Reference voltage offset for capacitive touch-sensor measurement
First Claim
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1. A method, comprising:
- stepping a sense voltage of a relaxation oscillator coupled to a touch sensitive capacitor to a first reference voltage;
ramping the sense voltage of the relaxation oscillator from the first reference voltage to a second reference voltage greater than the first reference voltage, wherein stepping the sense voltage comprises step-charging a capacitance to a voltage with the first reference voltage at a first time;
and stepping the sense voltage to a voltage less than the first reference voltage, wherein ramping the sense voltage comprises charging the capacitance with a current source until the voltage increases to the second reference voltage at a second time by disconnecting the capacitance from the first reference voltage and connecting the capacitance to the current source after the capacitance is disconnected from the first reference voltage.
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Abstract
Apparatus and methods for offsetting the reference voltage range of a relaxation-type oscillator decreases sensing time and reduces noise-induced jitter.
50 Citations
14 Claims
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1. A method, comprising:
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stepping a sense voltage of a relaxation oscillator coupled to a touch sensitive capacitor to a first reference voltage; ramping the sense voltage of the relaxation oscillator from the first reference voltage to a second reference voltage greater than the first reference voltage, wherein stepping the sense voltage comprises step-charging a capacitance to a voltage with the first reference voltage at a first time; and stepping the sense voltage to a voltage less than the first reference voltage, wherein ramping the sense voltage comprises charging the capacitance with a current source until the voltage increases to the second reference voltage at a second time by disconnecting the capacitance from the first reference voltage and connecting the capacitance to the current source after the capacitance is disconnected from the first reference voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus, comprising:
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a touch-sensitive capacitor; a relaxation oscillator, selectively coupled to the touch-sensitive capacitor, wherein the relaxation oscillator is configured to step-charge the touch sensitive capacitor to a first reference voltage to ramp-charge the touch-sensitive capacitor to a second reference voltage above the first reference voltage, and to stop-discharge the touch-sensitive capacitor to a voltage below the first reference voltage, and the relaxation oscillator includes; a switched voltage source equal to the first reference voltage to step charge the touch-sensitive capacitor to the first reference voltage at a first time, a switched current source to ramp-charge the touch sensitive capacitor of the second reference voltage at a second time, and a ground switch to step-discharge the touch sensitive capacitor to the voltage below the first reference voltage at a third time; and a first comparator to compare voltage of the touch-sensitive capacitor to the first reference voltage, wherein the first comparator is configured to; disconnect the ground switch from the touch-sensitive capacitor and connect the switched voltage source to the touch-sensitive capacitor when the voltage of the touch-sensitive capacitor is below the first reference voltage; and connect the switched current source to the touch-sensitive capacitor, after a first delay, when the voltage of the touch-sensitive capacitor is at or above the first reference voltage. - View Dependent Claims (9, 10, 11)
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12. An apparatus, comprising:
means for decreasing a sensing time for a capacitance sensor while moving a measurable part of a capacitance charge ramp of the capacitance sensor away from a ground potential, the means for decreasing comprising; means for stepping a sense voltage of a relaxation oscillator to a first reference voltage above the ground potential; means for ramping the sense voltage between the first reference voltage and a second reference voltage; means for stepping the sense voltage to a voltage below the first reference voltage; means for timing the measurable part of the capacitance charge ramp; means for step-charging a capacitance to a voltage with the first reference voltage at a first time; means for charging the capacitance with a current source until the voltage increases to the second reference voltage at a second time; means for disconnecting the capacitance from the first reference voltage; and means for connecting the capacitance to the current source after the capacitance is disconnected from the first reference voltage. - View Dependent Claims (13, 14)
Specification