k th  detecting period, the control circuit detects the reverse photoelectric currents of each LED from the second terminals through the k th  first terminal to determine whether LED in the k th  row is lighted up or not, wherein “M”, “N”, “i”, “j”, “k” are nature numbers and 0&lt;i&lt;=M; 0&lt;j&lt;=N; 0&lt;k&lt;=M.

Description:
This application claims priority of No. 097143453 filed in Taiwan R.O.C. on Nov. 11, 2008 under 35 USC 119, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates in general to the light emitted diode (LED) technology, and more particularly to an information input panel using LED matrix. 
     2. Related Art 
     Since the beginning of civilization, human record the information by using drawings and characters. As the development of technology, the information recording method of human being is changed from the hand writing by pen and paper to using the computer record. In earlier conventional art, the drawing panel is made of a plastic layer and a tremellose layer. When using an exclusive pen to the drawing panel, the tremellose layer will bind with the plastic layer to generate a pattern by pen point pressure. Another conventional structure of the drawing panel is made of ferruginous powder disposing on the plastic panel with iron net. When a magnetic pen draws on the drawing panel, the plastic panel magnetically pulls the ferruginous powder to show the drawing pattern. 
     The abovementioned drawing panels have a common advantage, which is reusable. However, the pattern will gradually disappear due to the fadeaway of its stickiness in the drawing panel of the first conventional art. In addition, in the iron powder type drawing panel of the second conventional art, due to the iron powder is been magnetization, it induce that the iron powder is attracted on the iron net. As time passes, the pattern of the drawing panel will become blurring. 
     The mainstream of the information input and display board is light emitted diode (LED) display, such as an LED display panel on bus or subway, or an LED badge and so on. However, if end user want to modify the display information outputted from the LED display panel, the LED display panel should be connected to a computer, and the specific software in the computer should be used, or the input device of the LED display panel and the built-in fonts of the LED display panel should be utilized to select the output information. Although the outputting figure of the display can be more flexible by using computer, the interconnection with computer and the specific software are prerequisite. On the contrary, by utilizing the built-in fonts, the outputting figure of the display will be relatively limited, so that the outputting figure cannot be modified at will. 
     SUMMARY OF THE INVENTION 
     It is therefore an objective of the present invention to provide an information input panel using light emitted diode matrix to facilitate the information input by user and to immediately display the inputted information. 
     The present invention achieves the above-identified or other objectives by providing an information input panel using light emitted diode matrix, which includes an LED matrix, a plurality of control circuits, wherein the LED matrix includes a plurality of LEDs, and each LED includes a first terminal and a second terminal. A first control terminal of each control circuit is coupled to the first terminal of the corresponding LED, and a second control terminal thereof is coupled to the second terminal of the corresponding LED. In a detecting period, the control circuits provide a reverse bias voltage for a preset period to the first terminal and the second terminal of the LEDs, and then the first terminals of the control circuits is set to a high impedance. Next, each control circuit detects the reverse photoelectric current of the coupled LED to determine whether the corresponding LED is lighted up or not. 
     The present invention additionally provides an information input panel using light emitted diode matrix. The panel includes an LED matrix, a first switching circuit, a second switching circuit and a control circuit. The LED matrix includes a plurality of LEDs. The first switching circuit includes a first terminal and a plurality of second terminals, wherein the second terminals of the first switching circuit are respectively coupled to the first terminals of the LEDs. The second switching circuit includes a first terminal and a plurality of second terminals, wherein the second terminals of the second switching circuit are respectively coupled to the second terminals of the LEDs. A first control terminal of the control circuit is coupled to the first terminal of the first switching circuit, and a second control terminal thereof is coupled to the first terminal of the second switching circuit. In the i th  detecting period, the first terminal of the first switching circuit is electrically connected to the i th  second terminal thereof, and the first terminal of the second switching circuit is electrically connected to the i th  second terminal thereof. At this time, the control circuit detects the reverse photoelectric current of the coupled i th  LED to determine whether the i th  LED is lighted up or not, wherein “i” is a nature number. 
