Micro-machined accelerometer with improved transfer characteristics

• US 6,386,032 B1
• Filed: 08/01/2000
• Issued: 05/14/2002
• Est. Priority Date: 08/26/1999
• Status: Expired due to Term

• Current Assignee: Analog Devices IMI, Inc. (Analog Devices, Inc.)
• Original Assignee: Analog Devices IMI, Inc. (Analog Devices, Inc.)
• Inventors: Clark, William A., Juneau, Thor, Lemkin, Mark A., Roessig, Allen W.
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US09/630,535
• Time in Patent Office: 651 Days
• Field of Search: 735/140.1, 735/141.5, 735/141.7, 735/143.2, 735/141.8, 735/040.2, 735/041.2, 735/040.3, 735/040.4
• US Class Current: 73/504.02
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

A micromechanical, dithered device comprising a substrate, a movable mass connected to the substrate by a suspension, a position sensor, a dither signal generator, a dither force transducer connected between the substrate and the movable mass, the input of the dither force transducer being connected to the output of the dither signal generator and a calculator taking as inputs at least the position sensor output and the dither signal generator output.

In one embodiment of the invention, the dithered device includes an electrostatic force transducer for applying feedback. In this embodiment, dither force may be directly applied to the mechanical proof-mass utilizing electrostatic structures similar to electrostatic structures used for feedback. The electrostatic dithering structures provide good matching between the feedback and dither electrodes, enabling the use of simple logic for subtraction of the dither signal from the accelerometer output.

Claims

1. A micromechanical, dithered device comprising:

a substrate;

a movable mass connected to said substrate by at least one flexible beam;

a position sensor having an output;

a dither signal generator having an output;

a dither force transducer connected to said substrate and to said movable mass, said dither force transducer having an input, the input of said dither force transducer connected to the output of said dither signal generator; and

a calculator having at least two inputs and one output, said calculator inputs connected to at least said position sensor output and said dither signal output.

2. The micromechanical, dithered device of claim 1 further including:

a force transducer connected to said substrate and to said movable mass; and

a feedback connection between said position sensor output and said force transducer.

3. The micromechanical, dithered device of claim 1 wherein said dither signal generator comprises a signal generator selected from the following list:

pseudorandom noise generator, random noise generator, tone generator comprising at least one tone.

4. A micromachined accelerometer having improved transfer characteristics comprising:

a sense-element having an output, a first input, and a second input;

sensing circuitry having an input and an output, the input of said sensing circuitry connected to the output of said sense-element;

a quantization circuit having an output;

a feedback connection between said quantization circuit output and said first input of said sense-element;

a dither signal generator having an output;

a connection between said dither signal generator output and said second input of said sense-element; and

a calculator having an input connected to said dither signal generator output, having an input connected to said quantization circuit output, and having an output.

5. The micromachined accelerometer of claim 4 wherein said sense-element comprises:

a substrate having a first conducting area and a second conducting area; and

a movable mass connected to said substrate by at least one flexible beam, said movable mass having a first conducting area and a second conducting area, each conducting area forming an air-gap capacitor with a corresponding conducting area on the substrate.

6. The micromachined accelerometer of claim 5 wherein said first and second substrate conducting areas are electrically isolated.

7. The micromachined accelerometer of claim 5 wherein said first and second substrate conducting areas are electrically connected.

8. The micromachined accelerometer of claim 5 wherein said first and second movable-mass conducting areas are electrically isolated.

9. The micromachined accelerometer of claim 5 wherein said first and second movable-mass conducting areas are electrically connected.

10. The micromachined accelerometer of claim 4 wherein said sense-element comprises:

a substrate having a first conducting area, a second conducting area, and a third conducting area; and

a movable mass connected to said substrate by at least one flexible beam, said movable mass having a first conducting area, a second conducting area, and a third conducting area, each conducting area forming an air-gap capacitor with a corresponding conducting area on the substrate.

11. The micromachined accelerometer of claim 5 wherein said sense-element further comprises:

a multiplexor comprising two or more switches, said multiplexor having a first terminal connected to at least one air-gap capacitor, having a second terminal, and having a third terminal.

12. The micromachined accelerometer of claim 11 wherein said multiplexor comprises a time-division multiplexor.

13. The micromachined accelerometer of claim 11 wherein said multiplexor comprises a frequency-division multiplexor.

14. The micromachined accelerometer of claim 4 wherein said dither signal generator comprises a signal generator selected from the following list:

pseudorandom noise generator, random noise generator, tone generator comprising at least one tone.

15. The micromachined accelerometer of claim 4 wherein said sensing circuitry, said quantization circuit, said dither signal generator, and said calculator operate at discrete, recurring time periods.

16. The micromachined accelerometer of claim 4 wherein said sensing circuitry operates continuously.

17. The micromachined accelerometer of claim 4 wherein said sense-element and said sensing circuitry are formed on a common substrate.

18. The micromachined accelerometer of claim 4 wherein said sense-element and said calculator are formed on separate substrates.

