Robust inertial sensor self-test
An inertial sensor such as a MEMS accelerometer or gyroscope has a proof mass that is driven by a self-test signal, with the response of the proof mass to the self-test signal being used to determine whether the sensor is within specification. The self-test signal is provided as a non-periodic self-test pattern that does not correlate with noise such as environmental vibrations that are also experienced by the proof mass during the self-test procedure. The sense output signal corresponding to the proof mass is correlated with the non-periodic self-test signal, such that an output correlation value corresponds only to the proof mass response to the applied self-test signal.
1. A method for performing a self-test of an inertial sensor, comprising:
generating, by processing circuitry of the inertial sensor, a drive signal;
generating, by processing circuitry of the inertial sensor, a non-periodic self-test signal pattern;
providing the drive signal to one or more drive electrodes of the inertial sensor;
providing the non-periodic self-test signal pattern to one or more self-test drive electrodes of the inertial sensor;
providing, by the one or more drive electrodes, the drive signal to a proof mass of the inertial sensor, wherein the drive signal functions as a carrier signal for a vibration of the proof mass;
driving, by the one or more self-test drive electrodes, the proof mass of the inertial sensor in accordance with the non-periodic self-test signal pattern;
sensing, by one or more sense electrodes of the inertial sensor, the movement of the proof mass while the proof mass is driven by the one or more self-test drive electrodes;
generating, by the processing circuitry of the inertial sensor, a received signal based on the sensed movement of the proof mass;
removing the carrier signal from the received signal to generate a sense signal;
correlating, by the processing circuitry, the sense signal directly with the non-periodic self-test signal pattern; and
identifying, by the processing circuitry, an error based on the correlating.
2. The method of claim 1 , wherein the non-periodic self-test signal pattern comprises an anti-symmetric chirp pattern.
3. The method of claim 1 , wherein the non-periodic self-test signal pattern comprises a zero-average random pattern.
4. The method of claim 3 , wherein the zero-average random pattern comprises a plurality of signal amplitudes.
5. The method of claim 1 , further comprising delaying the non-periodic self-test signal pattern before correlating, by the processing circuitry, the sense signal with the non-periodic self-test signal pattern.
6. The method of claim 5 , wherein the delaying corresponds to a delay in time, and wherein the delay in time corresponds to a propagation time for the non-periodic self-test signal pattern from the self-test drive electrodes receiving the non-periodic self-test signal pattern to the processing circuitry generating the sense signal.
7. The method of claim 1 , wherein identifying the error based on the correlating comprises:
determining a correlation value based on correlating the sense signal with the non-periodic self-test signal pattern;
comparing the correlation value to a high threshold value; and
identifying an error when the correlation value exceeds the high threshold value.
8. The method of claim 1 , wherein identifying the error based on the correlating comprises:
determining a correlation value based on correlating the sense signal with the non-periodic self-test signal pattern;
comparing the correlation value to a low threshold value; and
identifying an error when the correlation value is below the low threshold value.
9. The method of claim 1 , wherein the non-periodic self-test signal pattern is selected to reduce a correlation with vibrational noise within a frequency range of interest.
10. The method of claim 8 , wherein the frequency range of interest begins at 200 Hz.
11. The method of claim 8 , wherein the frequency range of interest begins at 1 kHz.
12. The method of claim 1 , wherein the inertial sensor comprises an accelerometer.
13. The method of claim 1 , wherein the inertial sensor comprises a gyroscope.
14. The method of claim 1 , wherein the sense signal comprises the non-periodic self-test signal pattern and an environmental signal, and wherein the environmental signal is substantially eliminated based on the correlating.
15. The method of claim 13 , wherein the environmental signal is gravity or sinusoidal vibrations with a broad frequency range.
16. The method of claim 1 , wherein the non-periodic self-test signal pattern comprises a multi-valued amplitude pattern.
17. An inertial sensor with self-test capability, comprising: a first signal generator that generates a drive signal; a second signal generator that generates a non-periodic self-test signal pattern; one or more drive electrodes that receive the drive signal; one or more self-test drive electrodes that receive the non-periodic self-test signal pattern; a proof mass that is driven by the one or more self-test drive electrodes in accordance with the non-periodic self-test signal pattern and by the one or more drive electrodes in accordance with the drive signal, wherein the drive signal functions as a carrier signal for a vibration of the proof mass; one or more sense electrodes that sense movement of the proof mass; sense circuitry coupled to the proof mass, wherein the sense circuitry is configured to generate a received signal based on the sensed movement of the proof mass detected by the one or more sense electrodes; a frequency mixer configured to remove the carrier signal from the received signal to generate a sense signal; and processing circuitry configured to correlate the sense signal directly with the non-periodic self-test signal pattern and identify an error based on the correlation.
18. The inertial sensor of claim 17 , wherein the non-periodic self-test signal pattern comprises an anti-symmetric chirp pattern.
19. The inertial sensor of claim 17 , wherein the non-periodic self-test signal pattern comprises a zero-average random pattern.
20. The inertial sensor of claim 19 , wherein the zero-average random pattern comprises a plurality of signal amplitudes.
21. A method for performing a self-test of an inertial sensor, comprising:
generating, by processing circuitry of the inertial sensor, a drive signal;
generating, by processing circuitry of the inertial sensor, a non-periodic self-test signal pattern;
providing the drive signal to a proof mass of the inertial sensor, wherein the drive signal functions as a carrier signal for a vibration of the proof mass;
driving the proof mass in accordance with the non-periodic self-test signal pattern;
sensing, by one or more sense electrodes of the inertial sensor, the movement of the proof mass while the proof mass is driven by the one or more self-test drive electrodes;
generating, by the processing circuitry of the inertial sensor, a received signal based on the sensed movement of the proof mass, wherein the sensed movement is based on the driving of the proof mass and an environmental vibration;
removing the carrier signal from the received signal to generate a sense signal;
correlating, by the processing circuitry, the sense signal directly with the non-periodic self-test signal pattern, wherein an environmental vibration portion of the signal is not correlated with the non-periodic self-test signal pattern and a driven portion of the sense signal is correlated with the non-periodic self-test signal pattern; and
identifying, by the processing circuitry, an error based on the correlating.