Compensation of changes in MEMS capacitive transduction

Patent metadata

Field	Value
Publication number	US-9000833-B2
Application number	US-201313786686-A
Country	US
Kind code	B2
Filing date	Mar 6, 2013
Priority date	Mar 6, 2013
Publication date	Apr 7, 2015
Grant date	Apr 7, 2015

Abstract

A method for compensating for strain on a MEMS device includes generating a signal indicative of a strain on the MEMS device in a first mode of operating a system including the MEMS device. The method includes compensating for the strain in a second mode of operating the system based on the signal. Generating the signal may include comparing an indicator of a resonant frequency of the MEMS device to a predetermined resonant frequency of the MEMS device. Generating the signal may include comparing a first output of a strain-sensitive device to a second output of a strain-insensitive device and generating an indicator thereof. Generating the signal may include sensing a first capacitive transduction of strain-sensitive electrodes of the MEMS device in the first mode and generating the signal based thereon. The strain-sensitive electrodes of the MEMS device may be disabled in the second mode.

First claim

What is claimed is:

1. A method of compensating for strain on a microelectromechanical system (MEMS) device comprising: generating a signal indicative of a strain on the MEMS device in a first mode of operating a system including the MEMS device, the signal being based on a first capacitive transduction of strain-sensitive electrodes of the MEMS device sensed in the first mode of operating the system; disabling the strain-sensitive electrodes of the MEMS device in a second mode of operating the system and operating the system in the second mode using second electrodes of the MEMS device, the second electrodes being less sensitive to strain than the first electrodes; and compensating for the strain in a second mode of operating the system based on the signal.

2. The method, as recited in claim 1 , wherein generating the signal comprises:
comparing an indicator of a resonant frequency of the MEMS device to a predetermined resonant frequency of the MEMS device.

3. A method of compensating for strain on a microelectromechanical system (MEMS) device comprising: generating a signal indicative of a strain on the MEMS device in a first mode of operating a system including the MEMS device in a first mode of operating a system including the MEMS device, wherein generating the signal comprises: comparing an indicator of a resonant frequency of the MEMS device to a predetermined resonant frequency of the MEMS device; determining the predetermined resonant frequency prior to attaching a substrate including the MEMS device to a second substrate; and generating the indicator of the resonant frequency after attaching the substrate including the MEMS device to the second substrate; and compensating for the strain in a second mode of operating the system based on the signal.

4. The method, as recited in claim 1 , wherein generating the signal comprises:
comparing a first output of the MEMS device configured to use strain-sensitive electrodes to a second output of the MEMS device configured to use less strain-sensitive electrodes and generating an indicator thereof.

5. The method, as recited in claim 1 , wherein generating the signal comprises:
comparing a first capacitance of the MEMS device formed using a substrate to a second capacitance of a second MEMS device formed using the substrate and generating the signal based thereon.

6. The method, as recited in claim 1 , wherein the compensating comprises:
adjusting a bias voltage of the MEMS device based on the signal.

7. The method, as recited in claim 1 , wherein the compensating comprises:
adjusting a force feedback signal of a sensor including the MEMS device based on the signal.

8. The method, as recited in claim 1 , wherein the compensating comprises:
adjusting a divider value of a phase-locked loop or frequency-locked loop responsive to an output signal of an oscillator including the MEMS device based on the signal.

9. An integrated circuit comprising:
a microelectromechanical system (MEMS) device comprising: first structures configured to operate as first plates of capacitive electrodes in the first mode of operation and configured to be inoperable in the second mode of operation, a resonance mode of the MEMS device having a first strain sensitivity in the first mode of operation; and second structures configured to operate as the first plates of the capacitive electrodes coupled to the strain sensor in the second mode of operation and configured to be inoperable in the first mode of operation, the resonance mode of the MEMS device having a second strain-sensitivity in the second mode of operation, the first sensitivity being less than the second strain sensitivity; a strain sensor configured to generate a signal indicative of a strain on the MEMS device in a first mode of operation of the integrated circuit; and a control circuit configured to provide a strain-compensating signal based on the signal in a second mode of operation of the integrated circuit.

10. The integrated circuit, as recited in claim 9 , further comprising:
a bias generator configured to generate the strain-compensating signal based on a target bias voltage and a compensation signal based on the signal,
wherein the strain-compensating signal is a bias voltage of the MEMS device.

11. The integrated circuit, as recited in claim 9 , wherein the first structures are disposed between the second structures and an axis of the MEMS device and the first structures comprise first suspended capacitive fingers anchored proximate to an anchor of a mass of the MEMS device and the second structures comprise second suspended capacitive fingers anchored distal from the anchor of the mass of the MEMS device.

12. The integrated circuit, as recited in claim 11 , wherein the first capacitive fingers are interdigitated with third capacitive fingers of second plates of the capacitive electrodes and the second capacitive fingers are interdigitated with fourth capacitive fingers of the second plates of the capacitive electrodes, wherein third and fourth capacitive fingers form a portion of the body of the MEMS device disposed between respective first and second capacitive fingers.

13. The integrated circuit, as recited in claim 9 , wherein the MEMS device forms a portion of a sensor circuit and the strain-compensating signal is combined with a force feedback control signal.

14. The integrated circuit, as recited in claim 9 , further comprising:
signal processing logic configured to generate an output signal based on a resonant frequency of the MEMS device,
wherein the strain-compensating signal is provided to the signal processing logic to compensate the output signal for a change to a resonant frequency of the MEMS device based on the strain on the MEMS device.

15. The integrated circuit, as recited in claim 14 , wherein the signal processing logic comprises:
a phase-locked loop (PLL) configured to generate an output signal based on a phase difference between an output of the MEMS device, a feedback signal, and a divider value generated based on the signal.

16. The integrated circuit, as recited in claim 15 , wherein in the first mode the control circuit is configured to generate the signal based on an output of a voltage-controlled oscillator of the PLL and a target resonant frequency.

17. The integrated circuit, as recited in claim 15 , wherein in the second mode the control circuit is configured to generate the divider value based on the signal.

18. The integrated circuit, as recited in claim 9 , wherein the strain sensor comprises:
a storage device configured to receive a target resonant frequency of the MEMS device in a third mode,
wherein the strain sensor is configured to generate the signal based on the target resonant frequency in the first mode.

Assignees

• Silicon Lab Inc

Inventors

• Caffee Aaron
• Quevy Emmanuel P

Classifications

• H02N1/006 Primary

  of the gap-closing type (H02N1/004 takes precedence) · CPC title

• B81B7/0045

  for reducing stress inside of the package structure · CPC title

• B81B7/008 Primary

  MEMS characterised by an electronic circuit specially adapted for controlling or driving the same (B81B7/0087 takes precedence; arrangements for starting, regulating, braking, or otherwise controlling an actuator H02N; control arrangements or circuits for visual indicators G09G3/00) · CPC title

• G01P15/125

  by capacitive pick-up · CPC title

• H03L7/1976

  using a phase accumulator for controlling the counter or frequency divider · CPC title