Methods and circuits for measuring mutual and self capacitance
First Claim
1. A capacitance measurement circuit comprising:
- a capacitance to current conversion circuit configured to operate in a self capacitance mode in a first operational state and configured to operate in a mutual capacitance mode in a second operational state; and
a current to code conversion circuit configured to output a digital value representative of a current generated by the capacitance to current conversion circuit;
wherein;
when the capacitance to current conversion circuit is configured to operate in the self capacitance mode, the capacitance to current conversion circuit comprises a sense capacitor between a first voltage potential and a plurality of switches, wherein the plurality of switches are configured to couple the sense capacitor alternately to a second voltage potential and to the current to code conversion circuit; and
when the capacitance to current conversion circuit is configured to operate in the mutual capacitance mode, the capacitance to current conversion circuit comprises a sense capacitor between a first electrode and a second electrode, the first electrode is coupled to an alternating voltage signal, and the second electrode is coupled to the current to code conversion circuit.
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Abstract
An embodiment of a capacitance measurement circuit may include multiple switches, a first node coupled with a first electrode and coupled with at least a first switch of the multiple switches, and a second node coupled with a second electrode and coupled with at least a second switch of the multiple switches, where the multiple switches are configured to reduce an influence of a self-capacitance of the first electrode and a self-capacitance of the second electrode on an output signal during measurement of a mutual capacitance between the first electrode and the second electrode, and where the multiple switches are configured to reduce an influence of the mutual capacitance on the output signal during measurement of at least one of the self-capacitance of the first electrode and the self-capacitance of the second electrode.
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Citations
16 Claims
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1. A capacitance measurement circuit comprising:
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a capacitance to current conversion circuit configured to operate in a self capacitance mode in a first operational state and configured to operate in a mutual capacitance mode in a second operational state; and a current to code conversion circuit configured to output a digital value representative of a current generated by the capacitance to current conversion circuit;
wherein;when the capacitance to current conversion circuit is configured to operate in the self capacitance mode, the capacitance to current conversion circuit comprises a sense capacitor between a first voltage potential and a plurality of switches, wherein the plurality of switches are configured to couple the sense capacitor alternately to a second voltage potential and to the current to code conversion circuit; and when the capacitance to current conversion circuit is configured to operate in the mutual capacitance mode, the capacitance to current conversion circuit comprises a sense capacitor between a first electrode and a second electrode, the first electrode is coupled to an alternating voltage signal, and the second electrode is coupled to the current to code conversion circuit. - View Dependent Claims (2, 3, 4, 5)
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6. A capacitance sensing system comprising:
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a first plurality of electrodes disposed along a first axis; a second plurality of electrodes disposed along a second axis; a capacitance to current conversion circuit coupled to the first plurality of electrodes and the second plurality of electrodes, the capacitance to current conversion circuit configured to operate in a self capacitance mode in a first operational state and configured to operate in a mutual capacitance mode in a second operational state; and a current to code conversion circuit, wherein the current to code conversion circuit is configured to output a digital value representative of a current generated by the capacitance to current conversion circuit;
wherein;when the capacitance to current conversion circuit is configured to operate in the self capacitance mode, the capacitance to current conversion circuit comprises a sense capacitor between a first voltage potential and a plurality of switches, wherein the plurality of switches are configured to couple the sense capacitor alternately to a second voltage potential and to the current to code conversion circuit; and when the capacitance to current conversion circuit is configured to operate in the mutual capacitance mode, the capacitance to current conversion circuit comprises a sense capacitor between a first electrode and a second electrode, the first electrode is coupled to an alternating voltage signal, and the second electrode is coupled to the current to code conversion circuit. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A method of measuring capacitance, comprising:
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at a capacitance sensing system having a first plurality of electrodes disposed along a first axis, a second plurality of electrodes disposed along a second axis, a capacitance to current conversion circuit coupled to the first plurality of electrodes and the second plurality of electrodes, and a current to code conversion circuit; in a first operational state, configuring the capacitance to current conversion circuit to convert a self capacitance to a first current, wherein the current conversion circuit comprises a sense capacitor between a first voltage potential and a plurality of switches, and wherein the plurality of switches are configured to couple the sense capacitor alternately to a second voltage potential and to the current to code conversion circuit; converting a self capacitance to the first current; converting the first current to a digital value representative of the self capacitance; in a second operational state, configuring the capacitance to current conversion circuit to convert a mutual capacitance to a second current, wherein the capacitance to current conversion circuit comprises a sense capacitor between a first electrode and a second electrode, the first electrode is coupled to an alternating voltage signal, and the second electrode is coupled to the current to code conversion circuit; converting a mutual capacitance to the second current; and converting the second current to a digital value representative of the mutual capacitance. - View Dependent Claims (13, 14, 15, 16)
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Specification