Signal processing circuit for electrostatic capacity type touch sensor

• US 8,878,812 B2
• Filed: 07/15/2010
• Issued: 11/04/2014
• Est. Priority Date: 07/15/2009
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Kobayashi, Kazuyuki, Suzuki, Tatsuya, Fukai, Kumiko, Kaneta, Yasuhiro
• Primary Examiner(s): Nguyen, Chanh
• Assistant Examiner(s): SEYOUM, TSEGAYE H
• Application Number:
  US12/837,029
• Publication Number:
  US 20110012863A1
• Time in Patent Office: 1,573 Days
• Field of Search: 345/174, 345/173, 178/18.03, 178 1805- 1807
• US Class Current: 345/174
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes

Abstract

There is offered a signal processing circuit for an electrostatic capacity type touch sensor capable of detecting a larger number of locations with a smaller number of touch pads as well as improving noise immunity. A selection circuit selects either a signal from a combination of the first and second kinds of touch pads outputted through the first and second output terminals CO1 and CO2 in a touch panel or a signal from a combination of the third and fourth kinds of touch pads outputted through the third and fourth output terminals CO3 and CO4. An electric charge amplifier outputs first and second output voltages V1 and V2 corresponding to a difference between capacitances of the touch pads on the touch panel based on the signals from the selected combination. A delta sigma type A/D converter converts the first and second output voltages V1 and V2 into digital signals.

Claims

1. A signal processing device comprising:

a touch panel comprising,

a plurality of pairs of touch pads, each of the touch pads being a first kind of touch pad, a second kind of touch pad, a third kind of touch pad or a fourth kind of touch pad, and each of the pairs of touch pads comprising two touch pads of a same kind or two touch pads of two different kinds, wherein each of the touch pads of the same kind are commonly connected to respective one of a first, second, third, or fourth output, each pair of touch pads arranged on a substrate and neighboring at least one other pair of touch pads and touch pads of different kinds are not commonly connected;

an excitation pad disposed between neighboring two of the pairs of touch pads; and

a signal processing circuit for the touch panel comprising, an alternating current power supply providing the excitation pad with an alternating voltage,

an electric charge amplifier generating a first output voltage corresponding to a difference between a capacitance of a first capacitor formed between the excitation pad and the first kind of touch pad and a capacitance of a second capacitor formed between the excitation pad and the second kind of touch pad and generating a second output voltage corresponding to a difference between a capacitance of a third capacitor formed between the excitation pad and the third kind of touch pad and a capacitance of a fourth capacitor formed between the excitation pad and the fourth kind of touch pad; and

a delta sigma type ND converter converting each of the first and second output voltages generated by the electric charge amplifier into a digital value.

2. The signal processing circuit of claim 1, further comprising a selection circuit selecting the first and second kinds of touch pads in a first phase and the third and fourth kinds of touch pads in a second phase, the electric charge amplifier generating the first output voltage in the first phase and generating the second output voltage in the second phase.

3. The signal processing circuit of claim 1, wherein the plurality of pairs of touch pads comprises a first pair of touch pads comprising the first kind of touch pad, a second pair of touch pads comprising the first kind of touch pad and the third kind of touch pad, a third pair of touch pads comprising the third kind of touch pad, a fourth pair of touch pads comprising the third kind of touch pad and the second kind of touch pad, fifth pair of touch pads comprising the second kind of touch pad, sixth pair of touch pads comprising the second kind of touch pad and the fourth kind of touch pad, a seventh pair of touch pads comprising the fourth kind of touch pad and a eighth pair of touch pads comprising the fourth kind of touch pad and the first kind of touch pad.

4. The signal processing circuit of claim 3, wherein first through eighth pairs of touch pads are arranged in order, clockwise, in a circle.

5. The signal processing circuit of claim 3 wherein the first through eighth pairs of touch pads are arranged in order in a line.

6. The signal processing device of claim 1, wherein the plurality of pairs of touch pads are arranged such that each pair of touch pads neighbors at least one other pair of touch pads, the excitation pad is contiguous formed between each neighboring pair of touch pads.

7. The signal processing circuit of claim 1, wherein the electric charge amplifier comprises a first feedback capacitor connected between an inverting output and a non-inverting input, and a second feedback capacitor connected between a non-inverting output and an inverting input, a first switch coupled in parallel with the first feedback capacitor and a second switch coupled in parallel with the second feedback capacitor, and wherein the first and second feedback capacitors have the same capacitance.

8. The signal processing circuit of claim 7, wherein, in each of the first and second phases, the electric charge amplifier is configured first in a charge accumulation mode where the first and second switches are closed, and then in a charge transfer mode where the first and second switches are opened and an output voltage is produced between the inverting output and the non-inverting output.

9. The signal processing circuit of claim 2, wherein, in each phase, the output voltage is either positive, zero, or negative responsive to a touch at one of the plurality of pairs of touch pads, and wherein the signal processing circuit comprises a control circuit that outputs an indication as to whether the output voltage of the electric charge amplifier was positive, zero, or negative in each phase.

10. The signal processing circuit of claim 9, wherein the control circuit normalizes a positive output voltage to a “

1” and

a negative output voltage to a “

−

1.”

