Sensing circuit for use with capacitive touch panel

• US 8,681,110 B2
• Filed: 10/12/2010
• Issued: 03/25/2014
• Est. Priority Date: 10/19/2009
• Status: Active Grant

• Current Assignee: Orise Technology Co., Ltd (FocalTech Systems Co.,Ltd)
• Original Assignee: Orise Technology Co., Ltd (FocalTech Systems Co.,Ltd)
• Inventors: Huang, Yen-Lin, Wang, Hsin-Hao
• Primary Examiner(s): Awad, Amr
• Assistant Examiner(s): FLORES, ROBERTO W
• Application Number:
  US12/902,522
• Publication Number:
  US 20110090173A1
• Time in Patent Office: 1,260 Days
• Field of Search: 345173-184, 178 1801- 2004, 324658-661, 324676-679, 324686-688, 324710-712
• US Class Current: 345/173
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• 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 of a capacitive touch panel includes an operation amplifier, a first switch, a second switch, first and second feedback capacitors, a third switch, a fourth switch, a fifth switch and a sixth switch. The operation amplifier includes a positive input terminal, a negative input terminal and an output terminal. A reference voltage is inputted into the positive input terminal. The first switch is connected between a receiving electrode and the negative input terminal. The second switch is connected between the negative input terminal and the output terminal. The third switch is connected to the negative input terminal and the first feedback capacitor. The fourth switch is connected to the first feedback capacitor and the output terminal. The fifth switch is connected to the negative input terminal and the second feedback capacitor. The sixth switch is connected to the second feedback capacitor and the output terminal.

Claims

1. A sensing circuit for use with a receiving electrode of a capacitive touch panel, a mutual capacitance having a first terminal connected to a driving electrode of the capacitive touch panel and having a second terminal connected to the receiving electrode, the driving electrode receiving a driving signal, the sensing circuit comprising:

an operation amplifier having a positive input terminal, a negative input terminal and an output terminal, wherein a reference voltage is inputted into the positive input terminal of the operation amplifier;

a first switch having a first terminal connected to the receiving electrode and the second terminal of the mutual capacitance and having a second terminal connected to the negative input terminal of the operation amplifier;

a second switch connected between the negative input terminal and the output terminal of the operation amplifier;

a feedback capacitor;

a third switch having a first terminal connected to the negative input terminal of the operation amplifier and a second terminal connected to a first terminal of the feedback capacitor;

a fourth switch having a first terminal connected to a second terminal of the feedback capacitor and a second terminal connected to the output terminal of the operation amplifier;

a fifth switch connected between the second terminal of the feedback capacitor and the negative input terminal of the operation amplifier;

a sixth switch connected between the first terminal of the feedback capacitor and the output terminal of the operation amplifier; and

a sensing circuit output terminal;

wherein the driving signal generates at least one pulse during a driving cycle, at a time of a rising edge of the pulse, the first switch, the third switch and the fourth switch are controlled to be in a close state, but the second switch, the fifth switch and the sixth switch are controlled to be in an open state;

at a time of a falling edge of the pulse, the first switch, the fifth switch and the six switch are controlled to be in a close state, but the second switch, the third switch and the fourth switch are controlled to be in an open state, and the feedback capacitor is charged in a first charging direction;

wherein said sensing circuit output terminal directly connects to said second switch, said forth switch, and sixth switch; and

wherein said third switch and said forth switch change states synchronously, and said fifth switch and said sixth switch change states synchronously.

2. The sensing circuit according to claim 1 wherein the feedback capacitor is charged in the first charging direction from the first terminal to the second terminal of the feedback capacitor.

3. The sensing circuit according to claim 1 wherein each pulse includes a first time interval and a second time interval, the rising edge of the pulse switched from a low-level state to a high-level state is within the first time interval, and the falling edge of the pulse switched from the high-level state to the low-level state is within the second time interval, wherein in the first time interval, the first switch, the third switch and the fourth switch are controlled to be in the close state, but the second switch, the fifth switch and the sixth switch are controlled to be in the open state.

4. The sensing circuit according to claim 3 wherein in the second time interval, the first switch, the fifth switch and the six switch are controlled to be in a close state, but the second switch, the third switch and the fourth switch are controlled to be in an open state.

5. The sensing circuit according to claim 1 wherein during a pre-charge cycle of the driving signal, the first switch, the second switch, the third switch and the fourth switch are controlled to be in a close state, so that the charge quantity stored in the feedback capacitor is zero.

6. The sensing circuit according to claim 1 wherein during an output cycle of the driving signal, a voltage drop is generated at the output terminal of the operation amplifier by the feedback capacitor.

7. The sensing circuit according to claim 6 wherein during the output cycle of the driving signal, the fifth switch and the sixth switch are controlled to be in the close state, but the first switch, the second switch, the third switch and the fourth switch are controlled to be in the open state.

8. The sensing circuit according to claim 6 wherein if the driving signal generates one pulse during the driving cycle, the voltage drop is equal to a third voltage value, wherein if the driving signal generates N pulses during the driving cycle, the voltage drop is equal to N times as large as the third voltage value.

9. The sensing circuit according to claim 8 wherein the third voltage value is equal to (2VyxCm/Ci), Vy is an amplitude of the pulses, Ci is a capacitance value of the feedback capacitor, and Cm is a capacitance value of the mutual capacitance.