Sensor device with reduced parasitic-induced error

• US 8,096,179 B2
• Filed: 04/09/2009
• Issued: 01/17/2012
• Est. Priority Date: 04/09/2009
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Bien, David E., Mijuskovic, Dejan
• Primary Examiner(s): Kirkland, III, Freddie
• Application Number:
  US12/421,513
• Publication Number:
  US 20100259318A1
• Time in Patent Office: 1,013 Days
• Field of Search: 735/040.2, 735/040.4, 735/041.2, 327/337, 327/551, 327/554
• US Class Current: 73/504.02
• CPC Class Codes: B81B 3/0086 Electrical characteristics, e.g. reducing driving voltage, improving resistance to peak voltage
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719

Abstract

A device (110) includes a sensing element (26) having drive nodes (34, 36) and sense nodes (42, 44). Parasitic capacitance (22) is present between drive node (34) and sense node (42). Likewise, parasitic capacitance (24) is present between drive node (36) and sense node (44). When a drive signal (56) is applied between drive nodes (34, 36), a parasitic current (70) between drive and sense nodes (34, 42) and a parasitic current (72) between drive and sense nodes (36,44) is created due to the parasitic capacitances (22, 24). A capacitive network (112) is coupled between the drive node (36) and the sense node (42) to create a correction current (134) through capacitive network (112) that cancels parasitic current (70). Likewise, a capacitive network (114) is coupled between the drive node (34) and the sense node (44) to create a correction current (138) through capacitive network (112) that cancels parasitic current (72).

Claims

1. A device comprising:

a sensor element having a first drive node and a first sense node, wherein a first parasitic current is present between said first drive node and said first sense node when a drive signal is applied at said first drive node; and

a capacitive network having a first input coupled to a voltage source and a first output coupled to said first sense node, said first capacitive network substantially canceling said first parasitic current when a second drive signal of opposite phase to said first drive signal is applied at said first input.

2. A device as claimed in claim 1 wherein:

said capacitive network is a first capacitive network;

said sensor element includes a second drive node and a second sense node, wherein a second parasitic current is present between said second drive node and said second sense node when said drive signal is applied between said first and second drive nodes;

said first input of said first capacitive network is coupled to said second drive node; and

said device further comprises a second capacitive network having a second input coupled to said first drive node and a second output coupled to said second sense node, said second capacitive network substantially canceling said second parasitic current.

3. A device as claimed in claim 2 wherein a first parasitic capacitance is present between said first drive node and said first sense node, a second parasitic capacitance is present between said second drive node and said second sense node, and:

said first capacitive network is a first adjustable network for providing a first effective capacitance that is substantially equivalent to said first parasitic capacitance; and

said second capacitive network is a second adjustable capacitive network for providing a second effective capacitance that is substantially equivalent to said second parasitic capacitance.

4. A device as claimed in claim 3 wherein said first parasitic capacitance differs from said second parasitic capacitance, and said first and second adjustable capacitive networks are separately tunable for obtaining said first and second effective capacitances.

5. A device as claimed in claim 2 wherein said sensor element comprises a movable structure adapted to oscillate in a first direction and a second direction perpendicular to said first direction, a first portion of said movable structure being spaced between said first and second drive nodes, and a second portion of said movable structure being spaced between said first and second sense nodes, wherein said drive signal applied at said first and second drive nodes oscillates said first portion of movable structure in said first direction and said first and second sense nodes detect motion of said second portion of said movable structure in said second direction occurring in response to oscillation of said first portion in said first direction, said motion in said second direction being responsive to a Coriolis force produced by rotation about an axis perpendicular to said first and second directions.

6. A device as claimed in claim 1 wherein said capacitive network is a two-port capacitive network.

7. A device as claimed in claim 1 wherein a parasitic capacitance is present between said first drive node and said first sense node, and said capacitive network comprises multiple capacitive circuits connected in parallel to produce an effective capacitance that is substantially equivalent to said parasitic capacitance.

8. A device as claimed in claim 7 wherein at least two of said capacitive circuits have different capacitances with respect to one another.

9. A device as claimed in claim 7 wherein at least one of said capacitive circuits has a capacitance that is no greater than said parasitic capacitance.

10. A device as claimed in claim 9 wherein said capacitance is less than one femtofarad.

11. A device as claimed in claim 7 wherein each of said capacitive circuits comprises:

a first capacitive element;

a second capacitive element;

a third capacitive element, said first, second, and third capacitive elements being connected in series;

a fourth capacitive element having a first end coupled between said first and second capacitive elements and a second end coupled to ground; and

a fifth capacitive element having a third end coupled between said second and third capacitive elements and a fourth end coupled to said ground.

