CAPACITIVE SENSOR AND MEASUREMENT SYSTEM

• US 20090160461A1
• Filed: 12/19/2007
• Published: 06/25/2009
• Est. Priority Date: 12/19/2007
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Brasseur, Georg, Werth, Tobias, Zangl, Hubert, Bretterklieber, Thomas, Motz, Mario, Hammerschmidt, Dirk, Holler, Gert
• Granted Patent: US 7,880,481 B2
• Time in Patent Office: Days
• US Class Current: 324/684
• CPC Class Codes: G01D 5/24 by varying capacitance

Abstract

A system includes a capacitive sensor including a first electrode and a second electrode. The system includes a measurement system configured to sense a capacitance between the first electrode and the second electrode and apply a first offset to the sensed capacitance to provide an offset compensated capacitance.

Claims

1. A system comprising:

a capacitive sensor including a first electrode and a second electrode; and

a measurement system configured to sense a capacitance between the first electrode and the second electrode and apply a first offset to the sensed capacitance to provide an offset compensated capacitance.

2. The system of claim 1, wherein the measurement system is configured to sense a conductance between the first electrode and the second electrode and apply a second offset to the sensed conductance to provide an offset compensated conductance.

3. The system of claim 2, wherein the measurement system is configured to amplify the offset compensated capacitance by a first gain and to amplify the offset compensated conductance by a second gain.

4. The system of claim 3, wherein the measurement system is configured to convert the amplified capacitance to a digital value and to convert the amplified conductance to a digital value.

5. The system of claim 4, wherein the measurement system is configured to alternately convert the amplified capacitance to a digital value and convert the amplified conductance to a digital value using a single analog to digital converter.

6. The system of claim 2, wherein the measurement system is configured to apply an excitation signal between the first and second electrodes and measure a displacement current between the first and second electrodes to sense the capacitance and the conductance.

7. The system of claim 2, wherein the sensed capacitance comprises a first capacitance component and a second capacitance component,

wherein the sensed conductance comprises a first conductance component and a second conductance component,

wherein the measurement system is configured to apply the first offset to provide an offset compensated first capacitance component and first conductance component, and

wherein the measurement system is configured to apply the second offset to provide an offset compensated second conductance component and second capacitance component.

8. A method for sensing, the method comprising:

providing a capacitive sensor including a first electrode and a second electrode;

sensing a capacitance between the first electrode and the second electrode; and

applying a first offset signal to the sensed capacitance to provide an offset compensated capacitance.

9. The method of claim 8, further comprising:

sensing a conductance between the first electrode and the second electrode; and

applying a second offset signal to the sensed conductance to provide an offset compensated conductance.

10. The method of claim 9, further comprising:

amplifying the offset compensated capacitance by a first gain; and

amplifying the offset compensated conductance by a second gain.

11. The method of claim 10, further comprising:

converting the amplified capacitance to a first digital value; and

converting the amplified conductance to a second digital value.

12. The method of claim 11, wherein converting the amplified capacitance to the first digital value and converting the amplified conductance to the second digital value comprises alternately converting the amplified capacitance and the amplified conductance using a single analog to digital converter.

13. The method of claim 8, wherein sensing the capacitance and sensing the conductance comprises:

applying an excitation signal between the first and second electrodes;

sensing a displacement current signal between the first and second electrodes; and

demodulating the displacement current signal to determine the capacitance and the conductance.

14. A system comprising:

a first transmitter electrode;

a second transmitter electrode;

a receiver electrode between the first and second transmitter electrodes; and

a circuit configured to apply a first excitation signal to the first transmitter electrode and a second excitation signal phase shifted 180°

from the first excitation signal to the second transmitter electrode to determine a sum of a first capacitance between the first transmitter electrode and the receiver electrode and a second capacitance between the second transmitter electrode and the receiver electrode.

15. The system of claim 14, further comprising:

a controller,

wherein the circuit is configured to pass an automobile seat occupancy signal to the controller based on the difference between the first capacitance and the second capacitance.

16. A sensor comprising:

a first transmitter electrode;

a second transmitter electrode;

a first receiver electrode;

a second receiver electrode; and

a circuit configured to apply a first excitation signal to the first transmitter electrode and a second excitation signal phase shifted 180°

from the first excitation signal to the second transmitter electrode to determine a sum of a first capacitance between the first transmitter electrode and the first receiver electrode and a second capacitance between the second transmitter electrode and the second receiver electrode.

17. The sensor of claim 16, wherein the first and second transmitter electrodes and the first and second receiver electrodes provide a seat occupancy sensor in an automobile.

18. The sensor of claim 16, wherein the first and second transmitter electrodes are between the first and second receiver electrodes.

19. The sensor of claim 18, wherein the first receiver electrode is spaced apart from the first transmitter electrode by a first distance, and

wherein the second receiver electrode is spaced apart from the second transmitter electrode by a second distance equal to the first distance.

20. The sensor of claim 18, wherein the first receiver electrode is spaced apart from the first transmitter electrode by a first distance, and

wherein the second receiver electrode is spaced apart from the second transmitter electrode by a second distance greater than the first distance.

21. A method for sensing, the method comprising:

providing a capacitive sensor including a first transmitter and receiver electrode pair for sensing a first capacitance and a second transmitter and receiver electrode pair for sensing a second capacitance;

applying a first excitation signal to the first transmitter electrode;

applying a second excitation signal to the second transmitter electrode, the second excitation signal phase shifted 180°

from the first excitation signal;

receiving a third signal from the first receiver electrode;

receiving a fourth signal from the second receiver electrode; and

determining a sum of the first capacitance and the second capacitance based on the third and fourth signals.

22. The method of claim 21, wherein providing the capacitive sensor comprises providing a seat occupancy sensor in an automobile.

23. The method of claim 21, wherein providing the capacitive sensor includes providing the first and second transmitter electrodes between the first and second receiver electrodes.

24. The method of claim 23, wherein providing the capacitive sensor includes providing the first receiver electrode spaced apart from the first transmitter electrode by a first distance and providing the second receiver electrode spaced apart from the second transmitter electrode by a second distance equal to the first distance.

25. The method of claim 23, wherein providing the capacitive sensor includes providing the first receiver electrode spaced apart from the first transmitter electrode by a first distance and providing the second receiver electrode spaced apart from the second transmitter electrode by a second distance greater than the first distance.