Measuring device with a micro-electromechanical capacitive sensor

• US 8,618,816 B2
• Filed: 07/06/2009
• Issued: 12/31/2013
• Est. Priority Date: 07/07/2008
• Status: Active Grant

• Current Assignee: Albert-Ludwigs-Universitã¤T Freiburg
• Original Assignee: Albert-Ludwigs-Universitã¤T Freiburg
• Inventors: He, Lin, Manoli, Yiannos, Buhmann, Alexander, Taschwer, Armin, Northemann, Thomas
• Primary Examiner(s): Koval, Melissa
• Assistant Examiner(s): MILLER, DANIEL R
• Application Number:
  US13/002,926
• Publication Number:
  US 20110115501A1
• Time in Patent Office: 1,639 Days
• Field of Search: 324658-690, 735/041.2, 735/143.2, 330252-254, 330/260
• US Class Current: 324/661
• CPC Class Codes: G01C 19/5726 Signal processing

Abstract

A measuring device has a micro-electromechanical capacitive sensor which has electrodes which move toward and away from each other for measurement of a mechanical deflection of a test mass. The measuring device has a charge integrator which has an operating amplifier which has at least one amplifier input connected to the sensor and an amplifier output which is fed back to the amplifier input via an integration capacitor. The amplifier input is connected via a high-resistance electrical resistor to a terminal for an electrical common-mode reference potential. In addition to the amplifier input, the operating amplifier has an auxiliary input. The amplifier output is connected to the auxiliary input via a deep pass.

Claims

1. A measuring device with at least one micro-electromechanical capacitive sensor (9a, 9b) comprising electrodes that move toward and away from each other to measure a mechanical deflection of a test mass (2), with a charge integrator comprising an operational amplifier (11) that has at least one amplifier input (13a, 13b) connected to the capacitive sensor (9a, 9b) and at least one amplifier output (15a, 15b) that is fed back via at least one integration capacitor (16a, 16b) to the amplifier input (13a, 13b), wherein:

the at least one amplifier input (13a, 13b) is connected via an electrical resistor (17a, 17b) to a terminal (18) for an electrical common-mode reference potential which is connected with a reference voltage source (42);

the operational amplifier (11) comprises at least one auxiliary input (20a, 20b) in addition to the at least one amplifier input (13a, 13b); and

the amplifier output (15a, 15b) is connected via a low pass (22) to the at least one auxiliary input (20a, 20b).

2. The measuring device as in claim 1, wherein the electrical resistor (17a, 17b) is formed by a FET, which, with its source-drain channel, connects the amplifier input (13a, 13b) to the terminal (18) for the common-mode reference potential and applies a control voltage with its gate.

3. The measuring device as in claim 2, wherein the control voltage is lower than the threshold voltage of the FET.

4. The measuring device as in claim 2, further comprising a voltage source (19) for generating the control voltage, of which the source output is connected to the gate of the FET, wherein the voltage source (19) has a control input that is control-connected to the terminal (18) for the common-mode reference potential in such a way that an electrical resistance of the source-drain channel of the FET remains substantially constant when a change of the common-mode reference potential occurs.

5. The measuring device as in claim 1, wherein:

the capacitive sensor (9a, 9b) is configured as a differential sensor with a non-inverting first measuring signal output and an inverting second measuring signal output and the operational amplifier (11) is configured as a differential operational amplifier (11) with a non-inverting first amplifier input (13a), an inverting second amplifier input (13b), a non-inverting first amplifier output (15a), and an inverting second amplifier output (15b);

the first measuring signal output is connected to the first amplifier input (13a) and the second measuring signal output is connected to the second amplifier input (13b);

the first amplifier output (15a) is fed back via a first integration capacitor (16a) to the second amplifier input (13b) and the second amplifier output (15b) is fed back via a second integration capacitor (16b) to the first amplifier input (13b); and

the first amplifier input (13a) is connected via a first electrical resistor (17a) and the second amplifier input (13b) is connected via a second electrical resistor (17b) to the terminal (18) for the common-mode reference potential.

6. A gyroscope with a measuring device as in claim 1, with a test mass (2) mounted on a holding device so that it is able to be deflected along a first axis (3) and a second axis (4) running perpendicular thereto and that is set into oscillation about a rest position toward the first axis (3) by means of a vibration exciter, wherein a capacitive sensor (9a, 9b) cooperates with the test mass (2) in such a way that a deflection of the test mass (2) from the rest position toward the second axis (4) is detectable.

