Patent ID: 7023222

Claim:
A capacitive sensing system comprising: a field generating circuit operative to produce a sensing field signal and to generate a capacitive sensing field, said sensing field signal operative to change in response to an object moving within capacitive sensing field; and a monitor circuit in communication with said field generating circuit operative to monitor said sensing field signal, said monitor circuit comprising: a reference signal counter operative to count and store digital pulses that occur during a first cycle of said signal field signal wherein said stored digital pulses correspond to a first digital value; a field generator signal counter operative to receive and store said first digital value from said reference signal counter, and operative to begin counting down from said first digital value at each new cycle of said sensing field signal, and operative to continue counting down until said field generator signal counter equals zero or until said new cycle ends, and operative to count to a second digital value that corresponds to the difference between the number of digital pulses occurring during said new cycle and the value stored in the reference signal counter; and a threshold compare circuit operative to receive the difference value and compare it to a predetermined value, and operative to generate an object detection signal when said difference value exceeds a predetermined threshold value.