Vernier scan architecture for self-mixing interferometry phase measurements
A method of estimating a velocity of an object using an SMI sensor. The method includes driving a light emitter of the SMI sensor with a chirped waveform. The chirped waveform includes a first chirp and a second chirp separated by a first time interval, and a third chirp separated from the second chirp by a second time interval. The method also includes deriving a frequency-based velocity from an output of the SMI sensor; generating a first comb of possible velocities in response to analyzing an output of the SMI sensor generated in response to the first chirp and the second chirp; generating a second comb of possible velocities in response to analyzing an output of the SMI sensor generated in response to the second chirp and the third chirp; and determining a velocity of the object using the first comb, the second comb, and the frequency-based velocity.
1. A method of estimating a velocity of an object using a self-mixing interferometry (SMI) sensor including a light emitter, comprising:
driving the light emitter with a waveform including a series of chirps, the series of chirps including,
a first chirp and a second chirp separated by a first time interval; and
a third chirp separated from the second chirp by a second time interval different from the first time interval;
deriving a frequency-based velocity from an output of the SMI sensor;
generating a first comb of possible velocities in response to analyzing an output of the SMI sensor generated in response to the first chirp and the second chirp;
generating a second comb of possible velocities in response to analyzing an output of the SMI sensor generated in response to the second chirp and the third chirp; and
determining the velocity of the object using the first comb of possible velocities, the second comb of possible velocities, and the frequency-based velocity.
2. The method of claim 1 , wherein determining the velocity of the object using the first comb of possible velocities, the second comb of possible velocities, and the frequency-based velocity, comprises:
identifying a third comb of possible velocities consisting of possible velocities appearing in both the first comb of possible velocities and the second comb of possible velocities; and
identifying a possible velocity, within the third comb of possible velocities, within a predetermined range of the frequency-based velocity.
3. The method of claim 1 , further comprising determining a first possible velocity in the first comb of possible velocities and a second possible velocity in the second comb of possible velocities are attributable to a possible velocity appearing in both the first comb of possible velocities and the second comb of possible velocities when the first possible velocity and the second possible velocity are within a velocity margin of error.
4. The method of claim 1 , wherein the first chirp, the second chirp, and the third chirp are defined by one of rising edges of the waveform or falling edges of the waveform.
5. The method of claim 1 , wherein:
the first chirp, the second chirp, and the third chirp are defined by rising edges of the waveform;
the series of chirps further includes,
a fourth chirp and a fifth chirp separated by the first time interval; and
a sixth chirp separated from the fifth chirp by the second time interval; and
the method further comprises,
generating a third comb of possible velocities in response to analyzing an output of the SMI sensor generated in response to the fourth chirp and the fifth chirp;
generating a fourth comb of possible velocities in response to analyzing an output of the SMI sensor generated in response to the fifth chirp and the sixth chirp; and
further determining the velocity of the object using the third comb of possible velocities and the fourth comb of possible velocities.
6. The method of claim 5 , wherein determining the velocity of the object using the first comb of possible velocities, the second comb of possible velocities, the third comb of velocity possibilities, the fourth comb of velocity possibilities, and the frequency-based velocity, comprises:
identifying a fifth comb of possible velocities consisting of possible velocities appearing in both the first comb of possible velocities and the second comb of possible velocities;
identifying a first possible velocity, within the fifth comb of possible velocities, that is within a predetermined range of the frequency-based velocity;
identifying a sixth comb of possible velocities consisting of possible velocities appearing in both the third comb of possible velocities and the fourth comb of possible velocities;
identifying a second possible velocity, within the sixth comb of possible velocities, that is within the predetermined range of the frequency-based velocity; and
determining the velocity of the object using the first possible velocity and the second possible velocity.
7. The method of claim 1 , further comprising:
deriving the frequency-based velocity of the object from a portion of the output of the SMI sensor that includes a response to a DC portion of the waveform.
8. An electronic device, comprising:
a housing;
a self-mixing interferometry (SMI) sensor mounted to the housing and having a light emitter configured to emit a beam of light from a resonant cavity of the light emitter, receive a returned portion of the beam of light into the resonant cavity, and produce an SMI signal indicative of a mixing of light within the resonant cavity;
a drive circuit operable to drive the light emitter with a chirped waveform; and
a processor configured to,
derive a frequency-based velocity of an object from the SMI signal;
use first portions of the SMI signal containing a response to a first pair of chirps in the chirped waveform, the first pair of chirps separated by a first time interval, to measure a first phase difference between the chirps and generate a first comb of possible velocities of the object;
use second portions of the SMI signal containing a response to a second pair of chirps in the chirped waveform, the second pair of chirps separated by a second time interval, to measure a second phase difference between the chirps and generate a second comb of possible velocities of the object; and
determine a velocity of the object using the first comb of possible velocities, the second comb of possible velocities, and the frequency-based velocity.
