Device for controlling the frequency of resonance of an oscillating micro-electromechanical system

• US 7,616,078 B2
• Filed: 09/28/2007
• Issued: 11/10/2009
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Lasalandra, Ernesto, Ungaretti, Tommaso, Prandi, Luciano
• Primary Examiner(s): Summons; Barbara
• Application Number:
  US11/864,424
• Publication Number:
  US 20080106351A1
• Time in Patent Office: 774 Days
• Field of Search: 333/186, 333/188, 333/200
• US Class Current: 333/186
• 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
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 9/02409 by application of a DC-bias voltage H03H9/02417 takes precedence

Abstract

A device for controlling the frequency of resonance of an oscillating micro-electromechanical system includes: a microstructure, having a first body and a second body, which is capacitively coupled to the first body and elastically oscillatable with respect thereto at a calibratable frequency of resonance, a relative displacement between the second body and the first body being detectable from outside; and an amplifier coupled to the microstructure for detecting the relative displacement. DC decoupling elements are arranged between the amplifier and the microstructure.

Claims

1. A device, comprising:

a microstructure including a first body and a second body, said second body being capacitively coupled to said first body and elastically oscillatable with respect thereto at a calibratable frequency of resonance, wherein a relative displacement between said second body and said first body is detectable;

an amplifier coupled to said microstructure for detecting said relative displacement;

a calibration circuit coupled to said microstructure for applying an electrostatic force between said first body and said second body so as to modify said frequency of resonance; and

DC decoupling elements arranged between said microstructure and said amplifier and arranged between said calibration circuit and said amplifier.

2. The device according to claim 1, wherein said microstructure comprises capacitive coupling elements arranged between said first body and said second body, and said calibration circuit comprises a shift voltage source, supplying to said capacitive coupling elements a shift voltage for modifying said frequency of resonance.

3. The device according to claim 2, wherein said DC decoupling elements are connected to inputs of said amplifier and to said capacitive coupling elements.

4. The device according to claim 3, wherein said amplifier is a fully differential amplifier.

5. The device according to claim 4, further comprising a common-mode voltage source for supplying a common-mode voltage to said amplifier.

6. The device according to claim 5, wherein said shift voltage is independent of said common-mode voltage.

7. The device according to claim 6, further comprising first switches for alternatively connecting and disconnecting said inputs of said amplifier and said common-mode voltage source, and second switches for alternatively connecting and disconnecting said capacitive-coupling elements and said shift voltage source.

8. The device according to claim 5, wherein said DC decoupling elements are connected between said shift voltage source and said common-mode voltage source.

9. The device according to claim 1, wherein said DC decoupling elements are of a capacitive type.

10. The device according claim 1, wherein said microstructure further comprises elastic connection elements for elastically connecting said first body and said second body, said elastic connection elements being shaped so as to enable oscillations of said second body with respect to said first body according to a pre-determined axis.

11. The device according to claim 10, wherein said elastic connection elements have an elastic constant and wherein said calibratable frequency of resonance is correlated to said elastic constant and to a mass of said second body.

12. An oscillating micro-electromechanical system comprising:

a microstructure including a first body and a second body, said second body capacitively coupled to said first body and elastically oscillatable with respect thereto at a calibratable frequency of resonance, wherein a relative displacement between said second body and said first body is detectable;

an amplifier coupled to said microstructure for detecting said relative displacement; and

means for controlling the frequency of resonance including means for decoupling the amplifier and the microstructure.

13. The oscillating micro-electromechanical system according to claim 12, further comprising a control unit co-operating with said means for controlling the frequency of resonance.

14. The oscillating micro-electromechanical system according to claim 12, wherein the means for decoupling includes first and second capacitances, the first capacitance being coupled between a first output of the microstructure and a first input of the amplifier, and the second capacitance being coupled between a second output of the microstructure and a second input of the amplifier.

15. A method for controlling the frequency of resonance of a micro-electromechanical system comprising the steps of:

setting in oscillation a microstructure including a first body, a second body, and capacitive-coupling elements, said second body capacitively coupled to said first body and elastically oscillatable with respect thereto at a calibratable frequency of resonance;

generating a signal based on a relative displacement between said second body and said first body;

amplifying said signal using an amplifier;

DC decoupling said amplifier from said microstructure;

supplying a common-mode voltage to said amplifier using a common-mode voltage source;

alternatively connecting and disconnecting inputs of said amplifier and said common-mode voltage source; and

alternatively connecting and disconnecting said capacitive-coupling elements and a shift voltage source of a calibration circuit, the calibration circuit coupled to said microstructure for applying an electrostatic force between said first body and said second body so as to modify said frequency of resonance.

16. The method of claim 15, further comprising the step of applying a DC shift voltage to the microstructure to adjust the frequency of resonance.

17. The method of claim 16, further comprising filtering DC components from said signal by filtering the DC shift voltage from said signal.

18. A MEMS system having a controllable resonance frequency, comprising:

a microstructure for generating a signal at a resonance frequency, the microstructure including

a stator having a plurality of fixed electrodes, and

a moveable body oscillatably coupled to the stator via mechanical elements and having a plurality of movable electrodes capacitively coupled to the plurality of fixed electrodes;

a shift voltage source electrically coupled to the plurality of fixed electrodes for adjusting the resonance frequency;

an amplifier having an input electrically coupled to the plurality of fixed electrodes for receiving the signal at the resonance frequency;

a DC decoupling capacitor having a first terminal and a second terminal, the first terminal being coupled to the amplifier input and the second terminal being coupled to the shift voltage source; and

a common-mode voltage source coupled to the amplifier input and the first terminal of the at least one DC decoupling capacitor.

19. The MEMS system of claim 18, wherein the amplifier is a differential amplifier.

20. The MEMS system of claim 18, wherein the mechanical elements are springs.

21. The MEMS system of claim 18, further comprising a control unit coupled to the shift voltage source for controlling the shift voltage source.

22. A device, comprising:

a microstructure including a first body, a second body, and capacitive coupling elements, said second body being capacitively coupled to said first body and elastically oscillatable with respect thereto at a calibratable frequency of resonance, wherein a relative displacement between said second body and said first body is detectable;

an amplifier coupled to said microstructure for detecting said relative displacement;

a calibration circuit comprising a shift voltage source;

DC decoupling elements arranged between said microstructure and said amplifier, said DC decoupling elements connected to inputs of said amplifier and to said capacitive coupling elements;

a common-mode voltage source for supplying a common-mode voltage to said amplifier; and

first switches for alternatively connecting and disconnecting inputs of said amplifier and said common-mode voltage source, and second switches for alternatively connecting and disconnecting said capacitive-coupling elements and said shift voltage source.

23. The device according to claim 22, wherein said calibration circuit is coupled to said microstructure for applying an electrostatic force between said first body and said second body so as to modify said frequency of resonance.

24. The device according to claim 23, wherein said capacitive coupling elements are arranged between said first body and said second body, and said shift voltage source supplies to said capacitive coupling elements a shift voltage for modifying said frequency of resonance.

25. The device according to claim 24, wherein said DC decoupling elements are connected to inputs of said amplifier and to said capacitive coupling elements.

26. The device according to claim 25, wherein said amplifier is a fully differential amplifier.

27. The device according to claim 26, further comprising a common-mode voltage source for supplying a common-mode voltage to said amplifier.

28. The device according to claim 27, wherein said shift voltage is independent of said common-mode voltage.