MEMS gyroscope self-test using a technique for deflection of the sensing mobile mass
A microelectromechanical system (MEMS) gyroscope sensor has a sensing mass and a quadrature error compensation control loop for applying a force to the sensing mass to cancel quadrature error. To detect fault, the quadrature error compensation control loop is opened and an additional force is applied to produce a physical displacement of the sensing mass. A quadrature error resulting from the physical displacement of the sensing mass in response to the applied additional force is sensed. The sensed quadrature error is compared to an expected value corresponding to the applied additional force and a fault alert is generated if the comparison is not satisfied.
1. A control circuit for a microelectromechanical system (MEMS) gyroscope sensor having a sensing mass, comprising:
a quadrature error compensation control loop for applying a cancelation force to the sensing mass to cancel quadrature error; and
a self-testing circuit comprising:
open loop circuitry configured to open the quadrature error compensation control loop and apply an additional force to produce a physical displacement of the sensing mass;
a sensing circuit configured to detect a quadrature error due to the physical displacement of the sensing mass in response to the applied additional force; and
a comparison circuit configured to compare the sensed quadrature error to an expected value corresponding to the applied additional force and generate a fault alert if the comparison is not satisfied.
2. The control circuit of claim 1 , wherein the detected quadrature error comprises a quadrature error signal having an in-phase component and wherein the comparison circuit operates to compare a magnitude of the in-phase component to a magnitude expected due to the physical displacement of the sensing mass, and wherein the fault alert is generated if the magnitudes are not substantially equal.
3. The control circuit of claim 1 , wherein the detected quadrature error comprises a quadrature error signal having a quadrature phase component, and wherein the comparison circuit operates to compare a magnitude of the quadrature-phase component to a magnitude expected due to the physical displacement of the sensing mass, and wherein the fault alert is generated if the magnitudes are not substantially equal.
4. The control circuit of claim 1 , wherein detected quadrature error comprises a quadrature error signal having an in-phase component and a quadrature phase component, and wherein the comparison circuit operates to compare magnitudes of the in-phase and quadrature-phase components, and wherein the fault alert is generated if the magnitudes are not substantially equal.
5. The control circuit of claim 1 , wherein said sensing circuit operates to sense movement of the sensing mass and generate a sensing signal, the sensing circuit including a demodulation circuit configured to demodulate the sensing signal in response to a reference clock phase.
6. The control circuit of claim 5 , wherein said MEMS gyroscope sensor further has a driving mass and said reference clock signal is derived from sensing oscillation of the driving mass.
7. The control circuit of claim 5 , wherein the quadrature error is detected from the demodulated sensing signal.
8. The control circuit of claim 5 , wherein the demodulation circuit demodulates the sensing signal to generate an in-phase component and a quadrature phase component for the quadrature error.
9. The control circuit of claim 8 , wherein the comparison circuit operates to compare a magnitude of the in-phase component to a magnitude expected due to the physical displacement of the sensing mass, and wherein the fault alert is generated if the magnitudes are not substantially equal.
10. The control circuit of claim 8 , wherein the comparison circuit operates to compare a magnitude of the quadrature-phase component to a magnitude expected due to the physical displacement of the sensing mass, and wherein the fault alert is generated if the magnitudes are not substantially equal.
11. The control circuit of claim 8 , wherein the comparison circuit operates to compare magnitudes of the in-phase and quadrature-phase components, and wherein the fault alert is generated if the magnitudes are not substantially equal.
12. The control circuit of claim 8 , wherein the reference clock phase has an in-phase component and a quadrature-phase component, and further comprising phase shifting circuitry configured to phase shift both the in-phase component and the quadrature-phase component of the reference clock phase so that both the in-phase component and quadrature phase component of the quadrature error have non-zero magnitudes.
13. The control circuit of claim 12 , wherein the comparing circuit operates to compare the non-zero magnitudes of the in-phase component and quadrature-phase component of the quadrature error, and the fault alert is generated if the non-zero magnitudes are not substantially equal.
14. The control circuit of claim 1 , wherein detected quadrature error comprises a quadrature error signal having an in-phase component, and further comprising a rate circuit configured to convert the in-phase component to a rate signal indicative of angular velocity, wherein the comparison circuit operates to compare a magnitude of the rate signal to a magnitude expected due to the physical displacement of the sensing mass, and the fault alert is generated if the magnitudes are not substantially equal.
15. The control circuit of claim 1 , wherein said open loop circuitry comprises:
an open loop control circuit responsive to assertion of a self-test signal to open the quadrature error compensation control loop;
a multiplexing circuit responsive to assertion of the self-test signal to apply the additional force with the cancelation force to displace the sensing mass.