Abstract:
Disclosed herein is a device including a differential amplification unit for supplying current to the touch panel; a signal amplification unit for amplifying the output voltage of the differential amplification unit; an analog-digital conversion unit for converting the analog output signal of the signal amplification unit into a digital signal; a control unit for measuring the signal output from the analog-digital conversion unit and detecting the position of an object when the object touches the touch panel; and a sine wave generating unit for providing a sine wave signal to the differential amplification unit in response to the output signal of the control unit, supplying a maximum current to the differential amplification unit while the touch panel is in a standby state, and controlling the level of the sine wave signal in response to conductivity of the object when the object touches the touch panel.

Description:
This application claims priority to an application entitled “Device for Controlling Touch Panel” filed in the Korean Intellectual Property Office on Jul. 22, 2004 and assigned Serial No. 2004-57116, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a device for controlling a touch panel, and more particularly, to a device for controlling a touch panel, which maintains the quantity of current output from a differential amplification unit at an appropriate level in order to prevent plus and minus power supply voltages from clamping due to saturation of the output signal of the differential amplification unit when an excessively large quantity of current is output from the differential amplification unit, to thereby generate no distortion in the output signal of the differential amplification unit and detect a correct touched point irrespective of the level of conductivity of an object touching a touch panel. 
   2. Background of the Related Art 
   With the development of computers using digital technologies, peripheral devices also have been developed. The computer peripheral devices include a monitor, a keyboard, a mouse, a microphone, speakers and so on. Particularly, the keyboard and microphone are used to input external data to a computer. Specifically, the keyboard inputs data to the computer in a manner that its keys are pushed and the microphone inputs data using its user&#39;s voice. However, the more effective and easier method for inputting data to the computer is that a user touches the screen of the monitor connected to the computer to input data to the computer. For example, it is easier for the user to produce graphics on paper using a pen than the keyboard or mouse. Thus, it is inconvenient for the user to produce graphics using the computer. 
   However, when the user directly processes graphics on a touch panel using a touch pen, he/she can process the graphic work very easy and delicately. Accordingly, portable devices including the touch panel are replacing the peripheral devices such as the keyboard and mouse. For example, PDA (Personal Digital Assistant) includes a touch panel and a touch pen instead of a keyboard having keys by which users manually input data such that the user operate the touch panel using the touch pen to input data or commands. 
   When people touch the touch panel in a prior art, however, a constant quantity of current is applied to the touch panel all the time. Accordingly, an excessively large quantity of current flows when a person with high conductivity touches the touch panel and a correct touched point cannot be detected when a person with low conductivity touches the touch panel. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention has been made in view of the above problems occurring in the prior art, and it is an object of the present invention is to provide a device for controlling a touch panel, which maintains the quantity of current output from a differential amplification unit at an appropriate level in order to prevent plus and minus power supply voltages from clamping due to saturation of the output signal of the differential amplification unit when an excessively large quantity of current is output from the differential amplification unit, to thereby generate no distortion in the output signal of the differential amplification unit and detect a correct touched point irrespective of the level of conductivity of an object touching a touch panel. 
   To accomplish the above object, according to the present invention, there is provided a device for controlling a touch panel including: a differential amplification unit for supplying current to the touch panel; a signal amplification unit for amplifying the output voltage of the differential amplification unit; an analog-digital conversion unit for converting the analog output signal of the signal amplification unit into a digital signal; a control unit for measuring the signal output from the analog-digital conversion unit and detecting the position of an object when the object touches the touch panel; and a sine wave generating unit for providing a sine wave signal to the differential amplification unit in response to the output signal of the control unit, supplying a maximum current to the differential amplification unit while the touch panel is in a standby state, and controlling the level of the sine wave signal in response to conductivity of the object when the object touches the touch panel. 
