Method and Apparatus for a Micromachined Multisensor

• US 20100043551A1
• Filed: 08/19/2008
• Published: 02/25/2010
• Est. Priority Date: 08/19/2008
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Kuang, Jinbo, Geen, John A., Kumar, Vineet
• Granted Patent: US 7,980,133 B2
• Time in Patent Office: Days
• US Class Current: 73/514.150
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01C 19/5726 Signal processing
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

In a micromachined devices having a movable shuttle driven in oscillation, measuring the electrical charge accumulated on opposing drive capacitors to determine the displacement of the movable shuttle. Alternately, in such a micromachined device, measuring the electrical charge accumulated on a drive capacitor and comparing the measured electrical charge to a nominal electrical charge to determine the displacement of the movable shuttle.

Claims

1. A method of detecting displacement of a MEMS structure, the method including:

providing at least one drive capacitor for electrostatically driving the MEMS structure, wherein the capacitance of the at least one drive capacitor varies as a function of the displacement of the MEMS structure;

charging the at least one drive capacitor;

measuring the electrical charge on the at least one drive capacitor; and

determining the displacement of the MEMS structure as a function of the electrical charge measured on the at least one drive capacitor.

2. The method of claim 1 further comprising charging the at least one drive capacitor with a drive voltage.

3. The method of claim 1 further comprising charging the at least one drive capacitor with a periodic alternating voltage.

4. The method of claim 3 wherein the periodic alternating voltage alternately charges and discharges the at least one drive capacitor.

5. The method of claim 3 wherein measuring the electrical charge on the at least one drive capacitor comprises measuring the charge discharged by the at least one drive capacitor during a discharge cycle of the periodic alternating voltage.

6. The method of claim 1 wherein measuring the electrical charge on the at least one drive capacitor comprises integrating the current discharged by the at least one drive capacitor.

7. The method of claim 1 wherein the MEMS structure comprises a shuttle of a gyroscope.

8. The method of claim 7 wherein the MEMS structure comprises one of two shuttles oscillating in antiphase.

9. The method of claim 1 further comprising

providing a second drive capacitor for electrostatically driving the MEMS structure;

alternately charging and discharging the first an second drive capacitors; and

measuring the electrical charge from the drive capacitor being discharged.

10. The method of claim 9 wherein measuring the charge comprises coupling the drive capacitor to an integrator.

11. A method of detecting the in-phase displacement of two MEMS structures oscillating in antiphase, the method including:

providing a first MEMS structure having a first drive capacitor and an opposing second drive capacitor;

providing a second MEMS structure having a third drive capacitor and an opposing fourth drive capacitor;

driving the first drive capacitor and the third drive capacitor with a first periodic drive signal having a high phase and a low phase;

driving the second drive capacitor and the fourth drive capacitor with a second periodic drive signal having a high phase and a low phase, where the second periodic signal is the inverse of the first periodic signal; and

measuring the discharge current from the first drive capacitor and the third drive capacitor during the low phase of the first drive signal.

12. The method of claim 11, wherein the method further comprises:

measuring the discharge current from the second drive capacitor and the fourth drive capacitor during the low phase of the second drive signal.

13. The method of claim 11 wherein measuring the discharge current from the first drive capacitor and the third drive capacitor comprises operably coupling the discharge current of the first drive capacitor and third drive capacitor to a first terminal of a differential integrator.

14. The method of claim 11 wherein measuring the discharge current from the first drive capacitor and the third drive capacitor comprises operably coupling the discharge current of the first drive capacitor and third drive capacitor to the input of a first single-ended integrator.

15. An apparatus for determining acceleration, the apparatus comprising:

a movable mass;

at least one drive capacitor for receiving an electrostatic force and vibrating the movable mass in response to the received electrostatic force; and

a measuring circuit operatively coupled with the at least one drive capacitor, the measuring circuit measuring the electrical charge on the at least one drive capacitor and producing a signal representing acceleration as a function of the measured electrical charge.

16. The apparatus as defined by claim 15 further comprising an output for delivering a rotational acceleration signal as a function of the Coriolis responsive movement of the movable mass.

17. The apparatus as defined by claim 15 wherein the measuring circuit measures discharge of charge from the at least one drive capacitor to produce the signal representing acceleration.

18. The apparatus as defined by claim 15 wherein the measuring circuit comprises an integrator to integrate the current discharged from the at least one drive capacitor.