| 摘要 |
<p>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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