Differential transmission for reduction of cross-talk in projective capacitive touch sensors

Abstract

Differential transmission is provided in a capacitive sensor for reducing cross-talk between rows and columns. A capacitive touch sensitive device as disclosed herein includes row conductors and column conductors, a first row signal generator for transmitting a first row signal on a first row conductor, a second row signal generator for transmitting a second row signal on a second row conductor, and a touch processor for identifying a touch event on the touch interface by processing signals present on at least one of the column conductors. The first and second row signals together form a differential row group of signals that cancel each other out or at least substantially mitigate each other so as to reduce cross-talk interference in the sensor.

1 . A method of reducing the baseline signal on a touch sensitive device having first conductors spaced apart from one another, and second conductors spaced apart from one another, the first conductors and the second conductors being oriented such that a touch event proximate to the touch sensitive device will cause a change in coupling therebetween, the method comprising:
 transmitting a plurality of signals forming a differential signal group on each of a plurality of the first conductors, respectively, at least one of the plurality of first conductors being spaced apart from at least one other of the plurality of first conductors by at least one conductor.   
     
     
         2 . The method of  claim 1 , further comprising:
 transmitting another plurality of signals forming another differential signal group on each of another plurality of the first conductors, respectively, at least one of the another plurality of first conductors being spaced apart from at least one other of the another plurality of first conductors by at least one conductor,   wherein each of the signals in the plurality of signals forming the differential signal group are orthogonal to each of the signals in the another plurality of signals forming another differential signal group.   
     
     
         3 . The method of  claim 1 , wherein at least two of the plurality of signals forming the differential signals group are 180 degrees out of phase with respect to each other. 
     
     
         4 . The method of  claim 1 , wherein each at least two of the plurality of signals are frequency orthogonal with respect to each other. 
     
     
         5 . The method of  claim 1 , wherein at least three of the plurality of signals are orthogonal with respect to each other. 
     
     
         6 . The method of  claim 1 , wherein at least two of the plurality of first conductors are spaced apart by a minimum physical spacing that maintains a minimum physical distance between the at least two of the plurality of first conductors. 
     
     
         7 . The method of  claim 6 , wherein the minimum physical spacing is larger than a linear measure of an object affecting a touch event. 
     
     
         8 . The method of  claim 6 , wherein the differential signals group has a maximum physical spacing for maintaining maximum physical distance between at least two of the plurality of first conductors. 
     
     
         9 . The method of  claim 1 , wherein the differential signals group is one of a plurality of differential signals groups and each of the plurality of differential signals groups are remapped between a first frame and a second frame. 
     
     
         10 . A touch sensitive device, comprising:
 first conductors spaced apart from one another;   second conductors spaced apart from one another, the first conductors and the second conductors being oriented such that a touch event proximate to the touch sensitive device will cause a change in coupling therebetween;   a transmitter adapted to transmit a plurality of signals forming a differential signal group on each of a plurality of the first conductors, respectively, at least one of the plurality of first conductors being spaced apart from at least one other of the plurality of first conductors by at least one conductor thereby reducing a baseline signal.   
     
     
         11 . The touch sensitive device of  claim 10 , wherein the transmitter is adapted to transmit another plurality of signals forming another differential signal group on each of another plurality of the first conductors, respectively, at least one of the another plurality of first conductors being spaced apart from at least one other of the another plurality of first conductors by at least one conductor, wherein each of the signals in the plurality of signals forming the differential signal group are orthogonal to each of the signals in the another plurality of signals forming another differential signal group. 
     
     
         12 . The touch sensitive device of  claim 10 , wherein at least two of the plurality of signals forming the differential signals group are 180 degrees out of phase with respect to each other. 
     
     
         13 . The touch sensitive device of  claim 10 , wherein each at least two of the plurality of signals are frequency orthogonal with respect to each other. 
     
     
         14 . The touch sensitive device of  claim 10 , wherein at least three of the plurality of signals are orthogonal with respect to each other. 
     
     
         15 . The touch sensitive device of  claim 10 , wherein at least two of the plurality of first conductors are spaced apart by a minimum physical spacing that maintains a minimum physical distance between the at least two of the plurality of first conductors. 
     
     
         16 . The touch sensitive device of  claim 15 , wherein the minimum physical spacing is larger than a linear measure of an object affecting a touch event. 
     
     
         17 . The touch sensitive device of  claim 10 , wherein the differential signals group has a maximum physical spacing for maintaining maximum physical distance between at least two of the plurality of first conductors. 
     
     
         18 . The touch sensitive device of  claim 10 , wherein the differential signals group is one of a plurality of differential signals groups and each of the plurality of differential signals groups are remapped between a first frame and a second frame.