   In an aspect of the present invention, the sine wave generating unit includes: a square wave controller for receiving a square wave signal from the control unit and controlling the level of the square wave signal; a triangle wave converter for converting the square wave signal output from the square wave controller into a triangle wave signal; and a sine wave generator for converting the triangle wave signal output from the triangle wave converter into a sine wave signal and supplying the sine wave signal to the differential amplification unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
       FIG. 1  illustrates the structure of a touch panel to which the present invention is applied; 
       FIG. 2  is a block diagram of a device for controlling a touch panel according to an embodiment of the present invention; 
       FIG. 3  is a circuit diagram of the differential amplification unit of  FIG. 2 ; 
       FIG. 4  is a circuit diagram of the sine wave generating unit of  FIG. 2 ; 
       FIG. 5  is a waveform diagram of signals used in the sine wave generating unit of  FIG. 4 ; and 
       FIG. 6  is a flow chart showing a touch panel controlling method according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 1  illustrates the structure of a touch panel  101  to which the present invention is applied. Referring to  FIG. 1 , the touch panel  101  includes a glass substrate  111 , a transparent conductive film  121  attached onto the glass substrate  111 , electrodes  131  respectively formed at the corners of the conductive film  121 , and wires  141  connected to the electrodes  131  and formed on the marginal portion of the conductive film  121 . One end of each wire  141  is connected to a differential amplification unit ( 211  of  FIG. 2 ). 
   When the electrodes  131  are provided with current through the wires  141 , current output from the electrodes  131  flows all over the conductive film  121 . 
     FIG. 2  is a block diagram of a device  201  for controlling a touch panel according to an embodiment of the present invention. Referring to  FIG. 2 , the touch panel controlling device  201  includes the differential amplification unit  211 , a signal amplification unit  221 , a filtering unit  231 , an analog-digital conversion unit  241 , a control unit  251  and a sine wave generating unit  261 . 
   The differential amplification unit  211  is connected to the electrodes ( 131  of  FIG. 1 ), receives a sine wave signal INn from the sine wave generating unit  261  and provides current OUTn to the electrodes ( 131  of  FIG. 1 ). When a specific object, for example, the hand of a user, touches the screen ( 151  of  FIG. 1 ) of the touch panel, the current OUTn output from the differential amplification unit  211  flows into the body of the user through the screen ( 151  of  FIG. 1 ) of the touch panel. Here, the quantity of current flowing from the differential amplification unit  211  to the touch panel ( 101  of  FIG. 1 ) depends on conductivity of the user. That is, the quantity of current output from the differential amplification unit  211  is increased in the case of a user with high conductivity (a person through which current flows well) but decreased in the case of a user with low conductivity (a person through which current does not flow well). 
   The output voltage Pn of the differential amplification unit  211  depends on the quantity of current output from the differential amplification unit  211 . That is, the output voltage Pn of the differential amplification unit  211  is increased when the quantity of current OUTn output from the differential amplification unit  211  is increased but decreased when the quantity of current OUTn is reduced. The differential amplification unit  211  includes a plurality of differential amplifiers  301 ,  302 ,  303  and  304  (referring to  FIG. 3 ), which are connected to the electrodes ( 131  of FIG) one to one. 
   The signal amplification unit  221  amplifies the output voltage Pn of the differential amplification unit  211  to a predetermined level. The signal amplification unit  221  includes a plurality of signal amplifiers (not shown), which are connected to the plurality of differential amplifiers ( 301 ,  302 ,  303  and  304  of  FIG. 3 ) one to one and amplify voltages output from the corresponding differential amplifiers. 
   The filtering unit  231  is connected to the signal amplification unit  221  and removes a noise included in the output signal of the signal amplification unit  221 . The filtering unit  231  includes a plurality of filters (not shown), which are connected to the plurality of signal amplifiers one to one and remove noises included in the signals output from the corresponding signal amplifiers. 
   The analog-digital conversion unit  241  converts an analog signal output from the filtering unit  231  into a digital signal. The analog-digital conversion unit  241  includes a plurality of analog-digital converters (not shown), which are connected to the plurality of filters of the filtering unit  231  one to one and convert analog signals output from the corresponding filters into digital signals. 
   The control unit  251  receives the output signal of the analog-digital conversion unit  241  and analyzes it to detect the position of the user&#39;s hand touching the screen ( 151  of  FIG. 1 ) of the touch panel. Specifically, the control unit  251  receives the digital signals output from the plurality of analog-digital converters of the analog-digital conversion unit  241  and compares the levels of the received digital signals to detect the position of the user&#39;s hand touching the screen of the touch panel. The control unit  251  calculates the rate of the quantity of current flowing from the differential amplification unit  211  to the user&#39;s hand to detect the position of the user&#39;s hand touching the screen of the touch panel. An object touching the touch panel ( 101  of  FIG. 1 ) includes a touch pen. The control unit  251  can be composed of a micro-controller or a CPU (Central Processing Unit). 
