Detection circuit for matrix touch pad
First Claim
1. A circuit for detecting user contact of one of a plurality of touch pads comprising:
- a plurality of drive lines and a plurality of sense lines, each of said touch pads being coupled to a difference combination of said drive and sense lines from any other of said touch pads;
driver circuit means for providing pulsed drive signals to said drive lines;
at least one amplifier having an input connected at a given time to one of said sense lines, an output and gain means for establishing the gain of said at least one amplifier; and
demodulating means responsive to said at least one amplifier output for determining which of said touch pads is being contacted by a user, wherein said demodulating means includes at least one comparator means responsive at said given time to the amplified sensed signal of said one of said sense lines for producing a pulse having a width that is a function of the time that the associated amplified sensed signal is above a given reference level.
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Accused Products
Abstract
A circuit for detecting user contact of one of a plurality of touch pads includes a plurality of drive lines and a plurality of sense lines coupled with the touch pads. A sense circuit responsive to the signals on the sense lines produces a pulse having a width that is proportional to the amplitude of each of the sense signals. A control circuit measures the width of the pulses produced by the sense circuit and compares each measured pulse width to a reference pulse width to distinguish between a touch and no-touch condition for each touch pad. The sense circuit is illustrated in the form of a comparator having a threshold input that is always exceeded by the sense signal to produce the variable width pulse. Separate amplifiers may be provided for each sense line.
166 Citations
24 Claims
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1. A circuit for detecting user contact of one of a plurality of touch pads comprising:
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a plurality of drive lines and a plurality of sense lines, each of said touch pads being coupled to a difference combination of said drive and sense lines from any other of said touch pads; driver circuit means for providing pulsed drive signals to said drive lines; at least one amplifier having an input connected at a given time to one of said sense lines, an output and gain means for establishing the gain of said at least one amplifier; and demodulating means responsive to said at least one amplifier output for determining which of said touch pads is being contacted by a user, wherein said demodulating means includes at least one comparator means responsive at said given time to the amplified sensed signal of said one of said sense lines for producing a pulse having a width that is a function of the time that the associated amplified sensed signal is above a given reference level. - View Dependent Claims (2, 3, 4, 5)
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6. A circuit for detecting user contact of one of a plurality of touch pads comprising:
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a plurality of drive lines and plurality of sense lines, each of said touch pads being coupled to a different combination of said drive and sense lines from any other of said touch pads; driver circuit means for providing a pulsed drive signal to each said drive line; sense circuit means for sensing signals produced on said sense lines, said sense circuit means including means for producing a pulse having a width that is proportional to the amplitude of each sensed signal; and control circuit means for measuring the width of pulses produced by sense circuit means and comparing each width to a reference pulse width. - View Dependent Claims (7, 8, 9, 10, 11, 12)
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13. A circuit for detecting user contact of one of a plurality of touch pads comprising:
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a plurality of drive lines and a plurality of sense lines, each of said touch pads being coupled to a different combination of said drive and sense lines from any other of said touch pads; driver circuit means for providing pulsed drive signals to said drive lines; a plurality of amplifier means each connected with one of said sense lines for amplifying the sensed signal on the associated said sense line; a plurality of demodulating means each responsive to one of said amplifier means for producing a pulse having a width that is proportional to the amplitude of the associated amplified sensed signal; control circuit means including an input, measuring means for measuring the width of pulses provided to said input and judging means for comparing each measurement to a reference pulse width; and multiplexing means for selectively connecting each said demodulating means to said control circuit means input. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. A circuit for detecting user contact of one of a plurality of touch pads comprising:
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a plurality of drive lines and a plurality of sense lines, each of said touch pads being coupled to a different combination of said drive and sense lines from any other of said touch pads; driver circuit means for providing pulsed drive signals to said drive lines; a plurality of amplifiers, each amplifier having an input connected to one of said sense lines, an output and gain means for establishing the gain of said amplifier; a plurality of comparators, each comparator having an input connected to the output of one of said amplifiers, an output and means establishing a reference level, wherein said comparator output is in a given state whenever the signal to the input is greater than the reference level for that particular comparator; a timer adapted to measuring the width of pulses; multiplexing means for selectively connecting each said comparator output to said timer; and judging means responsive to said timer for determining whether each pulse has a predetermined relationship to a reference pulse width. - View Dependent Claims (21, 22, 23, 24)
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Specification