PARAMETRIC AMPLIFICATION OF A MEMS GYROSCOPE BY CAPACITANCE MODULATION

• US 20090320591A1
• Filed: 04/30/2008
• Published: 12/31/2009
• Est. Priority Date: 12/12/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Johnson, Burgess R.
• Granted Patent: US 8,037,757 B2
• Time in Patent Office: Days
• US Class Current: 73/504.12
• 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

Abstract

Parametric amplification of the output of a MEMS gyroscope is achieved by modulating the sense capacitance, or an auxiliary capacitance having an applied DC voltage. The capacitance modulation is produced by the driven motion of the gyroscope mechanism, so the pump signal of the parametric amplifier is not subject to phase errors in the electronics. The capacitance modulation affects the mechanical gain of the sensor (transfer function from input force to sensor mechanism displacement), as well as the electrical gain of the sensor (transfer function from sensor mechanism displacement to output electrical signal). The mechanical and electrical gains of the sensor become phase-dependent, so the Coriolis rate signal can be amplified while the unwanted quadrature-phase signal is attenuated.

Claims

1. A method for operating a Micro-Electro-Mechanical Systems (MEMS) gyroscope sensor, comprising:

inducing a motor motion to a proof mass, the proof mass capacitively coupled to an electrode via a gap between mating comb fingers of at least one comb finger pair that define a capacitance between the proof mass and the electrode, the capacitance variable as a function of a displacement in a position of the mated comb fingers caused by the induced motor motion; and

producing a time-varying electrical output in response to a rotation of the MEMS gyroscope, wherein the time-varying electrical output is amplified by the capacitance variation caused by the induced motor motion.

2. The method of claim 1, wherein at least one of the mating comb fingers of the comb finger pair is defined by an end portion with a first width and an attaching portion with a second width less than the first width, wherein producing the time-varying electrical output comprises:

increasing the gap as the function of the displacement along a direction of the motor motion such that the variable capacitive coupling decreases as the function of the displacement.

3. The method of claim 1, wherein at least one of the mating comb fingers of the comb finger pair is defined by an end portion with a first width and an attaching portion with a second width greater than the first width, wherein producing the time-varying electrical output comprises:

decreasing the gap as the function of the displacement along a direction of the motor motion such that the variable capacitive coupling increases as the function of the displacement.

4. The method of claim 1, wherein at least one of the mating comb fingers of the comb finger pair is defined by a corrugated end portion, wherein producing the time-varying electrical output comprises:

decreasing the gap as the function of the displacement along a direction of the motor motion such that the variable capacitive coupling increases as the function of the displacement.

5. The method of claim 1, wherein a first mating comb finger of a first electrode and a first mating comb finger of the proof mass are each tilted at a first shallow angle with respect to an x-axis of the motor motion, further comprising:

increasing a first gap between the first mating comb finger of the first electrode and the first mating comb finger of the proof mass as the function of the displacement along a direction of the motor motion such that a first variable capacitive coupling decreases as the function of the displacement, and

wherein a second mating comb finger of a second electrode and a second mating comb finger of the proof mass are each tilted at a second shallow angle with respect to the x-axis of the motor motion, further comprising;

decreasing a second gap between the second mating comb finger of the second electrode and the second mating comb finger of the proof mass as the function of the displacement along the direction of the motor motion such that a second variable capacitive coupling increases as the function of the displacement.

6. The method of claim 1, wherein inducing the motor motion to the proof mass comprises:

inducing the motor motion at a predefined motor frequency;

generating a time-dependent variable electrostatic force produced by the variable capacitive coupling (C); and

modulating dC/dy at twice a motor frequency to cause a force F_y to be modulated at twice the motor frequency,

wherein the time-dependent variable electrostatic force along a y-axis is defined by;

7. The method of claim 6, wherein F_y(t) is a pump force operable to provide parametric amplification of a mechanical response of the proof mass to a Coriolis force.

8. The method of claim 6, wherein F_y(t) is a pump force operable to provide suppression of a response of the proof mass to a quadrature-phase force.

9. The method of claim 1, wherein the electrode is a sense electrode.

10. A Micro-Electro-Mechanical Systems (MEMS) sensor, comprising:

a proof mass with at least one proof mass comb finger, the proof mass comb finger comprising;

a proof mass comb finger end portion; and

a proof mass comb finger attaching portion that couples the proof mass comb finger end portion to the proof mass;

a sense electrode with at least one sense electrode comb finger separated from the proof mass comb finger by a gap, the gap defining a variable capacitive coupling between the proof mass comb finger and the sense electrode comb finger, the sense electrode comb finger comprising;

a sense electrode comb finger end portion; and

a sense electrode comb finger attaching portion that couples the sense electrode comb finger end portion to an anchor;

an electrical output operable to output a time-varying electrical output, the time-varying electrical output being amplified by a variation of the variable capacitive coupling produced by an induced motor motion of the proof mass.

11. The MEMS sensor of claim 10, wherein at least one of the proof mass comb finger end portion and the sense electrode comb finger end portion is wider than its respective attaching portion such that the gap increases as a function of a displacement along a direction of the motor motion, wherein the variable capacitive coupling decreases as the gap increases.

12. The MEMS sensor of claim 10, wherein at least one of the proof mass comb finger end portion and the sense electrode comb finger end portion is narrower than its respective comb finger attaching portion such that the gap decreases as a function of a displacement along a direction of the motor motion, wherein the variable capacitive coupling increases as the gap decreases.

13. The MEMS sensor of claim 10, wherein at least one of the proof mass comb finger end portion and the sense electrode comb finger end portion is corrugated such that the variable capacitive coupling increases as a function of a displacement along a direction of the motor motion.

14. The MEMS sensor of claim 10, wherein at least one of the proof mass comb finger end portion and the sense electrode comb finger end portion is corrugated such that the variable capacitive coupling decreases as the function of the displacement along a direction of the motor motion.

15. The MEMS sensor of claim 10, further comprising:

a first sense electrode comb finger tilted at a first angle with respect to an x-axis of the motor motion;

a first proof mass comb finger tilted at the first angle;

a second sense electrode comb finger tilted at a second angle with respect to the x-axis of the motor motion; and

a second proof mass comb finger tilted at the second angle,

wherein a first gap defined by the first sense electrode comb finger and the first proof mass comb finger increases as the function of the displacement along a direction of the motor motion such that a first variable capacitive coupling decreases as the function of the displacement, and wherein a second gap defined by the second sense electrode comb finger and the second proof mass comb finger decreases as the function of the displacement along the direction of the motor motion such that a second variable capacitive coupling increases as the function of the displacement.

16. The MEMS sensor of claim 10, further comprising:

at least one motor operable to induce the motor motion of the proof mass.

17. The MEMS sensor of claim 10, wherein the electrode is an auxiliary sense electrode.

18. A sensor, comprising:

a proof mass with at least one proof mass comb finger, the proof mass comb finger comprising;

a proof mass comb finger end portion; and

a proof mass comb finger attaching portion that couples the proof mass comb finger end portion to the proof mass;

an electrode with at least one electrode comb finger separated from the proof mass comb finger by a gap, the gap defining a variable capacitive coupling between the proof mass comb finger and the electrode comb finger, the electrode comb finger comprising;

an electrode comb finger end portion; and

an electrode comb finger attaching portion that couples the electrode comb finger end portion to an anchor;

an electrical output that is variable in response to a variation of the variable capacitive coupling produced by an induced motor motion of the proof mass.

19. The MEMS sensor of claim 18, wherein the electrode is the sense electrode.

20. The MEMS sensor of claim 18, wherein the electrode is an auxiliary electrode.