7. A measuring device with at least one micro-electromechanical capacitive sensor (9a, 9b) comprising electrodes that move toward and away from each other to measure a mechanical deflection of a test mass (2), with a charge integrator comprising an operational amplifier (11) that has at least one amplifier input (13a, 13b) connected to the capacitive sensor (9a, 9b) and at least one amplifier output (15a, 15b) that is fed back via at least one integration capacitor (16a, 16b) to the amplifier input (13a, 13b), wherein:

the capacitive sensor (9a, 9b) is configured as a differential sensor with a non-inverting first measuring signal output and an inverting second measuring signal output and the operational amplifier (11) is configured as a differential operational amplifier (11) with a non-inverting first amplifier input (13a), an inverting second amplifier input (13b), a non-inverting first amplifier output (15a), and an inverting second amplifier output (15b);

the first measuring signal output is connected to the first amplifier input (13a) and the second measuring signal output is connected to the second amplifier input (13b);

the first amplifier output (15a) is fed back via a first integration capacitor (16a) to the second amplifier input (13b) and the second amplifier output (15b) is fed back via a second integration capacitor (16b) to the first amplifier input (13a);

the first amplifier input (13a) is connected via a first electrical resistor (17a) and the second amplifier input (13b) is connected via a second electrical resistor (17b) to a terminal (18) for an electrical common-mode reference potential;

the operational amplifier (11) further comprises a first non-inverting auxiliary input (20a) in addition to the first amplifier input (13a) and a second inverting auxiliary input (20b) in addition to the second amplifier input (13b);

the second amplifier output (15b) is connected to a non-inverting first input terminal (23a) of a low pass (22) and the first amplifier output (15a) is connected to an inverting second input terminal (23b) of the low pass (22); and

a non-inverting first output terminal (24a) of the low pass (22) is connected to the first auxiliary input (20a) and an inverting second output terminal (24b) of the low pass (22) is connected to the second auxiliary input (20b).

8. The measuring device as in claim 7, wherein:

the second amplifier output (15b) is connected via a first resistor element (21a) to the first input terminal (23a) of the low pass (22) and the first amplifier output (15a) is connected via a second resistor element (21b) to the second input terminal (23b) of the low pass (22); and

the first input terminal (23a) of the low pass (22) is connected via a third resistor element (21c) to the second input terminal (23b) of the low pass (22).

9. The measuring device as in claim 8, wherein the low pass (22) comprises at least one voltage-controlled current source (29), of which an output (31a, 31b) is connected to an integration input of a Miller integrator (33).

10. The measuring device as in claim 9, wherein:

the first input terminal (23a) of the low pass (22) is connected to an input of a first transconductor (35a) and the second input terminal (23b) of the low pass (22) is connected to an input of a second transconductor (35b);

the first output terminal (24a) of the low pass (22) is connected to an output (31a) of the first transconductor (35a) and the second output terminal (24b) of the low pass (22) is connected to an output (31b) of the second transconductor (35b); and

the output (31b) of the second transconductor (35b) is connected via a first feedback branch (36a) to a first feedback terminal (37a) of the first transconductor (35a) and the output (31a) of the first transconductor (35a) is connected via a second feedback branch (36b) to a second feedback terminal (37b) of the second transconductor (35b).

11. The measuring device as in claim 10, wherein:

the first output terminal (24a) of the low pass (22) is connected to a reference potential terminal (39) via a first path comprising a source-drain channel of a first FET (25a) and a current source (38a) connected in series thereto; and

the second output terminal (24b) of the low pass (22) is connected to the reference potential terminal (39) via a second path comprising a source-drain channel of a second FET (25b) and another current source (38b) connected in series thereto; and

the gate of the first FET (25a) and the gate of the second FET (25b) are in each case connected to a control mechanism, which is configured in such a way that the FETs (25a, 25b) are operated below their threshold voltage.

12. A gyroscope with a measuring device as in claim 7, with a test mass (2) mounted on a holding device so that it is able to be deflected along a first axis (3) and a second axis (4) running perpendicular thereto and that is set into oscillation about a rest position toward the first axis (3) by means of a vibration exciter, wherein a capacitive sensor (9a, 9b) cooperates with the test mass (2) in such a way that a deflection of the test mass (2) from the rest position toward the second axis (4) is detectable.

