Measuring Device with a Micro-Electromechanical Capacitive Sensor

• US 20110115501A1
• Filed: 07/06/2009
• Published: 05/19/2011
• 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, Northemann, Thomas, Taschwer, Armin, Buhmann, Alexander
• Granted Patent: US 8,618,816 B2
• Time in Patent Office: Days
• 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 comprising electrodes that move toward and away from each other to measure a mechanical deflection of a test mass, with a charge integrator comprising an operational amplifier that has at least one amplifier input connected to the sensor and at least one amplifier output that is fed back via at least one integration capacitor to the amplifier input, wherein the at least one amplifier input is connected via a high-resistance electrical resistor to a terminal for an electrical common-mode reference potential, further wherein the operational amplifier comprises at least one auxiliary input in addition to the at least one amplifier input, and still further wherein the amplifier output is connected via a low pass to the at least one auxiliary input.

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

3. The measuring device as in claim 1, wherein the control voltage is lower than the threshold voltage of the MOSFET.

4. The measuring device as in claim 1, further comprising a voltage source for generating the control voltage, of which the source output is connected to the gate of the MOSFET, and further wherein the voltage source has a control input that is control-connected to the terminal for the common-mode reference potential in such a way that the electrical resistance of the source-drain channel of the MOSFET remains essentially constant when a change of the common-mode reference potential occurs.

5. The measuring device as in claim 1, wherein the capacitive sensor 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 is configured as a differential operational amplifier with a non-inverting first amplifier input, an inverting second amplifier input, a non-inverting first amplifier output, and an inverting second amplifier output, further wherein the first measuring signal output is connected to the first amplifier input and the second measuring signal output is connected to the second amplifier input, still further wherein the first amplifier output is fed back via a first integration capacitor to the second amplifier input and the second amplifier output is fed back via a second integration capacitor to the first amplifier input, and even still further wherein the first amplifier input is connected via a high-resistance first resistor and the second amplifier input is connected via a high-resistance second resistor to the terminal for the common-mode reference potential.

6. The measuring device as in claim 5, wherein the operational amplifier comprises a first non-inverting auxiliary input in addition to the first amplifier input and a second inverting auxiliary input in addition to the second amplifier input, further wherein the second amplifier output is connected to a non-inverting first input terminal of the low pass and the first amplifier output is connected to an inverting second input terminal of the low pass, and still further wherein a non-inverting first output terminal of the low pass is connected to the first auxiliary input and an inverting second output terminal of the low pass is connected to the second auxiliary input.

7. The measuring device as in claim 6, wherein the operational amplifier comprises a first non-inverting auxiliary input in addition to the first amplifier input and a second inverting auxiliary input in addition to the second amplifier input, further wherein the first amplifier output is connected to a non-inverting first input terminal of a low pass and the second amplifier output is connected to an inverting second input terminal of the low pass, and still further wherein an inverting first output terminal of the low pass is connected to the first auxiliary input and a non-inverting second output terminal of the low pass is connected to the second auxiliary input.

8. The measuring device as in claim 7, wherein the second amplifier output is connected via a first resistor element to the first input terminal of the low pass and the first amplifier output is connected via a second resistor element to the second input terminal of the low pass, and further wherein the first input terminal of the low pass is connected via a third resistor element to the second input terminal of the low pass.

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

10. The measuring device as in claim 9, wherein the first input terminal of the low pass is connected to an input of a first transconductor and the second input terminal of the low pass is connected to an input of a second transconductor, further wherein the first output terminal of the low pass is connected to an output of the first transconductor and the second output terminal of the low pass is connected to an output of the second transconductor, and still further wherein the output of the second transconductor is connected via a first feedback branch to a first feedback terminal of the first transconductor and the output of the first transconductor is connected via a second feedback branch to a second feedback terminal of the second transconductor.

11. The measuring device as in claim 10, wherein the first output terminal of the low pass connected to a reference potential terminal via a first path comprising a source-drain channel of a first FET and a current source connected in series thereto, further wherein the second output terminal of the low pass is connected to the reference potential terminal via a second path comprising a source-drain channel of a second FET and another current source connected in series thereto, and still further wherein the gate of the first FET and the gate of the second FET are in each case connected to a control mechanism, which is configured in such a way that the FETs are operated below their threshold voltage.

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