   The sine wave generating unit  261  supplies the sine wave signal INn to the differential amplification unit  211  in response to a control signal S 1  output from the control unit  251 . The sine wave generating unit  261  will be explained later in detail with reference to  FIG. 4 . 
     FIG. 3  is a circuit diagram of the differential amplification unit  211  of  FIG. 2 . Referring to  FIG. 3 , the differential amplification unit  211  includes the plurality of differential amplifiers  301 ,  302 ,  303  and  304 . The differential amplifiers  301 ,  302 ,  303  and  304  have the same configuration and operation so that only the configuration and operation of the differential amplifier  301  are explained. 
   The differential amplifier  301  includes a plurality of resistors R 1  to R 7 , a capacitor C 1  and an operational amplifier  311 . The differential amplifier  301  receives the sine wave signal INn from the sine wave generating unit  261  and provides current to the touch panel ( 101  of  FIG. 1 ). The differential amplifier  301  supplies a maximum current to the electrodes ( 131  of  FIG. 1 ) of the touch panel while the screen ( 151  of  FIG. 1 ) of the touch panel waits for an object to touch. Here, the output voltage P 1  of the operational amplifier  311  is zero because the same voltage is applied to the positive and negative input ports of the operational amplifier  311 . However, when an object, for example, the user&#39;s hand, touches the screen ( 151  of  FIG. 1 ) of the touch panel, the maximum current is output from the differential amplifier  301 . Then, a voltage different is generated between the positive and negative input ports of the operational amplifier  311 . The operational amplifier  311  amplifies the voltage difference to generate the output voltage P 1 . 
   The output voltage P 1  of the differential amplifier  301  depends on the quantity of current OUT 1  output from the differential amplifier  301 . That is, the voltage difference between the positive and negative input ports of the operational amplifier  311  is increased when the quantity of current OUT 1  output from the differential amplifier  301  is increased to result in an increase in the output voltage P 1  of the differential amplifier  301 . On the contrary, the voltage difference between the positive and negative input ports of the operational amplifier  311  is decreased when the quantity of current OUT 1  output from the differential amplifier  301  is reduced to result in a decrease in the output voltage P 1  of the differential amplifier  301 . 
   Here, when an excessively small quantity of current is output from the differential amplifier  301 , the amplitude of the output signal P 1  of the differential amplifier  301  becomes too small and thus it is difficult to detect the position of the object touching the touch panel ( 101  of  FIG. 1 ). On the contrary, when an excessively large quantity of current is output from the differential amplifier  301 , the output signal P 1  of the differential amplifier  301  is saturated to clamp plus power supply voltage VCC and minus power supply voltage VEE. Accordingly, the quantity of current output from the differential amplifier  301  should be maintained at an appropriate level in order to prevent the output signal P 1  of the differential amplifier  301  from being distorted and to detect the correct position of the object touching the touch panel. 
     FIG. 4  is a circuit diagram of the sine wave generating unit  261  of  FIG. 2 . The sine wave generating unit includes a square wave controller  411 , a triangle wave converter  421  and a sine wave generator  431 . 
   The square wave controller  411  receives a square wave signal S 1  and a control signal S 2  from the control unit ( 251  of  FIG. 2 ) and controls the level of the square wave signal S 1 . The square wave controller  411  includes a potentiometer  415 . The H-terminal of the potentiometer  415  is provided with the square wave signal S 1  having a predetermined level, for example, 5V, its L-terminal is grounded, and its W-terminal is connected to the triangle wave converter  421 . In this state, when the control signal S 2  is supplied from the control unit ( 251  of  FIG. 2 ) to the potentiometer  415 , the position of the W-terminal is adjusted in response to the state of the control signal S 2 . That is, the internal resistance of the potentiometer  415  is adjusted. Accordingly, the level of a square wave signal S 3  output from the W-terminal is controlled. 
