Automatic environmental compensation of capacitance based proximity sensors

  • US 8,050,876 B2
  • Filed: 07/18/2006
  • Issued: 11/01/2011
  • Est. Priority Date: 07/18/2005
  • Status: Active Grant
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First Claim
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1. A method of operating a capacitive sensor assembly comprising at least one capacitive sensor element and a capacitance-to-digital converter (CDC) that supplies output codes corresponding to sensor element capacitance, comprising acts of:

  • a. detecting changes in an ambient electric field value associated with the at least one capacitive sensor element;

    b. modifying at least one threshold value in response to changes in said ambient electric field value, wherein the at least one threshold value is used to determine whether a part of a human body has touched the at least one sensor element;

    c. determining whether or not proximity of the part of a human body to the at least one sensor element exists, wherein proximity comprises a part of the human body being close to, but not touching, the at least one sensor element, wherein determining further comprises;

    (i) filtering data associated with an output of the CDC for the at least one sensor element with a first filter to generate a first filtered output;

    (ii) filtering data associated with an output of the CDC for the at least one sensor element with a second filter to generate a second filtered output, wherein the second filtered output is different from the first filtered output; and

    (iii) determining whether or not proximity exists based on at least one of a first proximity condition being true or a second proximity condition being true, wherein the first proximity condition is based on a comparison between the first filtered output and its associated threshold, and wherein the second proximity condition is based on a comparison between the second filtered output and its associated threshold; and

    d. preventing the modification of one or more threshold values while proximity is determined to exist.

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