Pseudo Driven Shield

Abstract

In an embodiment, a touch-sensitive device includes a controller, a shield sensor, a plurality of first electrodes, and a plurality of second electrodes. The plurality of first electrodes spans a first direction and the plurality of second electrodes spans a second direction that is different than the first direction. The controller electrically couples the plurality of first electrodes to the shield sensor. The shield sensor charges the plurality of first electrodes to cause substantially equal voltages to be present on the plurality of first electrodes and the plurality of second electrodes.

1 .- 20 . (canceled) 
     
     
         21 . A touch-sensitive device comprising:
 a controller;   a shield sensor;   a plurality of first electrodes spanning a first direction; and   a plurality of second electrodes spanning a second direction that is different than the first direction;   wherein:
 the controller is operable to electrically couple the plurality of first electrodes to the shield sensor; and 
 the shield sensor is operable to charge the plurality of first electrodes to cause substantially equal voltages to be present on the plurality of first electrodes and the plurality of second electrodes. 
   
     
     
         22 . The device of  claim 21 , wherein each of the plurality of first electrodes is coupled to a single line that is coupled to the shield sensor. 
     
     
         23 . The device of  claim 21 , wherein:
 the plurality of first electrodes and the plurality of second electrodes form a symmetrical pattern such that an exposed area of the plurality of first electrodes and an exposed area of the plurality of second electrodes are equal; and   the exposed area of each of the first and second electrodes has a diamond pattern.   
     
     
         24 . The device of  claim 21 , the controller further operable to measure capacitances of the plurality of second electrodes while substantially equal voltages are present on the plurality of first electrodes and the plurality of second electrodes. 
     
     
         25 . The device of  claim 21 , the controller further operable to control a plurality of switches to electrically couple the plurality of first electrodes or the plurality of second electrodes to the shield sensor. 
     
     
         26 . The device of  claim 21 , 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. 
     
     
         27 . The device of  claim 21 , 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. 
     
     
         28 . A controller operable to:
 electrically couple a plurality of first electrodes to a shield sensor; and   charge the plurality of first electrodes to cause substantially equal voltages to be present on the plurality of first electrodes and a plurality of second electrodes;   wherein:
 the plurality of first electrodes span a first direction; and 
 the plurality of second electrodes span a second direction that is different than the first direction. 
   
     
     
         29 . The controller of  claim 28 , wherein each of the plurality of first electrodes is coupled to a single line that is coupled to the shield sensor. 
     
     
         30 . The controller of  claim 28 , wherein:
 the plurality of first electrodes and the plurality of second electrodes form a symmetrical pattern such that an exposed area of the plurality of first electrodes and an exposed area of the plurality of second electrodes are equal; and   the exposed area of each of the first and second electrodes has a diamond pattern.   
     
     
         31 . The controller of  claim 28 , the controller further operable to measure capacitances of the plurality of second electrodes while substantially equal voltages are present on the plurality of first electrodes and the plurality of second electrodes. 
     
     
         32 . The controller of  claim 28 , the controller further operable to control a plurality of switches to electrically couple the plurality of first electrodes or the plurality of second electrodes to the shield sensor. 
     
     
         33 . The controller of  claim 28 , 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. 
     
     
         34 . The controller of  claim 28 , 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. 
     
     
         35 . A method comprising:
 electrically coupling a plurality of first electrodes to a shield sensor; and   charging the plurality of first electrodes to cause substantially equal voltages to be present on the plurality of first electrodes and a plurality of second electrodes;   wherein:
 the plurality of first electrodes span a first direction; and 
 the plurality of second electrodes span a second direction that is different than the first direction. 
   
     
     
         36 . The method of  claim 35 , wherein each of the plurality of first electrodes is coupled to a single line that is coupled to the shield sensor. 
     
     
         37 . The method of  claim 35 , wherein:
 the plurality of first electrodes and the plurality of second electrodes form a symmetrical pattern such that an exposed area of the plurality of first electrodes and an exposed area of the plurality of second electrodes are equal; and   the exposed area of each of the first and second electrodes has a diamond pattern.   
     
     
         38 . The method of  claim 35 , the method further comprising measuring capacitances of the plurality of second electrodes while substantially equal voltages are present on the plurality of first electrodes and the plurality of second electrodes. 
     
     
         39 . The method of  claim 35 , the method further comprising controlling a plurality of switches to electrically couple the plurality of first electrodes or the plurality of second electrodes to the shield sensor. 
     
     
         40 . The method of  claim 35 , 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.