Methods and circuits for measuring mutual and self capacitance

• US 8,692,563 B1
• Filed: 12/19/2012
• Issued: 04/08/2014
• Est. Priority Date: 02/27/2008
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Maharyta, Andriy
• Primary Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US13/720,861
• Time in Patent Office: 475 Days
• Field of Search: 324/658, 324/649, 324/600, 324/686, 324/519, 702/47, 702/52, 340/562, 340/545.4, 733/350.4, 733/04.C, 735/143.2, 737/18, 737/24, 737/80, 738/623.37, 738/626.26
• US Class Current: 324/658
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01D 5/241 by relative movement of capacitor electrodes
• CPC Class Codes: G01D 5/2412 by varying overlap
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01R 17/00 Measuring arrangements involving comparison with a reference value, e.g. bridge
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 3/016 Input arrangements with force or tactile feedback as computer generated output to the user
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: H03K 17/962 Capacitive touch switches

Abstract

In an example embodiment, an apparatus includes a sensing device. The sensing device includes circuitry configured to sense self-capacitance and circuitry configured to sense mutual-capacitance, each configured to detect capacitance values corresponding to whether an object is proximate to a touch screen. The sensing device is configured to measure a first capacitance value using the self-capacitance circuitry during self-capacitance sensing operations and to measure a second capacitance value using the mutual-capacitance circuitry during mutual-capacitance sensing operations.

Claims

1. An apparatus comprising:

a capacitive sensor comprising a first electrode and a second electrode, wherein the first electrode is configured to have a first self-capacitance and the second electrode is configured to have a second self-capacitance, and wherein the first electrode and the second electrode are configured to have mutual capacitance between them;

a sensing device including circuitry configured to sense self-capacitance and circuitry configured to sense mutual-capacitance, each configured to detect capacitance values corresponding to whether an object is proximate to a touch screen, wherein the sensing device is configured to measure a first capacitance value from the capacitive sensor using the self-capacitance circuitry during self-capacitance sensing operations and to measure a second capacitance value from the capacitive sensor using the mutual-capacitance circuitry during mutual-capacitance sensing operations;

wherein the first capacitance value measured during the self-capacitance sensing operations corresponds to the first self-capacitance of the first electrode, and wherein the second capacitance value measured during the mutual-capacitance sensing operations corresponds to the mutual capacitance between the first electrode and the second electrode; and

wherein, during the self-capacitance sensing operations, the sensing device is configured to set voltages on the first electrode and the second electrode to a same voltage level.

2. The apparatus of claim 1, wherein the sensing device further includes a switching system that is configured to switch to the self-capacitance circuitry to measure the first capacitance value during the self-capacitance sensing operations and to switch to the mutual-capacitance circuitry to measure the second capacitance value during the mutual-capacitance sensing operations.

3. The apparatus of claim 1, wherein the first self-capacitance between the first electrode and a fixed voltage corresponds to the first capacitance value.

4. The apparatus of claim 1, wherein the sensing device further comprises a measurement circuit that is coupled to the self-capacitance circuitry and to the mutual-capacitance circuitry, wherein the measurement circuit is configured to measure the first capacitance value during the self-capacitance sensing operations and to measure the second capacitance value during the mutual-capacitance sensing operations.

5. The apparatus of claim 1, wherein, during mutual-capacitance sensing operations, the sensing device is configured to alternate a voltage level on the first electrode and keep a voltage level on the second electrode constant.

6. The apparatus of claim 1, wherein the sensing device further comprises:

a voltage source configured to output a voltage for use during capacitive sensing operations; and

a switching system configured to selectively couple the voltage to the self-capacitance circuitry or the mutual-capacitance circuitry during capacitance sensing operations.

7. The apparatus of claim 1, wherein the sensing device is configured to independently measure the first capacitance value using the self-capacitance circuitry and the second capacitance value using the mutual-capacitance circuitry.

8. The apparatus of claim 1, wherein the sensing device further comprises an integration capacitor coupled to the first electrode, wherein the integration capacitor is used to measure the first self-capacitance of the first electrode.

9. The apparatus of claim 8, wherein the integration capacitor is coupled to a fixed potential net during the mutual-capacitance sensing operations.

10. The apparatus of claim 1, wherein the sensing device is configured to set voltages on the first electrode and the second electrode to the same voltage level during a same stage of the self-capacitance sensing operations.

