Noise rejection and parasitic capacitance removal implementations
First Claim
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1. A capacitive sensing circuit comprising:
- a sense plate for reflecting a capacitance to be measured; and
a capacitance measurement circuit including;
a charge transfer circuit that, during a charge transfer cycle, introduces a charge on said sense plate which reflects a capacitance associated with said sense plate, said charge being introduced by applying a charging voltage of a fixed value to said sense plate, and transfers an amount of charge from said sense plate to said capacitance measurement circuit, said charge transfer cycle being repeated a number of times to form a complete capacitance measurement cycle; and
a charge subtracting circuit that effectively reduces the measured capacitance by removing an amount of charge from said capacitance measurement circuit during each charge transfer cycle, wherein, during each charge transfer cycle, the amount of said charge removed from said capacitance measurement circuit by the charge subtracting circuit is in a proportion to the amount of said charge transferred from said sense plate to said capacitance measurement circuit, which proportion remains the same for each charge transfer cycle in the complete capacitance measurement cycle, irrespective of an amount of charge accumulated in the measurement circuit throughout the complete capacitance measurement cycle.
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Abstract
A capacitive sensing circuit including a microchip and a sense plate, wherein the microchip comprises a hardware Q RF noise detector module that provides a logical indication of when noise impacts on the integrated circuit.
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Citations
18 Claims
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1. A capacitive sensing circuit comprising:
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a sense plate for reflecting a capacitance to be measured; and a capacitance measurement circuit including; a charge transfer circuit that, during a charge transfer cycle, introduces a charge on said sense plate which reflects a capacitance associated with said sense plate, said charge being introduced by applying a charging voltage of a fixed value to said sense plate, and transfers an amount of charge from said sense plate to said capacitance measurement circuit, said charge transfer cycle being repeated a number of times to form a complete capacitance measurement cycle; and a charge subtracting circuit that effectively reduces the measured capacitance by removing an amount of charge from said capacitance measurement circuit during each charge transfer cycle, wherein, during each charge transfer cycle, the amount of said charge removed from said capacitance measurement circuit by the charge subtracting circuit is in a proportion to the amount of said charge transferred from said sense plate to said capacitance measurement circuit, which proportion remains the same for each charge transfer cycle in the complete capacitance measurement cycle, irrespective of an amount of charge accumulated in the measurement circuit throughout the complete capacitance measurement cycle. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of sensing capacitance which includes the steps of:
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a) introducing a charge on a sense plate which reflects a capacitance associated with said sense plate, said charge being introduced by applying a charging voltage of a fixed value to said sense plate; and b) transferring a first amount of said sense plate charge to a capacitance measurement circuit;
wherein steps a) and b) combined define a charge transfer cycle and said charge transfer cycle is repeated a number of times to form a complete capacitance measurement cycle; andremoving a second amount of charge from the capacitance measurement circuit during each charge transfer cycle, wherein said first amount of charge that is transferred from said sense plate to said capacitance measurement circuit and said second amount of charge that is removed from said capacitance measurement circuit, stay in a proportion to one another that remains the same for all of said charge transfer cycles throughout the complete capacitance measurement cycle. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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Specification