Self-optimizing touch pad sensor circuit
First Claim
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.
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Abstract
A plurality of capacitive touch pad sensors are multiplexed to the input of a common charge transfer analog-to-digital converter (CTAD) under the control of a control logic circuit. The no-touch digital output of each touch pad is stored in a memory. The touch pads are then sequentially addressed and their output level is digitized in the CTAD and the digital output of each touch pad is compared to its no-touch value stored in the memory. If the digital value read is sufficiently different from the no-touch memorized value, a touch-detection signal is given. The no-touch digital reading in the memory is periodically updated, by a count of only one at most, if the updated no-touch value differs from the no-touch value in the memory.
114 Citations
9 Claims
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1. A touch pad sensor circuit comprising, in combination:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A touch pad sensor comprising, in combination:
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at least one capacitive touch pad; driver circuit means for providing a drive signal to said capacitive touch pad; An A/D converter circuit coupled to said driver circuit means through said capacitive touch pad; a first counter connected to said A/D circuit for producing a digital count representative of an output of said touch pad in one of touch and no-touch conditions; memory means for storing a last previous no-touch digital count representative of a last previous output of said touch pad; an up/down counter receiving said last previous no-touch digital count from said memory means; comparator means for comparing the counts in said first counter and in said up/down counter; circuit means connected between said comparator means and said up/down counter for increasing or decreasing the count in said up/down counter when said up/down counter contains a digital count received from said memory means which digital count is lower or higher respectively than the count in said first counter; and means for reading the last count in said up/down counter back into said memory means. - View Dependent Claims (9)
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Specification