Microelectromechanical device with position control driving and method for controlling a microelectromechanical device
A MEMS gyroscope includes: a microstructure having a fixed structure, a driving mass, movable with respect to the fixed structure according to a driving axis, and a sensing mass, mechanically coupled to the driving mass so as to be drawn in motion according to the driving axis and movable with respect to the driving mass according to a sensing axis, in response to rotations of the microstructure; and a driving device, for keeping the driving mass in oscillation with a driving frequency. The driving device includes a discrete-time sensing interface, for detecting a position of the driving mass with respect to the driving axis and a control stage for controlling the driving frequency on the basis of the position of the driving mass.
1. A microelectromechanical device comprising:
a microstructure including a fixed structure and a driving mass movable with respect to the fixed structure with a first degree of freedom according to a driving axis; and
a sensing device forming a microelectromechanical loop with the microstructure, the microelectromechanical loop being configured to keep the driving mass in oscillation according to the driving axis at a driving frequency; wherein the sensing device comprises:
a discrete-time sensing interface coupled to the microstructure and configured to sense a discrete-time position of the driving mass with respect to the driving axis, the sensing interface including a discrete-time charge amplifier configured to sense the discrete-time position of the driving mass and provide a discrete-time detection signal that indicates the discrete-time position of the driving mass; and
a controller configured to control an oscillation amplitude of the microelectromechanical loop based on the discrete-time detection signal that indicates the discrete-time position of the driving mass.
2. A device according to claim 1 , wherein the discrete-time charge amplifier is a discrete-time fully-differential charge amplifier.
3. A device according to claim 2 , wherein the microstructure includes feedback sensing terminals capacitively coupled to the driving mass and the charge amplifier has inputs respectively coupled to the feedback sensing terminals.
4. A device according to claim 1 , wherein the charge amplifier comprises:
a fully-differential operational amplifier having first and second inputs and first and second outputs;
a first amplification capacitor coupled between the first input and the first output of the operational amplifier; and
a second amplification capacitor coupled between the second input and the second output of the operational amplifier.
5. A device according to claim 4 , wherein the sensing interface comprises a correlated double-sampling (CDS) stage coupled to the first and second outputs of the operational amplifier.
6. A device according to claim 5 , wherein the CDS stage comprises;
a first CDS capacitor having a first terminal, coupled to the first output of the operational amplifier, and a second terminal;
a second CDS capacitor having a first terminal, coupled to the second output of the operational amplifier, and a second terminal;
a first CDS switch configured to selectively couple the second terminal of the first CDS capacitor to a reference line configured to be set at a reference voltage; and
a second CDS switch configured to selectively couple the second terminal of the second CDS capacitor to the reference line.
7. A device according to claim 6 , wherein the CDS switches are configured to be controlled so as to be closed in an offset sampling step and open in a sensing step of a correlated double sampling cycle.
8. A device according to claim 7 , wherein the CDS stage comprises a reset switch coupled between the first and second outputs of the operational amplifier and configured to be closed in a reset step and open in the offset sampling step and in the sensing step.
9. A device according to claim 1 , wherein the controller comprises a phase shift module cascaded to the charge amplifier and configured to receive the discrete-time detection signal and produce a continuous-time phase-shifted detection signal having a phase shift in a range of 90°±40°.
10. A device according to claim 9 , wherein the controller comprises a low-pass filter arranged downstream of the phase shift module, having a passband that includes the driving frequency, and configured to reduce from the continuous-time phase-shifted detection signal undesired signal components at least 30 dB.
11. A device according to claim 10 , wherein the controller comprises:
a variable gain amplifier configured to produce a continuous-time driving signal based on the continuous-time phase-shifted detection signal and drive the driving mass with the continuous-time driving signal; and
a control device configured to control a gain of the variable gain amplifier so as to maintain oscillation conditions of the microelectromechanical loop.
12. A method, comprising:
controlling a microelectromechanical device provided with a microstructure that includes a fixed structure, and a driving mass movable with respect to the fixed structure with a first degree of freedom according to a driving axis, the controlling including:
discrete-time sensing a discrete-time position of the driving mass with respect to the driving axis, the discrete-time sensing including producing a discrete-time detection signal that indicates the discrete-time position of the driving mass;
converting the discrete-time detection signal to a continuous-time detection signal; and
controlling an oscillation amplitude of the driving mass based on the continuous-time detection signal.
13. A method according to claim 12 , wherein the sensing comprises sensing using a discrete-time fully-differential charge amplifier that produces the discrete-time detection signal.
14. A method according to claim 12 , comprising sensing displacements of a sensing mass that is coupled to the driving mass.
15. A method according to claim 14 , comprising:
detecting an oscillation phase of a microelectromechanical loop that includes the driving mass;
generating a reading signal based on the detected oscillation phase, the reading signal having a frequency that is a multiple of the driving frequency, and
transmitting the reading signal to the driving mass.
