Device and method for automatic calibration of a microelectromechanical structure included in a control loop

• US 6,577,975 B2
• Filed: 11/13/2001
• Issued: 06/10/2003
• Est. Priority Date: 11/16/2000
• Status: Expired due to Term

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Chiesa, Enrico
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Dougherty, Anthony T.
• Application Number:
  US10/001,269
• Publication Number:
  US 20020143484A1
• Time in Patent Office: 574 Days
• Field of Search: 702/87, 702/94, 735/141.8, 735/143.2, 310/40.MM, 318/560, 318/632
• US Class Current: 702/94
• CPC Class Codes: G01D 3/066 Balancing a force which represents the measuring value, by means of a reference force
• CPC Class Codes: G01P 15/0888 for indicating angular acceleration
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A sensing device having a microelectromechanical structure made of semiconductor material, and a control loop for controlling the microelectromechanical structure, the microelectromechanical structure including a stator element and a rotor element electrostatically coupled together, and the control loop including a position interface supplying a position signal indicative of the position of the rotor element, and a one-bit quantizer receiving the position signal and supplying a corresponding bit sequence. The sensing device further includes a calibration device for calibrating the microelectromechanical structure, including a microactuator made of semiconductor material and coupled to the rotor element, and a driving circuit for driving the microactuator, and receiving the bit sequence and supplying to the microactuator a driving signal correlated to a mean value of the bit sequence in a given time window.

Claims

1. A sensing device comprising a microelectromechanical structure made of semiconductor material, and a control loop for controlling said microelectromechanical structure, said microelectromechanical structure comprising:

a stator element and a rotor element electrostatically coupled together, and said control loop comprising interface means coupled to said microelectromechanical structure and supplying a position signal indicative of the position of said rotor element; and

calibration means for calibrating said microelectromechanical structure, said calibration means including actuator means made of semiconductor material and coupled to said rotor element, and first driving means, for driving said actuator means, said first driving means receiving said position signal and supplying to said actuator means a driving signal correlated to a mean value of said position signal.

2. The sensing device of claim 1 wherein said control loop further comprises quantizer means receiving said position signal and supplying a corresponding sequence of samples;

said first driving means receiving said sequence of samples and supplying said driving signal correlated to a mean value of said sequence of samples.

3. The sensing device of claim 2 wherein said quantizer means are one-bit quantizer means.

4. The sensing device of claim 2 wherein said mean value is a moving average of said sequence of samples in a given time window.

5. The sensing device of claim 1 wherein said control loop further comprises second driving means for driving said microelectromechanical structure;

said second driving means comprising first signal generating means generating in succession a first driving signal such as to bring about the application, on said rotor element, of a first torque greater than a normal torque used during normal operation of said microelectromechanical structure, and a second driving signal to bring about the application, on said rotor element, of a second torque comparable to the normal torque of said microelectromechanical structure; and

wherein said first driving means comprise second signal generating means generating in succession a first driving signal for said actuator means as a function of a first mean value of the position signal resulting from the application, on said rotor element, of said first torque, and a second driving signal for said actuator means as a function of said first mean value and of a second mean value of the position signal resulting from the application, on said rotor element, of said second torque.

6. The sensing device of claim 5 wherein said second signal generating means generate said second driving signal as a function of said first and second mean values and of the ratio between said first torque and said second torque.

7. The sensing device of claim 5 wherein said second signal generating means comprise pulse width modulation means receiving a reference driving signal and said first and second mean values, and supplying said first and second driving signals, said first driving signal obtained by pulse width modulating said reference driving signal as a function of said first mean value, and said second driving signal obtained by pulse width modulating said reference driving signal as a function of said first and second mean values.

8. The sensing device of claim 5, further comprising biasing means supplying to said second driving means a first biasing voltage higher than the normal torque used during normal operation of said microelectromechanical structure so as to bring about the application, on said rotor element, of said first torque, and a second biasing voltage comparable to the normal torque used during normal operation of said microelectromechanical structure so as to bring about the application, on said rotor element, of said second torque.

9. A calibration method for calibrating a sensor device having a microelectromechanical structure made of semiconductor material, and a control loop for controlling said microelectromechanical structure, said microelectromechanical structure including a stator element and a rotor element electrostatically coupled together, and said control loop including interface means coupled to said microelectromechanical structure and supplying a position signal indicative of the position of said rotor element, said calibration method comprising the step of moving said rotor element, wherein said step of moving said rotor element comprises the steps of:

providing actuator means made of semiconductor material and coupled to said rotor element; and

supplying, to said actuator means, a driving signal correlated to a mean value of said position signal.

