Quadrature error compensation circuit for a MEMS gyroscope
MEMS gyroscopes are often integrated in modern electronic products for measuring orientation or rotation in those products. However, these MEMS gyroscopes are often inaccurate. The invention provides a compensation circuit to compensate for errors causing a distortion of a measured Coriolis force. The compensation circuit demodulates an input signal provided by the MEMS gyroscope to produce a quadrature signal indicative of the quadrature error and provides a compensation signal to the MEMS gyroscope for actively compensating the quadrature error.
1. A compensation circuit for a MEMS gyroscope configured to produce a gyroscope signal indicative of a rotation, the compensation circuit comprising:
a demodulator adapted to demodulate the gyroscope signal by using a clock signal to produce a quadrature signal indicative of a quadrature error of the MEMS gyroscope;
an adjustment unit adapted to adjust a DC compensation signal in dependence of the quadrature signal to produce an adjusted DC compensation signal, wherein the adjustment unit is configured to determine a sign of the quadrature signal, the sign being a positive sign or a negative sign, subtract an adjustment value from the DC compensation signal to produce the adjusted DC compensation signal when the quadrature signal is the positive sign, and add the adjustment value to the DC compensation signal to produce the adjusted DC compensation signal when the quadrature signal is the negative sign; and
an output unit adapted to output the adjusted DC compensation signal to the MEMS gyroscope to compensate for the quadrature error.
2. The compensation circuit according to claim 1 , wherein the clock signal is synchronous with a drive signal driving the MEMS gyroscope.
3. The compensation circuit according to claim 2 , wherein the clock signal has a phase, which is substantially 0 degrees −90 degrees or −180 degrees shifted relative to a phase of the drive signal.
4. The compensation circuit according to claim 1 , wherein the demodulator is an amplitude demodulator.
5. The compensation circuit according to claim 1 , wherein the adjustment unit comprises a low pass filter adapted to filter the quadrature signal.
6. The compensation circuit according to claim 1 , adapted to set the DC compensation signal to a predetermined value during initialization of the compensation circuit.
7. The compensation circuit according to claim 1 , wherein the adjustment unit utilizes only the sign of the quadrature signal to determine whether the adjustment value is to be subtracted from or added to the DC compensation signal to produce the adjusted DC compensation signal.
8. The compensation circuit according to claim 1 , wherein the adjustment unit comprises a digitizing unit adapted to digitize the DC compensation signal.
9. The compensation circuit according to claim 1 , further comprising a multiplexer adapted to couple multiple MEMS gyroscopes with the compensation circuit adapted to reduce respective quadrature errors.
10. The compensation circuit according to claim 1 , further comprising a demultiplexer adapted to provide multiple DC compensation signals to multiple MEMS gyroscopes adapted to reduce respective quadrature errors.
11. A system adapted to measure a Coriolis force comprising:
a first device adapted to measure a first Coriolis force comprising
a first MEMS gyroscope comprising a first mass adapted to vibrate along a first trajectory, the first MEMS gyroscope being configured to produce a first Coriolis signal indicative of the Coriolis force, wherein the first Coriolis signal comprises a quadrature error;
a first compensation circuit comprising:
a first demodulator adapted to demodulate the first Coriolis signal by using a first clock signal to produce a first quadrature signal indicative of a first quadrature error;
a first adjustment unit adapted to adjust a first DC compensation signal in dependence of the first quadrature signal to produce an adjusted first DC compensation signal, wherein the first adjustment unit is configured to determine a sign of the first quadrature signal, the sign being a positive sign or a negative sign, subtract an adjustment value from the first DC compensation signal to produce the adjusted first DC compensation signal when the first quadrature signal is the positive sign, and add the adjustment value to the first DC compensation signal to produce the adjusted first DC compensation signal when the first quadrature signal is the negative sign; and
a first output unit adapted to output the adjusted first DC compensation signal to the first MEMS gyroscope to compensate for the first quadrature error.
12. The system according to claim 11 , wherein the first clock signal is synchronous with a first drive signal driving the first MEMS gyroscope.
13. The system according to claim 12 , wherein the first clock signal has a phase, which is substantially 0 degrees −90 degrees or −180 degrees shifted relative to a phase of the first drive signal.
14. The system according to claim 11 , wherein the first demodulator is an amplitude demodulator.
15. The system according to claim 11 , wherein the first adjustment unit comprises a low pass filter adapted to filter the first quadrature signal.
16. The system according to claim 11 , adapted to set the first DC compensation signal to a predetermined value during initialization of the system.
17. The system according to claim 11 , adapted to measure a second Coriolis force comprising:
a second MEMS gyroscope comprising a second mass adapted to vibrate along a second trajectory, the second MEMS gyroscope being configured to produce a second Coriolis signal indicative of the Coriolis force, which second Coriolis signal may contain a quadrature error;
a second compensation circuit comprising:
a second demodulator adapted to demodulate the second Coriolis signal by using a second clock signal to produce a second quadrature signal indicative of a second quadrature error;
a second adjustment unit adapted to adjust a second DC compensation signal in dependence of the second quadrature signal to produce an adjusted second DC compensation signal, wherein the second adjustment unit is configured to determine the sign of the second quadrature signal, subtract the adjustment value from the second DC compensation signal to produce the adjusted second DC compensation signal when the second quadrature signal is the positive sign, and add the adjustment value to the second DC compensation signal to produce the adjusted second DC compensation signal when the second quadrature signal is the negative sign; and
a second output unit adapted to output the adjusted second DC compensation signal to the second MEMS gyroscope to compensate for the second quadrature error;
wherein the first and second trajectories are substantially on a same axis; and
wherein the first and second mass are adapted to vibrate with a 180 degrees phase difference.
18. A method for compensating a quadrature error of a MEMS gyroscope, the method comprising:
demodulating an input signal provided by the MEMS gyroscope by using a clock signal to produce a quadrature signal indicative of a quadrature error;
adjusting a DC compensation signal in dependence of the quadrature signal to produce an adjusted DC compensation signal, the adjusting operation comprising:
determining the sign of the quadrature signal;
subtracting the adjustment value from the DC compensation signal to produce the adjusted DC compensation signal when the quadrature signal is the positive sign; and
adding the adjustment value to the DC compensation signal to produce the adjusted DC compensation signal when the quadrature signal is the negative sign; and
providing the adjusted DC compensation signal to the MEMS gyroscope to compensate for a quadrature error of the MEMS gyroscope.
19. A method according to claim 18 , wherein the clock signal is synchronous with a drive signal driving the MEMS gyroscope.
20. The method according to claim 18 , wherein the subtracting and adding operations only utilize the sign of the quadrature signal to determine whether the adjustment value is to be subtracted from or added to the DC compensation signal to produce the adjusted DC compensation signal.