     In the information input panel using light emitted diode matrix according to the preferred embodiment of the present invention, when each first terminal of the LEDs is cathode, and each second terminal of the LEDs is anode, the control circuit includes a tri-state controller, a comparator, a counting circuit and a judging circuit. The tri-state controller is coupled to the first control terminal and the second terminal of the control circuit. In the detecting period, the tri-state controller provides a common voltage to the second control terminal of the control circuit and a power supply voltage to the first terminal of the control circuit for a preset period, and then the tri-state controller set the first control terminal of the control circuit to a high impedance state. The comparator includes a first input terminal, a second input terminal and an output terminal. The first input terminal thereof receives a preset voltage, and the second input terminal thereof is coupled to the first control terminal of the control circuit. In the detecting period, a voltage level of a comparing signal outputted from the output terminal of the comparator is changed from the first saturation voltage to the second saturation voltage when the voltage of the first control terminal of the control circuit is smaller than the preset voltage. The counting circuit is coupled to the output terminal of the comparator. From the beginning of the detecting period, a counting value is accumulated for each preset time. When the voltage level of the comparing signal is changed from the first saturation voltage to the second saturation voltage, the accumulating is stopped and the counting value is outputted. The judging circuit is coupled to the counting circuit for receiving the counting value. When the counting value is smaller than a preset value, the LED is lighted up. 
     Similarly, when each first terminal of the LEDs is cathode, and each second terminal of the LEDs is anode, the control circuit includes a tri-state controller, an analog-to-digital converter (ADC) and a judging circuit. The tri-state controller is coupled to the first control terminal and the second terminal of the control circuit. In the detecting period, the tri-state controller provides the common voltage to the second control terminal of the control circuit, and the power supply voltage to the first control terminal of the control circuit for a preset period, after that, the tri-state controller set the first control terminal of the control circuit to a high impedance state. The ADC includes an input terminal and an output terminal, wherein the input terminal thereof is coupled to the first control terminal of the control circuit. In the predetermined period before the end of the detecting period, a digital value is outputted by the ADC according to the voltage of the first control terminal of the control circuit. The judging circuit is coupled to the ADC for receiving the digital value. When the digital value is smaller than a preset value, the LED is lighted up. 
     When each first terminal of the LEDs is anode, and each second terminal of the LEDs is cathode, the control circuit includes a tri-state controller, a comparator, a counting circuit and a judging circuit. The tri-state controller is coupled to the first control terminal and the second control terminal of the control circuit. In the detecting period, the tri-state controller provides a power supply voltage to the second control terminal of the control circuit, and provides a common voltage to the first control terminal of the control circuit for a preset period, after that, the tri-state controller sets the first control terminal of the control circuit to the high impedance. The comparator includes a first input terminal, a second input terminal and an output terminal. The first input terminal thereof receives a preset voltage, and a second input terminal is coupled to the first control terminal of the control circuit. In the detecting period, the voltage level of a comparing signal outputted from the output terminal of the comparator is changed from the first saturation voltage to the second saturation voltage if the voltage of the first control terminal of the control circuit is larger than the preset voltage. The counting circuit is coupled to the output terminal of the comparator. From the beginning of the detecting period, a counting value is accumulated for each preset time until the voltage level of the comparing signal is changed from the first saturation voltage to the second saturation voltage, and then the accumulating is stopped and the accumulated counting value is outputted. The judging circuit is coupled to the counting circuit for receiving the counting value. When the counting value is smaller than a preset value, the LED is lighted up. 
     Similarly, when each first terminal of the LEDs is anode, and each second terminal of the LEDs is cathode, the control circuit includes a tri-state controller, an analog-to-digital converter (ADC) and a judging circuit. The tri-state controller is coupled to the first control terminal and the second terminal of the control circuit. In the detecting period, the tri-state controller provides the power supply voltage to the second control terminal of the control circuit, and provide the common voltage to the first control terminal of the control circuit for a preset period, after that, the tri-state controller set the first control terminal of the control circuit to the high impedance. The ADC includes an input terminal and an output terminal, wherein the input terminal thereof is coupled to the first control terminal of the control circuit. In the predetermined period before the end of the detecting period, a digital value is outputted by the ADC according to the voltage of the first control terminal of the control circuit. The judging circuit is coupled to the ADC for receiving the digital value. When the digital value is larger than a preset value, the LED is controlled to light up. 
     The present invention additionally provides an information input panel using a light emitted diode (LED) matrix. The panel includes the LED matrix and a control circuit. The LED matrix includes N×M LEDs, wherein each LED includes a first terminal and a second terminal. The control circuit includes N first control terminals and M second control terminals, wherein the i th  first control terminal is coupled to the first terminals of the LEDs in the i th  row, the j th  second control terminal is coupled to the second terminals of the LEDs in the j th  column. In the k th  detecting period, the control circuit detects the reverse photoelectric currents flowing from the each of the second control terminal of the control circuit through the M coupled LEDs to the k th  first control terminal of the control circuit to determine whether LED in the k th  row is lighted up. When the reverse photoelectric current of the specific LED in the k th  row is larger than a predetermined value, the specific LED is lighted up. Wherein “M”, “N”, “i”, “j”, “k” are nature numbers and 0&lt;i&lt;=M, 0&lt;j&lt;=N, 0&lt;k&lt;=M o    
     In the information input panel using light emitted diode matrix according to the preferred embodiment of the present invention, when the first terminal of each LED is cathode, and the second terminal of each LED is anode, the control circuit includes a horizontal control circuit, a vertical control circuit and M current detecting circuits. The horizontal control circuit includes the N first control terminals. The vertical control circuit includes the M second control terminals. In the k th  detecting period, the k th  first control terminal of the horizontal control circuit is set to a power supply voltage, the M second control terminals of the vertical control circuit is set to a common voltage for a preset period, and then to a high impedance state. After that, the p th  current detecting circuit determines the reverse photoelectric current of the p th  LED in the k th  row according to the variation of a terminal voltage of the p th  second control terminal with respect to time. If the reverse photoelectric current of the p th  LED in the k th  row is larger than the preset value, in the k th  lightened period, the k th  first control terminal of the horizontal control circuit is set to the common voltage, and the p th  second control terminal is set to the power supply voltage to light up the p th  LED in the k th  row, wherein “p” is a nature number. 
     Similarly, if the first terminal of each LED is anode, the second terminal of the LED is cathodes, and the control circuit includes a horizontal control circuit, a vertical control circuit and M current detecting circuits. However, the difference is as follows. In the k th  detecting period, the k th  first control terminal of the horizontal control circuit is set to a common voltage, the M second terminals are set to a power supply voltage for a preset period, and then to a high impedance state. After that, the p th  current detecting circuit determines the reverse photoelectric current of p th  LED in the k th  row according to the variation of a terminal voltage of the p th  second control terminal with respect to time. If the reverse photoelectric current of the p th  LED in the k th  row is larger than the preset value, in the k th  lightened period, the k th  first control terminal of the horizontal control circuit is set to the power supply voltage, and the p th  second control terminal is set to the common voltage to light up the p th  LED in the k th  row. 
     The spirit of the present invention is to utilize the LED matrix to be a display device and an input device. In other words, end user can directly input information through a laser pen or another light emitting element to the LED matrix. The major principle of the present invention is to apply the photoelectric effect, which make the reverse photoelectric current be generated when the LED receives light, for detecting the light source. Therefore, the present invention at least has the advantages of: 
     1. reducing the complication of data input; 
     2. freeing from additional optical sensing element; 
     3. being adapted for a novice and a child to use; 
     4. showing the result immediately after input; and 
     5. freeing from the computer as the medium interface. 
     Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention. 
         FIG. 1  is a block diagram showing an information input panel of a light emitted diode (LED) matrix according to an embodiment of the present invention. 
         FIG. 2  is a circuit block diagram showing an information input panel of a LED matrix according to an embodiment of the present invention. 
         FIG. 3  is a circuit block diagram showing an information input panel of a LED matrix according to another embodiment of the present invention. 
         FIG. 4A  is a circuit block diagram showing an information input panel of a LED matrix according to the other embodiment of the present invention. 
         FIG. 4B  is a detail circuit block diagram showing an information input panel of a LED matrix according to  FIG. 4A  of an embodiment of the present invention. 
         FIG. 5A  is a circuit block diagram for experimentation of a photoelectric effect when the LED is in a reverse bias according to an embodiment of the present invention. 
         FIG. 5B  is a charging and discharging waveform showing a photoelectric effect when the LED is in a reverse bias according to  FIG. 5A  of an embodiment of the present invention. 
         FIG. 6  is a detail circuit block diagram showing the control circuit C 201 ˜C 206  on  FIG. 2  according to an embodiment of the present invention. 
         FIG. 7  is another detail circuit block diagram showing the control circuit C 201 ˜C 206  on  FIG. 2  according to an embodiment of the present invention. 
         FIG. 8  is a voltage waveform of the control terminal IO 2  in  FIG. 7  according to an embodiment of the present invention. 
         FIG. 9A  and  FIG. 9B  respectively are the detail circuit block diagrams showing the current detecting circuit  404 ˜ 405  on  FIG. 4B  according to an embodiment of the present invention. 
