Ratiometric mutual-capacitance-to-code converter
First Claim
1. A capacitance sensing circuit, comprising:
- a set of bridge switches coupled with a reference cell and a sensor cell, wherein the set of bridge switches is configured to;
over a first phase, increase a voltage difference between a first modulation capacitor and a second modulation capacitor, andover a second phase, decrease the voltage difference at a rate corresponding to a difference between a capacitance of the sensor cell and a capacitance of the reference cell; and
a comparator configured to;
generate an output based on comparing a first voltage of the first modulation capacitor with a second voltage of the second modulation capacitor, andinitiate a transition between the first phase and the second phase in response to the comparing.
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Abstract
An embodiment of a capacitance sensing circuit includes a set of bridge switches coupled with a reference cell and a sensor cell. The set of bridge switches is configured to, over a first phase, increase a voltage difference between a first modulation capacitor and a second modulation capacitor, and over a second phase, decrease the voltage difference at a rate corresponding to a difference between a capacitance of the sensor cell and a capacitance of the reference cell. The capacitance sensing circuit also includes a comparator configured to generate an output based on comparing a first voltage of the first modulation capacitor with a second voltage of the second modulation capacitor, and initiate a transition between the first phase and the second phase in response to the comparing.
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Citations
21 Claims
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1. A capacitance sensing circuit, comprising:
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a set of bridge switches coupled with a reference cell and a sensor cell, wherein the set of bridge switches is configured to; over a first phase, increase a voltage difference between a first modulation capacitor and a second modulation capacitor, and over a second phase, decrease the voltage difference at a rate corresponding to a difference between a capacitance of the sensor cell and a capacitance of the reference cell; and a comparator configured to; generate an output based on comparing a first voltage of the first modulation capacitor with a second voltage of the second modulation capacitor, and initiate a transition between the first phase and the second phase in response to the comparing. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A capacitance sensing method, comprising:
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over a first phase, increasing a voltage difference between a first voltage of a first modulation capacitor and a second voltage of a second modulation capacitor; over a second phase, decreasing the voltage difference at a rate corresponding to a difference between a capacitance of the sensor cell and a capacitance of the reference cell; comparing the first voltage with the second voltage; and in response to the comparing, transitioning between the first phase and the second phase. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A capacitance sensing system, comprising:
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a capacitive sensor cell; a reference cell; a transmit (TX) driver configured to supply a TX signal to each of the reference cell and the capacitive sensor cell; a first modulation capacitor; a second modulation capacitor; a set of bridge switches coupled with the reference cell and capacitive sensor cell and configured to; over a first phase, increase a voltage difference between a first voltage of the first modulation capacitor and a second voltage of the second modulation capacitor, and over a second phase, decrease the voltage difference at a rate corresponding to a difference between a capacitance of the capacitive sensor cell and a capacitance of the reference cell; and a comparator configured to; generate an output based on comparing the first voltage with the second voltage, and initiate a transition between the first phase and the second phase in response to the comparing. - View Dependent Claims (19, 20, 21)
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Specification