Automatic environmental compensation of capacitance based proximity sensors
First Claim
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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Accused Products
Abstract
Improved capacitive sensor operation is achieved with improved discrimination between environmental drift and apparent drift attributable to human proximity to the sensor. A proximity algorithm detects conditions interpreted as indicating a user is close to, but not touching, a sensor. When such proximity is detected, ambient value calibration is halted, thereby avoiding treating the human'"'"'s proximity as environmental drift requiring compensation and preventing miscalculation of calibration. The proximity algorithm employs two moving-average filters (implemented in hardware or software) to monitor the CDC output values over time and to make appropriate adjustments to a signal representing the ambient, while distinguishing environmental drift from proximity-induced pseudo-drift. Accurate ambient values allow for improved proximity detection by providing this environmentally compensated average value to an adaptive threshold algorithm which features a fast attack, slow decay peak detection to automatically track and compensate for different response characteristics (typically finger sizes).
205 Citations
32 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of operating a capacitive sensor assembly having at least one capacitive sensor element and a capacitance-to-digital converter (CDC) that supplies output codes corresponding to sensor element capacitance, the method comprising:
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a. performing ambient electric field value calibration of a CDC output, wherein calibration comprises measuring changes in an ambient electric field value associated with a capacitor sensor element; b. performing a proximity algorithm to detect at least one condition interpreted as indicating that a part of a human body is close to, but not touching, the sensor element, wherein touching of the sensor element is detected separately from the proximity algorithm, the proximity algorithm employing first and second moving average filters to monitor the CDC output values over time to detect said at least one condition, wherein performing the proximity algorithm further comprises; (i) filtering data associated with the CDC output for the sensor element with the first filter to generate a first filtered output; (ii) filtering data associated with the CDC output for the sensor element with the second filter to generate a second filtered output, wherein the second filtered output is different from the first filtered output; and (iii) detecting the at least one condition based on at least one of a first comparison between the first filtered output and its associated threshold or a second comparison between the second filtered output and its associated threshold; and c. halting ambient electric field value calibration of the CDC output when the proximity algorithm indicates said at least one condition persists. - View Dependent Claims (15, 16)
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17. A method of operating a capacitive sensor assembly having at least one capacitive sensor element and a capacitance-to-digital converter (CDC) that supplies output codes corresponding to sensor element capacitance, the method comprising:
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a. using a multi-step proximity algorithm, detecting from an output of the CDC at least one condition indicative of a user being close to, but not touching, a sensor element; and b. halting measurement of changes in an ambient electric field value of the sensor assembly while said at least one condition persists; wherein the proximity algorithm employs at least a first step and a second step to distinguish environmental drift from proximity induced pseudo-drift; wherein the first step comprises; filtering data associated with the output of the CDC for the sensor element with a first filter to generate a first filtered output; and comparing the first filtered output and its associated threshold to determine whether or not a first proximity condition exists; wherein the second step comprises; filtering data associated with the output of the CDC for the sensor element with a second filter to generate a second filtered output, wherein the second filter is different from the first filter; and comparing the second filtered output and its associated threshold to determine whether or not a second proximity condition exists. - View Dependent Claims (18, 19)
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20. A calibration assembly for use with a capacitive sensor assembly having at least one capacitive sensor element and a capacitance-to-digital converter (CDC) that supplies output codes corresponding to sensor element capacitance, comprising a processor executing one or more sequences of program instructions to:
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a. detect changes in an ambient electric field value associated with the at least one capacitive sensor element; b. modify 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; and c. detect 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 the program instructions to detect proximity further comprise program instructions to; (i) filter 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) filter 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) determine 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) prevent the modification of the at least one threshold value while said proximity is detected. - View Dependent Claims (21, 22, 23, 24, 25)
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26. A calibration assembly comprising:
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capacitive sensor assembly having at least one capacitive sensor element; a capacitance-to-digital converter (CDC) that supplies output codes corresponding to sensor element capacitance; and a processor executing instructions to; a. perform ambient electric field value calibration of a CDC output, wherein calibration comprises measuring changes in an ambient electric field value associated with the capacitive sensor element; b. perform a proximity algorithm to detect at least one condition indicating that a part of a human body is close to, but not touching, the at least one capacitive sensor element, wherein touching of the sensor element is detected separately from the proximity algorithm, the proximity algorithm employing first and second moving average filters to monitor the CDC output values over time to detect said at least one condition, wherein the instructions to perform the proximity algorithm further comprise instructions to; (i) filter data associated with the CDC output for the sensor element with the first filter to generate a first filtered output; (ii) filter data associated with the CDC output for the sensor element with the second filter to generate a second filtered output, wherein the second filtered output is different from the first filtered output; and (iii) detect the at least one condition based on at least one of a first comparison between the first filtered output and its associated threshold or a second comparison between the second filtered output and its associated threshold; and c. halt ambient electric field value calibration of the CDC output when the proximity algorithm indicates said at least one condition persists. - View Dependent Claims (27, 28)
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29. A calibration assembly comprising:
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a capacitive sensor assembly having at least one capacitive sensor element; a capacitance-to-digital converter (CDC) that supplies output codes corresponding to sensor element capacitance; and a processor adapted to; a. use a multi-step proximity algorithm to detect from an output of the CDC at least one proximity condition indicative of a part of a human body being close to, but not touching, a sensor element such that environmental drift can be distinguished from proximity-induced pseudo drift, wherein the multi-step proximity algorithm comprises; a first filter configured to filter data associated with the output of the CDC for the sensor element to generate a first filtered output; and one or more blocks configured to compare the first filtered output and its associated threshold to determine whether or not a first proximity condition exists; a second filter configured to filter data associated with the output of the CDC for the sensor element to generate a second filtered output, wherein the second filter is different from the first filter; and one or more blocks configured to compare the second filtered output and its associated threshold to determine whether or not a second proximity condition exists; and b. halt ambient electric field value calibration of the sensor assembly while said at least one condition persists. - View Dependent Claims (30, 31, 32)
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Specification