PIEZOELECTRIC SENSOR DYNAMIC RANGE IMPROVEMENT

• US 20090241666A1
• Filed: 03/31/2008
• Published: 10/01/2009
• Est. Priority Date: 03/31/2008
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Wang, Li-Peng, Gerfers, Friedel
• Granted Patent: US 8,499,630 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• CPC Class Codes: G01P 15/09 by piezoelectric pick-up
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A MEMS piezoelectric sensor comprises a plurality of capacitors some of which may be used for sensing and others used for feedback. The capacitors may be switched to connect or disconnect selected capacitors from the sensor. Embodiments convert a two port sensor into a four port sensor without significant changes in hardware design and improve SNR and correct for offset and out-of-axis errors due to process mismatch and variations.

Claims

1. A micro electromechanical system (MEMS) sensor, comprising:

a frame;

a beam;

a proof mass; and

a plurality of arms connecting the frame to the proof mass, each arm comprising an inner capacitor between the proof mass and the beam and an outer capacitor between the beam and the frame; and

a plurality of switches, one connected to each of the capacitors for connecting or disconnecting selected capacitors.

2. The sensor as recited in claim 1 wherein half of the capacitors are used for outputting a sensor signal half of the capacitors are used for a feedback signal.

3. The sensor as recited in claim 1 further comprising a feedback loop comprising:

an analog sensor signal from the outer capacitors;

an analog to digital converter for converting the analog sensor signals into a digital sensor signal;

a decimator and gain circuit receiving the digital sensor signal and controlling the plurality of switches; and

a digital to analog converter for converting the digital sensor signal to an analog sensor signal which is fed back to the inner capacitors.

4. The sensor as recited in claim 3 further comprising:

a loop filter prior to the analog to digital converter.

5. The sensor as recited in claim 1 wherein the frame is generally square and the plurality of arms comprise one arm at each corner extending inward to the proof mass centered in the frame.

6. The sensor as recited in claim 5 wherein capacitors on one side of the proof mass are used to output a sense signal and capacitors on a left side of the proof mass are used for receive feedback.

7. The sensor as recited in claim 6 wherein the feedback comprises one of a positive reference voltage and a negative reference voltage.

8. A method comprising:

providing a frame;

providing a beam;

providing a plurality of arms connecting the frame to a proof mass, each arm comprising an inner capacitor between the proof mass and the beam and an outer capacitor between the beam and the frame; and

connecting and disconnecting selected capacitors based on a sensed signal.

9. The method as recited in claim 8 further comprising:

designating half of the capacitors as sensor capacitors to output a sensor signal and designating half of the capacitors as feedback capacitors to be used for a feedback signal.

10. The method as recited in claim 8 further comprising:

dividing a single sensing period into to halves wherein the capacitors are used to output a sense signal during a first half and the capacitors are used for feedback in a second half.

11. The method as recited in claim 8 further comprising:

determining a mismatch term Δ

C for the capacitors;

adding the mismatch term Δ

C in a first sampling instant; and

subtracting the mismatch term Δ

C in a next sampling instant.

12. The method as recited in claim 8 further comprising:

converting an analog sensor signal from the sensor capacitors to a digital sensor signal;

supplying the digital sensor signal to a decimator and gain circuit to control the plurality of switches for connecting an disconnecting selected ones of the capacitors; and

converting the digital sensor signal to an analog signal to be fed back to the feedback capacitors.

13. The method as recited in claim 12 wherein the inner capacitors are the feedback capacitors and the outer capacitors are the sensor capacitors.

14. The method as recited in claim 13 further comprising:

filtering the sensor signal prior to digital conversion.

15. The method as recited in claim 8 wherein the frame is generally square and the plurality of arms comprise one arm at each corner extending inward to the proof mass centered in the frame.

16. The method as recited in claim 15 wherein capacitors on one side of the proof mass are used to output a sense signal and capacitors on a left side of the proof mass are used for receive feedback.

17. The method as recited in claim 16 wherein the feedback comprises one of a positive reference voltage and a negative reference voltage.