Controlling opening angle of a resonating mirror

Patent metadata

Field	Value
Publication number	US-9740002-B2
Application number	US-201514937155-A
Country	US
Kind code	B2
Filing date	Nov 10, 2015
Priority date	Nov 10, 2015
Publication date	Aug 22, 2017
Grant date	Aug 22, 2017

Abstract

A device described herein includes a movable MEMS mirror, with a driver configured to drive the movable MEMS mirror with a periodic signal such that the MEMS mirror oscillates at its resonance frequency. A feedback measuring circuit is configured to measure a signal flowing through the movable MEMS mirror. A processor is configured to sample the signal at first and second instants, generate an error signal as a function of a difference between the signal at the first instant in time and the signal at the second instant in time, and determine the opening angle of the movable MEMS mirror as a function of the error signal.

First claim

The invention claimed is:

1. A device for coupling to a movable MEMS mirror, comprising:
a driver circuit configured to drive the movable MEMS mirror with a periodic signal such that the movable MEMS mirror oscillates at its resonance frequency;
a feedback measuring circuit configured to measure a signal flowing through the movable MEMS mirror; and
a processing circuit configured to:
sample the signal at first and second instants in time;
generate an error signal as a function of a difference between the signal at the first instant in time and the signal at the second instant in time; and
determine an opening angle of the movable MEMS mirror as a function of the error signal.

2. The device of claim 1 , wherein the processing circuit is configured to generate the error signal as a function of a difference between a current of the signal at the first instant in time and a current of the signal at a second instant in time.

3. The device of claim 1 , wherein the processing circuit is further configured to control the opening angle of the movable MEMS mirror as a function of the error signal.

4. The device of claim 3 , wherein the processing circuit controls the opening angle of the movable MEMS mirror by causing the driver circuit to change the periodic signal so that the error signal equals a value associated with a desired opening angle.

5. The device of claim 4 , wherein the driver circuit changes the periodic signal by changing a voltage of the periodic signal.

6. The device of claim 4 , wherein an error signal of zero is associated with the desired opening angle.

7. The device of claim 1 , wherein the opening angle of the movable MEMS mirror is determined based upon a sum of the error signal and a first constant, divided by a second constant.

8. The device of claim 7 , wherein the first constant is between 450 and 500, and wherein the second constant is between 24 and 30.

9. The device of claim 8 , wherein the first constant is 476.8, and wherein the second constant is 26.6.

10. The device of claim 1 , wherein the movable MEMS mirror has a capacitance associated therewith; and wherein the current of the signal is a function of a voltage of the signal and a derivative of the capacitance associated with the movable MEMS mirror.

11. The device of claim 1 , wherein the feedback measuring circuit comprises a current sensing amplifier circuit having an input coupled to the movable MEMS mirror and an output coupled to the processing circuit.

12. The MEMS device of claim 1 , wherein the movable MEMS mirror comprises a stator and a rotor rotatably coupled thereto; and wherein the driver circuit is configured to drive either the rotor or the stator with the periodic signal.

13. The device of claim 11 , wherein the periodic signal has a varying voltage; and wherein the rotor moves with respect to the stator due to electrostatic forces therebetween.

14. The device of claim 11 , wherein the periodic signal has a varying current; and wherein the rotor moves with respect to the stator due to magnetic forces therebetween.

15. A method, comprising:
driving a movable MEMS mirror with a periodic signal such that the MEMS mirror oscillates;
measuring a signal flowing through the movable MEMS mirror as it oscillates;
sampling the signal at first and second instants in time;
generating an error signal as a function of a difference between a current of the signal at the first instant in time and a current of the signal at the second instant in time; and
determining the opening angle of the movable MEMS mirror as a function of the error signal.

16. The method of claim 15 , further comprising controlling the opening angle of the movable MEMS mirror as a function of the error signal.

17. The method of claim 16 , wherein controlling the opening angle of the movable MEMS mirror comprises changing the periodic signal so that the error signal equals a value associated with a desired opening angle.

18. The method of claim 17 , wherein an error signal of zero is associated with the desired opening angle.

19. A device for coupling to a movable MEMS mirror, comprising:
a driver circuit configured to drive the movable MEMS mirror with a periodic drive signal causing the movable MEMS mirror to oscillate;
a sensing circuit configured to sense a periodically varying current signal flowing through the movable MEMS mirror; and
a processing circuit configured to:
sample the periodically varying current signal at first and second instants in time;
determine an opening angle of the movable MEMS mirror from a comparison of the sampled periodically varying current signal at the first instant in time to the sampled periodically varying current signal at the second instant in time; and
adjust the periodic drive signal to cause a change in the determined opening angle to equal a reference opening angle.

20. The device of claim 19 , wherein the movable MEMS mirror comprises a stator and a rotor rotatably coupled thereto; and wherein the driver circuit is configured to drive either the rotor or the stator with the periodic drive signal.

21. The device of claim 19 , wherein the comparison produces an error signal and the adjustment of the periodic drive signal causes a magnitude of the error signal to move to a value associated with the reference opening angle.

22. The device of claim 21 , wherein the adjustment of the periodic drive signal is an adjustment of drive voltage level.

23. The device of claim 21 , wherein the value of zero for the error signal zero is associated with the reference opening angle.

Assignees

• St Microelectronics Int Nv
• St Microelectronics Ltd

Inventors

• Kolodkin Mark

Classifications

• G02B26/0841 Primary

  the reflecting element being moved or deformed by electrostatic means · CPC title

• G02B26/085

  the reflecting means being moved or deformed by electromagnetic means · CPC title