Readout method and electronic bandwidth control for a silicon in-plane tuning fork gyroscope

• US 8,061,201 B2
• Filed: 07/11/2008
• Issued: 11/22/2011
• Est. Priority Date: 07/13/2007
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Sharma, Ajit, Zaman, Mohammad Faisal, Ayazi, Farrokh
• Primary Examiner(s): Kwok; Helen C.
• Application Number:
  US12/218,087
• Publication Number:
  US 20090064781A1
• Time in Patent Office: 1,229 Days
• Field of Search: 735/041.2, 735/040.4, 735/041.4, 735/041.6, 735/041.5
• US Class Current: 73/504.12
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis

Abstract

Disclosed are methods and a sensor architecture that utilizes the residual quadrature error in a gyroscope to achieve and maintain perfect mode-matching, i.e., ˜0 Hz split between the drive and sense mode frequencies, and to electronically control sensor bandwidth. In a reduced-to-practice embodiment, a 6 mW, 3V CMOS ASIC and control algorithm are interfaced to a mode-matched MEMS tuning fork gyroscope to implement an angular rate sensor with bias drift as low as 0.15°/hr and angle random walk of 0.003°/√hr, which is the lowest recorded to date for a silicon MEMS gyroscope. The system bandwidth can be configured between 0.1 Hz and 1 kHz.

Claims

1. Sensor apparatus comprising:

(1) a microelectromechanical systems gyroscope comprising;

an electrically-conductive substrate having a lower support layer and an upper flexible support layer;

first and second separated proof masses that lie in and are supported by the upper flexible support layer and that are separated from the lower support layer;

first and second drive electrodes disposed at distal ends of the proof masses that are insulatively supported by the lower support layer and that are separated from the upper flexible support layer;

a central drive electrode disposed between the separated proof masses that is insulatively supported by the lower support layer and that is separated from the upper flexible support layer;

sense electrodes disposed adjacent to the proof masses that are insulatively supported by the lower support layer and that are separated from the upper flexible support layer;

quadrature nulling electrodes disposed at distal ends of the proof masses that are insulatively supported by the lower support layer and that are separated from the upper flexible support layer; and

(2) control circuitry coupled to the lower support layer, the drive, sense, and quadrature nulling electrodes that comprises a mode-matching algorithm that adaptively biases the gyroscope so that drive and sense mode frequencies are equalized, or are electronically controlled to enhance the bandwidth of the gyroscope.

2. The apparatus recited in claim 1 wherein the first and second drive electrodes are disposed adjacent distal ends of the respective proof masses.

3. The apparatus recited in claim 1 wherein adjacent ends of the respective proof masses and the drive electrodes comprise pluralities of interdigitated projections that form comb drives.

4. The apparatus recited in claim 1 wherein the lower support layer comprises one or more anchors that couple the upper flexible support layer to the lower support layer.

5. The apparatus recited in claim 4 wherein the drive and sense mode frequencies are controlled to be at resonance.

6. The apparatus recited in claim 1 wherein the quadrature nulling electrodes are controlled by the control circuitry to mechanically balance the proof masses.

7. The apparatus recited in claim 1 wherein:

the proof masses are driven into drive mode resonance by the drive electrodes and exhibit sense mode resonance induced by rotation and residual quadrature error sensed by the sense electrodes;

and the control circuitry processes the residual quadrature error to generate a polarization voltage applied to the substrate to minimizing the frequency difference between drive and sense resonant modes.

8. The apparatus recited in claim 7 wherein the control circuitry processes the residual quadrature error to apply a polarization voltage to the gyroscope that separates the drive mode resonance from the sense mode resonance to control operational bandwidth of the gyroscope.

9. Sensor apparatus comprising:

a gyroscope that is driven into drive mode resonance by drive electrodes and exhibit sense mode resonance induced by rotation and residual quadrature error sensed by sense electrodes; and

control circuitry coupled to the drive electrodes and sense electrodes that processes the residual quadrature error to generate a polarization voltage applied to the gyroscope to minimize the frequency difference between drive and sense resonant modes.

10. The apparatus recited in claim 9 wherein the control circuitry applies a polarization voltage to the gyroscope that separates the drive mode resonance from the sense mode resonance to control operational bandwidth of the gyroscope.

11. The apparatus recited in claim 10 wherein the control circuitry further adjusts the gain of the gyroscope in proportion to the change in bandwidth of the gyroscope to control the sensitivity of the gyroscope.

12. The apparatus recited in claim 9 wherein the control circuitry applies a tuning/balancing voltage to selected sense electrodes to tune the drive and sense resonant modes of the gyroscope.

13. The apparatus recited in claim 10 wherein the control circuitry further applies a tuning/balancing voltage to selected sense electrodes to tune the drive and sense resonant modes of the gyroscope.

14. The apparatus recited in claim 9 wherein the gyroscope comprises a microelectromechanical systems tuning fork gyroscope having a plurality of proof masses.