METHODS AND SYSTEMS FOR DETECTING A CAPACITANCE USING SWITCHED CHARGE TRANSFER TECHNIQUES
First Claim
1. A circuit for measuring a measurable capacitance at a first electrical node, the circuit comprising:
- a passive impedance statically coupled between the first electrical node and a second electrical node;
a filter capacitance coupled between the second electrical node and a third electrical node; and
a controller coupled to the first electrical node, wherein the controller is configured to perform a charge transfer process for a number of times greater than one, wherein the charge transfer process comprises applying a predetermined voltage to the first electrical node for a period of time and allowing the measurable capacitance to share charge with the filter capacitance through the passive impedance, and wherein the controller is further configured to determine a value of the measurable capacitance as a function of a voltage on the filter capacitance and the number of times.
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Abstract
Methods, systems and devices are described for detecting a measurable capacitance using charge transfer techniques. According to various embodiments, a charge transfer process is performed for two or more times. During the charge transfer process, a pre-determined voltage is applied to the measurable capacitance, and the measurable capacitance is then allowed to share charge with a filter capacitance through a passive impedance that remains coupled to both the measurable capacitance and to the filter capacitance throughout the charge transfer process. The value of the measurable capacitance can then be determined as a function of a representation of a charge on the filter capacitance and the number of times that the charge transfer process was performed. Such a detection scheme may be readily implemented using conventional components, and can be particularly useful in sensing the position of a finger, stylus or other object with respect to an input sensor.
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Citations
25 Claims
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1. A circuit for measuring a measurable capacitance at a first electrical node, the circuit comprising:
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a passive impedance statically coupled between the first electrical node and a second electrical node;
a filter capacitance coupled between the second electrical node and a third electrical node; and
a controller coupled to the first electrical node, wherein the controller is configured to perform a charge transfer process for a number of times greater than one, wherein the charge transfer process comprises applying a predetermined voltage to the first electrical node for a period of time and allowing the measurable capacitance to share charge with the filter capacitance through the passive impedance, and wherein the controller is further configured to determine a value of the measurable capacitance as a function of a voltage on the filter capacitance and the number of times. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A device for measuring a measurable capacitance, the device comprising:
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a filter capacitance means for storing charge;
means for applying a pre-determined voltage to the measurable capacitance;
passive impedance means statically coupled to both the measurable capacitance and the filter capacitance means for allowing the measurable capacitance to share charge with the filter capacitance means; and
means for determining a value of the measurable capacitance as a function of a representation of a charge on the filter capacitance means.
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20. A proximity sensor comprising:
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a sensor electrode having a measurable capacitance;
a switch coupled to the measurable capacitance;
a passive network coupled to the measurable capacitance and the switch, the passive network comprising a passive impedance and a filter capacitance, wherein the passive impedance statically couples the measurable capacitance to the filter capacitance; and
a controller coupled to the switch, wherein the controller is configured to perform a charge transfer process for a number of times greater than one, wherein the charge transfer process comprises applying a pre-determined voltage to the measurable capacitance using the switch and allowing the measurable capacitance to share charge with the filter capacitance through the passive impedance, and wherein the controller is further configured to determine a value of the measurable capacitance as a function of a representation of a charge of the filter capacitance and the number of times. - View Dependent Claims (21, 22, 23, 24, 25)
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Specification