READING CIRCUIT FOR A MULTI-AXIS MEMS GYROSCOPE HAVING DETECTION DIRECTIONS INCLINED WITH RESPECT TO THE REFERENCE AXES, AND CORRESPONDING MULTI-AXIS MEMS GYROSCOPE

• US 20100132463A1
• Filed: 11/25/2009
• Published: 06/03/2010
• Est. Priority Date: 11/26/2008
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Caminada, Carlo, Prandi, Luciano
• Granted Patent: US 8,459,109 B2
• Time in Patent Office: Days
• US Class Current: 73/504.120
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure

Abstract

A multi-axis gyroscope includes a microelectromechanical structure configured to rotate with respective angular velocities about respective reference axes, and including detection elements, which are sensitive in respective detection directions and generate respective detection quantities as a function of projections of the angular velocities in the detection directions. The gyroscope including a reading circuit that generates electrical output signals, each correlated to a respective one of the angular velocities, as a function of the detection quantities. The reading circuit includes a combination stage that combines electrically with respect to one another electrical quantities correlated to detection quantities generated by detection elements sensitive to detection directions different from one another, so as to take into account a non-zero angle of inclination of the detection directions with respect to the reference axes.

Claims

1. A reading circuit for a multi-axis gyroscope provided with a microelectromechanical structure configured to rotate with respective angular velocities about respective reference axes, and including first and second detection elements that are sensitive along first and second detection directions, respectively, the first and second directions being different from one another and are configured to generate respective detection quantities as a function of projections of said angular velocities in said first and second detection directions;

the reading circuit comprising;

a combination stage configured to combine electrically together electrical quantities correlated to detection quantities generated by the first and second detection elements, so as to take into account a non-zero angle of inclination of said first and second detection directions with respect to said reference axes; and

an output stage configured to provide electrical output signals based on combined electrical quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities.

2. The circuit according to claim 1, wherein said combination stage is configured to:

receive electrical quantities from third and fourth detection elements that are sensitive along the first and second detection directions, respectively, and

combine electrically together the electrical quantities correlated to the detection quantities generated by each of said first, second, third, and fourth detection elements.

3. The circuit according to claim 1, wherein said detection quantities include capacitive variations due to displacements of said detection elements with respect to associated fixed electrodes as a function of said projections of said angular velocities in said detection directions;

said circuit comprising;

an input stage configured to convert said capacitive variations into modulated electrical signals and then demodulate said modulated electrical signals based on a reference signal;

wherein the output stage is configured to receive intermediate electrical signals correlated to the electrical signals demodulated by said input stage and to process said intermediate electrical signals for generating said electrical output signals; and

said combination stage is upstream of said output stage and is configured to provide said intermediate electrical signals with respective information contents exclusively associated to a respective one of said angular velocities.

4. The circuit according to claim 3, wherein said microelectromechanical structure is further provided with a driving mass, configured to be actuated at a resonance frequency and at a driving angular velocity;

and wherein said input stage comprises;

a charge-amplifier element configured to amplify said capacitive variations and generate said modulated electrical signals, of a DSB-SC (Dual Side Band-Suppressed Carrier) type, amplitude-modulated with a carrier correlated to said driving angular velocity; and

a demodulator element cascaded to said charge-amplifier element and configured to demodulate said modulated electrical signals of a DSB-SC type; and

wherein said output stage comprises;

a sampler element configured to sample said intermediate electrical signals and generate sampled electrical signals; and

a filter stage cascaded to said sampler element and configured to filter said sampled electrical signals, removing at least a frequency component correlated to said resonance frequency, for generating said electrical output signals.

5. The circuit according to claim 3, wherein said input stage comprises distinct input-measuring chains for said angular velocities, respectively, and said output stage comprises distinct output-measuring chains for said angular velocities, respectively;

and wherein said combination stage is between said input stage and said output stage and includes an adder element configured to execute respective summations of the electrical signals demodulated by each of said input-measuring chains so as to generate said intermediate electrical signals.