         FIG. 10  is a circuit block diagram showing an information input panel of an LED matrix according to an embodiment of the present invention. 
         FIG. 11  is a circuit block diagram showing an information input panel of an LED matrix according to an embodiment of the present invention. 
         FIG. 12  is a circuit block diagram showing an information input panel of an LED matrix according to an embodiment of the present invention. 
         FIG. 13A  is a circuit block diagram for experimentation of an photoelectric effect when the LED is in a reverse bias according to an embodiment of the present invention. 
         FIG. 13B  is a charging and discharging waveform showing an photoelectric effect when the LED is in a reverse bias according to  FIG. 13A  of an embodiment of the present invention. 
         FIG. 14  is a detail circuit block diagram showing the control circuit C 1001 ˜C 1006  on  FIG. 10  according to an embodiment of the present invention. 
         FIG. 15  is another detail circuit block diagram showing the control circuit C 1001 ˜C 1006  on  FIG. 10  according to an embodiment of the present invention. 
         FIG. 16  is a voltage waveform of the control terminal IO 2  in  FIG. 15  according to an embodiment of the present invention. 
         FIG. 17A  and  FIG. 17B  respectively are the detail circuit block diagrams showing the current detecting circuit  1204 ˜ 1205  on  FIG. 12  according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements. 
       FIG. 1  is a block diagram showing an information input panel of a light emitted diode (LED) matrix according to an embodiment of the present invention. Referring to  FIG. 1 , the design of the information input panel is to utilize a laser pen  102  or a resembling light emitted device to directly draw on the LED matrix  101  for performing the information input. In order to make one of ordinary skill in the art to implement the present invention, the following embodiments are provided to illustrate the spirit of the invention. 
       FIG. 2  is a circuit block diagram showing an information input panel of a LED matrix according to an embodiment of the present invention. Referring to  FIG. 2 , the embodiment uses six LED D 201 ˜D 206  to be an example. In this embodiment, each LED D 201 ˜D 206  is assigned to a corresponding control circuit for detecting the reverse photoelectric current of the coupled LED D 201 ˜D 206  to determine whether the coupled LED D 201 ˜D 206  is lighted up or not. The detail circuit of the control circuit C 201 ˜C 206  will be described on the following. The further details are omitted at this paragraph. 
       FIG. 3  is a circuit block diagram showing an information input panel of a LED matrix according to another embodiment of the present invention. Referring to  FIG. 3 , similarly, for convenience of the explanation, the information input panel in this embodiment uses six LEDs D 201 ˜D 206  to be an example. In particular, only one control circuit C 301  is provided for control the LEDs D 201 ˜D 206 . The control method thereof is to utilize the switching circuits SW 301  and SW 302  to sequentially switch with time to determine which the LED D 201 ˜D 206  is coupled to the control circuit C 301 . During a first period, two control terminal IO 1  and IO 2  of the control circuit C 301  are respectively coupled to the two terminal of the LED D 201  to detect the reverse photoelectric current of the LED D 201 ; during a second period, the two control terminal IO 1  and IO 2  of the control circuit C 301  are respectively coupled to the two terminal of the LED D 202  to detect the reverse photoelectric current of the LED D 202  . . . and so on. The control mechanism of the information input panel using LED matrix is to utilize the concept of the Time Division Multiplexing (TDM). 
       FIG. 4A  is a circuit block diagram showing an information input panel of a LED matrix according to the other embodiment of the present invention. Referring to  FIG. 4A , the information input panel of the embodiment is to utilize six LEDs D 201 ˜D 206  as an example as well. In particular, the design of the information input panel in this embodiment is to utilize a concept of an array. In other words, the six LEDs D 201 ˜D 206  can be regarded as a 2×3 matrix. The anodes of the LEDs in each row are respectively coupled to the horizontal control terminals IO 1 - 1 , IO 1 - 2  and IO 1 - 3  of the control C 401  and the cathodes of the LEDs in each column are respectively coupled to the vertical control terminals IO 2 - 1  and IO 2 - 2  of the control C 401 . Similarly, the design of the circuit in this embodiment still utilizes the concept of TDM. For example, during a first period, the control circuit C 401  enables the terminals IO 1 - 1 , IO 2 - 1  and IO 2 - 2  for detecting the reverse photoelectric currents of the LED D 201  and D 202 ; during a second period, the control circuit C 401  enable the terminals IO 1 - 2 , IO 2 - 1  and IO 2 - 2  for detecting the reverse photoelectric currents of the LED D 203  and D 204 ; during a third period, the control circuit C 401  enable the terminals IO 1 - 3 , IO 2 - 1  and IO 2 - 2  for detecting the reverse photoelectric currents of the LED D 205  and D 206 . 
