Pseudo driven shield
In one embodiment, a touch-sensitive device includes a controller, horizontal electrodes, and vertical electrodes. The touch-sensitive device further includes a first plurality of switches that couple the horizontal electrodes to a first plurality of sensors, a second plurality of switches that couple the vertical electrodes to a second plurality of sensors, and a third and fourth plurality of switches that couple the horizontal and vertical electrodes to a shield sensor. The controller is operable to perform simultaneous hovering, touch, and proximity detection by selectively controlling the first, second, third, and fourth plurality of switches. The hovering, touch, and proximity detection includes causing substantially equal voltages to be present on the horizontal and vertical electrodes while measuring capacitances using the shield sensor and either the first or second plurality of sensors.
1. A touch sensor for a touch-sensitive device comprising:
a controller;
a plurality of horizontal electrodes;
a plurality of vertical electrodes;
a first plurality of switches operable to electrically couple the plurality of horizontal electrodes to a first plurality of sensors;
a second plurality of switches operable to electrically couple the plurality of vertical electrodes to a second plurality of sensors;
a third plurality of switches operable to electrically couple the plurality of horizontal electrodes to a shield sensor; and
a fourth plurality of switches operable to electrically couple the plurality of vertical electrodes to the shield sensor;
wherein:
the controller is operable to perform simultaneous hovering, touch, and proximity detection by selectively controlling the first, second, third, and fourth plurality of switches;
the hovering, touch, and proximity detection comprises causing substantially equal voltages to be present on the plurality of horizontal and vertical electrodes while:
measuring capacitances of electrodes electrically coupled to the shield sensor; and
measuring capacitances of electrodes electrically coupled to either the first or second plurality of sensors;
the capacitance measurements of the electrodes electrically coupled to the shield sensor and the electrodes electrically coupled to either the first or second plurality of sensors are performed simultaneously; and
the shield sensor is operable to sense capacitances from the plurality of horizontal electrodes and the plurality of vertical electrodes.
2. The touch sensor of claim 1 , wherein the shield sensor comprises a shield current source sensor, and electrodes coupled to the shield current source sensor are charged with current sources that are tuned to produce a similar charging curve as electrodes of the touch sensor that are not coupled to the shield current source sensor.
3. The touch sensor of claim 1 , wherein the shield sensor comprises a shield current source sensor, and the plurality of horizontal and vertical electrodes are charged with limited currents that are tuned to produce identical charging.
4. The touch sensor of claim 1 , wherein the shield sensor comprises a sampling capacitor that has a value that produces identical voltages on electrodes coupled to the shield sensor as voltages on electrodes of the touch sensor not coupled to the shield sensor.
5. The touch sensor of claim 1 , wherein:
controlling the first, second, third, and fourth plurality of switches comprises:
closing the first plurality of switches to couple each of the plurality of horizontal electrodes to a particular one of the first plurality of sensors;
opening the second plurality of switches to decouple the plurality of vertical electrodes from the second plurality of sensors;
opening the third plurality of switches to decouple the plurality of horizontal electrodes from the shield sensor; and
closing the fourth plurality of switches to couple all electrodes of the plurality of vertical electrodes to the shield sensor.
6. The touch sensor of claim 1 , wherein:
controlling the first, second, third, and fourth plurality of switches comprises:
opening the first plurality of switches to decouple the plurality of horizontal electrodes from the first plurality of sensors;
closing the second plurality of switches to couple each of the plurality of vertical electrodes to a particular one of the second plurality of sensors;
closing the third plurality of switches to couple all electrodes of the plurality of horizontal electrodes to the shield sensor; and
opening the fourth plurality of switches to decouple the vertical electrodes from the shield sensor.
7. The touch sensor of claim 1 , wherein:
the first, second, third, and fourth plurality of switches comprise analog switches; and
the first and second plurality of sensors each comprise one of:
a current source sensor; or
a capacitive sensor.
8. The touch sensor of claim 1 , wherein the first and second plurality of sensors and the shield sensor each comprise a sample capacitor, the sample capacitor of the shield sensor being a capacitor in a range of 5 nF to 100 nF.
9. A device comprising:
a controller configured to:
selectively control a first, second, third, and fourth plurality of switches of a touch sensor, wherein:
the first plurality of switches are operable to electrically couple a plurality of first electrodes of the touch sensor to a plurality of sensors;
the second plurality of switches are operable to electrically couple a plurality of second electrodes of the touch sensor to the plurality of sensors;
the third plurality of switches are operable to electrically couple the plurality of first electrodes to a shield sensor; and
the fourth plurality of switches are operable to electrically couple the plurality of second electrodes to the shield sensor, wherein the shield sensor is operable to sense capacitances from the plurality of first electrodes and the plurality of second electrodes; and
cause substantially equal voltages to be present on the plurality of first and second electrodes while:
measuring capacitances of electrodes electrically coupled to the shield sensor; and
measuring capacitances of electrodes electrically coupled to either the first or second plurality of sensors;
wherein the capacitance measurements of the electrodes electrically coupled to the shield sensor and the electrodes electrically coupled to either the first or second plurality of sensors are performed simultaneously.
