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

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 claim 16 , 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.

18. The method of claim 15 , wherein the first time is a time where a derivative of a capacitance of the oscillating mirror with respect to time is zero.

19. The method of claim 15 , wherein the second sample of the digital mirror sense signal is sampled at a second time between the first time and a time at which digital mirror sense signal has reached a maximum.

20. The method of claim 15 , wherein the second sample of the digital mirror sense signal is sampled at a second time between the first time and a time at which the digital mirror sense signal has reached a minimum.

21. The method of claim 15 , wherein the third sample of the digital mirror sense signal is sampled at a third time after the first time and after the digital mirror sense signal has reached a minimum.

22. The method of claim 15 , wherein the first, second, and third samples are sampled after a phase of the analog mirror sense signal has locked.

23. The method of claim 15 , further comprising generating a control signal to act as a feedback signal for use in generating a driving signal for the oscillating mirror.

24. The method of claim 15 , further comprising generating 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.

25. 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;

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 after 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;

determining a raw opening angle of the oscillating mirror 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; and

determining an opening angle of the oscillating mirror as a function of the opening angle error.

26. The method of claim 25 , wherein the first time is a time where a derivative of a capacitance of the oscillating mirror with respect to time is zero.

27. The method of claim 25 , wherein the second sample of the digital mirror sense signal is sampled at a second time between the first time and a time at which digital mirror sense signal has reached a maximum.

28. The method of claim 25 , wherein the second sample of the digital mirror sense signal is sampled at a second time between the first time and a time at which the digital mirror sense signal has reached a minimum.

29. The method of claim 25 , wherein the third sample of the digital mirror sense signal is sampled at a third time after the first time and after the digital mirror sense signal has reached a minimum.

30. The method of claim 25 , wherein the first, second, and third samples are sampled after a phase of the analog mirror sense signal has locked.

31. 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; and

control circuitry configured to:

determine a raw opening angle measurement as a function of the digital mirror sense signal;

subtract 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

determine an opening angle of the oscillating mirror as a function of the opening angle error.

32. The electronic device of claim 31 , 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.

33. The electronic device of claim 31 , 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.