Touch panel

• US 8,436,822 B2
• Filed: 12/21/2009
• Issued: 05/07/2013
• Est. Priority Date: 06/24/2009
• Status: Active Grant

• Current Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated)
• Original Assignee: Himax Technologies Ltd. (Himax Technologies Incorporated)
• Inventors: Chang, Yaw-Guang, Hsu, Chin-Feng
• Primary Examiner(s): Feild, Joseph
• Assistant Examiner(s): HOFFNER, LINH NGUYEN
• Application Number:
  US12/643,585
• Publication Number:
  US 20100326744A1
• Time in Patent Office: 1,233 Days
• Field of Search: 178/18.05, 345/173, 345/66, 345/55
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A touch panel has a panel capacitor, a first capacitor, and a second capacitor. The panel capacitor and the first capacitor are charged and discharged cyclically according to a first phase signal and a second phase signal, such that an input voltage associated with the panel capacitor and the first capacitor is applied to a control circuit. The control circuit charges and discharges a second capacitor based on the input voltage and a reference voltage to compensate the difference between the input voltage and the reference voltage. The capacitance of the panel capacitor could be calculated based on the frequency of charging and discharging the second capacitor.

Claims

1. A touch panel, comprising:

a first clock phase generator, generating a first phase signal and a second phase signal according to a first clock signal;

a panel capacitor;

a first capacitor;

a second capacitor;

a first switch, turned on/off based on a voltage level of the first phase signal, wherein a first end of the first switch is coupled to a first reference voltage, and a second end of the first switch is coupled to the panel capacitor;

a second switch, turned on/off based on a voltage level of the second phase signal, wherein a first end of the second switch is coupled to the panel capacitor;

a third switch, turned on/off based on the voltage level of the first phase signal, wherein a first end of the third switch is coupled to a second reference voltage, and a second end of the third switch is coupled to the first capacitor;

a fourth switch, turned on/off based on the voltage level of the second phase signal, wherein a first end of the fourth switch is coupled to the first capacitor, and a second end of the fourth switch is coupled to a second end of the second switch;

a control circuit, coupled to the second end of the second switch and the second end of the fourth switch, wherein the control circuit generates a third phase signal and a fourth phase signal based on a third reference voltage and a voltage level of the second end of the second switch;

a fifth switch, turned on/off based on a voltage level of the third phase signal, wherein a first end of the fifth switch is coupled to the second reference voltage, and a second end of the fifth switch is coupled to the second capacitor; and

a sixth switch, turned on/off based on a voltage level of the fourth phase signal, wherein a first end of the sixth switch is coupled to the second capacitor, and a second end of the sixth switch is coupled to the second end of the second switch and the second end of the fourth switch.

2. The touch panel as claimed in claim 1, wherein when the first phase signal is at a first state, the second phase signal is at a second state, and when the second phase signal is at the first state, the first phase signal is at the second state,

wherein when the third phase signal is at the first state, the fourth phase signal is at the second state, and when the fourth phase signal is at the first state, the third phase signal is at the second state.

3. The touch panel as claimed in claim 1, wherein the control circuit comprises a logic operator, the logic operator generates the third phase signal and the fourth phase signal according to the first phase signal, the second phase signal, and a latched signal.

4. The touch panel as claimed in claim 3, wherein the control circuit further comprises:

an integrator, outputting an integrated signal based on the third reference voltage and the voltage level of the second end of the second switch, wherein a first input terminal of the integrator is coupled to the third reference voltage, and a second input terminal of the integrator is coupled to the second end of the second switch, the second end of the fourth switch, and the second end of the sixth switch;

an operational amplifier, comparing the third voltage with the integrated signal so as to output an amplified signal, wherein a first input terminal of the operational amplifier is coupled to the third reference voltage, and a second input terminal of the operational amplifier is coupled to an output terminal of the integrator; and

a latch circuit, coupled to an output terminal of the operational amplifier, wherein the latch circuit latches the amplified signal according to the first clock signal so as to output the latched signal to the logic operator.