       FIG. 4B  is a detail circuit block diagram showing an information input panel of an LED matrix according to  FIG. 4A  of an embodiment of the present invention. Referring to  FIG. 4B , the control circuit in this embodiment is separated into a horizontal control circuit  402 , a vertical control circuit  403  and the current detecting circuits  404 ˜ 405 . The current detecting circuits  404 ˜ 405  are only coupled to the vertical control circuit  403 . In addition, the terminals of the horizontal control circuit  402  and the vertical control circuit  403  respectively have tri-state function. In order to illustrate the principle of the detection of the reverse photoelectric current of the LED(s) D 201 ˜D 206  by the control circuit C 301 , C 201 ˜C 206  or the current detecting circuits  404 ˜ 405 , the following paragraph in corporation with a voltage waveform with respect to time when the LED is in a reverse bias is provided to illustrate. 
       FIG. 5A  is a circuit block diagram for experimentation of a photoelectric effect when the LED is in a reverse bias according to an embodiment of the present invention. Referring to  FIG. 5A , in this experiment, the control terminal IO 2  of the control circuit C 501  provides a power supply voltage to the cathode of the LED D 501 , and the control terminal IO 1  of the control circuit C 501  provides the ground voltage GND to the anode of the LED D 501 . After that, the control terminal IO 2  of the control circuit C 501  is set to a tri-state, that is, a high impedance state. Since the LED D 501  is in the reverse bias, there is a little photoelectric current flowing through the LED D 501  when the LED D 501  is illuminated. In addition, a stray capacitance Cx will be generated in the circuit layout of the D 501 , so that the stray capacitance Cx will be slowly discharged. The voltage of the cathode of the LED D 501  will be reduced. Certainly, if the stray capacitance Cx is replaced by a general capacitor, the stabilization of the operation of the circuit will be raised. 
       FIG. 5B  is a charging and discharging waveform showing a photoelectric effect when the LED is in a reverse bias according to  FIG. 5A  of an embodiment of the present invention. Referring to  FIG. 5A  and  FIG. 5B , the waveform  502  is a discharging waveform of the LED D 501  when no light source approaches the LED  501 ; the waveform  503  is a discharging waveform when a light source approaches the LED D 501 . In observation on the waveforms, it should be known that the photoelectric current is generated when the LED D 501  receives the illumination of a light source, and the more the intensity of illumination of a light source is received by the LED D 501 , the larger the value of the photoelectric current is generated. Thus, the discharging rate of the stray capacitance Cx is raised. In observation on the waveform  502 , it should be known that the discharging rate of the stray capacitance Cx is smaller since the LED D 501  did not receive the illumination of a light source. 
     From the abovementioned waveforms  502  and  503 , it should be known that the reverse photoelectric current of the LED D 501  is in direct proportion to the variation of the voltage of the cathode of the LED D 501  with respect to time. As long as the voltage of the cathode of the LED D 501  is continuously detected, the reverse photoelectric current of the LED D 501  can be determined so that whether a light source is closed to the LED D 501  can be detected. Therefore, in the design of the abovementioned control circuits C 301 , C 201 ˜C 206  or the current detecting circuits  404 ˜ 405 , a preset reference voltage Vref can be set therein, wherein the preset reference voltage Vref is between the power supply voltage VDD and the ground voltage GND. As long as the control circuits C 301 , C 201 ˜C 206  or the current detecting circuit  404  calculates the period during which the voltage of the cathode of the LED is discharged from the power supply voltage to the preset reference voltage, whether a light source is closed to the LED D 501  can be determined. 
     Thus, in the abovementioned embodiments, when the control circuits C 301 , C 201 ˜C 206  detect the reverse photoelectric current of the LED, they supply the detected LED a reverse bias for a preset period so that the stray capacitance Cx is charged. After that, the control circuits C 301 , C 201 ˜C 206  determine whether the detected LED receives the illumination of a light source according to the period during which the voltage of the cathode of the detected LED reaches the preset reference voltage Vref so that whether a forward bias is provided to the detected LED can be determined. When the period during which the voltage of the cathode of the detected LED reaches the preset reference voltage Vref is shorter than T 2 , it represent that the detected LED is illuminated by a light source, at this time, the forward bias can be provided to the detected LED to light it up. 
