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.