Method and apparatus to measure self-capacitance using a single pin
AssigneeAtmel Corporation
InventorMartin John Simmons
Life of this patent
Estimating the term…
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.
Claims16
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.
A method, comprising:
- 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.
A non-transitory computer-readable medium comprising instructions which, when implemented by one or more machines, cause the one or more machines to:
- 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.
Dependencies are inferred from the claim text.