Sensor and Method for Measuring a Variable Affecting a Capacitive Component

• US 20080106275A1
• Filed: 10/14/2005
• Published: 05/08/2008
• Est. Priority Date: 10/15/2004
• Status: Abandoned Application

• Current Assignee: Valtion Teknillinen Tutkimuskeskus
• Original Assignee: Valtion Teknillinen Tutkimuskeskus
• Inventors: Sipola, Hannu, Seppa, Heikki
• Application Number:
  US11/665,386
• Publication Number:
  US 20080106275A1
• Time in Patent Office: Days
• US Class Current: 324/680
• CPC Class Codes: G01L 9/12 by making use of variations in capacitance , i.e. electric circuits therefor
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01R 17/08 in which a force or torque representing the measured value is balanced by a force or torque representing the reference value
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

The invention relates to a sensor and method for measuring a variable affecting a micro-electromechanical component. The invention is based on creating electronics, which are preferably integrated in a single circuit and which exploit the pull-in point of a micro-electromechanical sensor component such as a direct-current reference, for measuring a variable affecting the sensor, in which case an alternating or a direct-current is arranged over the sensor with the aid of a feedback connection, so that the arrangement operates very close to the pull-in point of the sensor.

Claims

1. Sensor for measuring a variable affecting a micro-electromechanical component, characterized in that the sensor comprises

electronics, which are integrated in a single circuit and

the sensor is arranged to exploit the pull-in point of a micro-electromechanical sensor component, for measuring a variable affecting the sensor,

whereby an alternating or a direct-current voltage is arranged over the sensor with the aid of a feedback connection, so that the arrangement operates very close to the pull-in point of the sensor, and

force-balance measurement is applied, whereby the capacitance of the sensor is kept essentially in constant magnitude.

2. Sensor in accordance with claim 1 for measuring a variable affecting a micro-electromechanical component, characterized in that it comprises:

an essentially capacitive micro-electromechanical bridge circuit in a single integrated circuit comprising a micro-electromechanical sensor capacitance (105), which bridge circuit comprises;

a first (106) and a second (107) bridge capacitance connected in series, and,

along with them a reference capacitance (104) and a sensor capacitance (105) connected in series.

3. Sensor according to claim 2, characterized in that

the alternating-current or direct-current voltage over the sensor is arranged to be dimensioned with the aid of a feedback coupling, in such a way that the system operates very close to the pull-in point of the sensor capacitance (105), in which case mechanical noise will be the dominant type of noise in the measuring system,

the bridge circuit is arranged to be held in a force balance using a control current, in such a way that the potential of a point A between the sensor capacitance (105) and the reference capacitance (104) essentially corresponds to the potential of a point B between the bridge capacitances, and

the variable affecting the sensor is arranged to be interpreted on the basis of the control current.

4. Sensor according to any of claims 2-3, characterized in that it is arranged to measure pressure, acceleration, microwave power, thermal, biological, chemical, optical, or magnetic conditions.

5. Sensor according to any of claims 2-4, characterized in that it is arranged as a micro-electromechanical microphone, power meter, pressure sensor, acceleration sensor, thermometer, pH-meter, or magnetic-field meter.

6. Sensor according to any of claims 2-5, characterized in that the sensor capacitance (105) comprises a direct-current voltage reference.

7. Direct-current voltage reference according to claim 6, characterized in that it comprises a sensor flip-flop (20-29).

8. Sensor according to any of claims 2-6, characterized in that the sensor capacitance (105) is arranged to be held essentially constant.

9. Sensor according to any of claims 2-7, characterized in that the sensor is integrated in the IC circuit of the reading electronics of the measuring system.

10. Sensor according to any of claims 2-8, characterized in that it is feedback coupled by bringing either a dc or an ac signal from the output (102) of the electronics, which is arranged to create a force compensating the force caused by the variable being measured.

11. Sensor according to any of claims 2-9, characterized in that the other capacitances (104, 106, 107) required by the bridge of the bridge circuit are integrated in connection with the sensor component (105) and/or with the IC circuit, to which the sensor component is attached.

12. Sensor according to any of claims 2-10, characterized in that the measuring system comprising the sensor is arranged to measure insensitive electronics without a special circuit tuned for noise adjustment, in which case the dominant type of noise in the measuring system comprising the sensor is mechanical noise.

13. Sensor according to any of claims 2-11, characterized in that the reference capacitance (104) is inside the sensor component and/or its temperature coefficient is the same as the temperature coefficient of the sensor capacitance (105).

14. Method for measuring a variable affecting a micro-electromechanical component, characterized in that in it measurement takes place:

with help of electronics, which are integrated in a single circuit and

the sensor exploits the pull-in point of a micro-electromechanical sensor component, for measuring a variable affecting the sensor,

whereby an alternating or a direct-current voltage is arranged over the sensor with the aid of a feedback connection, so that the arrangement operates very close to the pull-in point of the sensor, and

force-balance measurement is applied, whereby the capacitance of the sensor is kept essentially in constant magnitude.

15. Method for measuring a variable affecting a micro-electromechanical component, characterized in that in it measurement takes place:

using an essentially capacitive micro-electromechanical bridge circuit in a single integrated circuit comprising a micro-electromechanical sensor capacitance (105), which bridge circuit comprises;

a first (106) and a second bridge capacitance (107) connected in series, and

along with them a reference capacitance (104) and a sensor capacitance (105) connected in series.

16. Method according to claims 15, characterized in that

the alternating-current or direct-current voltage over the sensor is dimensioned with the aid of a feedback coupling in such a way that the system operates very close to the pull-in point of the sensor capacitance (105), so that mechanical noise is the dominant type of noise in the measuring system,

the bridge circuit is held in a force balance using a control current, in such a way that the potential of a point A between the senor capacitance (105) and the reference capacitance (104) essentially corresponds to the potential of a point B between the bridge capacitances, and

the variable affecting the sensor is arranged to be interpreted on the basis of the control current.

17. Method according to any of claims 15-16 characterized in that pressure, acceleration, microwave power, thermal, biological, chemical, optical, or magnetic conditions are measured.

18. Method according to any of claims 15-17, characterized in that the sensor is used as a micro-electromechanical microphone, power meter, pressure sensor, acceleration sensor, thermometer, pH-meter, or magnetic-field meter.

19. Method according to any of claims 15-18, characterized in that the sensor capacitance (105) comprises a direct-current voltage reference.

20. Direct-current voltage reference according to claim 19, characterized in that it comprises a sensor flip-flop (20-29).

21. Method according to any of claims 15-20, characterized in that the sensor capacitance (105) is arranged to be held essentially constant.

22. Method according to any of claims 15-21, characterized in that the sensor is integrated in the IC circuit of the reading electronics of the measuring system.

23. Method according to any of claims 15-22, characterized in that it is feedback coupled by bringing either a dc or an ac signal from the output (102) of the electronics, which is arranged to create a force compensating the force caused by the variable being measured.

24. Method according to any of claims 15-23, characterized in that the other capacitances (104, 106, 107) required by the bridge of the bridge circuit are integrated in connection with the sensor component (105) and/or with the IC circuit, to which the sensor component (105) is attached.

25. Method according to any of claims 15-24, characterized in that the measuring system comprising the sensor is arranged to measure insensitive electronics without a separate circuit tuned for noise adjustment, whereby the dominant type of noise in the measuring system comprising the sensor is mechanical noise.

26. Method according to any of claims 15-25, characterized in that the reference capacitance (104) is inside the sensor component and/or its temperature coefficient is the same as the temperature coefficient of the sensor capacitance (105).