Capacitive distance sensor

• US 6,114,862 A
• Filed: 03/09/1998
• Issued: 09/05/2000
• 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): BROWN, GLENN WARNER
• Application Number:
  US09/040,261
• Time in Patent Office: 911 Days
• Field of Search: 324/661, 324/662, 324/663, 324/671, 324/686, 324/687, 324/688, 324/690
• US Class Current: 324/662
• 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. A sensor device comprising:

an array of distance detecting cells for detecting a distance between an object and the sensor device, wherein the cells each comprise a capacitive distance sensor that includes a first capacitor plate positioned for facing the object and thereby defining a capacitive element indicative of the distance being detected therebetween;

a second capacitor plate positioned for facing the object, the first and second plates each having a respective sidewall portion that face each other, the respective plates each having a plurality of sidewall faces that are adjacent to and facing each other; and

one or more grounding elements positioned between the cells of the array, each cell having one or more of the grounding elements positioned between the cell and one or more adjacent cells, each grounding element being coupled to ground to provide a discharge path for electrostatic discharge.

2. The sensor device of claim 1 wherein the one or more grounding elements includes a grounding element grid that includes grounding grid segments between each cell and its immediately adjacent cells.

3. 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.

4. The sensor device of claim 3 wherein the first capacitor plate surrounds the second capacitor plate in a plane.

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

6. 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.

7. The sensor device of claim 1 wherein the first capacitor plate of each cell includes two rectangular portions positioned in diagonally opposite sections of the 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.