10. The device of claim 9 , wherein the shield sensor comprises a shield current source sensor, and electrodes coupled to the shield current source sensor are charged with current sources that are tuned to produce a similar charging curve as electrodes of the touch sensor that are not coupled to the shield current source sensor.
11. The device of claim 9 , wherein the shield sensor comprises a shield current source sensor, and the plurality of first and second electrodes are charged with limited currents that are tuned to produce identical charging.
12. The device of claim 9 , wherein the shield sensor comprises a sampling capacitor that has a value that produces identical voltages on electrodes coupled to the shield sensor as voltages on electrodes of the touch sensor not coupled to the shield sensor.
13. The device of claim 9 , wherein:
controlling the first, second, third, and fourth plurality of switches comprises:
closing the first plurality of switches to couple each of the plurality of first electrodes to a particular one of the plurality of sensors;
opening the second plurality of switches to decouple the plurality of second electrodes from the plurality of sensors;
opening the third plurality of switches to decouple the plurality of first electrodes from the shield sensor; and
closing the fourth plurality of switches to couple all electrodes of the plurality of second electrodes to the shield sensor.
14. The device of claim 9 , the controller further configured to select two or more first electrodes of the plurality of first electrodes as a group of electrodes to measure, wherein:
first electrodes of the plurality of first electrodes not selected to be in the selected group of electrodes comprise a non-selected group of electrodes; and
controlling the first, second, third, and fourth plurality of switches comprises:
closing switches of the first plurality of switches that are associated with the selected group of electrodes in order to couple each of the selected group of electrodes to one of the plurality of sensors;
opening switches of the first plurality of switches that are associated with the non-selected group of electrodes in order to decouple the non-selected group of electrodes from the plurality of sensors;
opening switches of the third plurality of switches that are associated with the selected group of electrodes in order to decouple the selected group of electrodes from the shield sensor;
closing switches of the third plurality of switches that are associated with the non-selected group of electrodes in order to couple the non-selected group of electrodes to the shield sensor;
opening the second plurality of switches to decouple the plurality of second electrodes from the plurality of sensors; and
closing the fourth plurality of switches to couple the second electrodes to the shield sensor.
15. The device of claim 9 , wherein:
the plurality of first electrodes comprise horizontal electrodes; and
the plurality of second electrodes comprise vertical electrodes.
16. A method comprising:
selectively controlling a first, second, third, and fourth plurality of switches of a touch sensor, wherein:
the first plurality of switches are operable to electrically couple a plurality of horizontal electrodes of the touch sensor to a first plurality of sensors;
the second plurality of switches are operable to electrically couple a plurality of vertical electrodes of the touch sensor to a second plurality of sensors;
the third plurality of switches are operable to electrically couple the plurality of horizontal electrodes to a shield sensor; and
the fourth plurality of switches are operable to electrically couple the plurality of vertical electrodes to the shield sensor, wherein the shield sensor is operable to sense capacitances from the plurality of horizontal electrodes and the plurality of vertical electrodes; and
causing substantially equal voltages to be present on the plurality of horizontal and vertical electrodes while:
measuring capacitances of electrodes electrically coupled to the shield sensor; and
measuring capacitances of electrodes electrically coupled to either the first or second plurality of sensors;
wherein the capacitance measurements of the electrodes electrically coupled to the shield sensor and the electrodes electrically coupled to either the first or second plurality of sensors are performed simultaneously.
17. The method of claim 16 , wherein the shield sensor comprises a shield current source sensor, wherein:
electrodes coupled to the shield current source sensor are charged with current sources that are tuned to produce a similar charging curve as electrodes of the touch sensor that are not coupled to the shield current source sensor; or
the plurality of horizontal and vertical electrodes are charged with limited currents that are tuned to produce identical charging.
18. The method of claim 16 , wherein the shield sensor comprises a sampling capacitor that has a value that produces identical voltages on electrodes coupled to the shield sensor as voltages on electrodes of the touch sensor not coupled to the shield sensor.
19. The method of claim 16 , wherein:
controlling the first, second, third, and fourth plurality of switches comprises:
closing the first plurality of switches to couple each of the plurality of horizontal electrodes to a particular one of the first plurality of sensors;
opening the second plurality of switches to decouple the plurality of vertical electrodes from the second plurality of sensors;
opening the third plurality of switches to decouple the plurality of horizontal electrodes from the shield sensor; and
closing the fourth plurality of switches to couple all electrodes of the plurality of vertical electrodes to the shield sensor.
20. The method of claim 16 , wherein:
controlling the first, second, third, and fourth plurality of switches comprises:
opening the first plurality of switches to decouple the plurality of horizontal electrodes from the first plurality of sensors;
closing the second plurality of switches to couple each of the plurality of vertical electrodes to a particular one of the second plurality of sensors;
closing the third plurality of switches to couple all electrodes of the plurality of horizontal electrodes to the shield sensor; and
opening the fourth plurality of switches to decouple the vertical electrodes from the shield sensor.