# Patent

## Title
Control method, circuit, and electronic system utilizing the same

## Abstract

A control circuit for a touch panel including a capacitor module coupled to a node. The control circuit includes a power supply, a discharging unit, and a compared unit. The power supply provides a voltage to the node. The discharging unit discharges the node. The compared unit generates an output signal according to the voltage of the node.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority of Taiwan Patent Application No. 097109143, filed on Mar. 14, 2008, the entirety of which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a control circuit, and more particularly to a control circuit for a touch panel.
2. Description of the Related Art
To communicate information, conventional computers or work stations utilize keyboards or a mouse to serve as input devices. However, the input devices of the conventional computers or work stations cannot speedily transmit or change certain types of information formats.
With the development of technology, input devices for electronic products have achieved great diversity. Among the various input devices, touch panels have been widely used as main input devices and are gradually replacing the conventional input devices.
BRIEF SUMMARY OF THE INVENTION
According to the invention, control methods and control circuits for touch panels are provided. The touch panel comprises a capacitor module coupled to a node. An exemplary embodiment of a control method comprises: providing a voltage to the node during a first period; discharging the node during a second period; and generating an output signal according to the voltage of the node.
An exemplary embodiment of a control circuit comprises a power supply, a discharging unit, and a compared unit. The power supply provides a voltage to the node. The discharging unit discharges the node. The compared unit generates an output signal according to the voltage of the node.
Electronic systems are also provided. An exemplary embodiment of an electronic system comprises a power converter and a touch panel. The power converter generates an operation power. The touch panel receives the operation power and comprises a capacitor module and a control circuit. The capacitor module is coupled to a node. The control circuit controls the voltage of the node and comprises a power supply, a discharging unit, and a compared unit. The power supply provides a voltage to the node. The discharging unit discharges the node. The compared unit generates an output signal according to the voltage of the node.
A detailed description is given in the following embodiments with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be more fully understood by referring to the following detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 is a schematic diagram of an exemplary embodiment of an electronic system according to the present invention;
FIG. 2 is a schematic diagram of an exemplary embodiment of a touch panel according to the present invention;
FIG. 3A is a schematic diagram of the output signal SOUT1 when the touch panel is not touched;
FIG. 3B is a schematic diagram of the output signal SOUT1 when the touch panel is touched;
FIG. 4 is a schematic diagram of another exemplary embodiment of the touch panel according to the present invention;
FIG. 5A is a schematic diagram of the output signal SOUT2 when the touch panel is not touched;
FIG. 5B is a schematic diagram of the output signal SOUT2 when the touch panel is touched;
FIGS. 6A and 6B are schematic diagrams of the compared unit; and
FIG. 7 is a flowchart of a control method.



