Sensing circuit for capacitive touch panel

• US 8,305,360 B2
• Filed: 09/04/2009
• Issued: 11/06/2012
• Est. Priority Date: 09/08/2008
• Status: Active Grant

• Current Assignee: InnoLux Corporation
• Original Assignee: Chi Mei Innolux Corporation (InnoLux Corporation)
• Inventors: Wu, Tse-Hung
• Primary Examiner(s): Bibbins, Latanya
• Application Number:
  US12/554,635
• Publication Number:
  US 20100060610A1
• Time in Patent Office: 1,159 Days
• Field of Search: 345/173, 345/174
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A sensing circuit for a capacitive touch panel is disclosed. By adding a path for a noise to pass through, the noise is differentially processed through two paths which have the same electrical conditions with each other. The noise is then decreased significantly, and a sensing signal can be detected correctly.

Claims

1. A sensing circuit for a capacitive touch panel, comprising:

a sensing signal part for generating a sensing signal according to a capacitance of the capacitive touch panel and a noise which is received by the sensing signal part, wherein the capacitance of the capacitive touch panel at a touched condition is different from the capacitance of the capacitive touch panel at an untouched condition, wherein the sensing signal part comprises;

a sensing unit for receiving the noise through a parasitic capacitance, the sensing unit having a first equivalent capacitance or a second equivalent capacitance, wherein the first equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the touched condition and the parasitic capacitance, and the second equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; and

a sensing signal generating unit coupled to the sensing unit, for generating the sensing signal according to the first equivalent capacitance and the noise or according to the second equivalent capacitance and the noise;

a reference signal part for receiving the noise and outputting a reference signal, the reference signal part having the same electrical conditions as the sensing signal part, wherein the reference signal part comprises;

a reference unit, for receiving the noise, the reference unit having a third capacitance, wherein the third capacitance simulates the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance; and

a reference signal generating unit coupled to the reference unit, for outputting the reference signal according to the third equivalent capacitance and the noise,

wherein the reference unit has the same circuits as the sensing unit, and the reference signal generating unit has the same circuits as the sensing signal generating unit; and

an integrator for receiving the sensing signal and the reference signal, subtracting the reference signal from the sensing signal to generate an output signal.

2. The sensing circuit of claim 1, wherein the reference signal part has a capacitance substantially equal to a capacitance of the sensing signal part at the untouched condition.

3. The sensing circuit of claim 1, wherein the reference signal part has a plurality of electrical elements, and the electrical elements are connected in a manner so as to simulate equivalent circuits of the sensing signal part.

4. The sensing circuit of claim 1, wherein the integrator comprises:

a first differential amplifier having an inverting input, a non-inverting input, and an output;

a first resistor having a first end coupled to the sensing signal part and a second end coupled to the inverting input; and

a first capacitor having a first end coupled to the inverting input and a second end coupled to the output.

5. The sensing circuit of claim 4, wherein the integrator further comprises a ground match unit, the ground match unit comprises:

a second resistor having a first end coupled to the reference signal part and a second end coupled to the non-inverting input; and

a second capacitor having a first end coupled to the non-inverting input and a second end coupled to a ground,

wherein a resistance of the second resistor is substantially equal to a resistance of the first resistor, and a capacitance of the second capacitor is substantially equal to a capacitance of the first capacitor.

6. The sensing circuit of claim 1, wherein the sensing signal part further comprises a first filter coupled between the sensing signal generating unit and the integrator for filtering out high-frequency components of the sensing signal generated by the sensing signal generating unit, and the reference signal part further comprises a second filter coupled between the reference signal generating unit and the integrator for filtering out high-frequency components of the reference signal, and the second filter has the same circuits as the first filter.

7. The sensing circuit of claim 1, further comprising:

a first coupling capacitor through which a controlling signal being coupled to the sensing signal generating unit; and

a second coupling capacitor through which the controlling signal being coupled to the reference signal generating unit, wherein a capacitance of the first coupling capacitor is substantially equal to a capacitance of the second coupling capacitor.

8. The sensing circuit of claim 1, wherein the reference unit comprises a capacitor, a capacitance of the capacitor is substantially equal to the parasitic capacitance, and the noise is coupled to the reference unit through the capacitor.

