Patent Document ID: 4145748
Application ID: 05863875
Patent Flag: 1

Claim One:
1. A touch pad sensor circuit comprising, in combination: a plurality of drive lines; a plurality of sense lines; a plurality of capacitive touch pads, each having an input coupled to one of said drive lines and an output coupled to one of said sense lines, each touch pad being coupled between a different combination of drive and sense lines from any other touch pad; driver circuit means for providing a drive signal to a selected one of said plurality of drive lines; an A/D converter circuit; means for selectively coupling each one of said plurality of sense lines to said A/D converter circuit; control logic means coupled to said driver circuit means for determining the sequence in which each of said drive lines is selected to receive said drive signal in sequential manner; said control logic means also for causing said coupling means to couple sequential ones of said sense lines to said A/D converter circuit; a counter connected to said A/D converter circuit for producing a count of the digital output thereof; memory means coupled to said control logic means for storing a digital value representative of the magnitude of an output signal of each of said touch pads in a no-touch condition without contact thereof by an outside influence with said touch pad; up/down counter means for receiving the no-touch digital value stored in said memory means for the one touch pad then coupled between a drive line having said driving signal thereon and said A/D converter circuit; and comparator circuit means for comparing the digital output count of said counter and the no-touch digital value in said up/down counter means to produce an output signal when the count of the A/D converter circuit differs from the count in said up/down counter means by more than a preselected amount.