Method and apparatus for converting capacitance to voltage

• US 6,356,085 B1
• Filed: 05/09/2000
• Issued: 03/12/2002
• Est. Priority Date: 05/09/2000
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Andersen, Dean, Ryat, Marc
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Hamdan, Wasseem H.
• Application Number:
  US09/566,908
• Time in Patent Office: 672 Days
• Field of Search: 324/658, 324/671, 324/158.1, 324/607, 324/76.17, 735/143.2
• US Class Current: 324/658
• CPC Class Codes: G01N 27/228 Circuits therefor measuring capacitance per se G01R27/26
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03M 3/434 with multi-level feedback

Abstract

An apparatus for converting capacitance in a capacitive sensor into a voltage signal. A capacitive sensor monitors a physical parameter. A capacitance of the sensor varies with the physical parameter. A voltage supply applies an alternating voltage to the capacitive sensor, which creates an output signal from the sensor. A modulator modulates the output signal, which produces a voltage signal that corresponds to the capacitance of the sensor.

Claims

1. An apparatus comprising:

a capacitive sensor;

a voltage supply configured to apply a voltage to said capacitive sensor, thereby producing a sensor output signal; and

a modulator configured to receive as an input said sensor output signal, wherein said modulator comprises;

a first integrator configured such that an input of said first integrator is electrically responsive to said sensor output signal;

a second integrator configured such that an input of said second integrator is electrically responsive to an output of said first integrator;

a comparator configured such that an input of said comparator is electrically responsive to an output of said second integrator.

2. The apparatus of claim 1, wherein said voltage applied to said capacitive sensor comprises a periodically alternating voltage.

3. The apparatus of claim 1, wherein said modulator comprises a first order modulator.

4. The apparatus of claim 1, wherein said modulator comprises:

an integrator configured such that an input of said integrator is electrically responsive to said sensor output signal; and

a comparator configured such that an input of said comparator is electrically responsive to an output of said integrator.

5. The apparatus of claim 4, wherein said modulator further comprises at least one feedback capacitor that is electrically connected to an input of said integrator.

6. The apparatus of claim 4, wherein said modulator further comprises at least two feedback capacitors that are electrically connected to an input of said integrator, and an output of said comparator controls said feedback capacitors.

7. The apparatus of claim 1, wherein said modulator comprises a second order modulator.

8. The apparatus of claim 1, wherein said modulator further comprises:

at least one first feedback capacitor that is electrically connected to an input of said first integrator; and

at least one second feedback capacitor that is electrically connected to an input of said second integrator.

9. The apparatus of claim 1, wherein said modulator further comprises

a first set of at least two feedback capacitors that are electrically connected to an input of said first integrator;

and

a second set of at least two feedback capacitors that are electrically connected to an input of said second integrator.

10. The apparatus of claim 9, wherein an output of said comparator controls said first set of at least two feedback capacitors.

11. The apparatus of claim 9, wherein an output of said comparator controls said second set of at least two feedback capacitors.

12. The apparatus of claim 1, wherein said capacitive sensor comprises at least two capacitors.

13. The apparatus of claim 12, wherein said voltage supply periodically applies said voltage first to a first plate of one of said at least two capacitors and then to a first plate of another of said at least two capacitors.

14. The apparatus of claim 13, wherein a second plate of said one of said at least two capacitors is electrically connected to a second plate of said other of said at least two capacitors.

15. The apparatus of claim 1, in which said modulator comprises at least one integrator.

16. The apparatus of claim 15, wherein said at least on integrator comprises a single-ended amplifier.

17. The apparatus of claim 15, wherein said at least one integrator comprises at least one switch for placing the integrator into an integration mode.

18. The apparatus of claim 17, wherein said at least one integrator comprises at least one additional switch for placing the integrator into a reset mode.

19. The apparatus of claim 18, wherein a periodic digital clock controls said at least one switch and said at least one additional switch.

20. An apparatus comprising:

capacitive sensor means for monitoring a physical parameter;

voltage supply means for applying a voltage to said capacitive sensor, thereby producing a sensor output signal; and

modulating means for modulating said sensor output signal, wherein said modulating means comprises;

first integrating means for integrating said sensor output signal;

second integrating means for integrating an output of said first integrating means; and

comparing means for comparing an output of said second integrating means to a reference signal.

21. The apparatus of claim 20 wherein said voltage applied to said capacitive sensor means comprises a periodically alternating voltage.

22. The apparatus of claim 20, wherein said modulating means comprises:

integrating means for integrating said sensor output signal; and

comparing means for comparing an output of said integrating means to a reference signal.

23. The apparatus of claim 22, wherein said modulating means further comprises feedback means for feeding a signal into an input of said integrating means.

24. The apparatus of claim 23, wherein an output of said comparing means controls said feedback means.

25. The apparatus of claim 21, wherein said modulating means further comprises:

first feedback means for feeding a first signal into an input of said first integrating means; and

second feedback means for feeding a second signal into an input of said second integrating means.

26. The apparatus of claim 25, wherein an output of said comparing means controls said first feedback means and said second feedback means.

27. A method comprising:

applying a voltage to a capacitive sensor, thereby producing a sensor output signal; and

modulating said sensor output signal, wherein the step of modulating said sensor output signal comprises;

integrating said sensor output signal, thereby producing a first integrated signal;

integrating said first integrated signal, thereby producing a second integrated signal; and

comparing said second integrated signal to a reference signal, thereby producing a comparator output signal.

28. The method of claim 27, wherein said voltage applied to said capacitive sensor comprises a periodically alternating voltage.

29. The method of claim 27, wherein the step of modulating said sensor output signal comprises:

integrating said sensor output signal, thereby producing an integrated signal; and

comparing said integrated signal to a reference signal, thereby producing a comparator output signal.

30. The method of claim 29, wherein the step of modulating said sensor output signal further comprises controlling a feedback signal in accordance with said comparator output signal.

31. The method of claim 29, wherein the step of modulating said sensor output signal further comprises controlling feedback signals in accordance with said comparator output signal.

32. The method of claim 27 further including switching between a modulating mode and a reset mode.