Capacitive distance sensor

• US 6,437,583 B1
• Filed: 07/11/2000
• Issued: 08/20/2002
• Est. Priority Date: 02/14/1996
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Tartagni, Marco, Kramer, Alan, Gupta, Bhusan
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): HAMDAN, WASSEEM H
• Application Number:
  US09/614,093
• Time in Patent Office: 770 Days
• Field of Search: 324/661, 324/662, 324/663, 324/671, 324/686, 324/687, 324/688, 324/690, 382/124, 341/33
• US Class Current: 324/687
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01B 7/287 using a plurality of fixed, simultaneously operating transducers G01B7/293 takes precedence
• CPC Class Codes: G01B 7/34 for measuring roughness or irregularity of surfaces
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

A distance sensor has a capacitive element in turn having a first capacitor plate which is positioned facing a second capacitor plate whose distance is to be measured. In the case of fingerprinting, the second capacitor plate is defined directly by the skin surface of the finger being printed. The sensor comprises an inverting amplifier, between the input and output of which the capacitive element is connected to form a negative feedback branch. By supplying an electric charge step to the input of the inverting amplifier, a voltage step directly proportional to the distance being measured is obtained at the output.

Claims

1. An integrated sensor device for detecting a distance between the sensor device and an object, the sensor device comprising:

a first capacitor plate for forming a first capacitance between the first capacitor plate and the object when positioned adjacent to the object;

a second capacitor plate for forming a second capacitance between the second capacitor plate and the object when positioned adjacent to the object, the first and second capacitor plates being arranged in a substantially planar pattern in which a plurality of faces of the first capacitor plate are positioned adjacent to and facing a plurality of faces of the second capacitor plate; and

an amplifier having an input and an output, the input being connected to one of the first and second capacitor plates and the output being connected to another one of the first and second capacitor plates to form a negative feedback branch that includes the first and second capacitances, whereby an output voltage is established at the amplifier output that is proportional to a distance between the first capacitor plate and the object.

2. The sensor device of claim 1, further comprising a layer of insulating material contacting outer surfaces of the first and second capacitor plates, such that the insulating material is positioned between the capacitor plates and the object.

3. The sensor device of claim 1, further comprising:

a grounding element surrounding the first and second capacitor plates in a plane, the grounding element being coupled to ground to provide a discharge path for electrostatic discharge caused by the object.

4. The sensor device of claim 1 wherein the first and second capacitor plates are arranged in an interdigitating pattern in which fingers of the first capacitor plate are interspersed with fingers of the second capacitor plate.

5. The sensor device of claim 4 wherein the first capacitor plate surrounds the second capacitor plate in a plane.

6. The sensor device of claim 1 wherein the first and second capacitor plates are arranged in a spiral pattern.

7. The sensor device of claim 1 wherein the first capacitor plate is C-shaped and has two ends that define a gap and the second capacitor plate includes an inner portion surrounded on at least three sides by the first capacitor plate, an outer portion positioned outside the first capacitor plate, and a connector portion connecting the inner portion with the outer portion.

8. The sensor device of claim 1 wherein the first capacitor plate includes two rectangular portions positioned in diagonally opposite sections of a rectangular sensor cell and a connector portion that connects the two rectangular portions and the second capacitor plate includes two rectangular portions positioned in diagonally opposite sections of the rectangular sensor cell and a connector portion that connects the two rectangular portions of the second capacitor plate and crosses the connector portion of the first capacitor plate.

9. An integrated sensor device for detecting a distance between the sensor device and an object, the sensor device comprising:

a plurality of individual sensor cells having first and second adjacent capacitor plates and insulation therebetween, each capacitor plate having a first face for facing the object and a plurality of sidewall faces facing a plurality of sidewall faces of the adjacent capacitor plate within the sensor cell;

an insulating layer covering the first faces of the first and second capacitor plates; and

an inverting amplifier having an input coupled to one of the first and second capacitor plates and an output coupled to another one of the first and second capacitor plates,

whereby the object positioned adjacent to the insulating layer opposite the sensor cells forms a third capacitor plate that faces the first face of the respective first and second capacitor plates, and in combination with the first and second capacitor plates, defines a pair of feedback capacitances between the input and the output of the inverting amplifier.

10. The sensor device of claim 9, wherein the plurality of individual sensor cells further comprises a substantially planar array of sensor cells.

11. The sensor device of claim 10, further comprising a ground ring surrounding each sensor cell.

12. The sensor device of claim 11, wherein the second faces of the first and second capacitor plates each further comprise a plurality of second faces.

13. The sensor device of claim 11, wherein the first face of each of the first and second capacitor plates firther comprises a substantially equal area.

14. The sensor device of claim 11, wherein the insulating layer covering the first faces of the first and second capacitor plates further comprises a dielectric insulating layer.

15. The sensor device of claim 11, further comprising horizontal and vertical scanning stages coupled to the individual sensor cells of the array of sensor cells, whereby the individual cells are enabled according to a predetermined scanning pattern.

16. An integrated sensor device for detecting a distance between the sensor device and an object, the sensor device comprising:

a first capacitor electrode, the first electrode having a top face and a plurality of side faces, the side faces being in a different plane than its top face;

a second capacitor electrode, the second electrode having a top face and a plurality of side faces, the side faces being in a different plane than its top face;

an amplifier circuit having an input terminal and an output terminal;

an electrical connection between the first capacitor electrode and the input terminal of the amplifier circuit;

an electrical connection between the second capacitor electrode and the output terminal of the amplifier circuit;

an insulating material positioned between the first and second electrodes, the first and second electrodes being positioned having their top faces generally parallel to each other and the plurality of respective side faces positioned facing each other to form a capacitor between the respective side faces of the two electrodes; and

an insulating layer positioned over the first and second electrodes, the insulating layer having an upper surface for receiving an object whose distance from the sensor device is to be measured.

17. The sensor according to claim 16 in which the first capacitor electrode has at least six side faces, in addition to the top face.

18. The sensor according to claim 17 in which the first capacitor electrode has at least nine side faces, in addition to the top face.

19. The sensor according to claim 17 in which the second capacitor electrode has at least six side faces, each of the six side faces being adjacent a respective side face of the first capacitor electrode.

20. The sensor according to claim 18 in which the second capacitor electrode has at least nine faces, each of the nine faces being adjacent to a respective side face of the first capacitor electrode.

21. An integrated capacitive fingerprint sensor for outputting a fingerprint pattern of a fingerprint of a user, the fingerprint sensor comprising:

a plurality of capacitor sensor cells, each having a capacitor therein;

a first capacitor plate within each sensor cell, each capacitor plate having a top face, a bottom face, and a plurality of side faces;

a second capacitor plate within each sensor cell, each second capacitor plate having a top face, a bottom face and a plurality of side faces, at least some of the plurality of the side faces of the first capacitor plate being adjacent to and facing a plurality of the side faces of the second capacitor plate;

a feedback circuit having the first capacitor plate coupled to the input of the feedback circuit and the second capacitor plate coupled to the output of the feedback circuit to provide a negative feedback path having the capacitor formed by the first and second capacitor plates as part of the negative feedback path;

an insulating layer between the first and second capacitor plates for providing a first capacitive feedback value when the fingerprint is not adjacent the capacitive sensor and a second capacitive feedback value different from the first capacitance feedback value when the fingerprint is adjacent the capacitive sensor.