11. A signal processing device comprising:

a touch panel comprising;

a plurality of pairs of touch pads, each of the touch pads being one of either a first kind of touch pad, a second kind of touch pad, a third kind of touch pad or a fourth kind of touch pad, and each of the pairs of touch pads comprising two touch pads of a same kind or two touch pads of two different kinds, wherein each of the touch pads of the same kind are commonly connected to respective one of a first, second, third, or fourth output, each pair of touch pads arranged on a substrate and neighboring at least one other pair of touch pads and touch pads of different kinds are not commonly connected;

an excitation pad disposed between each neighboring pairs of touch pads and connected to an excitation input; and

a signal processing circuit for the touch panel comprising;

an alternating current power supply connected to the excitation input;

a multiplexer receiving the first, second, third, and fourth outputs of the touch panel that selectively provides either the first and second outputs in a first phase or the third and fourth outputs in a second phase as first and second outputs of the multiplexer; and

an electric charge amplifier generating a first output voltage corresponding to a difference between the first and second outputs of the multiplexer during the first phase and a second output voltage corresponding to a difference between the first and second outputs of the multiplexer during the second phase;

wherein the first output voltage corresponding to a difference between a capacitance of a first capacitor formed between the excitation pad and the first kind of touch pad and a capacitance of a second capacitor formed between the excitation pad and the second kind of touch pad and generating the second output voltage corresponding to a difference between a capacitance of a third capacitor formed between the excitation pad and the third kind of touch pad and a capacitance of a fourth capacitor formed between the excitation pad and the fourth kind of touch pad.

12. The signal processing circuit of claim 11, wherein the plurality of pairs of touch pads comprises a first pair of touch pads comprising the first kind of touch pad, a second pair of touch pads comprising the first kind of touch pad and the third kind of touch pad, a third pair of touch pads comprising the third kind of touch pad, a fourth pair of touch pads comprising the third kind of touch pad and the second kind of touch pad, fifth pair of touch pads comprising the second kind of touch pad, sixth pair of touch pads comprising the second kind of touch pad and the fourth kind of touch pad, a seventh pair of touch pads comprising the fourth kind of touch pad and a eighth pair of touch pads comprising the fourth kind of touch pad and the first kind of touch pad.

13. The signal processing circuit of claim 12, wherein first through eighth pairs of touch pads are arranged in order, clockwise, in a circle.

14. The signal processing circuit of claim 12 wherein the first through eighth pairs of touch pads are arranged in order in a line.

15. The signal processing circuit of claim 11, wherein the electric charge amplifier comprises a first feedback capacitor connected between an inverting output and a non-inverting input, and a second feedback capacitor connected between a non-inverting output and an inverting input, a first switch coupled in parallel with the first feedback capacitor and a second switch coupled in parallel with the second feedback capacitor, and wherein the first and second feedback capacitors have the same capacitance.

16. The signal processing circuit of claim 11, further comprising a voltage amplifier in series with the electric charge amplifier and provides an amplified output of the first and second output voltages to a delta sigma type A/D converter.

17. The signal processing circuit of claim 11, wherein, in each of the first and second phases, the electric charge amplifier is configured first in a charge accumulation mode where the first and second switches are closed, and then in a charge transfer mode where the first and second switches are opened and an output voltage is produced between the inverting output and the non-inverting output.

18. The signal processing circuit of claim 11, wherein, in each phase, the output voltage is either positive, zero, or negative responsive to a touch at one of the plurality of pairs of touch pads, and wherein the signal processing circuit comprises a control circuit that outputs an indication as to whether the output voltage of the electric charge amplifier was positive, zero, or negative in each phase.

19. The signal processing circuit of claim 18, wherein the control circuit normalizes a positive output voltage to a “

1” and

a negative output voltage to a “

−

1.”

20. A method of forming a signal processing circuit, comprising:

forming a touch panel having a plurality of pairs of touch pads, each of the touch pads being a first kind of touch pad, a second kind of touch pad, a third kind of touch pad or a fourth kind of touch pad, and each of the pairs of touch pads having two touch pads of a same kind or two touch pads of two different kinds;

forming the touch panel to further include an excitation pad disposed between neighboring two of the pairs of touch pads;

wherein each of the touch pads of the same kind are commonly connected to respective one of a first, second, third, or fourth output, each pair of touch pads arranged on a substrate and neighboring at least one other pair of touch pads and touch pads of different kinds are not commonly connected;

forming a signal processing circuit for the touch panel to include an alternating current power supply providing the excitation pad with an alternating voltage;

forming the signal processing circuit to include an electric charge amplifier generating a first output voltage corresponding to a difference between a capacitance of a first capacitor formed between the excitation pad and the first kind of touch pad and a capacitance of a second capacitor formed between the excitation pad and the second kind of touch pad and generating a second output voltage corresponding to a difference between a capacitance of a third capacitor formed between the excitation pad and the third kind of touch pad and a capacitance of a fourth capacitor formed between the excitation pad and the fourth kind of touch pad; and

forming the signal processing circuit to further include a delta sigma type A/D converter converting each of the first and second output voltages generated by the electric charge amplifier into a digital value.