Sensor and sensing method utilizing symmetrical differential readout

• US 8,056,413 B2
• Filed: 09/11/2008
• Issued: 11/15/2011
• Est. Priority Date: 09/11/2007
• Status: Active Grant

• Current Assignee: Micro Inertial LLC
• Original Assignee: Evigia Systems, Inc.
• Inventors: Yazdi, Navid
• Primary Examiner(s): Kwok; Helen C.
• Application Number:
  US12/208,402
• Publication Number:
  US 20090064782A1
• Time in Patent Office: 1,160 Days
• Field of Search: 735/041.3, 735/041.2, 735/041.4, 735/041.6, 735/040.4
• US Class Current: 73/504.13
• CPC Class Codes: G01C 19/5677 of essentially two-dimensional vibrators, e.g. ring-shaped vibrators
• CPC Class Codes: G01C 19/5684 the devices involving a micromechanical structure

Abstract

A sensor and sensing method capable of full-differential symmetry to minimize bias drift and improve stability of the sensor output. The sensor includes a sensing element, sense electrodes capacitively coupled to the sensing element to generate capacitive outputs that vary in response to the motion of the sensing element, and a differential readout device. The sense electrodes are electrically separable into at least two pairs of differential sense electrodes. The readout device performs a sampling sequence of at least two sampling cycles during which the readout device samples the capacitive outputs of the sense electrodes and produces at least two differential outputs based on the difference between the capacitive outputs within each pair of differential sense electrodes. The readout device then calculates an average of the differential outputs of the sampling sequence to produce an output of the differential readout device, and thereafter repeats the sampling sequence and calculation.

Claims

1. A sensor adapted to achieve differential symmetry at an output thereof, the sensor comprising:

a sensing element that responds with motion to an environmental input;

a plurality of sense electrodes capacitively coupled to the sensing element to generate a corresponding plurality of capacitive outputs that vary in response to motion of the sensing element, the sense electrodes being electrically separable into at least two pairs of differential sense electrodes, the differential sense electrodes of each pair detecting motion of the sensing element at different locations of the sensing element;

differential readout means for performing a sampling sequence comprising at least two sampling cycles during which the differential readout means samples the capacitive outputs of the sense electrodes and produces at least two differential outputs based on the difference between the capacitive outputs within each pair of the differential sense electrodes, calculating an average of the at least two differential outputs of the sampling sequence to produce an output of the differential readout means, and then repeating the sampling sequence and calculation; and

means for connecting different pairs of the differential sense electrodes at a sampling rate and at instances to achieve dynamically generated symmetry at the output of the differential readout means.

2. The sensor according to claim 1, wherein the connecting means comprises switches individually coupled in series with each of the sense electrodes and operable to electrically separate the sense electrodes into the at least two pairs of differential sense electrodes by connecting and disconnecting the capacitive outputs of the sense electrodes to the differential readout means.

3. The sensor according to claim 1, wherein the sensing element is a symmetrical vibrating ring and the sense electrodes surround the perimeter of the vibrating ring and are capacitively coupled to the vibrating ring.

4. The sensor according to claim 3, wherein the vibrating ring has four symmetrical quadrants, the plurality of sense electrodes comprises four sense electrodes, and a corresponding one of the sense electrodes is located in each of the four symmetrical quadrants of the vibrating ring.

5. The sensor according to claim 4, wherein in each sampling sequence the capacitive outputs from the sense electrodes in each of the four quadrants are sampled.

6. The sensor according to claim 4, wherein the differential readout means samples the capacitive outputs of the sense electrodes to produce a differential output from the difference in the capacitive outputs of a first and second of the sense electrodes, a differential output from the difference in the capacitive outputs of a third and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the first and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the third and second of the sense electrodes.

7. The sensor according to claim 1, wherein the differential readout means samples the capacitive outputs of the sense electrodes to produce a differential output from the difference in the capacitive outputs of a first and second of the sense electrodes, a differential output from the difference in the capacitive outputs of a third and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the first and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the third and second of the sense electrodes.

8. The sensor according to claim 1, wherein the sensor has an even number of the sense electrodes.

9. The sensor according to claim 1, wherein the sense electrodes of each pair of differential sense electrodes are diametrically opposite each other relative to the sensing element.

10. The sensor according to claim 1, wherein the sensor has an odd number of the sense electrodes.

11. A sensing method performed with the sensor of claim 1, the method comprising operating the differential readout means to:

perform the sampling sequence comprising at least two sampling cycles during which the differential readout means samples the capacitive outputs of the sense electrodes and produces at least two differential outputs based on the difference between the capacitive outputs within each pair of the differential sense electrodes;

calculate an average of the at least two differential outputs of the sampling sequence to produce an output of the differential readout means, and then

repeat the sampling sequence and calculation;

wherein the sampling sequence performed by the differential readout means comprises operating the connecting means to switch and choose different pairs of the differential sense electrodes at a sampling rate and at instances to achieve dynamically generated symmetry at the output of the differential readout means.

12. The sensing method according to claim 11, wherein the connecting means comprises switches individually coupled in series with each of the sense electrodes and operable to electrically separate the sense electrodes into the at least two pairs of differential sense electrodes by connecting and disconnecting the capacitive outputs of the sense electrodes to the differential readout means.

13. The sensing method according to claim 11, wherein the sensing element is a symmetrical vibrating ring and the sense electrodes surround the perimeter of the vibrating ring and are capacitively coupled to the vibrating ring.

14. The sensing method according to claim 13, wherein the vibrating ring has four symmetrical quadrants, the plurality of sense electrodes comprises four sense electrodes, and one of the sense electrodes is located in each of the four symmetrical quadrants of the vibrating ring.

15. The sensing method according to claim 14, wherein in each sampling sequence the capacitive outputs from sense electrodes in each of the four quadrants are sampled.

16. The sensing method according to claim 14, wherein the differential readout means samples the capacitive outputs of the sense electrodes to produce a differential output from the difference in the capacitive outputs of a first and second of the sense electrodes, a differential output from the difference in the capacitive outputs of a third and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the first and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the third and second of the sense electrodes.

17. The sensing method according to claim 11, wherein the differential readout means samples the capacitive outputs of the sense electrodes to produce a differential output from the difference in the capacitive outputs of a first and second of the sense electrodes, a differential output from the difference in the capacitive outputs of a third and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the first and fourth of the sense electrodes, a differential output from the difference in the capacitive outputs of the third and second of the sense electrodes.

18. The sensing method according to claim 11, wherein the sensor has an even number of the sense electrodes.

19. The sensing method according to claim 11, wherein each pair of differential sense electrodes are diametrically opposite each other relative to the sensing element.

20. The sensing method according to claim 11, wherein the sensor has an odd number of the sense electrodes.

21. A sensor comprising:

a sensing element having flexural modes that respond to an environmental input;

a plurality of sense electrodes capacitively coupled to the sensing element to generate a corresponding plurality of capacitive outputs that vary in response to motion of the sensing element, the sense electrodes being electrically separable into at least two pairs of differential sense electrodes, the differential sense electrodes of each pair detecting motion at nodes of a first flexural mode of the sensing element at different locations of the sensing element;

differential readout means for performing a sampling sequence comprising at least two sampling cycles during which the differential readout means samples the capacitive outputs of the sense electrodes and produces at least two differential outputs based on the difference between the capacitive outputs within each pair of the differential sense electrodes, calculating an average of the at least two differential outputs of the sampling sequence to produce an output of the differential readout means, and then repeating the sampling sequence and calculation; and

means for connecting to different pairs of the differential sense electrodes during each sampling cycle.