Device and method for touch sensing
An embodiment of the present disclosure relates to a method of detection of a touch contact by a sensor including a first step of comparison of a voltage with a first voltage threshold; and a second step of comparison of the voltage with a second voltage threshold, the second step being implemented if the first voltage threshold has been reached within a duration shorter than a first duration threshold, the second voltage threshold being higher than the first voltage threshold.
1. A touch sensor comprising:
a contact capacitor comprising a contact region;
a first switch having a first conduction terminal coupled to a first electrode of the contact capacitor;
a reference capacitor having a first electrode coupled to a first power node;
a second switch having a first conduction terminal coupled to a second electrode of the reference capacitor, and a second conduction terminal coupled to a second conduction terminal of the first switch;
a third switch having a first conduction terminal coupled to a second power node, and a second conduction terminal coupled to the first conduction terminal of the first switch;
a fourth switch having a first conduction terminal coupled to the first conduction terminal of the first switch, and a second conduction terminal coupled to the first power node; and
a comparator configured to compare a contact voltage of the contact region with first and second voltage thresholds, the second voltage threshold being higher than the first voltage threshold.
2. The touch sensor according to claim 1 , wherein the contact voltage is across the contact capacitor.
3. The touch sensor according to claim 2 , wherein the contact region is configured to be charged and discharged into the contact capacitor.
4. The touch sensor according to claim 2 , wherein the reference capacitor is switchably coupled to the comparator in parallel with the contact capacitor.
5. The touch sensor according to claim 1 , further comprising a digital-to-analog converter coupled to the comparator and configured to generate the first and second voltage thresholds.
6. The touch sensor according to claim 1 , further comprising a plurality of contact regions configured to be selectively coupled to the comparator.
7. The touch sensor according to claim 1 , further comprising a Schmitt trigger providing the second voltage threshold.
8. An electronic device comprising:
a package; and
a touch sensor disposed in the package, the touch sensor comprising:
a contact capacitor having a contact region on an external surface of the package;
a first switch having a first conduction terminal coupled to a first electrode of the contact capacitor;
a reference capacitor having a first electrode coupled to a first power node;
a second switch having a first conduction terminal coupled to a second electrode of the reference capacitor, and a second conduction terminal coupled to a second conduction terminal of the first switch;
a third switch having a first conduction terminal coupled to a second power node, and a second conduction terminal coupled to the first conduction terminal of the first switch;
a fourth switch having a first conduction terminal coupled to the first conduction terminal of the first switch, and a second conduction terminal coupled to the first power node;
a comparator having a first input coupled to the second conduction terminals of the first and second switches, and a second input coupled to an output of a reference voltage generator; and
a touch sensor signal provided by an output of the comparator.
9. The electronic device of claim 8 , further comprising:
a fifth switch having a first conduction terminal coupled to the second power node, and a second conduction terminal coupled to the first conduction terminal of the second switch; and
a sixth switch having a first conduction terminal coupled to the first conduction terminal of the second switch, and a second conduction terminal coupled to the first power node.
10. The electronic device of claim 9 , wherein:
the third, fourth, fifth, and sixth switches are transistors;
the first power node is ground; and
the second power node is a power supply voltage.
11. The electronic device of claim 9 , further comprising a microcontroller coupled to the touch sensor signal, and to control inputs of the first, second, third, fourth, fifth, and sixth switches.
12. The electronic device of claim 8 , further comprising:
a counting circuit coupled to the touch sensor signal; and
a second comparator coupled to the counting circuit.
13. The electronic device of claim 8 , wherein the reference voltage generator is a digital-to-analog converter.
14. An electronic device comprising:
a package; and
a touch sensor disposed in the package, the touch sensor comprising:
a contact capacitor having a contact region on an external surface of the package;
a first switch having a first conduction terminal coupled to a first electrode of the contact capacitor;
a reference capacitor having a first electrode coupled to a first power node, and a second electrode coupled to a second conduction terminal of the first switch;
a comparator having a first input coupled to the second conduction terminal of the first switch, and a second input coupled to an output of a reference voltage generator;
a second switch having a first conduction terminal coupled to an output of the comparator;
a Schmitt trigger having an input coupled to the second conduction terminal of the first switch;
a third switch having a first conduction terminal coupled to an output of the Schmitt trigger;
a fourth switch having a first conduction terminal coupled to a second power node, and a second conduction terminal coupled to the first conduction terminal of the first switch;
a fifth switch having a first conduction terminal coupled to the first conduction terminal of the first switch, and a second conduction terminal coupled to the first power node; and
a touch sensor signal provided by second conduction terminals of the second and third switches.
15. The electronic device of claim 14 , further comprising:
a sixth switch having a first conduction terminal coupled to the second power node, and a second conduction terminal coupled to the first conduction terminal of the second switch; and
a seventh switch having a first conduction terminal coupled to the first conduction terminal of the second switch, and a second conduction terminal coupled to the first power node.
16. The electronic device of claim 15 , wherein:
the fourth, fifth, sixth, and seventh switches are transistors;
the first power node is ground; and
the second power node is a power supply voltage.
17. The electronic device of claim 15 , further comprising a microcontroller coupled to the touch sensor signal, and to control inputs of the first, second, third, fourth, fifth, sixth, and seventh switches.
18. The electronic device of claim 14 , further comprising:
a counting circuit coupled to the touch sensor signal; and
a second comparator coupled to the counting circuit.