   That is, the control unit ( 251  of  FIG. 1 ) generates the control signal S 2  to reduce the level of the square wave signal S 3  output from the square wave controller  411  when a large quantity of current OUTn is output from the differential amplification unit ( 211  of  FIG. 2 ) but increases the level of the square wave signal S 3  when a small quantity of current OUTn is output from the differential amplification unit to control the differential amplification unit ( 211  of  FIG. 2 ) to output an appropriate quantity of current. Accordingly, unnecessary current is not output from the differential amplification unit ( 211  of  FIG. 2 ) and the correct position of the object touching the screen ( 151  of  FIG. 1 ) of the touch panel is detected. 
   The triangle wave converter  421  receives the square wave signal S 3  output from the square wave controller  411  and converts it into a triangle wave signal S 4 , as shown in  FIG. 5 . The triangle wave converter  421  includes an operational amplifier  425 , resistors R 11  and R 12  and a capacitor C 11 . 
   The sine wave generator  431  receives the triangle wave signal S 4  output from the triangle wave converter  421 , converts it into the sine wave signal INn, as shown in  FIG. 5 , and provides the sine wave signal INn to the differential amplification unit ( 211  of  FIG. 2 ). The sine wave generator  431  includes an operational amplifier  435 , resistors R 21  and R 22  and a capacitor C 21 . 
     FIG. 6  is a flow chart showing a touch panel controlling method according to an embodiment of the present invention. The touch panel controlling method will now be explained with reference to  FIGS. 1 and 2 . 
   In the step  611 , the control unit  251  applies the control signal S 2  to the sine wave generating unit  261  such that the differential amplification unit  211  supplies the maximum current to the touch panel  101 . Since the maximum current is applied to the touch panel  101 , the quantity of current sufficient for detecting a touched point is output from the differential amplification unit  211  even if a user with very low conductivity touches the touch panel. Thus, the control unit  251  can recognize that an object touches the touch panel. 
   When the object touches the touch panel  101  in the step  615 , the control unit  251  checks conductivity of the object in step  617 . That is, the control unit  251  checks the quantity of current flowing from the differential amplification unit  211  to the touch panel  101 . 
   When the quantity of current flowing from the differential amplification unit  211  to the touch panel  101  is large, the control unit  251  applies the control signal S 2  to the sine wave generating unit  261  to reduce the level of the sine wave signal INn transmitted from the sine wave generating unit  261  to the differential amplification unit  211  in the step  621 . Then, the level of the signal Pn output from the differential amplification unit  211  is decreased. When this process is repeated such that the output signal Pn of the differential amplification unit  211  reaches an appropriate level, the level of the sine wave signal INn supplied to the differential amplification unit  211  is fixed and the control unit  251  detects the position of the object touching the touch panel  101 . 
   When the quantity of current flowing from the differential amplification unit  211  to the touch panel  101  is small, the control unit  251  increases the level of the sine wave signal INn transmitted from the sine wave generating unit  261  to the differential amplification unit  211  in the step  625 . 
   When the object is removed from the touch panel  101 , the quantity of current flowing from the differential amplification unit  221  to the touch panel  101  is reduced. Then, the control unit  251  senses the reduction in the quantity of current and increases the quantity of current supplied from the differential amplification unit  211  to the touch panel  101  to the maximum level. 
   In the step  631 , the control unit  251  measures the output voltage Pn of the differential amplification unit  211  to detect the position of the object touching the touch panel  101 . 
   As described above, the touch panel controlling device of the present invention supplies the maximum current to the touch panel when the touch panel is in the standby state, measures conductivity of a user when the user touches the touch panel, and reduces the level of the sine wave signal supplied from the sine wave generating unit to the differential amplification unit when the quantity of current flowing into the body of the user is large. When the quantity of current flowing into the body of the user is small, the touch panel controlling device of the present invention increases the level of the sine wave signal transmitted from the sine wave generating unit to the differential amplification unit. In this manner, the present invention controls the quantity of current supplied from the differential amplification unit to the touch panel to become an appropriate level in response to conductivity of the user touching the touch panel. This prevents unnecessary consumption of current and detects the correct touched point irrespective of conductivity of the user. 
   While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.