SENSING CIRCUIT FOR USE WITH CAPACITIVE TOUCH PANEL

• US 20110157081A1
• Filed: 12/23/2010
• Published: 06/30/2011
• Est. Priority Date: 12/31/2009
• 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
• Granted Patent: US 8,421,774 B2
• Time in Patent Office: Days
• 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 of a capacitive touch panel includes a first switch, a second switch, a third switch, a feedback capacitor, a fourth switch and an operation amplifier. The first switch and the second switch have respective first ends connected with a receiving electrode. The third switch has a first end connected with a second end of the first switch. The feedback capacitor has a first end connected with the second end of the first switch. The fourth switch has a first end connected with a second end of the feedback capacitor. The operation amplifier has a positive input terminal connected with a ground terminal, a negative input terminal connected with the fourth switch, and an output terminal connected with the second, third and fourth switches. These switches are controlled during a driving cycle of the driving signal, so that an output voltage is outputted from the operation amplifier.

Claims

1. A sensing circuit for a capacitive touch panel, connected with a receiving electrode of the capacitive touch panel, wherein a mutual capacitance is existed between a driving electrode of the capacitive touch panel and the receiving electrode, and the driving electrode receives a driving signal, the sensing circuit comprising:

a first switch, having a first end connected with the receiving electrode;

a second switch, having a first end connected with the receiving electrode;

a third switch, having a first end connected with a second end of the first switch;

a feedback capacitor, having a first end connected with the second end of the first switch;

a fourth switch, having a first end connected with a second end of the feedback capacitor; and

an operation amplifier, having a positive input terminal connected with a ground terminal, a negative input terminal connected with the first end of the fourth switch, and an output terminal connected with a second end of the second switch, a second end of the third switch and a second end of the fourth switch,

wherein a driving cycle of the driving signal includes N sub-driving cycles, when the sensing circuit is during high-level time intervals of the N sub-driving cycles, the first switch and the fourth switch are in the close state, and the second switch and the third switch are in the open state, otherwise, when the sensing circuit is during low-level time intervals of the N sub-driving cycles, the first switch and the fourth switch are in the open state, and the second switch and the third switch are in the close state, then an output voltage is generated from the output terminal of the operation amplifier during the low-level time interval of the N^th sub-driving cycle, where N is an integer.

2. The sensing circuit according to claim 1, wherein the driving signal includes the driving cycle and a reset cycle.

3. The sensing circuit according to claim 2, wherein during the reset cycle, the first switch, the second switch, the third switch and the fourth switch are controlled to be in the close state, so that there is no charge quantity stored in the feedback capacitor and the mutual capacitance.

4. The sensing circuit according to claim 1, wherein the output voltage is obtained as:

5. The sensing circuit according to claim 2, wherein the output voltage generated during the low-level time interval of the N^th sub-driving cycle is N times as large as the output voltage generated during the low-level time interval of the first sub-driving cycle.

6. A sensing circuit for a capacitive touch panel, connected with a receiving electrode of the capacitive touch panel, wherein a mutual capacitance is existed between a driving electrode of the capacitive touch panel and the receiving electrode, the driving electrode receives a driving signal, the sensing circuit comprising:

a first switch, having a first end connected with the receiving electrode;

a second switch, having a first end connected with the receiving electrode;

a third switch, having a first end connected with a second end of the first switch;

a feedback capacitor, having a first end connected with the second end of the first switch;

a fourth switch, having a first end connected with a second end of the feedback capacitor; and

an operation amplifier, having a positive input terminal connected with a ground terminal, a negative input terminal connected with the first end of the fourth switch, and an output terminal connected with a second end of the second switch, a second end of the third switch and a second end of the fourth switch,

wherein a driving cycle of the driving signal includes N sub-driving cycles and each of the N sub-driving cycles includes a first phase, a second phase, a third phase and a fourth phase, when the sensing circuit is during the first phase, the driving signal is in a floating condition, the first switch and the second switch are in the open state, and the third switch and the fourth switch are in the close state, when the sensing circuit is during the second phase, the driving signal is a low-level voltage, the first switch and the fourth switch are in the close state, and the second switch and the third switch are in the open state, when the sensing circuit is during the third phase, the driving signal is a high-level voltage, the first switch and the fourth switch are in the close state, and the second switch and the third switch are in the open state, otherwise, when the sensing circuit is during the fourth phase, the driving signal is the low-level voltage, the first switch and the fourth switch are in the open state, and the second switch and the third switch are in the close state, and then an output voltage is generated from the output terminal of the operation amplifier during the fourth phase of the N^th sub-driving cycle, where N is an integer.

7. The sensing circuit according to claim 6, wherein the driving signal includes the driving cycle and a reset cycle.

8. The sensing circuit according to claim 7, wherein during the reset cycle, the first switch, the second switch, the third switch and the fourth switch are controlled to be in the close state, so that there is no charge quantity stored in the feedback capacitor and the mutual capacitance.

9. The sensing circuit according to claim 6, wherein the driving electrode is connected with a first end of a fifth switch and a first end of a sixth switch, a second end of the fifth switch receives the high-level voltage, and a second end of the sixth switch receives the low-level voltage, wherein during the first phase, the fifth switch and the sixth switch are in the open state, wherein during the second phase, the sixth switch is in the close state, and the fifth switch is in the open state, wherein during the third phase, the fifth switch is in the close state, and the sixth switch is in the open state, otherwise, wherein during the fourth phase, the sixth switch is in the close state and the fifth switch is in the open state.

10. The sensing circuit according to claim 6, wherein the output voltage is obtained as:

11. A sensing circuit for a capacitive touch panel, connected with a receiving electrode of the capacitive touch panel, wherein a mutual capacitance is existed between a driving electrode of the capacitive touch panel and the receiving electrode, and the driving electrode is connected to a ground terminal, the sensing circuit comprising:

a first switch, having a first end connected with the receiving electrode;

a second switch, having a first end connected with the receiving electrode;

a third switch, having a first end connected with a second end of the first switch;

a feedback capacitor, having a first end connected with the second end of the first switch;

a fourth switch;

an operation amplifier, having a positive input terminal connected with the ground terminal, a negative input terminal connected with a first end of the fourth switch, and an output terminal connected with a second end of the second switch, a second end of the third switch and a second end of the fourth switch;

a fifth switch, having a first end connected with a voltage source and a second end connected with a second end of the feedback capacitor; and

a sixth switch, having a first end connected with the second end of the feedback capacitor and a second end connected with the first end of the fourth switch,

wherein a driving cycle of the driving signal includes N sub-driving cycles, and each of the N sub-driving cycles includes a first phase and a second phase, when the sensing circuit is during the first phase, the first switch, the fourth switch and the fifth switch are in the close state, and the second switch, the third switch and the sixth switch are in the open state, otherwise, when the sensing circuit is during the second phase, the first switch, the fourth switch and the fifth switch are in the open state, and the second switch, the third switch and the sixth switch are in the close state, and then an output voltage is generated from the output terminal of the operation amplifier during the second phase of the N^th sub-driving cycle, where N is an integer.

12. The sensing circuit according to claim 11, wherein the driving signal further includes a rest cycle, wherein during the reset cycle, the first switch, the second switch, the third switch, the fourth switch and the sixth switch are controlled to be in the close state, and the fifth switch is controlled to be the open state, so that there is no charge quantity stored in the feedback capacitor and the mutual capacitance.

13. The sensing circuit according to claim 11, wherein the output voltage is obtained as: