MEMS mass bias to track changes in bias conditions and reduce effects of flicker noise

Patent metadata

Field	Value
Publication number	US-9252707-B2
Application number	US-201213721642-A
Country	US
Kind code	B2
Filing date	Dec 20, 2012
Priority date	Dec 20, 2012
Publication date	Feb 2, 2016
Grant date	Feb 2, 2016

Abstract

A technique for tracking changes in bias conditions of a microelectromechanical system (MEMS) device includes applying an electrode bias signal to an electrode of the MEMS device. The technique includes applying a mass bias signal to a mass of the MEMS device suspended from a substrate of the MEMS device. The technique includes generating the mass bias signal based on a target mass-to-electrode bias signal level and a signal level of the electrode bias signal.

First claim

What is claimed is:

1. A method comprising:
applying an electrode bias signal to an electrode of a microelectromechanical system (MEMS) device;
applying a mass bias signal to a mass of the MEMS device suspended from a substrate of the MEMS device; and
generating the mass bias signal based on a target mass-to-electrode bias signal level and a signal level of the electrode bias signal,
wherein generating the mass bias signal comprises:
replicating the electrode bias signal to generate a replica electrode bias signal; and
boosting a signal level of the replica electrode bias signal by the target mass-to-electrode bias signal level to generate the mass bias signal.

2. The method, as recited in claim 1 ,
wherein
the replica electrode bias signal is provided to a node during a first time interval and
the node is boosted by the target mass-to-electrode bias signal level during a second time interval to generate the mass bias signal.

3. The method, as recited in claim 1 , further comprising:
generating a signal on the electrode based on the mass bias signal, the electrode bias signal, and displacement of the mass of the MEMS device.

4. The method, as recited in claim 1 , wherein the MEMS device is configured in an oscillator and the applying the mass bias signal inhibits change to a frequency of oscillation of the mass in response to changes in the electrode bias signal.

5. The method, as recited in claim 1 , wherein the MEMS device is configured as an accelerometer and the applying the mass bias signal inhibits phase noise in an output signal.

6. The method, as recited in claim 1 , further comprising:
generating a signal on the mass based on the mass bias signal, the electrode bias signal, and displacement of the mass of the MEMS device.

7. A method comprising:
applying an electrode bias signal to an electrode of a microelectromechanical system (MEMS) device;
applying a mass bias signal to a mass of the MEMS device suspended from a substrate of the MEMS device; and
generating the mass bias signal based on a target mass-to-electrode bias signal level and a signal level of the electrode bias signal, wherein generating the mass bias signal comprises:
buffering the electrode bias signal to generate a buffered electrode bias signal; and
boosting the buffered electrode bias signal by the target mass-to-electrode bias signal level to generate the mass bias signal.

8. The method, as recited in claim 7 , wherein generating the mass bias signal comprises:
providing the buffered electrode bias signal to a node during a first time interval
wherein the buffered electrode bias signal is boosted during a second time interval to generate the mass bias signal.

9. The method, as recited in claim 7 , further comprising:
generating a signal on the electrode based on the mass bias signal, the electrode bias signal, and displacement of the mass of the MEMS device.

10. The method, as recited in claim 7 , wherein the MEMS device is configured in an oscillator and the applying the mass bias signal inhibits change to a frequency of oscillation of the mass in response to changes in the electrode bias signal.

11. The method, as recited in claim 7 , further comprising:
generating a signal on the mass based on the mass bias signal, the electrode bias signal, and displacement of the mass of the MEMS device.

12. The method, as recited in claim 7 , wherein the MEMS device is configured as an accelerometer and the applying the mass bias signal inhibits phase noise in an output signal.

13. An apparatus comprising:
a microelectromechanical system (MEMS) device comprising:
a first electrode configured to receive an electrode bias signal; and
a mass suspended from a substrate, the mass being configured to receive a mass bias signal; and

a mass bias signal generator configured to generate the mass bias signal based on a target mass-to-electrode bias signal and a signal level of the electrode bias signal, the mass bias signal generator comprising a charge pump configured to receive a signal having the electrode bias signal level, the charge pump being configured to boost the electrode bias signal level by a target plate-to-electrode signal level to thereby generate the mass bias signal.

14. The apparatus, as recited in claim 13 , wherein the mass bias signal generator comprises:
a first node
wherein the charge pump is configured to provide the target plate-to-electrode signal to the first node during a first time interval,
wherein during a second time interval, the charge pump boosts a signal level on the first node by the electrode bias signal level and the charge pump provides the mass bias signal to the mass.

15. The apparatus, as recited in claim 13 , further comprising:
an electrode bias signal generator configured to generate the electrode bias signal and provide the electrode bias signal level to the mass bias signal generator.

16. The apparatus, as recited in claim 13 , wherein the mass bias signal generator comprises:
a buffer configured to generate a buffered version of the electrode bias signal having a same signal level as the electrode bias signal.

17. The apparatus, as recited in claim 13 , further comprising:
a replica electrode bias signal generator configured to generate a replica of the electrode bias signal and provide the replica to the mass bias signal generator.

18. The apparatus, as recited in claim 13 , further comprising:
a second electrode configured to receive the electrode bias signal; and
an amplifier coupled between the first and second electrodes, the amplifier being configured to generate the electrode bias signal.

19. The apparatus, as recited in claim 18 , further comprising:
a first resistor coupled between the first and second electrodes; and
a capacitor coupled to at least one of the first and second electrodes,
wherein the MEMS device is configured as part of an oscillator.

20. The apparatus, as recited in claim 13 , wherein the MEMS is configured to sense displacement of the mass with respect to the substrate and generate an indicator thereof based on the electrode bias signal.

Assignees

• Silicon Lab Inc

Inventors

• Seth Manu
• Caffee Aaron

Classifications

• H03B5/362 Primary

  the amplifier being a single transistor (H03B5/364 - H03B5/368 take precedence) · CPC title

• H03B5/366

  and comprising means for varying the frequency by a variable voltage or current · CPC title