19. The micromachined accelerometer of claim 4 wherein the output of said calculator comprises a quantity representative of an acceleration selected from the following list:

translational acceleration applied to the accelerometer, angular acceleration applied to the accelerometer, Coriolis acceleration generated in response to a rotation rate applied to the accelerometer.

20. A micromachined accelerometer having improved transfer characteristics comprising:

(a) a substrate;

(b) a movable mass connected to said substrate by at least one flexible beam;

(c) a transducer group including at least one transducer, said at least one transducer comprising;

a dither input, and a dither output;

a feedback input and a feedback output;

a position output, said position output responsive to the relative position between said mass and said substrate;

(d) sensing circuitry having an input and an output;

(e) a dither signal generator having an output;

(f) a connection between said dither signal generator output and said dither input;

(g) a quantization circuit having an output;

(h) a feedback connection between said quantization circuit output and said feedback input; and

(i) a calculator having an input connected to said dither signal generator output, having an input connected to said quantizer output, and having an output.

21. The micromachined accelerometer of claim 20 wherein said dither output and said feedback output comprise forces, the magnitude of each force being controlled by a common reference voltage.

22. The micromachined accelerometer of claim 20 wherein said dither output and said feedback output comprise forces, said dither output and said feedback outputs occurring simultaneously.

23. The micromachined accelerometer of claim 20 wherein said transducer group comprises:

a substrate having a first conducting area and a second conducting area; and

a movable mass connected to said substrate by at least one flexible beam, said movable mass having a first conducting area and a second conducting area each conducting area forming an air-gap capacitor with a corresponding conducting area on the substrate.

24. The micromachined accelerometer of claim 23 wherein said first and second substrate conducting areas are electrically isolated.

25. The micromachined accelerometer of claim 23 wherein said first and second substrate conducting areas are electrically connected.

26. The micromachined accelerometer of claim 23 wherein said first and second movable-mass conducting areas are electrically isolated.

27. The micromachined accelerometer of claim 23 wherein said first and second movable-mass conducting areas are electrically connected.

28. The micromachined accelerometer of claim 20 wherein said transducer group further comprises:

a multiplexor comprising two or more switches, said multiplexer having a first terminal connected to at least one air-gap capacitor, having a second terminal, and having a third terminal.

29. The micromachined accelerometer of claim 28 wherein said multiplexor comprises a time-division multiplexor.

30. The micromachined accelerometer of claim 28 wherein said multiplexor comprises a frequency-division multiplexor.

31. The micromachined accelerometer of claim 20 wherein said dither signal generator comprises a signal generator selected from the following list:

pseudorandom noise generator, random noise generator, tone generator comprising at least one tone.

32. The micromachined accelerometer of claim 20 wherein:

said feedback output comprises a feedback impulse, the feedback impulse having a maximum magnitude;

said dither output comprises a dither impulse, the dither impulse having a maximum magnitude; and

said maximum magnitude of the feedback impulse is a power of 2 times greater than said maximum magnitude of the dither impulse.

33. The micromachined accelerometer of claim 20 wherein:

said feedback output comprises a feedback impulse, the feedback impulse having a maximum magnitude;

said dither output comprises a dither impulse, the dither impulse having a maximum magnitude; and

said maximum magnitude of the dither impulse is 10 percent or less than said maximum magnitude of the feedback impulse.

34. The micromachined accelerometer of claim 20 wherein said calculator comprises:

a first filter having an input and an output, the input connected to said dither signal generator output;

a second filter having an input and an output, the input connected to said quantizer output; and

a summer having a first input, a second input, and an output, the first input connected to said first filter output, and the second input connected to said second filter output.

35. The micromachined accelerometer of claim 34 wherein said calculator further comprises a third filter having an input and an output, said third filter input connected to said summer output.

36. The micromachined accelerometer of claim 34 wherein said first filter comprises a sinc¹ filter and said second filter comprises a sinc¹ filter.

37. The micromachined accelerometer of claim 20 wherein said calculator comprises:

a gain-scaler having an input and an output, the input connected to said dither signal generator output; and

a summer having a first input, a second input, and an output, the first input connected to said quantizer output, and the second input connected to said gain-scaler output.

38. The micromachined accelerometer of claim 37 wherein said calculator further comprises a filter having an input and an output, said filter connected to said summer output.

39. A micromachined accelerometer having improved transfer characteristics comprising:

(a) a substrate;

(b) a movable mass connected to said substrate by at least one flexible beam;

(c) a time-multiplexed transducer group at least periodically comprising;

a dither transducer, said dither transducer having an input, and having an output force;

a feedback transducer, said feedback transducer having an input, and having an output force;

a position transducer having an output responsive to the relative position between said mass and said substrate;

(d) sensing circuitry having an input and an output;

(e) a dither signal generator having an output;

(f) a connection between said dither signal generator output and said dither transducer input;

(g) a quantization circuit having an output;

(h) a feedback connection between said quantization circuit output and said feedback transducer input; and

(i) a calculator having an input connected to said dither signal generator output, having an input connected to said quantizer output, and having an output.