6. The circuit according to claim 5, wherein said adder element is a switched-capacitance adder.

7. The circuit according to claim 5, wherein said reference axes include a pitch reference axis and a roll reference axis and the angular velocities include a pitch angular velocity and a roll angular velocity act about the pitch and roll reference axes, respectively, the microelectromechanical structure including a third detection element sensitive in the first detection direction and a fourth detection element sensitive in the second detection direction, the first, second, third and fourth detection elements being associated with first, second, third, and fourth fixed electrodes, respectively, said first detection direction and said second detection direction being inclined by an angle comprised between 40°

and 50°

with respect to said pitch and roll reference axes;

wherein said input stage comprises;

a first input-measuring chain connected to said first fixed electrode and third fixed electrode and configured to generate a first electrical signal demodulated as a function of the difference of the capacitive variations associated with said first fixed electrode and third fixed electrode; and

a second input-measuring chain connected to said second fixed electrode and fourth fixed electrode and configured to generate a second electrical signal demodulated as a function of the difference of the capacitive variations associated with said second fixed electrode and fourth fixed electrode; and

wherein said adder element is configured to execute a sum and a difference of said first and second demodulated electrical signals for generating first and second intermediate electrical signals, respectively, the adder element being configured to send, substantially at a same time, the first and second intermediate signals to a first one and to a second one of said output-measuring chains, respectively.

8. The circuit according to claim 1, wherein said reference axes include a pitch reference axis and a roll reference axis and the angular velocities include a pitch angular velocity and a roll angular velocity about the pitch and roll reference axes, respectively, and the microelectromechanical structure includes a third detection element sensitive in the first detection direction, and a fourth detection element sensitive in the second detection direction, said first detection direction and said second detection direction being inclined by an angle comprised between 40°

and 50 with respect to said pitch and roll reference axes;

wherein said first detection element and second detection element and said third detection element and fourth detection element are arranged, in pairs, on opposite sides with respect to said roll reference axis, and said first detection element and fourth detection element and said second detection element and third detection element are arranged, in pairs, on opposite sides with respect to said pitch reference axis; and

wherein said combination stage is configured so as to;

execute a first combination operation by adding with a first sign electrical quantities correlated to the detection quantities generated by said first detection element and second detection element and with a second sign, opposite to the first, electrical quantities correlated to the detection quantities generated by said third detection element and fourth detection element for generating a first output signal correlated to said roll angular velocity; and

execute a second combination operation by adding with said first sign electrical quantities correlated to the detection quantities generated by said first detection element and fourth detection element and with said second sign electrical quantities correlated to the detection quantities generated by said second detection element and third detection element for generating a second output signal correlated to said pitch angular velocity.

9. The circuit according to claim 1, wherein said electrical quantities coincide with said detection quantities and include capacitive variations due to displacements of said detection elements with respect to associated fixed electrodes as a function of said projections of said angular velocities in said respective detection directions;

and wherein said combination stage has inputs configured to be electrically connected to said fixed electrodes so as to receive at input said capacitive variations, and is configured to implement combinations of the capacitive variations generated by said detection elements sensitive to said detection directions different from one another.

10. The circuit according to claim 9, wherein said combination stage has an input configured to receive phase signals and comprises a set of switch elements configured to be driven by said phase signals for short-circuiting in pairs said fixed electrodes and implementing said combinations of said capacitive variations.

11. The circuit according to claim 10, comprising a charge-amplifier element cascaded to said combination stage;

wherein said microelectromechanical structure has a pitch reference axis and a roll reference axis, and the angular velocities include a pitch angular velocity and a roll angular velocity about the pitch and roll reference axes, respectively, and is moreover provided with a third detection element sensitive in a first detection direction, and a fourth detection element sensitive in a second detection direction, the first, second, third and fourth detection elements being associated with first, second, third, and fourth fixed electrodes, respectively, said first detection direction and said second detection direction being inclined by an angle comprised between 40° and

50°

with respect to said pitch and roll reference axes;

wherein said set of switch elements comprises;

a first switch element connected between said first fixed electrode and said second fixed electrode and controlled by a first one of said phase signals;

a second switch element connected between said third fixed electrode and fourth fixed electrode and controlled by said first phase signal;

a third switch element connected between said second fixed electrode and third fixed electrode and controlled by a second one of said phase signals; and

a fourth switch element connected between said first fixed electrode and fourth fixed electrode and controlled by said second phase signal; and

wherein said combination stage is configured to provide a direct connection between said first fixed electrode and a first input of said charge-amplifier element and a direct connection between said third fixed electrode and a second input of said charge-amplifier element.

12. The circuit according to claim 10, comprising an input stage provided with a single input-measuring chain cascaded to said combination stage and configured so as to convert said combinations of capacitive variations into modulated electrical signals and then demodulate said electrical signals as a function of a reference signal;

wherein said set of switch elements is configured to be driven by said phase signals to implement a respective combination of said capacitive variations for each of said angular velocities, and supply at distinct times said respective combinations of said capacitive variations to said single input-measuring chain according to a time-division scheme, as a function of a value of said phase signals.