9. The sensing circuit of claim 1, further comprising an amplifying unit coupled to the integrator, for amplifying the output signal generated by the integrator.

10. An electronic apparatus, comprising a capacitive touch panel, the capacitive touch panel comprising the sensing circuit of claim 1, wherein the electronic apparatus is a mobile phone, a digital camera, a Personal Digital Assistant, a notebook, a desktop computer, a television, a Global Positioning System, a vehicle display, an aeronautical display, or a portable DVD player.

11. A sensing circuit for a capacitive touch panel, comprising:

a sensing signal path for generating a sensing signal according to a capacitance of the capacitive touch panel and a noise which is received by the sensing signal path, wherein the capacitance of the capacitive touch panel at a touched condition is different from the capacitance of the capacitive touch panel at an untouched condition, wherein the sensing signal path comprises;

a sensing unit for receiving the noise through a parasitic capacitance, the sensing unit having a first equivalent capacitance or a second equivalent capacitance, wherein the first equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the touched condition and the parasitic capacitance, and the second equivalent capacitance is an equivalent capacitance of the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance;

a sensing signal generating unit coupled to the sensing unit, for generating the sensing signal according to the first equivalent capacitance and the noise or according to the second equivalent capacitance and the noise,

a first resistor having a first end coupled to the sensing signal generating unit and a second end coupled to an inverting input of the first differential amplifier; and

a first capacitor having a first end coupled to the inverting input of the first differential amplifier and a second end coupled to an output of the first differential amplifier;

a reference signal path for receiving the noise and outputting a reference signal, the reference signal path having the same electrical conditions as the sensing signal path, wherein the reference signal path comprises;

a reference unit for receiving the signal, the reference unit having a third capacitance, wherein the third capacitance simulates the capacitance of the capacitive touch panel at the untouched condition and the parasitic capacitance;

a reference signal generating unit coupled to the reference unit, for outputting the reference signal according to the third equivalent capacitance and the noise;

a second resistor having a first end coupled to the reference signal generating unit and a second end coupled to a non-inverting input of the first differential amplifier; and

a second capacitor having a first end coupled to the non-inverting input of the first differential amplifier and a second end coupled to a ground,

wherein the reference unit has the same circuits as the sensing unit, the reference signal generating unit has the same circuits as the sensing signal generating unit, a resistance of the second resistor is the same as a resistance of the first resistor, and a capacitance of the second capacitor is the same as a capacitance of the first capacitor; and

a first differential amplifier for receiving the sensing signal and the reference signal, subtracting the reference signal from the sensing signal to generate an output signal.

12. The sensing circuit of claim 11, wherein the reference signal path has a capacitance substantially equal to a capacitance of the sensing signal path at the untouched condition.

13. The sensing circuit of claim 11, wherein the reference signal path has a plurality of electrical elements, and the electrical elements are connected in a manner so as to simulate equivalent circuits of the sensing signal path.

14. The sensing circuit of claim 11, wherein the sensing signal path further comprises a first filter coupled between the sensing signal generating unit and the first end of the first resistor for filtering out high-frequency components of the sensing signal generated by the sensing signal generating unit, the reference signal path further comprises a second filter coupled between the reference signal generating unit and the first end of the second resistor for filtering out high-frequency components of the reference signal, and the second filter has the same circuits as the first filter.

15. The sensing circuit of claim 11, further comprising:

a first coupling capacitor through which a controlling signal being coupled to the sensing signal generating unit; and

a second coupling capacitor through which the controlling signal being coupled to the reference signal generating unit, wherein a capacitance of the first coupling capacitor is substantially equal to a capacitance of the second coupling capacitor.

16. The sensing circuit of claim 11, wherein the reference unit comprises a capacitor, a capacitance of the capacitor is substantially equal to the parasitic capacitance, and the noise is coupled to the reference unit through the capacitor.

17. The sensing circuit of claim 11, further comprising an amplifying unit coupled to the first differential amplifier, for amplifying the output signal generated by the first differential amplifier.

18. An electronic apparatus, comprising a capacitive touch panel, the capacitive touch panel comprising the sensing circuit of claim 11, wherein the electronic apparatus is a mobile phone, a digital camera, a Personal Digital Assistant, a notebook, a desktop computer, a television, a Global Positioning System, a vehicle display, an aeronautical display, or a portable DVD player.