10. The calibration method of claim 9, for a control loop further including quantizer means receiving said position signal and supplying a corresponding sequence of samples, wherein said step of driving said actuator means comprises the step of:

supplying, to said actuator means, a driving signal correlated to a mean value of said sequence of samples.

11. The calibration method of claim 9 wherein said quantizer means perform a one-bit quantization of said position signal.

12. The calibration method of claim 9 wherein said mean value is a moving average of said sequence of samples in a given time window.

13. The calibration method of claim 9 wherein said step of moving said rotor element comprises the steps of:

driving said microelectromechanical structure by means of said control loop in such a way as to apply to said rotor element a first torque higher than a normal torque used during normal operation of said microelectromechanical structure;

supplying to said actuator means a first driving signal correlated to a first mean value of the position signal resulting from the application of said first torque;

then driving said microelectromechanical structure by means of said control loop in such a way as to apply to said rotor element a second torque comparable to the normal torque; and

supplying, to said actuator means, a second driving signal correlated to said first mean value and to a second mean value of the position signal resulting from the application of said second torque.

14. The calibration method of claim 13 wherein said step of supplying said second driving signal to said actuator means comprises the step of generating said second driving signal as a function of said first and second mean values and of the ratio between said first torque and said second torque.

15. The calibration method of claim 13 wherein said steps of supplying to said driving means a first and a second driving signal comprises the steps of:

generating said first driving signal by pulse width modulating a third driving signal as a function of said first mean value; and

generating said second driving signal by pulse width modulating said third driving signal as a function of said first and second mean values.

16. The calibration method of claim 13 for a control loop having second driving means for driving said microelectromechanical structure, wherein said step of driving said microelectromechanical structure by means of said control loop in such a way that a first torque is applied to said rotor element comprises the step of supplying to said second driving means a first biasing voltage higher than a normal biasing voltage used during normal operation of said microelectromechanical structure, and said step of driving said microelectromechanical structure by means of said control loop in such a way that a second torque is applied to said rotor element comprises the step of supplying to said driving means a second biasing voltage comparable to the normal biasing voltage used during normal operation of said microelectromechanical structure.

17. A sensing device, comprising:

an inertial sensor comprising a stator element and a rotor element electrostatically coupled together;

a position interface circuit coupled to the inertial sensor and configured to generate a position signal indicative of the position of the rotor element;

a quantizer coupled to the position interface and configured to receive the position signal and to generate a sequence of samples;

a main actuator coupled to the output of the quantizer for receiving the sequence of samples and configured to modify a position of the rotor element;

an adder having an output coupled to the inertial sensor and a first input coupled to the actuator;

a computation circuit having an input coupled to the output of the quantizer and configured to generate a mean value of the sequence of samples;

a processing circuit having an input coupled to the computation circuit and configured to receive the mean value of the sequence of samples and to generate a driving signal; and

a secondary actuator having an input coupled to the processing circuit and an output coupled to the adder, the secondary actuator configured to generate a calibration acceleration signal to be applied to the rotor to compensate for voltage offsets and component mismatches.

18. A sensing device, comprising:

an inertial sensor comprising a stator element and a rotor element electrostatically coupled together;

a main feedback branch coupled to the inertial sensor and including a main actuator configured to generate a primary feedback signal for changing the position of the rotor element relative to the stator element; and

a secondary feedback branch coupled to the main feedback branch and to the inertial sensor, the secondary feedback branch comprising a computation circuit configured to receive a sequence of sample signals from the main feedback branch and to generate a mean value signal corresponding to the mean value of the sequence of samples, a processing circuit having an input coupled to the computation circuit and configured to generate a driving signal in response to the mean value signal, and a secondary actuator having an input coupled to the processing circuit and configured to receive the driving signal and to generate a secondary feedback signal that is received by an adder coupled to the input of the inertial sensor.

19. A method of calibrating an inertial sensor having a stator element and a rotor element electrostatically coupled together and controlled through a main feedback branch having a quantizer generating a sequence of samples to a main actuator that generates a first feedback signal, the method comprising:

receiving the sequence of samples in a secondary feedback branch coupled and parallel to the main feedback branch and generating a secondary feedback signal that is added to the primary feedback signal from the main actuator.

20. A method of calibrating an inertial sensor having a stator element and a rotor element electrostatically coupled together and controlled by a main feedback branch having a quantizer that generates a sequence of samples to a main actuator that in turn generates a first feedback signal to the inertial sensor, the calibration method comprising:

receiving the sequence of samples at a computation circuit and generating therefrom a mean value signal;

receiving the mean value signal at a processing circuit and generating therefrom a voltage calibration signal;

receiving the voltage calibration signal at a secondary actuator and generating therefrom a secondary feedback signal; and

adding the secondary feedback signal to the primary feedback signal and combining the same with an input signal and outputting the sum thereof to the inertial sensor.