5. The touch panel as claimed in claim 4, wherein the control circuit further comprises a counter, the counter counts a number of pulses of the latched signal within a predetermined period, and the touch panel calculates the capacitance of the panel capacitor according to the number.

6. The touch panel as claimed in claim 5, wherein the control circuit further comprises a signal processor, the signal processor selects a capacitor from a plurality of capacitors as the first capacitor based on the number.

7. The touch panel as claimed in claim 4, wherein a voltage level of the integrated signal is greater than the third reference voltage when the voltage level of the second end of the second switch is less than the third reference voltage, and the voltage level of the integrated signal is less than the third reference voltage when the voltage level of the second end of the second switch is greater than the third reference voltage.

8. The touch panel as claimed in claim 3, wherein the latched signal is at a first state when the voltage level of the second end of the second switch is less than the third reference voltage, and the latched signal is at a second state when the voltage level of the second end of the second switch is greater than the third reference voltage.

9. The touch panel as claimed in claim 8, wherein when the latched signal is at the second state, the fifth switch and the sixth switch are turned off.

10. The touch panel as claimed in claim 8, wherein only when the latched signal is at the first state, the fifth switch could be turned on by the third phase signal, and the sixth switch could be turned on by the fourth phase signal.

11. The touch panel as claimed in claim 1, further comprising:

a second clock phase generator, generating a fifth phase signal and a sixth phase signal according to a second clock signal, wherein when the fifth phase signal is at a first state, the sixth phase signal is at a second state, and when the sixth phase signal is at the first state, the fifth phase signal is at the second state,

wherein the control circuit comprises a logic operator, the logic operator generates the third phase signal and the fourth phase signal according to the fifth phase signal, the sixth phase signal, and a latched signal.

12. The touch panel as claimed in claim 11, wherein a frequency of the second clock signal is N times of a frequency of the first clock signal, where N is an integer.

13. The touch panel as claimed in claim 11, wherein the control circuit further comprises:

an integrator, outputting an integrated signal based on the third reference voltage and the voltage level of the second end of the second switch, wherein a first input terminal of the integrator is coupled to the third reference voltage, and a second input terminal of the integrator is coupled to the second end of the second switch, the second end of the fourth switch, and the second end of the sixth switch;

an operational amplifier, comparing the third voltage with the integrated signal so as to output an amplified signal, wherein a first input terminal of the operational amplifier is coupled to the third reference voltage, and a second input terminal of the operational amplifier is coupled to an output terminal of the integrator; and

a latch circuit, coupled to an output terminal of the operational amplifier, wherein the latch circuit latches the amplified signal according to the first clock signal so as to output the latched signal to the logic operator.

14. The touch panel as claimed in claim 13, wherein the control circuit further comprises a counter, the counter counts a number of pulses of the latched signal within a predetermined period, and the touch panel calculates the capacitance of the panel capacitor according to the number.

15. The touch panel as claimed in claim 14, wherein the control circuit further comprises a signal processor, the signal processor selects a capacitor from a plurality of capacitors as the first capacitor based on the number.

16. The touch panel as claimed in claim 13, wherein a voltage level of the integrated signal is greater than the third reference voltage when the voltage level of the second end of the second switch is less than the third reference voltage, and the voltage level of the integrated signal is less than the third reference voltage when the voltage level of the second end of the second switch is greater than the third reference voltage.

17. The touch panel as claimed in claim 11, wherein the latched signal is at a first state when the voltage level of the second end of the second switch is less than the third reference voltage, and the latched signal is at a second state when the voltage level of the second end of the second switch is greater than the third reference voltage.

18. The touch panel as claimed in claim 17, wherein when the latched signal is at the second state, the fifth switch and the sixth switch are turned off.

19. The touch panel as claimed in claim 17, wherein only when the latched signal is at the first state, the fifth switch could be turned on by the third phase signal, and the sixth switch could be turned on by the fourth phase signal.