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