     In addition, the abovementioned waveforms had already and clearly described that discharging time of the capacitor Cx relates to the intensity of the illumination of a light source. However, in the design stage, if it is only consider that the abovementioned control circuits C 301 , C 201 ˜C 206  or the abovementioned current detecting circuits  404 ˜ 405  are used for counting the period during which the voltage of the cathode of the LED is discharged from the power supply voltage to the preset reference voltage, the detecting period will be prolonged, and the response time of the entire circuit will be negatively affected as well. Therefore, the control strategy of the control circuits C 301 , C 201 ˜C 206  or the current detecting circuits  404 ˜ 405  can be to set a preset time Tpre therein. When the preset time Tpre expires from the beginning of the detecting period, the voltage of the capacitor Cx is not lower than the abovementioned reference voltage Vref, it represents that the coupled LED does not receives the illumination of a light source. In accordance with such design, the detecting period can be fixed. Therefore, the detecting speed of the TDM system, such as the circuit on  FIG. 3 ,  FIG. 4A  or  FIG. 4B , will be increased. 
       FIG. 6  is a detail circuit block diagram showing the control circuit C 201 ˜C 206  on  FIG. 2  according to an embodiment of the present invention. Referring to  FIG. 6 , in this embodiment, the control circuit includes a comparator  601 , a counting circuit  602 , a judging circuit  603  and a capacitor Cx. The positive terminal of the comparator  601  receives the preset reference voltage Vref, and the negative terminal of the comparator  601  is coupled to the control terminal IO 2  of the control circuit. The capacitor Cx may be the stray capacitance induced by the cathode of the LED D 601  to ground or an additional capacitor. 
     Before the detection, the capacitor Cx will be charged to the power supply voltage. When the detection is beginning, the electric charge on the capacitor Cx is discharged to the control terminal IO 1  through the LED D 601 . At this time, the comparing signal VP outputted from the output terminal of the comparator  601  is a negative saturation voltage. When the capacitor Cx is discharged to a voltage lower than the preset reference voltage Vref, the voltage of the control terminal IO 2 , that is, the voltage of the negative terminal of the comparator  601 , is smaller than the preset reference voltage Vref on the positive terminal of the comparator  601  so that the comparing signal VP outputted from the output terminal of the comparator  601  is a positive saturation voltage. From the beginning of the detecting period, the counting circuit accumulates a counting value CV for each preset time, that is, for each clock period CLK. When the voltage of the comparing signal VP outputted from the output terminal of the comparator  601  is changed from the negative saturation voltage to the positive saturation voltage, the accumulating is stopped and the accumulated counting value CV is outputted. According to the foregoing embodiment, in fact, the counting value CV represents the discharging time during which the voltage of the cathode of the LED D 601  is discharged from the power supply voltage VDD to the preset reference voltage Vref. When the discharging time becomes shorter, it represents that the LED D 601  received the illumination of a light source, and the outputted counting value CV is smaller. When the discharging time becomes longer, it represents that the LED D 601  did not receive the illumination of a light source, and the outputted counting value CV is larger. The judging circuit  603  receives the counting value CV. When the counting value CV is smaller than a preset value, it represents that the LED D 601  received the illumination of a light source, and the judging circuit  603  controls the LED D 601  to light up. 
       FIG. 7  is another detail circuit block diagram showing the control circuit C 201 ˜C 206  on  FIG. 2  according to an embodiment of the present invention. Referring to  FIG. 7 , the difference between the embodiment of  FIG. 7  and the embodiment of  FIG. 6  is that the comparator  601  and the counting circuit  602  are replaced by an analog-to-digital converter (ADC)  701 .  FIG. 8  is a voltage waveform of the control terminal IO 2  in  FIG. 7  according to an embodiment of the present invention. Referring to  FIG. 7  and  FIG. 8 , in this embodiment, each of the periods TP 801 , TP 802  and TP 803  are equal. The period TP 801  and the period TP 802  are the period during which the LED D 601  did not receive the illumination of a light source. The period T 803  is the period during which the LED D 601  received the illumination of a light source. According to the abovementioned waveforms, it can be regard that if the periods are equal, the final storing charge of the capacitor Cx as well as the voltage of the control terminal IO 2  would be influenced by whether the LED D 601  received the illumination of a light source. The ADC  701  samples the voltage of the control terminal IO 2  at each final time T 804 , T 805  and T 806  of the period TP 801 , TP 802  and TP 803  and transfers the sampled voltage of the control terminal IO 2  to a digital value DV. Generally speaking, the higher the voltage is sampled by the ADC  701 , the larger the digital value DV is outputted. Therefore, when the LED D 601  receives the illumination of a light source, the digital value DV will apparently become smaller. In this embodiment, the judging circuit  603  stores a preset value. When the received digital value DV is smaller than the preset value, it represents that the LED D 601  received the illumination of a light source, so that the judging circuit  603  thus controls the LED D 601  to light up. 
     In abovementioned embodiment, one of ordinary skill in the art should know that if the positive terminal of the comparator  601  is exchanged with the negative terminal thereof in other design, the only difference is that the voltage of the comparing signal VP is changed from the original positive (negative) saturation voltage to the negative (positive) saturation voltage. Thus, as long as the requirement for stopping the accumulating of the counting circuit  602  is transformed into the condition when the voltage of the comparing signal VP is changed from the positive saturation voltage to the negative saturation voltage, the operation of the above embodiment is the same. Such the abovementioned design is only an option on design, so the description is omitted. In addition, the circuit diagrams on the  FIG. 6  and  FIG. 7  in the abovementioned embodiment is for the detail illustration on the control circuit C 201 ˜C 206 . However, one of the ordinary skill in the art should know that the circuit on the  FIG. 6  or  FIG. 7  can be applied to the control circuit C 301  on  FIG. 3  or the current detecting circuits  404 ˜ 405  on  FIG. 4B .  FIG. 9A  and  FIG. 9B  respectively are the detail circuit block diagrams showing the current detecting circuit  404 ˜ 405  on  FIG. 4B  according to an embodiment of the present invention. Referring to  FIGS. 9A and 9B , the operating concept of both of the circuits is the same as that of both of the circuits on  FIG. 6  and  FIG. 7 . However, the difference is the judging circuit  603  is used for determining the value of the reverse photoelectric current according to the counting value CV on  FIG. 9A  or the digital value DV on  FIG. 9B . Since the abovementioned embodiments already completely describes the principle of the detection of the reverse photoelectric current of the LED so that the description is omitted. 
     The abovementioned embodiments describe to detect the reverse photoelectric current based on the voltage of the cathode of the LED. Hereinafter, the LED is disposed on reverse direction to be an example so that one of ordinary skill in the art can use a different method to implement according to the present invention.  FIG. 10  is a circuit block diagram showing an information input panel of an LED matrix according to an embodiment of the present invention.  FIG. 11  is a circuit block diagram showing an information input panel of an LED matrix according to an embodiment of the present invention.  FIG. 12  is a circuit block diagram showing an information input panel of an LED matrix according to an embodiment of the present invention. Referring to  FIG. 10 ,  FIG. 11  and  FIG. 12 , it is easy to realize that the difference between the configuration of the circuits on  FIG. 10 ,  FIG. 11  and  FIG. 12  and the configuration of the circuits on  FIG. 3  and  FIG. 4B  is only the inverse coupling on the cathode terminal and the anode terminal of the LEDs D 201 ˜D 206 . Thus, the detection of the reverse photoelectric current of the LEDs D 201 ˜D 206  depends on the anode terminals of the LEDs D 201 ˜D 206 . The circuit for detection of the reverse photoelectric current by the anodes of the LEDs D 201 ˜D 206  is provided to be an example so that one of ordinary skill in the art can implement the abovementioned circuit according to the spirit of the invention. 
       FIG. 13A  is a circuit block diagram for experimentation of a photoelectric effect when the LED is in a reverse bias according to an embodiment of the present invention.  FIG. 13B  is a charging and discharging waveform showing a photoelectric effect when the LED is in a reverse bias according to  FIG. 13A  of an embodiment of the present invention. Referring to  FIG. 13A  and  FIG. 13B , when the cathode of the LED D 1301  is coupled to the control terminal IO 1 , and the anode of the LED D 1301  is coupled to the control terminal IO 2 , the control procedure of the control circuit  1301  comprises the following steps. In step  1 , the control terminal IO 1  supplies the power supply voltage VDD. In step  2 , the control terminal IO 2  supplies the ground voltage GND and then the control terminal IO 2  is set to a high impedance state. In step  3 , a detection is performed, wherein the voltage waveform diagram of the control terminal IO 2  is shown as  FIG. 13B . The waveform  1302  is a voltage of the control terminal IO 2  with respect to time when the LED D 1301  received the illumination of a light source. The waveform  1303  is a voltage of the control terminal IO 2  with respect to time when the LED D 1301  did not receive the illumination of a light source. In the waveforms  1302  and  1303 , it can be observed that when the LED D 1301  received the illumination of a light source, the reverse photoelectric current is increased so that the charging speed of the capacitor Cx is increased. 