11. A method comprising:

selecting a type of capacitance sensing operation to perform with a sensing device that includes a self-capacitance circuitry and a mutual-capacitance circuitry;

wherein the sensing device is coupled to a capacitive sensor comprising a first electrode and a second electrode, wherein the first electrode is configured to have a first self-capacitance and the second electrode is configured to have a second self-capacitance, and wherein the first electrode and the second electrode are configured to have mutual capacitance between them;

performing a self-capacitance sensing operation to measure a first capacitance value from the capacitive sensor using the self-capacitance circuitry and performing a mutual-capacitance sensing operation to measure a second capacitance value from the capacitive sensor using the mutual-capacitance circuitry;

wherein the first capacitance value measured during the self-capacitance sensing operation corresponds to the first self-capacitance of the first electrode, and wherein the second capacitance value measured during the mutual-capacitance sensing operation corresponds to the mutual capacitance between the first electrode and the second electrode; and

wherein, during the self-capacitance sensing operation, the sensing device is configured to set voltages on the first electrode and the second electrode to a same voltage level.

12. The method of claim 11, wherein each of the first capacitance value and the second capacitance value corresponds to whether an object is proximate to a touch screen.

13. The method of claim 11, further comprising independently measuring the first capacitance value using the self-capacitance circuitry and measuring the second capacitance value using the mutual-capacitance circuitry.

14. The method of claim 11, wherein measuring the first capacitance value using the self-capacitance circuitry is performed when the selected type of capacitance sensing operation is the self-capacitance sensing operation.

15. The method of claim 11, wherein measuring the second capacitance value using the mutual-capacitance circuitry is performed when the selected type of capacitance sensing operation is the mutual-capacitance sensing operation.

16. The method of claim 11, further comprising dynamically switching between performing the self-capacitance sensing operation to measure the first capacitance value using the self-capacitance circuitry and performing the mutual-capacitance sensing operation to measure the second capacitance value using the mutual-capacitance circuitry.

17. The method of claim 11, wherein performing the self-capacitance sensing operation and performing the mutual-capacitance sensing operation comprise using a measurement circuit to measure the first capacitance value during the self-capacitance sensing operation and to measure the second capacitance value during the mutual-capacitance sensing operation.

18. The method of claim 11, wherein performing the self-capacitance sensing operation comprises coupling an integration capacitor to the first electrode.

19. The method of claim 18, wherein performing the mutual-capacitance sensing operation comprises coupling the integration capacitor to a fixed potential net.

20. The method of claim 11, wherein the sensing device is configured to set voltages on the first electrode and the second electrode to the same voltage level during a same stage of the self-capacitance sensing operation.

21. A device comprising:

a capacitive sensor comprising a first electrode and a second electrode, wherein the first electrode is configured to have a first self-capacitance and the second electrode is configured to have a second self-capacitance, and wherein the first electrode and the second electrode are configured to have mutual capacitance between them;

a sensing device configured to detect capacitance values corresponding to whether an object is proximate to a touch screen, wherein the sensing device is configured to selectively switch between performing self-capacitance sensing operations to measure a first capacitance value from the capacitive sensor and performing mutual-capacitance sensing operations to measure a second capacitance value from the capacitive sensor;

wherein the first capacitance value measured during the self-capacitance sensing operations corresponds to the first self-capacitance of the first electrode, and wherein the second capacitance value measured during the mutual-capacitance sensing operations corresponds to the mutual capacitance between the first electrode and the second electrode; and

wherein, during the self-capacitance sensing operations, the sensing device is configured to set voltages on the first electrode and the second electrode to a same voltage level.

22. The device of claim 21, wherein the sensing device is configured to measure the first capacitance value corresponding to the first self-capacitance between the first electrode and a fixed voltage during self-capacitance sensing operations.

23. The device of claim 21, wherein, during the mutual-capacitance sensing operations, the sensing device is configured to alternate a voltage level on the first electrode and keep a voltage level on the second electrode constant.

24. The device of claim 21, wherein the sensing device is configured to dynamically switch between measuring the first capacitance value in self-capacitance sensing operations and measuring the second capacitance value in mutual-capacitance sensing operations.

25. The device of claim 21, wherein the sensing device is configured to independently measure the first capacitance value using self-capacitance circuitry and the second capacitance value using mutual-capacitance circuitry.

26. The device of claim 21, wherein the sensing device further includes a switching system that is configured to switch to a self-capacitance circuitry to measure the first capacitance value during the self-capacitance sensing operations and to switch to a mutual-capacitance circuitry to measure the second capacitance value during the mutual-capacitance sensing operations.

27. The device of claim 21, wherein the sensing device further comprises a measurement circuit that is coupled to a self-capacitance circuitry and to a mutual-capacitance circuitry, wherein the measurement circuit is configured to measure the first capacitance value during the self-capacitance sensing operations and to measure the second capacitance value during the mutual-capacitance sensing operations.

28. The device of claim 21, wherein the sensing device further comprises an integration capacitor coupled to the first electrode, wherein the integration capacitor is used to measure the first self-capacitance of the first electrode.

29. The device of claim 28, wherein the integration capacitor is coupled to a fixed potential net during the mutual-capacitance sensing operations.

30. The device of claim 21, wherein the sensing device is configured to set voltages on the first electrode and the second electrode to the same voltage level during a same stage of the self-capacitance sensing operations.