Method and apparatus to measure self-capacitance using a single pin
First Claim
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1. A touch sensor system, comprising:
- at least one input port to receive an input signal from at least one electrode, the at least one electrode having a capacitance;
an Analog to Digital Converter (ADC) having an ADC input and an ADC output;
a capacitor coupled to the ADC input;
a multiplexer (MUX) having multiple MUX inputs and a MUX output that is coupled to the ADC input, wherein the at least one input port is coupled to one of the multiple MUX inputs;
a first switch for coupling a first reference voltage to a first input of the multiple MUX inputs;
a second switch for coupling a second reference voltage to the first input of the multiple MUX inputs;
a switch controller operable to;
control the first switch to apply the first reference voltage to the first input of the MUX; and
control the second switch to apply the second reference voltage to the first input of the MUX; and
a sensor controller operable to;
receive a first digital value from the ADC output after application of the first reference voltage;
receive a second digital value from the ADC output after application of the second reference voltage;
determine, based at least upon the first and second digital values, an amount of mains interference;
remove the determined amount of mains interference from the first digital value; and
determine a change in the capacitance of the at least one electrode as a function of the first digital value.
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Abstract
A method for measuring capacitance in a sensor device using an internal reference circuit element(s), and without implementing additional circuitry and devices external to the sensor device, is described. In some embodiments a method uses an output pin of the sensor device and an internal reference capacitor of the sensor device to identify a touch applied to a touch point or electrode coupled to the touch sensor. The method applies reference voltages to charge the reference capacitor and measure a signal received from an electrode, wherein the touch sensor controls switching within the touch sensor to apply the reference voltages to the reference capacitor.
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Citations
16 Claims
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1. A touch sensor system, comprising:
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at least one input port to receive an input signal from at least one electrode, the at least one electrode having a capacitance; an Analog to Digital Converter (ADC) having an ADC input and an ADC output; a capacitor coupled to the ADC input; a multiplexer (MUX) having multiple MUX inputs and a MUX output that is coupled to the ADC input, wherein the at least one input port is coupled to one of the multiple MUX inputs; a first switch for coupling a first reference voltage to a first input of the multiple MUX inputs; a second switch for coupling a second reference voltage to the first input of the multiple MUX inputs; a switch controller operable to; control the first switch to apply the first reference voltage to the first input of the MUX; and control the second switch to apply the second reference voltage to the first input of the MUX; and a sensor controller operable to; receive a first digital value from the ADC output after application of the first reference voltage; receive a second digital value from the ADC output after application of the second reference voltage; determine, based at least upon the first and second digital values, an amount of mains interference; remove the determined amount of mains interference from the first digital value; and determine a change in the capacitance of the at least one electrode as a function of the first digital value. - View Dependent Claims (2, 3, 4)
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5. A method, comprising:
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controlling a first switch to charge a reference capacitor to a first voltage level, the reference capacitor coupled to an input of an Analog to Digital Converter (ADC); receiving a first analog signal from a touch sensor electrode at the input of the ADC; converting the first analog signal to a first digital value provided at an output of the ADC; controlling a second switch to charge the reference capacitor to a second voltage level by applying a second voltage; receiving a second analog signal from the touch sensor electrode at the input to the ADC; converting the second analog signal to a second digital value at the output of the ADC; determining, based at least upon the first and second digital values, an amount of mains interference; removing the determined amount of mains interference from the first digital value; detecting a touch to the touch sensor device based on the first digital value. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13)
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14. A non-transitory computer-readable medium comprising instructions which, when implemented by one or more machines, cause the one or more machines to:
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control a first switch to charge a reference capacitor to a first voltage level, the reference capacitor coupled to an input of an Analog to Digital Converter (ADC); receive a first analog signal from a touch sensor electrode at the input of the ADC; convert the first analog signal to a first digital value provided at an output of the ADC; control a second switch to charge the reference capacitor to a second voltage level; receive a second analog signal from the touch sensor electrode at the input to the ADC; convert the second analog signal to a second digital value at the output of the ADC; determine, based at least upon the first and second digital values, an amount of mains interference; remove the determined amount of mains interference from the first digital value; detect a touch to the touch sensor device based on the first and second digital values. - View Dependent Claims (15, 16)
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Specification