       FIG. 14  is a detail circuit block diagram showing the control circuit C 1001 ˜C 1006  on  FIG. 10  according to an embodiment of the present invention. Referring to  FIG. 6  and  FIG. 14 , the difference between the two circuits is that the coupling of the LED D 1401  in  FIG. 14  is opposite to that of the LED D 601  in  FIG. 6 . Thus, when the detection is performed, the capacitor Cx is discharged to the ground voltage, after that, the control terminal IO 1  continuously supplies the power supply voltage VDD so that the capacitor Cx is charged. When the voltage of the control terminal IO 2  is charged to the preset reference voltage Vref, the voltage of the comparing signal VP is changed from the positive saturation voltage to the negative saturation voltage, and the accumulating is stopped by the counting circuit  1401 . The operating principle of the control circuit in  FIG. 14  is similar to that of the control circuit in  FIG. 6 , so that the detail description is omitted. 
       FIG. 15  is another detail circuit block diagram showing the control circuit C 1001 ˜C 1006  on  FIG. 10  according to an embodiment of the present invention.  FIG. 16  is a voltage waveform of the control terminal IO 2  in  FIG. 15  according to an embodiment of the present invention. Referring to  FIG. 15 ,  FIG. 7 ,  FIG. 16  and  FIG. 8 , similarly, the difference between the circuits on  FIG. 15  and  FIG. 7  is that the coupling of the LED D 1401  on  FIG. 15  is opposite to the coupling of the LED D 601  on  FIG. 7 . Similarly, in the periods TP 1601  and TP 1602 , the LED D 1401  did not receive the illumination of a light source, the charging speed of control terminal IO 2  is slower so that the measured voltage on the control terminal IO 2  at the time point T 1604  and T 1605  is smaller, and the outputted digital value DV of the ADC  1501  is smaller. At this time, the judging circuit  1503  did not light up the LED D 1401 . In the period T 1603 , the LED received the illumination of a light source, the charging speed of the control terminal IO 2  is faster so that the measured voltage of the control terminal IO 2  at the time point T 1606  is larger, and the outputted digital value DV of the ADC  1051  is relatively larger. At this time, the judging circuit  1503  is triggered to light up the LED D 1401 . 
     The circuits of the abovementioned embodiments depicted on  FIG. 14  and  FIG. 15  is the illustration of the detail circuit of the control circuits C 1001 ˜C 1006 , however, one of ordinary skill in the art should know that the circuit depicted on the  FIG. 14  and  FIG. 15  can be applied to the control circuit C 1101  on  FIG. 11  or the current detecting circuits  1204 ˜ 1205  on  FIG. 12 .  FIG. 17A  and  FIG. 17B  respectively are the detail circuit block diagrams showing the current detecting circuit  1204 ˜ 1205  on  FIG. 12  according to an embodiment of the present invention. Referring to  FIG. 17A  and  FIG. 17B , the operating principle of the two circuits is the same as that of the circuit on  FIG. 14  and  FIG. 15 . The difference thereof is the judging circuit  1503  is used for determining the value of the reverse photoelectric current of the LED D 1401  according to the counting value CV on  FIG. 17A  or the digital value DV on  FIG. 17B . Since the principle of detection of the reverse photoelectric current of the LED D 1401  is completely described, the detail description is omitted. 
     In summary, the spirit of the present invention is to utilize the LED matrix to be a display device and an input device. In other words, end user can directly input information through a laser pen or another light emitting element to the LED matrix. The major principle of the present invention is to apply the photoelectric effect, which make the reverse photoelectric current be generated when the LED receives light, for detecting the light source. Therefore, the present invention at least has the advantages of: 
     1. reducing the complication of data input; 
     2. freeing from additional optical sensing element; 
     3. being adapted for a novice and a child to use; 
     4. showing the result immediately after input; and 
     5. freeing from the computer as the medium interface. 
     While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.