Demodulation phase calibration using external input

1. A method for determining a phase error for a micro-electromechanical system (MEMS) device, comprising:

receiving a first signal from the MEMS device, wherein the first signal comprises an in-phase component and a quadrature component;

applying an external signal to the MEMS device, wherein the phase of the external signal corresponds to the phase of the quadrature component;

receiving a second signal from the MEMS device, wherein the second signal is generated by the MEMS device based on the external signal, and wherein the second signal comprises a modified in-phase component and a modified quadrature component; and

determining the phase error for the MEMS device based on the modified in-phase component and the modified quadrature component.

2. The method of claim 1 , wherein determining the phase error is based on (1) a change in amplitude between the in-phase component and the modified in-phase component and (2) a change in amplitude between the quadrature component and the modified quadrature component.

3. The method of claim 2 , wherein determining the phase error further comprises determining an arctangent of the change in quadrature components and the change in in-phase components.

4. The method of claim 2 , further comprising:

identifying the in-phase component from the first signal;

identifying the quadrature component from the first signal;

identifying the modified in-phase component from the second signal; and

identifying the modified quadrature component from the second signal.

5. The method of claim 1 , wherein applying the external signal comprises generating an AC signal and providing the AC signal as a drive signal to the MEMS device.

6. The method of claim 5 , wherein the phase of the AC signal corresponds to the phase of the quadrature component.

7. The method of claim 5 , wherein generating the AC signal comprises generating a drive signal and modifying the phase of the drive signal based on a calibration factor.

8. The method of claim 1 , wherein applying the external signal to the MEMS device comprises applying a DC signal to one or more DC quadrature tuning electrodes of the MEMS device.

9. The method of claim 8 , wherein the MEMS device comprises a proof mass, and wherein the DC quadrature tuning electrodes are located on a substrate that is parallel to the proof mass.

10. The method of claim 1 , further comprising correcting a demodulation phase angle based on the phase error.

11. The method of claim 1 , further comprising:

determining a temperature of the MEMS device; and

associating the temperature with the phase error.

12. The method of claim 1 , further comprising modifying a phase of a drive signal of the MEMS device based on the phase error.

13. The method of claim 1 , further comprising determining that a force sensed by the MEMS device is less than a threshold, wherein the external signal is applied only when the force is less than the threshold.

14. The method of claim 1 , wherein the external signal is applied periodically.

15. The method of claim 1 , wherein the external signal is applied in response to a signal generated by processing circuitry of the MEMS device.

16. The method of claim 1 , wherein the MEMS device comprises a MEMS gyroscope.

17. The method of claim 1 , wherein applying the external signal comprises applying an electrostatic force or applying a piezoelectric force.

18. The method of claim 1 , wherein the external signal comprises a sine wave or a square wave.

19. The method of claim 1 , wherein the external signal comprises a periodic signal, and wherein the frequency of the periodic signal comprises an integer multiple of a drive frequency of the MEMS device.

20. A micro-electromechanical system (MEMS) device, comprising:

a suspended spring-mass system;

a sense system, wherein the sense system receives a first signal based on movement of the suspended spring-mass system, wherein the first signal comprises an in-phase component and a quadrature component;

a drive system, wherein the drive system applies an external signal to the MEMS device, wherein the phase of the external signal corresponds to the phase of the quadrature component, wherein the sense system receives a second signal generated by the suspended spring-mass system based on the external signal, and wherein the second signal comprises a modified in-phase component and a modified quadrature component; and

processing circuitry configured to determine a phase error for the MEMS device based on the modified in-phase component and the modified quadrature component.

21. A device comprising:

a sensor device configured to generate a first signal and a second signal, wherein the first signal comprises an in-phase component and a quadrature component, wherein the second signal is based on an external signal applied to the sensor device and has a phase that corresponds to the phase of the quadrature component, and wherein the second signal generated by a suspended spring-mass system comprises a modified in-phase component and a modified quadrature component; and

a processing unit configured to determine a phase error for the sensor device based on the modified in-phase component and the modified quadrature component.