DETAILED DESCRIPTION OF THE INVENTION
The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
FIG. 1 is a schematic diagram of an exemplary embodiment of an electronic system. The electronic system 100 can be a personal digital assistant (PDA), a cellular phone, a digital camera, a television, a global positioning system (GPS), a car display, an avionics display, a digital photo frame, a notebook computer (NB), or a personal computer (PC). As shown in FIG. 1, the electronic system 100 comprises a power converter 110 and a touch panel 120. The power converter 110 generates an operation power VOP. The touch panel 120 receives the operation power VOP and displays images. In one embodiment, the power converter 110 can be a converter for transforming an alternating current (AC) to a direct-current (DC) or a DC to a DC.
FIG. 2 is a schematic diagram of an exemplary embodiment of a touch panel. The touch panel 120 comprises a capacitor module 210 and a control circuit 220. In one embodiment, the capacitor module 210 and a color filter (not shown) of the touch panel 120 are disposed on a substrate. In other embodiments, the capacitor module 210 is disposed on a substrate and the color filter is disposed on another substrate. Since the color filter is well known to those skilled in the field, the description of the color filter is omitted for brevity. In other embodiments, the control circuit 220 is integrated into a chip.
In this embodiment, the touch panel 120 is a capacitive touch panel. When the touch panel 120 is not touched, the capacitor module 210 only comprises a parasitic capacitor Cpar. When the touch panel 120 is touched, the capacitor module 210 comprises the parasitic capacitor Cpar and a detection capacitor Csen. The capacitance of the detection capacitor Csen is determined by the touched area. When the touched area is larger, the capacitance of the detection capacitor Csen is higher. Thus, the capacitance of the capacitor module 210 is increased.
Since the capacitor module 210 is coupled to a node A, the voltage of the node A relates to the capacitance of the capacitor module 210. When the capacitance of the capacitor module 210 is higher, the capacitor module 210 can store more charges. The voltage of the node A is higher.
In this embodiment, the control circuit 220 comprises a compensating capacitor Cmod, a power supply 221, a discharging unit 222, a compared unit 223, and a determination unit 224. Different touch panels may comprise of different capacitances in parasitic capacitors due to manufacturing procedures. Thus, the compensating capacitor Cmod is utilized to compensate for the parasitic capacitors. In other embodiments, the compensating capacitor Cmod can be omitted.
The power supply 221 provides voltage VDD to the node A. When a pre-charge switch SWpre is turned on, the node A can receive the voltage VDD. In this embodiment, since the voltage VDD is a DC voltage, one terminal of the parasitic capacitor Cpar receives common voltage (Vcom) DCVCOM. The common voltage is well known to those skilled in the field such that the description of the common voltage is omitted.
During a first period, the pre-charge switch SWpre of the power supply 221 is turned on for charging the capacitor module 210. At this time, the voltage of the node A is increased. In one embodiment, when the voltage of the node A arrives at a first preset value, the pre-charge switch SWpre is turned off to stop charging the capacitor module 210. In another embodiment, when the voltage of the node A arrives at the first preset value and the duration, that the voltage of the node A arrives at the first preset value, arrives at a preset timing, the pre-charge switch SWpre is turned off.
During a second period, the discharging unit 222 discharges the node A. In this embodiment, the discharging unit 222 comprises modules 310 and 320 for executing two discharging stages. The module 310 discharges the node A by a first current. The module 320 discharges the node A by a second current less than the first current. In some embodiments, only one module discharges the node A. Thus, the node A is discharged by a single current.
In this embodiment, each the modules 310 and 320 comprises a discharging switch and a current source. When the discharging switch SWdis1 of the module 310 is turned on, the current source CS1 makes the node A discharge with a first current. When the discharging switch SWdis2 of the module 320 is turned on, the current source CS2 makes the node A discharge with a second current. When the node A is discharged by the first current and the duration, the node A is discharged by the first current, arrives at a preset timing, the node A is discharged by the second current. When the node A is discharged by the second current and the voltage of the node A is less than a second preset value, the discharging switch SWdis2 is turned off to stop discharging the node A.
The compared unit 223 generates an output signal SOUT1 according to the voltage of the node A. Thus, if the voltage of the node A exceeds the first preset value during the first period, a first transition occurs in the output signal SOUT1 generated by the compared unit 223. Thus, the output signal SOUT1 comprises a first edge. If the voltage of the node A is less than the second preset value during the second period, a second transition occurs in the output signal SOUT1 generated by the compared unit 223. Thus, the output signal SOUT1 comprises a second edge opposite to the first edge. For example, if the first edge is a rising edge, the second edge is a falling edge.
The time points for occurrence of the first and the second transitions are determined by the capacitance of the capacitor module 210. In this embodiment, the time points for occurrence of the first and the second transitions are detected by the determination unit 224. When the touch panel 120 is touched, the capacitance of the capacitor module 210 is higher causing a longer timing difference between the first and the second transitions. When the touch panel 120 is not touched, the capacitance of the capacitor module 210 is smaller causing a shorter timing difference between the first and the second transitions. Therefore, it is obtained whether the touch panel 120 is touched or not according to the timing difference between the first and the second transitions.
For example, when the timing difference between the first and the second transitions of the output signal SOUT1 exceeds a preset value, it represents that the touch panel 120 is touched. When the timing difference between the first and the second transitions of the output signal SOUT1 is less than the preset value, it represents the touch panel 120 is not touched. In other embodiments, the determination unit 224 can be omitted or integrated into other processing unit (not shown).
FIG. 3A is a schematic diagram of the output signal SOUT1 when the touch panel is not touched. Referring to FIG. 2, since a charging signal Spre is at a high level during a period P1, the pre-charge switch SWpre is turned on. When the voltage VA of the node A arrives at a preset value Vref1, the output signal SOUT1 occurs a first transition. In this embodiment, the output signal SOUT1 is changed from a low level to a high level.
Since the charging signal Spre is at a low level during a period P2, the pre-charge switch SWpre is turned off. During a period P21, the discharging switch SWdis1 is turned on such that the voltage VA of the node A is reduced. During a period P22, the discharging switch SWdis2 is turned on such that the voltage VA of the node A is continuously reduced. When the voltage VA of the node A arrives at a preset value Vref2, occurrence of the output signal SOUT1 is at a second transition. Additionally, since the node A is discharged by a larger current during the period P21, the falling slope is steeper. During the period P22, since the node A is discharged by a smaller current, the falling slope is more gradual.
FIG. 3B is a schematic diagram of the output signal SOUT1 when the touch panel is touched. Since the touch panel 120 is touched, the capacitor module 210 has a larger capacitance. Thus, a larger discharging time is required such that the voltage VA of the node A is less than the preset value Vref2. Therefore, the pulse width of the output signal shown in FIG. 3B is larger than the pulse width of the output signal shown in FIG. 3A.
The change of the output signal SOUT1 is described in greater detail with reference to FIG. 3B. During a period P3, since the charging signal Spre is at a high level, the pre-charge switch SWpre is turned on. When the voltage VA of the node A arrives at the preset value Vref1, occurrence of the output signal SOUT1 is at a first transition. In this embodiment, the output signal SOUT1 is changed from a low level to a high level.
Since the charging signal Spre is at a low level during a period P4, the pre-charge switch SWpre is turned off. During a period P41, the discharging switch SWdis1 is turned on such that the voltage VA of the node A is reduced. During a period P42, the discharging switch SWdis2 is turned on such that the voltage VA of the node A is continuously reduced. When the voltage VA of the node A arrives at a preset value Vref2, occurrence of the output signal SOUT1 is at a second transition. In this embodiment, it is obtained whether the touch panel is touched or not according to the duration, that the output signal SOUT1 is at the high level.
FIG. 4 is a schematic diagram of another exemplary embodiment of the touch panel. The touch panel 120 comprises a capacitor module 410 and a control circuit 420. Since the capacitor module 410 is similar to the capacitor module 210, the description of the capacitor module 410 is omitted. In this embodiment, the control circuit 420 comprises a power supply 421, a discharging unit 422, a compared unit 423, and a determination unit 424. Since the discharging unit 422, the compared unit 423, and the determination unit 424 are similar to the discharging unit 222, the compared unit 223, and the determination unit 224, the descriptions of the discharging unit 422, the compared unit 423, and the determination unit 424 are omitted.
In this embodiment, an AC voltage ACVCOM (shown in FIG. 5A) is utilized to charge the capacitor module 410. Referring to FIG. 5A, when the AC voltage ACVCOM is at a high level, an activation switch SWact of the power supply 421 is turned on. At this time, the AC voltage ACVCOM charges the capacitor module 410 and a storage capacitor Cstore. Thus, the voltage VB of a node B arrives at a preset value Vref1. Since the capacitor module 410 is coupled to the node B and the node B is coupled to the storage capacitor Cstore, the voltage of the storage capacitor Cstore equals to the voltage of the capacitor module 410. The voltage of the storage capacitor Cstore reacts to the node B. When the voltage VB of the node B arrives at the preset value Vref1, an output signal SOUT2 occurs a first transition.
When the AC voltage ACVCOM is at a low level, an activation switch SWact of the power supply 421 is turned off. At this time, the node B is discharged by the discharging unit 422. When the voltage VB of a node B is less than a preset value Vref2, occurrence of the output signal SOUT2 is at a second transition. Thus, it is obtained whether the touch panel is touched or not according to the timing difference between the first and the second transitions.
FIG. 5A is a schematic diagram of the output signal SOUT2 when the touch panel is not touched. FIG. 5B is a schematic diagram of the output signal SOUT2 when the touch panel is touched. FIGS. 5A and 5B are similar to FIGS. 4A and 4B such that the descriptions of FIGS. 5A and 5B are omitted. When a DC voltage or an AC voltage is utilized to charge the capacitor module, it is obtained whether the touch panel is touched or not according to the output signal.
FIGS. 6A and 6B are schematic diagrams of the compared unit. The compared unit shown in FIG. 6A is a Schmitt trigger comparator. The compared unit shown in FIG. 6B is a difference pair comparator.
FIG. 7 is a flowchart of a control method according to the invention. The control method can be applied in a touch panel. The touch panel comprises a capacitor module coupled to a node. During a first period, a voltage is provided to the node (step 710). The voltage may be a DC voltage or an AC voltage. Since the capacitor module is coupled to the node, when the voltage is provided to the node, the node is charged by the voltage. Thus, the voltage of the node is increased. In other embodiments, when the voltage of the node arrives at a first preset value, the voltage stops charging the node.
During a second period, the node is discharged (step 720). In one embodiment, the node is discharged by a first current. When the duration, that the node is discharged by the first current, arrives at a preset timing, the node is discharged by a second current less than the first current. In another embodiment, the node is discharged by a single current.
An output signal is generated according to the voltage of the node (step 730). In this embodiment, when the step 710 is executed, the voltage of the node is increased. When the voltage of the node arrives at a first preset value, occurrence of the output signal is at a first transition. When the step 720 is executed, the voltage of the node is reduced. When the voltage of the node is less than a second preset value, occurrence of the output signal is at a second transition. Thus, it is obtained whether the touch panel is touched or not according to the timing difference between the first and the second transitions.
If the touch panel is touched, the capacitance of the capacitor module is increased. Thus, when the capacitor module executes a charging action and a discharging action, the capacitance of the capacitor module is obtained according to the charging result and the discharging result. If the sum of the charging time and the discharging time exceeds a preset value due to the capacitance of the capacitor module being increased, it represents that the touch panel is touched. Similarly, if the sum of the charging time and the discharging time is less than the preset value due to the capacitance of the capacitor module being reduced, it represents that the touch panel is not touched.
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

