Use of electronic attenuator for MEMS oscillator overdrive protection

Patent metadata

Field	Value
Publication number	US-8981860-B2
Application number	US-201213721630-A
Country	US
Kind code	B2
Filing date	Dec 20, 2012
Priority date	Dec 20, 2012
Publication date	Mar 17, 2015
Grant date	Mar 17, 2015

Abstract

An apparatus includes a microelectromechanical system (MEMS) device configured as part of an oscillator. The MEMS device includes a mass suspended from a substrate of the MEMS, a first electrode configured to provide a first signal based on a displacement of the mass, and a second electrode configured to receive a second signal based on the first signal. The apparatus includes an amplifier coupled to the first electrode and a first node. The amplifier is configured to generate an output signal, the output signal being based on the first signal and a first gain. The apparatus includes an attenuator configured to attenuate the output signal based on a second gain and provide as the second signal an attenuated version of the output signal.

First claim

What is claimed is:

1. An apparatus comprising:
a microelectromechanical system (MEMS) device configured as part of an oscillator comprising:
a mass suspended from a substrate of the MEMS;
a first electrode configured to provide a first signal based on a displacement of the mass; and
a second electrode configured to receive a second signal based on the first signal;

an amplifier coupled to the first electrode and a first node, the amplifier configured to generate an output signal, the output signal being based on the first signal and a first gain;
an attenuator configured to attenuate the output signal based on a second gain and provide as the second signal an attenuated version of the output signal; and
an automatic amplitude control module configured to generate a feedback signal based on a reference signal level and the second signal, wherein the amplifier adjusts the first gain based on the feedback signal.

2. An apparatus comprising:
a microelectromechanical system (MEMS) device configured as part of an oscillator comprising:
a mass suspended from a substrate of the MEMS;
a first electrode configured to provide a first signal based on a displacement of the mass; and
a second electrode configured to receive a second signal based on the first signal;

an amplifier coupled to the first electrode and a first node, the amplifier configured to generate an output signal, the output signal being based on the first signal and a first gain; and
an attenuator configured to attenuate the output signal based on a second gain and provide as the second signal an attenuated version of the output signal,
wherein the attenuator comprises a pulse-generator and the second signal is a pulsed signal having a same period as the first signal and a pulse width based on the first gain, the second signal having a duty-cycle substantially less than a duty cycle of the first signal.

3. The apparatus, as recited in claim 2 , further comprising:
an automatic amplitude control module configured to generate a feedback signal based on a reference signal level and the second signal, wherein the amplifier adjusts the first gain based on the feedback signal.

4. The apparatus, as recited in claim 1 , wherein the attenuator generates the second signal based on a reference signal level.

5. The apparatus, as recited in claim 3 , wherein a fundamental frequency of the second signal times the pulse width of the second signal is much less than one.

6. The apparatus, as recited in claim 1 , further comprising:
a buffer configured to convert the output signal to a digital signal.

7. The apparatus, as recited in claim 1 , further comprising:
a feedback resistor coupled between an output node of the amplifier and an input node of the amplifier.

8. The apparatus, as recited in claim 1 , wherein the first gain is based on a reference signal level.

9. The apparatus, as recited in claim 1 , wherein the second gain has a value between approximately one-half and approximately one-thousandth.

10. The apparatus, as recited in claim 1 , wherein the second gain is based on a power budget of the apparatus.

11. The apparatus, as recited in claim 1 , wherein a combined gain of the MEMS and the amplifier is approximately a reciprocal of the second gain.

12. A method comprising:
amplifying a first signal on a first electrode of a microelectromechanical system (MEMS) device configured as part of an oscillator to generate an output signal, the output signal being based on the first signal and a first gain;
attenuating the output signal based on a second gain to generate a second signal and providing the second signal to a second electrode of the MEMS device; and
adjusting the first gain based on a reference signal level and the second signal.

13. The method, as recited in claim 12 , wherein the attenuating comprises:
generating as the second signal, a pulse signal having a same period as the first signal and a pulse width based on the first gain, a duty-cycle of the second signal being substantially less than a duty cycle of the first signal.

14. The method, as recited in claim 12 , wherein the attenuating is further based on a reference signal level.

15. The method, as recited in claim 13 , wherein a fundamental frequency of the second signal times the pulse width of the second signal is much less than one.

16. The method, as recited in claim 12 , wherein the second gain has a value between approximately one-half and approximately one-thousandth.

17. The method, as recited in claim 12 , wherein a gain applied to the second signal in generating the output signal is approximately a reciprocal of the second gain.

18. An apparatus comprising:
a microelectromechanical system (MEMS) device configured as an oscillator;
means for amplifying a first signal on a first electrode of the MEMS device to generate an output signal;
means for attenuating the output signal to generate a second signal on a second electrode of the MEMS device; and
means for adjusting a gain of the means for amplifying in response to a reference signal level and the second signal.

19. The apparatus, as recited in claim 18 , wherein the means for attenuating comprises means for generating as the second signal, a pulse signal having a same period as the first signal and a pulse width based on the first gain, a duty-cycle of the second signal being substantially less than a duty cycle of the first signal.

Assignees

• Silicon Lab Inc

Inventors

• Caffee Aaron
• Seth Manu
• Drost Brian

Classifications

• H03B2200/001

  Hartley oscillator · CPC title

• H03B5/30 Primary

  with frequency-determining element being electromechanical resonator · CPC title

• B81B7/02

  containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] (B81B7/04 takes precedence) · CPC title