12. A device as claimed in claim 1 wherein:

said capacitive network comprises multiple capacitive circuits connected in parallel to produce an effective capacitance; and

said device further comprises;

multiple control circuits, one each of said control circuits being coupled with one each of said capacitive circuits; and

a digital control element coupled to said each of said control circuits to selectively include ones of said capacitive circuits to produce said effective capacitance.

13. A device as claimed in claim 12 wherein:

each of said control circuits comprises a switch element interposed between said one each of said capacitive circuits and ground; and

said digital control element comprises multiple logic gates, one each of said logic gates being associated with each said switch element, wherein said each of said logic gates provides a bit having one of a first state and a second state, said first state actuating a corresponding said switch element to provide a shunt to ground, and said second state de-actuating said corresponding said switch element to remove said shunt to ground.

14. A device as claimed in claim 13 wherein said switch element comprises a metal oxide semiconductor (MOS) transistor.

15. A method of substantially cancelling parasitic current in a device, said device including a sensor element having a first drive node, a second drive node, a first sense node, and a second sense node, a first capacitive network having a first input coupled to said second drive node and a first output coupled to said first sense node, a second capacitive network having a second input coupled to said first drive node and a second output coupled to said second sense node, and said method comprising:

adjusting said first capacitive network to provide a first effective capacitance that is substantially equivalent to a first determined parasitic capacitance between said first drive node and said first sense node, said first parasitic capacitance causing a first parasitic current upon application of a drive signal to said sensor element;

adjusting said second capacitive network to provide a second effective capacitance that is substantially equivalent to a second determined parasitic capacitance between said second drive node and said second sense node, said second parasitic capacitance causing a second parasitic current upon application of said drive signal to said sensor element; and

applying said drive signal at said first and second drive nodes to drive said sensor element, said drive signal concurrently being applied to said first and second capacitive networks to form a first correction current through said first capacitive network that is substantially equivalent and opposite in phase to said first parasitic current and to form a second correction current through said second capacitive network that is substantially equivalent and opposite in phase to said second parasitic current such that said first and second parasitic currents are substantially cancelled.

16. A method as claimed in claim 15 wherein prior to said adjusting said first and second capacitive networks, said method further comprises:

determining said first parasitic capacitance between said first drive node and said first sense node; and

determining said second parasitic capacitance between said second drive node and said second sense node.

17. A method as claimed in claim 15 wherein said first parasitic capacitance differs from said second parasitic capacitance, and said first and second capacitive networks are separately adjustable for obtaining said first and second effective capacitances that differ from one another.

18. A method as claimed in claim 15 wherein:

said first capacitive network includes multiple first capacitive circuits connected in parallel to produce said first effective capacitance;

said second capacitive network includes multiple second capacitive circuits connected in parallel to produce said second effective capacitance;

said adjusting said first capacitive network comprises utilizing digital control to selectively include ones of said first capacitive circuits to produce said first effective capacitance; and

said adjusting said second capacitive network comprises utilizing said digital control to selectively include ones of said second capacitive circuits to produce said second effective capacitance.

19. A device comprising:

a resonator element having a first drive node, a second drive node, a first sense node, and a second sense node, wherein a first parasitic capacitance is present between said first drive node and said first sense node to produce a first parasitic current, a second parasitic capacitance is present between said second drive node and said second sense node to produce a second parasitic current between said second drive node and said second sense node, said first and second parasitic currents being present when a drive signal is applied between said first and second drive nodes;

a first capacitive network including multiple first capacitive circuits connected in parallel to produce a first effective capacitance that is substantially equivalent to said first parasitic capacitance, said first capacitive network having a first input connected to said second drive node and having a first output connected to said first sense node, said first capacitive network forming a first correction current when said drive signal is applied between said first and second drive nodes that is substantially equivalent and opposite in phase to said first parasitic current to substantially cancel said first parasitic current; and

a second capacitive network including multiple second capacitive circuits connected in parallel to produce a second effective capacitance that is substantially equivalent to said second parasitic capacitance, said second capacitive network having a second input connected to said first drive node and a second output connected to said second sense node, said second capacitive network forming a second correction current when said drive signal is applied between said first and second drive nodes that is substantially equivalent and opposite in phase to said second parasitic current to substantially cancel said second parasitic current.

20. A device as claimed in claim 19 further comprising:

multiple first control circuits, one each of said first control circuits being coupled with one each of said first capacitive circuits;

a first digital control element coupled to said each of said first control circuits to selectively include ones of said first capacitive circuits to produce said first effective capacitance;

multiple second control circuits, one each of said second control circuits being coupled with one each of said second capacitive circuits; and

a second digital control element coupled to said each of said second control circuits to selectively include ones of said second capacitive circuits to produce said second effective capacitance.