## Claims

1. A control method for a touch panel, which comprises a capacitor module coupled to a node, comprising:
providing a voltage to the node during a first period;
discharging the node during a second period; and
generating an output signal according to the voltage of the node;
wherein the node is discharged by a first current during the second period,
wherein the node is discharged by a second current when the duration, that the node is discharged by the first current, arrives at a preset timing,
wherein a first transition occurs in the output signal when the voltage of the node arrives at a first preset value and a second transition occurs in the output signal when the voltage of the node is less than a second preset value; and wherein the touch panel is touched or not according to the timing difference between the first and the second transitions.

2. The control method as claimed in claim 1, wherein the voltage is not provided to the node when the voltage of the node arrives at the first preset value.

3. The control method as claimed in claim 1, wherein the second current is less than the first current.

4. The control method as claimed in claim 3, wherein the node is not discharged when the voltage of the node is less than the second preset value.

5. A control circuit for a touch panel comprising a capacitor module coupled to a node, comprising:
a power supply providing a voltage to the node;
a discharging unit discharging the node; and
a compared unit generating an output signal according to the voltage of the node
wherein the discharging unit comprises a first module to discharge the node by a first current and a second module to discharge the node by a second current which is less than the first current,
wherein a first transition occurs in the output signal when the voltage of the node arrives at a first preset value and a second transition occurs in the output signal when the voltage of the node is less than a second preset value.

6. The control circuit as claimed in claim 5, further comprising a determination unit, wherein the determination unit obtains whether the touch panel is touched or not according to a timing difference between the first and the second transitions.

7. The control circuit as claimed in claim 6, wherein the node is discharged by the second current when the duration, that the node is discharged by the first current, arrives at a preset timing.

8. The control circuit as claimed in claim 7, wherein the second module stops discharging the node when the node is discharged by the second current and the voltage of the node is less than the second preset value.

9. An electronic system, comprising:
a power converter generating an operation power; and
a touch panel receiving the operation power and comprising:
a capacitor module coupled to a node; and
a control circuit controlling the voltage of the node and comprising:
a power supply providing a voltage to the node;
a discharging unit discharging the node; and
a compared unit generating an output signal according to the voltage of the node wherein the discharging unit comprises a first module to discharge the node by a first current and a second module to discharge the node by a second current which is less than the first current,
wherein a first transition occurs in the output signal when the voltage of the node arrives at a first preset value and a second transition occurs in the output signal when the voltage of the node is less than a second preset value, and wherein the electronic system further comprises a determination unit obtaining whether the touch panel is touched or not according to a timing difference between the first and the second transitions.

10. The electronic system as claimed in claim 9, wherein the second module stops discharging the node when the node is discharged by the second current and the voltage of the node is less than the second preset value.

11. The electronic system as claimed in claim 10, wherein the node is discharged by the second current when the duration, that the node is discharged by the first current, arrives at a preset timing.

12. An electronic system as claimed in claim 9, wherein the touch panel further comprises a color filter and the color filter and the capacitor module are disposed on a substrate.