Envelope detection circuit for detection of opening angle of a movable MEMS mirror

Patent metadata

Field	Value
Publication number	US-11226480-B2
Application number	US-202016897491-A
Country	US
Kind code	B2
Filing date	Jun 10, 2020
Priority date	Dec 12, 2016
Publication date	Jan 18, 2022
Grant date	Jan 18, 2022

Abstract

An electronic device includes an analog to digital converter receiving an analog mirror sense signal from an oscillating mirror and generating a digital mirror sense signal therefrom, and a digital signal processing block. The digital signal processing block cooperates with the analog to digital converter to take a first sample of the digital mirror sense signal at a first time where a derivative of capacitance of the digital mirror sense signal crosses zero, take a second sample of the digital mirror sense signal at a second time between a peak of the digital mirror sense signal and the first time, and take a third sample of the digital mirror sense signal at a third time after the digital mirror sense signal has reached a minimum. Control circuitry determines an opening angle of the oscillating mirror as a function of the first, second, and third samples.

First claim

The invention claimed is:

1. An electronic device, comprising:
an input configured to receive a mirror sense signal from an oscillating mirror; and
processing circuitry configured to:
determine an opening angle of the oscillating mirror as a function of a value of the mirror sense signal when a derivative of capacitance of the mirror sense signal crosses zero,
determine a value of the mirror sense signal at a time between when the derivative of capacitance of the mirror sense signal crosses zero and a peak of the mirror sense signal occurs, and
determine a value of the mirror sense signal after the mirror sense signal has reached a minimum.

2. The electronic device of claim 1 , wherein the processing circuitry is configured to determine the opening angle of the oscillating mirror by:
determining a raw opening angle measurement as a function of a value of the mirror sense signal when the derivative of capacitance of the mirror sense signal crosses zero, a value of the mirror sense signal at a time between when the derivative of capacitance of the mirror sense signal crosses zero and a peak of the mirror sense signal occurs, and a value of the mirror sense signal after the mirror sense signal has reached a minimum;
subtracting the raw opening angle measurement from a calibrated opening angle measurement so as to produce an opening angle error; and
determining the opening angle of the oscillating mirror as a function of the opening angle error.

3. The electronic device of claim 1 , wherein the processing circuitry is further configured to generate a control signal to act as a feedback signal for use in generating a driving signal for the oscillating mirror.

4. The electronic device of claim 1 , wherein the processing circuitry is further configured to generate a signal for stopping generation of a laser impinging on the oscillating mirror, as a function of a lack of sufficient change in the opening angle of the oscillating mirror over a given period of time.

5. An electronic device, comprising:
an analog to digital converter configured to receive an analog mirror sense signal from an oscillating mirror and to generate a digital mirror sense signal therefrom;
a digital signal processing block configured cooperate with the analog to digital converter to:
take a first sample of the digital mirror sense signal at a first time where a derivative of capacitance of the digital mirror sense signal crosses zero;
take a second sample of the digital mirror sense signal at a second time between a peak of the digital mirror sense signal and the first time; and
take a third sample of the digital mirror sense signal at a third time after the digital mirror sense signal has reached a minimum; and

control circuitry configured to determine an opening angle of the oscillating mirror as a function of the first, second, and third samples.

6. The electronic device of claim 5 , wherein the control circuitry is configured to determine the opening angle of the oscillating mirror by:
determining a raw opening angle measurement as a function of the first, second, and third samples;
subtracting the raw opening angle measurement from a calibrated opening angle measurement so as to produce an opening angle error, the calibrated opening angle measurement being a known opening angle error at a desired opening angle; and
determining the opening angle of the oscillating mirror as a function of the opening angle error.

7. The electronic device of claim 6 , wherein the raw opening angle measurement is calculated as:

RawOA
⁢

C
Measurement

=



s
0

-

s
zeroCross

s
1

-

s
zeroCross



where RawOAC Measurement is the raw opening angle measurement, where s zeroCross is the first sample, where s 0 is the second sample, and where s 1 is the third sample.

8. The electronic device of claim 5 , wherein the first time is a time where a derivative of a capacitance of the oscillating mirror with respect to time is zero.

9. The electronic device of claim 5 , wherein the digital signal processing block takes the second sample of the digital mirror sense signal at a second time between the first time and a time at which the digital mirror sense signal has reached a maximum.

10. The electronic device of claim 5 , wherein the digital signal processing block takes the second sample of the digital mirror sense signal at a second time between the first time and a time at which the digital mirror sense signal has reached a minimum.

11. The electronic device of claim 5 , wherein the digital signal processing block takes the third sample of the digital mirror sense signal at a third time after the first time and after the digital mirror sense signal has reached a minimum.

12. The electronic device of claim 5 , wherein the digital signal processing block takes the first, second, and third samples after a phase of the analog mirror sense signal has locked.

13. The electronic device of claim 5 , wherein the control circuitry is further configured to generate a control signal to act as a feedback signal for use in generating a driving signal for the oscillating mirror.

14. The electronic device of claim 5 , wherein the control circuitry is further configured to generate a signal for stopping generation of a laser impinging on the oscillating mirror, as a function of a lack of sufficient change in the opening angle of the oscillating mirror over a given period of time.

15. A method, comprising:
receiving an analog mirror sense signal from an oscillating mirror;
digitizing the analog mirror sense signal to thereby generate a digital mirror sense signal therefrom;
generating a first sample by sampling the digital mirror sense signal at a first time where a derivative of capacitance of the digital mirror sense signal crosses zero;
generating a second sample by sampling the digital mirror sense signal at a second time between a peak of the digital mirror sense signal and the first time;
generating a third sample by sampling the digital mirror sense signal at a third time after the digital mirror sense signal has reached a minimum; and
determining an opening angle of the oscillating mirror as a function of the first, second, and third samples.

16. The method of claim 15 , wherein the opening angle of the oscillating mirror is determined by:
determining a raw opening angle measurement as a function of the first, second, and third samples;
subtracting the raw opening angle measurement from a calibrated opening angle measurement so as to produce an opening angle error, the calibrated opening angle measurement being a known opening angle error at a desired opening angle; and
determining the opening angle of the oscillating mirror as a function of the opening angle error.

17. The method of

Assignees

• St Microelectronics Ltd

Inventors

• Haran Elik
• Duvdevany Offir
• Petrushevsky Naomi

Classifications

• G02B26/105 Primary

  with one or more pivoting mirrors or galvano-mirrors (G02B26/101 takes precedence) · CPC title

• G01R19/04

  Measuring peak values {or amplitude or envelope} of AC or of pulses · CPC title

• G02B26/0833

  the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD (G02B26/0825 takes precedence; micromechanical devices in general B81B) · CPC title

• H02P25/032

  Reciprocating, oscillating or vibrating motors · CPC title

• G02B26/085 Primary

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