13. The circuit according to claim 12, wherein the output stage includes respective output-measuring chains for said angular velocities, the output-measuring chains being configured to receive the electrical signals demodulated by said single input-measuring chain and to process said demodulated electrical signals for generating said electrical output signals;

the circuit further comprising a demultiplexer stage cascaded to said single input-measuring chain and having an input configured to receive said phase signals, and configured to supply said demodulated electrical signals at output from said single input-measuring chain to a selected one of the output-measuring chains, selected between said respective output-measuring chains according to a value of said phase signals.

14. A multi-axis gyroscope, comprising:

a microelectromechanical structure configured to rotate with respective angular velocities about respective reference axes, and including first and second detection elements sensitive along first and second detection directions, respectively, the first and second directions being different from one another, and are configured to generate respective detection quantities as a function of projections of said angular velocities in said first and second detection directions, said first detection directions being inclined with respect to said reference axes by a non-zero angle of inclination; and

a reading circuit including;

a combination stage configured to combine electrically together electrical quantities correlated to detection quantities generated by the first and second detection elements, so as to take into account the non-zero angle of inclination of said first and second detection directions with respect to said reference axes; and

an output stage configured to provide electrical output signals based on combined electrical quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities.

15. The gyroscope according to claim 14, wherein said reference axes include a pitch reference axis and a roll reference axis and the angular velocities include a pitch angular velocity and a roll angular velocity about the pitch and roll reference axes, respectively, the microelectromechanical structure including:

a third detection element sensitive in the first detection direction, and a fourth detection element sensitive in the second detection direction, said first detection direction and second detection direction being inclined by an angle comprised between 40° and

50°

with respect to said pitch and roll reference axes;

a substrate;

elastic anchoring elements;

first, second, third, and fourth elastic supporting elements; and

a driving mass anchored to the substrate via the elastic anchoring elements, and configured to be actuated with a driving movement at a resonance frequency;

said first, second, third, and fourth detection elements comprising first, second, third, and fourth sensing masses, respectively, the first, second, third, and fourth sensing masses being suspended within, and coupled to, said driving mass via the first, second, third, and fourth elastic supporting elements, respectively, so as to be fixed with respect to said driving mass in said driving movement and perform a respective detection movement in response to pitch and roll movements at said pitch and roll angular velocities, respectively.

16. The gyroscope according to claim 15, wherein said reference axes include a yaw reference axis, along which a yaw movement at a yaw angular velocity acts, the microelectromechanical structure including:

fifth and sixth elastic supporting elements; and

fifth and sixth detection element sensitive to said yaw angular velocity, the fifth and sixth detection elements including respective fifth and sixth sensing masses suspended within, and coupled to, said driving mass via the fifth and sixth elastic supporting elements, respectively, so as to be fixed with respect to said driving mass in said driving movement and perform a respective detection movement in response to said yaw movement at the yaw angular velocity.

17. The gyroscope according to claim 15, wherein said first and third detection elements are aligned in said first detection direction and said second and fourth detection elements are aligned in said second detection direction.

18. The gyroscope according to claim 15, further comprising:

a first die of semiconductor material in which said microelectromechanical structure; and

a second die of semiconductor material, the second die including a driving circuit configured to drive said driving mass and integrated together with said reading circuit in said second die;

said first die and second die being arranged within a same package.

19. An electronic device, comprising:

a control circuit configured to manage said electronic device as a function respective angular velocities; and

a multi-axis gyroscope that includes;

a microelectromechanical structure configured to rotate with the respective angular velocities about respective reference axes, and including first and second detection elements sensitive along first and second detection directions, respectively, the first and second directions being different from one another, and are configured to generate respective detection quantities as a function of projections of said angular velocities in said first and second detection directions, said first detection directions being inclined with respect to said reference axes by a non-zero angle of inclination; and

a reading circuit including;

a combination stage configured to combine electrically together electrical quantities correlated to detection quantities generated by the first and second detection elements, so as to take into account the non-zero angle of inclination of said first and second detection directions with respect to said reference axes; and

an output stage configured to provide electrical output signals based on combined electrical quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities.

20. The device according to claim 19, of a portable type, chosen in the group consisting of:

a PDA (Personal Digital Assistant) device;

a portable computer;

a mobile phone;

a digital audio player;

a photographic camera or video camera; and

a video game console.