13. A measuring device with at least one micro-electromechanical capacitive sensor (9a, 9b) comprising electrodes that move toward and away from each other to measure a mechanical deflection of a test mass (2), with a charge integrator comprising an operational amplifier (11) that has at least one amplifier input (13a, 13b) connected to the capacitive sensor (9a, 9b) and at least one amplifier output (15a, 15b) that is fed back via at least one integration capacitor (16a, 16b) to the amplifier input (13a, 13b), wherein:

the capacitive sensor (9a, 9b) is configured as a differential sensor with a non-inverting first measuring signal output and an inverting second measuring signal output and the operational amplifier (11) is configured as a differential operational amplifier (11) with a non-inverting first amplifier input (13a), an inverting second amplifier input (13b), a non-inverting first amplifier output (15a), and an inverting second amplifier output (15b);

the first measuring signal output is connected to the first amplifier input (13a) and the second measuring signal output is connected to the second amplifier input (13b);

the first amplifier output (15a) is fed back via a first integration capacitor (16a) to the second amplifier input (13b) and the second amplifier output (15b) is fed back via a second integration capacitor (16b) to the first amplifier input (13a);

the first amplifier input (13a) is connected via a first electrical resistor (17a) and the second amplifier input (13b) is connected via a second electrical resistor (17b) to a terminal (18) for an electrical common-mode reference potential;

the operational amplifier (11) further comprises a first non-inverting auxiliary input (20a) in addition to the first amplifier input (13a) and a second inverting auxiliary input (20b) in addition to the second amplifier input (13b);

the first amplifier output (15a) is connected to a non-inverting first input terminal (23a) of a low pass (22) and the second amplifier output (15b) is connected to an inverting second input terminal (23b) of the low pass; and

an inverting first output terminal (24b) of the low pass (22) is connected to the first auxiliary input (20a) and a non-inverting second output terminal (24a) of the low pass (22) is connected to the second auxiliary input (20b).

14. The measuring device as in claim 13, wherein:

the second amplifier output (15b) is connected via a first resistor element (21a) to the first input terminal (23a) of the low pass (22) and the first amplifier output (15a) is connected via a second resistor element (21b) to the second input terminal (23b) of the low pass (22); and

the first input terminal (23a) of the low pass (22) is connected via a third resistor element (21c) to the second input terminal (23b) of the low pass (22).

15. The measuring device as in claim 14, wherein the low pass (22) comprises at least one voltage-controlled current source (29), of which an output (31a, 31b) is connected to an integration input of a Miller integrator (33).

16. The measuring device as in claim 15, wherein:

the first input terminal (23a) of the low pass (22) is connected to an input of a first transconductor (35a) and the second input terminal (23b) of the low pass (22) is connected to an input of a second transconductor (35b);

the first output terminal (24a) of the low pass (22) is connected to an output (31a) of the first transconductor (35a) and the second output terminal (24b) of the low pass (22) is connected to an output (31b) of the second transconductor (35b); and

the output (31b) of the second transconductor (35b) is connected via a first feedback branch (36a) to a first feedback terminal (37a) of the first transconductor (35a) and the output (31a) of the first transconductor (35a) is connected via a second feedback branch (36b) to a second feedback terminal (37b) of the second transconductor (35b).

17. The measuring device as in claim 16, wherein:

the first output terminal (24a) of the low pass (22) is connected to a reference potential terminal (39) via a first path comprising a source-drain channel of a first FET (25a) and a current source (38a) connected in series thereto; and

the second output terminal (24b) of the low pass (22) is connected to the reference potential terminal (39) via a second path comprising a source-drain channel of a second FET (25b) and another current source (38b) connected in series thereto; and

the gate of the first FET (25a) and the gate of the second FET (25b) are in each case connected to a control mechanism, which is configured in such a way that the FETs (25a, 25b) are operated below their threshold voltage.

18. A gyroscope with a measuring device as in claim 13, with a test mass (2) mounted on a holding device so that it is able to be deflected along a first axis (3) and a second axis (4) running perpendicular thereto and that is set into oscillation about a rest position toward the first axis (3) by means of a vibration exciter, wherein a capacitive sensor (9a, 9b) cooperates with the test mass (2) in such a way that a deflection of the test mass (2) from the rest position toward the second axis (4) is detectable.