9. The electronic device of claim 8 , wherein determining the velocity of the object using the first comb of possible velocities, the second comb of possible velocities, and the frequency-based velocity, comprises:
identifying a third comb of possible velocities consisting of possible velocities appearing in both the first comb of possible velocities and the second comb of possible velocities; and
identifying a possible velocity, within the third comb of possible velocities, within a predetermined range of the frequency-based velocity.
10. The electronic device of claim 9 , wherein the processor is configured to determine a first possible velocity in the first comb of possible velocities and a second possible velocity in the second comb of possible velocities are attributable to a possible velocity appearing in both the first comb of possible velocities and the second comb of possible velocities when the first possible velocity and the second possible velocity are within a velocity margin of error.
11. The electronic device of claim 8 , wherein both the first pair of chirps and the second pair of chirps are defined by one of rising edges of the chirped waveform or falling edges of the chirped waveform.
12. The electronic device of claim 8 , wherein:
both the first pair of chirps and the second pair of chirps are defined by rising edges of the chirped waveform; and
the processor is configured to,
use third portions of the SMI signal containing a response to a third pair of chirps in the chirped waveform, the third pair of chirps defined by falling edges of the chirped waveform, to measure a third phase difference between the chirps and generate a third comb of possible velocities of the object; and
further determine the velocity of the object using the third comb of possible velocities.
13. The electronic device of claim 8 , wherein:
both the first pair of chirps and the second pair of chirps are rising edges of the chirped waveform;
a third pair of chirps and a fourth pair of chirps in the chirped waveform are falling edges of the chirped waveform and
the processor is configured to,
use third portions of the SMI signal containing a response to a third pair of chirps, the third pair of chirps separated by the first time interval, to measure a third phase difference between the chirps and generate a third comb of possible velocities of the object;
use fourth portions of the SMI signal containing a response to the fourth pair of chirps, the fourth pair of chirps separated by the second time interval, to measure a fourth phase difference between the chirps and generate a fourth comb of possible velocities of the object; and
further determine the velocity of the object using the third comb of possible velocities and the fourth comb of possible velocities.
14. The electronic device of claim 13 , wherein determining the velocity of the object using the first comb of possible velocities, the second comb of possible velocities, the third comb of velocity possibilities, the fourth comb of velocity possibilities, and the frequency-based velocity, comprises:
identifying a fifth comb of possible velocities consisting of possible velocities appearing in both the first comb of possible velocities and the second comb of possible velocities;
identifying a first possible velocity, within the fifth comb of possible velocities, within a predetermined range of the frequency-based velocity;
identifying a sixth comb of possible velocities consisting of possible velocities appearing in both the third comb of possible velocities and the fourth comb of possible velocities;
identifying a second possible velocity, within the sixth comb of possible velocities, within the predetermined range of the frequency-based velocity; and
determining the velocity of the object using the first possible velocity and the second possible velocity.
15. The electronic device of claim 8 , wherein the chirped waveform comprises a set of triangular bursts.
16. The electronic device of claim 15 , wherein:
the chirped waveform comprises a first triangular burst, a second triangular burst, and a third triangular burst;
the first time interval is defined between corresponding portions of the first triangular burst and the second triangular burst; and
the second time interval is defined between corresponding portions of the second triangular burst and the third triangular burst.
17. The electronic device of claim 8 , wherein the processor derives the frequency-based velocity of the object from a portion of the SMI signal that includes a response to a DC portion of the chirped waveform.
18. The electronic device of claim 8 , further comprising:
a crown attached to the housing; wherein,
the SMI sensor is positioned to emit light toward or adjacent the crown; and
the processor is configured to change a state of the electronic device in response to an amplitude and a direction of the velocity of the object.
19. The electronic device of claim 8 , further comprising:
a display viewable through a surface of the housing; wherein,
the processor is configured to scroll content displayed on the display in response to an amplitude and a direction of the velocity of the object.
20. The electronic device of claim 8 , wherein:
the housing is an earbud housing;
the object is a fingertip;
the electronic device comprises a speaker mounted to the housing; and
the processor is configured to adjust a volume of the speaker in proportion to an amplitude and a direction of the velocity of the object.