Touch sensing method and apparatus
First Claim
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1. A method for determining the capacitance of a variable capacitor, the method comprising:
- generating a subject signal having a subject frequency which varies in response to variation in the capacitance of a variable capacitor;
generating a reference signal having a reference frequency which does not vary in response to variation in the capacitance of the variable capacitor;
generating from the subject signal and the reference signal a resultant signal having a resultant frequency which is indicative of the relationship between the subject frequency and the reference frequency; and
determining from the resultant frequency the capacitance of the variable capacitor, wherein the step of determining comprises;
generating from the resultant signal an adjusted resultant signal whose frequency is controlled by a control signal;
maintaining the adjusted resultant signal at a substantially constant desired frequency by manipulation of the control signal; and
determining, from the control signal for which the adjusted resultant signal has the desired frequency, the capacitance of the variable capacitor.
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Abstract
Method and apparatus for determining small variations in capacitance, typically in a capacitive touch sensing device, includes a reference signal of a first frequency and a sample signal of a second frequency. The reference and sample signals are mixed and filtered to isolate the beat frequency therebetween, which is then measured to provide an indication of the variation in the sample frequency. The measurement can then be manipulated by a microprocessor or microcontroller to provide desired control signals. The apparatus is susceptible of digital implementation and single chip implementation.
320 Citations
18 Claims
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1. A method for determining the capacitance of a variable capacitor, the method comprising:
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generating a subject signal having a subject frequency which varies in response to variation in the capacitance of a variable capacitor; generating a reference signal having a reference frequency which does not vary in response to variation in the capacitance of the variable capacitor; generating from the subject signal and the reference signal a resultant signal having a resultant frequency which is indicative of the relationship between the subject frequency and the reference frequency; and determining from the resultant frequency the capacitance of the variable capacitor, wherein the step of determining comprises; generating from the resultant signal an adjusted resultant signal whose frequency is controlled by a control signal; maintaining the adjusted resultant signal at a substantially constant desired frequency by manipulation of the control signal; and determining, from the control signal for which the adjusted resultant signal has the desired frequency, the capacitance of the variable capacitor. - View Dependent Claims (2, 3, 4)
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5. In a touch pad for cursor control or other touch sensitive device, a method of generating a signal representative of the presence of an object such as a finger in proximity to the touch pad or other touch sensitive device comprising the steps of
establishing a reference signal of a first frequency, detecting a second signal having a frequency within a predetermined range of the first frequency, which frequency changes based on the proximity of an object such as a finger to a capacitive sensor, said second signal being produced from one of a plurality of conductive lines in an array of conductive lines, mixing the first and second frequencies to develop at least a beat frequency between the first and second frequencies, and determining the beat frequency as an indicia of the change of capacitance resulting from the proximity of a finger or other object to the capacitive sensor.
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6. A method for representing a change in value of a touch sensing device comprising the steps of
establishing a reference signal of a first frequency, generating a sample signal of a second frequency which varies in response to a position of an object, mixing the reference and the sample signals, filtering the mixed signal to yield a beat frequency of the reference and sample signals, and monitoring the beat frequency to determine a representation of the variation in the sample signal.
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11. A touch sensing device for digitally sensing variations in capacitance comprising, in a single integrated circuit:
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a microcontroller for communicating with a host, means for connecting to a variable capacitance which varies in accordance with the presence of an object near the capacitance, a first digital circuit forming an oscillator when connected to said variable capacitance; a second digital oscillator circuit for providing a reference frequency; a digital mixer connected to said first and second digital circuits; a digital filter connected to said mixer; and a counter connected to said digital filter.
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12. In a capacitive joystick, a method of generating a signal representative of a change in capacitance comprising the steps of:
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establishing a reference signal of a first frequency, detecting a second signal having a frequency within a predetermined range of the first frequency, which frequency changes based on changes in the capacitance of at least a portion of the capacitive sensor, said second signal corresponding to a position of said joystick, mixing the first and second frequencies to develop at least a beat frequency between the first and second frequencies, and determining the beat frequency as an indicia of the change of capacitance resulting from the changes in the capacitance of at least a portion of the capacitive sensor.
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13. A touchpad comprising:
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an array of conductive traces; a first oscillator circuit forming an oscillator when connected to one of said conductive traces; a coupling circuit configured to selectively connect said traces to said circuit; a second oscillator circuit configured to provide a reference frequency; a mixer coupled to outputs of said first and second oscillator circuits; a filter coupled to an output of said mixer; and a counter coupled to an output of said filter. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification