Capacitive sensing employing a repeatable offset charge
First Claim
1. A processor-readable storage medium having stored thereon instructions executable by the processor to perform steps of a method for sensing the presence of an object or body portion in contact with or close proximity to another object, the method comprising:
- providing a first conductor capacitively coupled to a ground to thereby form a scoop capacitor having a capacitance which varies in relation to the proximity of said object or body portion to said conductor;
a pair of second and third conductors forming a bucket capacitor having a capacitance which is larger than a maximum capacitance of said scoop capacitor; and
an input threshold switch;
performing switching to selectively;
connect at least one of said scoop capacitor and said bucket capacitor to a voltage source to charge said at least one capacitor, set a charge of said bucket capacitor at a repeatable non-zero reference level, vary the charge of said bucket capacitor from said reference level in relation to a relative size of said scoop capacitor, and apply a voltage of said bucket capacitor to said input threshold switch;
detecting an input state of said input threshold switch;
determining a value (TouchVal) relating to a number of cycles of said varying of the bucket capacitor charge, corresponding to a detection of a transition of said input threshold switch; and
generating, based upon TouchVal, a signal indicative of an ON state wherein said object or body portion is in contact with or close proximity to said another object, and an OFF state wherein said object or body portion is not in contact with or close proximity to said object.
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Accused Products
Abstract
Capacitive proximity sensing is carried out by detecting a relative change in the capacitance of a “scoop” capacitor formed by a conductor and a surrounding ground plane. Charge is transferred between the “scoop” capacitor and a relatively large “bucket” capacitor, and a voltage of the bucket capacitor is applied to an input threshold switch. A state transition (e.g., from low to high, or high to low) of the input threshold switch is detected and a value (TouchVal) indicative of a number of cycles of charge transfer required to reach the state transition is determined. The presence or absence of an object or body portion in close proximity to or contact with a device can be determined by comparing TouchVal with a predetermined threshold value (TouchOff). In order to lessen the time required for detection, and/or improve the sensitivity thereof, the bucket capacitor may initially be charged to a repeatable non-zero reference level closer to the charge level that will cause a state transition. TouchOff can be adjusted to take into account environmentally induced (non-touch related) changes in the capacitance of the scoop capacitor. Power management may be provided in a user operated data input device utilizing the inventive proximity sensing.
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Citations
17 Claims
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1. A processor-readable storage medium having stored thereon instructions executable by the processor to perform steps of a method for sensing the presence of an object or body portion in contact with or close proximity to another object, the method comprising:
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providing a first conductor capacitively coupled to a ground to thereby form a scoop capacitor having a capacitance which varies in relation to the proximity of said object or body portion to said conductor;
a pair of second and third conductors forming a bucket capacitor having a capacitance which is larger than a maximum capacitance of said scoop capacitor; and
an input threshold switch;
performing switching to selectively;
connect at least one of said scoop capacitor and said bucket capacitor to a voltage source to charge said at least one capacitor, set a charge of said bucket capacitor at a repeatable non-zero reference level, vary the charge of said bucket capacitor from said reference level in relation to a relative size of said scoop capacitor, and apply a voltage of said bucket capacitor to said input threshold switch;
detecting an input state of said input threshold switch;
determining a value (TouchVal) relating to a number of cycles of said varying of the bucket capacitor charge, corresponding to a detection of a transition of said input threshold switch; and
generating, based upon TouchVal, a signal indicative of an ON state wherein said object or body portion is in contact with or close proximity to said another object, and an OFF state wherein said object or body portion is not in contact with or close proximity to said object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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Specification