16. A system comprising:
a control unit; and
a microelectromechanical device coupled to the control unit and configured to be controlled by the control unit, the device including:
a microstructure including a fixed structure and a driving mass movable with respect to the fixed structure with a first degree of freedom according to a driving axis; and
a sensing device forming a microelectromechanical loop with the microstructure, the microelectromechanical loop being configured to keep the driving mass in oscillation according to the driving axis at a driving frequency; wherein the sensing device comprises:
a discrete-time sensing interface coupled to the microstructure and configured to sense a discrete-time position of the driving mass with respect to the driving axis, the sensing interface including a discrete-time charge amplifier configured to sense the discrete-time position and provide a discrete-time detection signal that indicates the discrete-time position of the driving mass; and
a controller configured to control an oscillation amplitude of the microelectromechanical loop based on the discrete-time detection signal that indicates the discrete-time position of the driving mass.
17. A system according to claim 16 , wherein the charge amplifier comprises:
a fully-differential operational amplifier having first and second inputs and first and second outputs;
a first amplification capacitor coupled between the first input and the first output of the operational amplifier; and
a second amplification capacitor coupled between the second input and the second output of the operational amplifier.
18. A system according to claim 17 , wherein the sensing interface comprises a correlated double-sampling (CDS) stage coupled to the first and second outputs of the operational amplifier.
19. A system according to claim 18 , wherein the CDS stage comprises;
a first CDS capacitor having a first terminal, coupled to the first output of the operational amplifier, and a second terminal;
a second CDS capacitor having a first terminal, coupled to the second output of the operational amplifier, and a second terminal;
a first CDS switch configured to selectively couple the second terminal of the first CDS capacitor to a reference line configured to be set at a reference voltage; and
a second CDS switch configured to selectively couple the second terminal of the second CDS capacitor to the reference line.
20. A system according to claim 19 , wherein the CDS stage comprises a reset switch coupled between the first and second outputs of the operational amplifier and configured to be closed in a reset step and open in an offset sampling step and in a sensing step.
21. A system according to claim 16 , wherein the controller comprises a phase shift module cascaded to the charge amplifier and configured to receive the discrete-time detection signal and produce a continuous-time phase-shifted detection signal having a phase shift in a range of 90°±40°.
22. A system according to claim 16 , wherein the controller comprises:
a variable gain amplifier configured to produce a continuous-time driving signal based on the continuous-time phase-shifted detection signal and drive the driving mass with the continuous-time driving signal; and
a control device configured to control a gain of the variable gain amplifier so as to maintain oscillation conditions of the microelectromechanical loop.
23. A sensing device comprising:
a discrete-time sensing interface configured to sense a discrete-time position of a driving mass with respect to a driving axis and produce a discrete-time detection signal that indicates the discrete-time position of the driving mass, the driving mass being part of a microstructure that includes a fixed structure, and the driving mass is movable with respect to the fixed structure with a first degree of freedom according to a driving axis;
a converter configured to convert the discrete-time detection signal to a continuous-time detection signal; and
a driving amplifier coupled to the converter and configured to control an oscillation amplitude of the driving mass based on the continuous-time detection signal.
24. A sensing device according to claim 23 , wherein the sensing interface comprises a discrete-time fully-differential charge amplifier configured to produce the discrete-time detection signal.
25. A sensing device according to claim 24 , wherein the charge amplifier includes a fully-differential operational amplifier that includes:
first and second inputs and first and second outputs,
a first amplification capacitor coupled between the first input and the first output of the operational amplifier; and
a second amplification capacitor coupled between the second input and the second output of the operational amplifier.
26. A sensing device according to claim 25 , wherein the sensing interface comprises a correlated double-sampling (CDS) stage coupled to the first and second outputs of the operational amplifier, the CDS stage including:
a first CDS capacitor having a first terminal, coupled to the first output of the operational amplifier, and a second terminal;
a second CDS capacitor having a first terminal, coupled to the second output of the operational amplifier, and a second terminal;
a first CDS switch configured to selectively couple the second terminal of the first CDS capacitor to a reference line configured to be set at a reference voltage; and
a second CDS switch configured to selectively couple the second terminal of the second CDS capacitor to the reference line.
27. A sensing device according to claim 26 , wherein the CDS switches are configured to be controlled so as to be closed in an offset sampling step and open in a sensing step of a correlated double sampling cycle.
28. A sensing device according to claim 27 , wherein the CDS stage comprises a reset switch coupled between the first and second outputs of the operational amplifier and configured to be closed in a reset step and open in the offset sampling step and in the sensing step.
29. A sensing device according to claim 24 , wherein the converter includes a phase shift module coupled between the sensing interface and the driving amplifier and configured to convert the discrete-time detection signal to a continuous-time detection signal and introduce a phase shift in a range of 90°±40°.
30. A sensing device according to claim 24 , further comprising a low-pass filter coupled between the sensing interface and the driving amplifier, having a passband that includes a driving frequency, and configured to reduce undesired signal components at least 30 dB.
31. A sensing device according to claim 24 , wherein the driving amplifier is a variable gain amplifier, the sensing device further comprising a control device configured to control a gain of the variable gain amplifier so as to maintain oscillation conditions of the driving mass.