Methods and circuits for measuring mutual and self capacitance

• US 8,358,142 B2
• Filed: 02/27/2009
• Issued: 01/22/2013
• 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): TANG, MINH NHUT
• Application Number:
  US12/395,462
• Publication Number:
  US 20120043971A1
• Time in Patent Office: 1,425 Days
• Field of Search: None
• 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

A capacitance measurement circuit for measuring self and mutual capacitances may include a first electrode capacitively coupled with a second electrode, a first plurality of switches coupled with the first electrode, and a second plurality of switches coupled with the second electrode, wherein, during a first operation stage, the first plurality of switches is configured to apply a first initial voltage to the first electrode and the second plurality of switches is configured to apply a second initial voltage to the second electrode, and wherein, during a second operation stage, the first plurality of switches is configured to connect the first electrode with a measurement circuit, and the second plurality of switches is configured to connect the second electrode with a constant voltage.

Claims

1. A capacitance measurement circuit, comprising:

a first electrode capacitively coupled with a second electrode;

a first plurality of switches coupled with the first electrode; and

a second plurality of switches coupled with the second electrode, wherein, during a first operation stage, the first plurality of switches is configured to apply a first initial voltage to the first electrode and the second plurality of switches is configured to apply a second initial voltage to the second electrode, and wherein, during a second operation stage, the first plurality of switches is configured to connect the first electrode with a measurement circuit, and the second plurality of switches is configured to connect the second electrode with a constant voltage.

2. The capacitance measurement circuit of claim 1, wherein the measurement circuit is configured to generate an output signal based on a current generated by operation of the first plurality of switches.

3. The capacitance measurement circuit of claim 1, wherein the second initial voltage is approximately equal to the first initial voltage.

4. The capacitance measurement circuit of claim 1, wherein the first initial voltage is approximately equal to a voltage supplied by the measurement circuit to the first electrode during the second operation stage.

5. The capacitance measurement circuit of claim 4, further comprising a buffer configured to generate the first initial voltage based on the voltage supplied by the measurement circuit.

6. A capacitance measurement method, comprising:

applying a first initial voltage to a first electrode during a first operation stage, wherein the first electrode is capacitively coupled with a second electrode;

applying a second initial voltage to the second electrode during the first operation stage;

connecting the first electrode with a measurement circuit during a second operation stage; and

connecting the second electrode to a constant voltage during the second operation stage.

7. The capacitance measurement method of claim 6, further comprising generating an output signal based on a net current detected by the measurement circuit during the first operation stage and the second operation stage.

8. The capacitance measurement method of claim 6, wherein the second initial voltage is approximately equal to the first initial voltage.

9. The capacitance measurement method of claim 6, wherein the first initial voltage is approximately equal to a voltage supplied by the measurement circuit to the first electrode during the second operation stage.

10. The capacitance measurement method of claim 9, further comprising buffering the voltage supplied by the measurement circuit to generate the first initial voltage.

11. A capacitance measurement circuit, comprising:

a first electrode capacitively coupled with a second electrode;

a first plurality of switches coupled with the first electrode;

a second plurality of switches coupled with the second electrode, wherein the first plurality of switches is configured to generate a current by connecting the first electrode to a first node during a first operation stage and a second node during a second operation stage, and wherein the second plurality of switches is configured to minimize a voltage difference between the second electrode and the first electrode during the first operation stage and during the second operation stage; and

a measurement circuit configured to generate an output signal based on the current generated by the first plurality of switches.

12. The capacitance measurement circuit of claim 11, wherein the second plurality of switches is further configured to:

during the first operation stage, connect the second electrode to a voltage approximately equal to a voltage supplied by the measurement circuit to the first electrode; and

during the second operation stage, connect the second electrode to a voltage approximately equal to the constant voltage.

13. The capacitance measurement circuit of claim 12, further comprising a buffer configured to generate the voltage approximately equal to the voltage supplied by the measurement circuit to the first electrode.

14. The capacitance measurement circuit of claim 11, wherein the second node is connected to a ground.

15. A capacitance measurement method, comprising:

generating a net current by connecting a first electrode to a first node during a first operation stage, wherein the first electrode is capacitively coupled to a second electrode;

connecting the first electrode to a second node during a second operation stage; and

minimizing a voltage difference between the second electrode and the first electrode during the first operation stage and the second operation stage; and

generating an output signal based on the net current.

16. The capacitance measurement method of claim 15, wherein the net current is detected by the measurement circuit during the first operation stage and the second operation stage.

17. The capacitance measurement method of claim 15, wherein minimizing the voltage difference comprises:

during the first operation stage, connecting the second electrode to a voltage approximately equal to a voltage supplied by the measurement circuit to the first electrode; and

during the second operation stage, connecting the second electrode to a voltage approximately equal to the constant voltage.

18. The capacitance measurement method of claim 17, further comprising using a buffer connected to the measurement circuit to generate the voltage approximately equal to the voltage supplied by the measurement circuit to the first electrode.

19. The capacitance measurement method of claim 15, wherein the second node is connected to a ground.