Reducing common mode noise in touch applications

Abstract

A processing device performs a first scan of a first plurality of electrodes along a first axis in a capacitive sense array to generate a first plurality of capacitance values corresponding to a mutual capacitance at electrode intersections of the capacitive sense array. The processing device performs a second scan of a second plurality of electrodes along a second axis in the capacitive sense array to generate a second plurality of capacitance values corresponding to the mutual capacitance at the electrode intersections of the capacitive sense array. The processing device determines a first coordinate of a conductive object proximate to the capacitive sense array based on the a first subset of first plurality of signals and a second coordinate of the conductive object based on a second subset of the second plurality of signals.

What is claimed is: 
     
         1 . A method comprising:
 performing a first scan of a first plurality of electrodes along a first axis in a capacitive sense array to obtain a first plurality of capacitance values corresponding to a mutual capacitance at electrode intersections of the capacitive sense array;   performing a second scan of a second plurality of electrodes along a second axis in the capacitive sense array to obtain a second plurality of capacitance values corresponding to the mutual capacitance at the electrode intersections of the capacitive sense array;   identifying a first subset of the first plurality of capacitance values and a second subset of the second plurality of capacitance values based on the first scan and the second scan; and   determining, by a processing device, a first coordinate of a conductive object proximate to the capacitive sense array based on the first subset and a second coordinate of the conductive object based on the second subset.   
     
     
         2 . The method of  claim 1 , wherein identifying the first subset and the second subset comprises:
 combining a first group of the first plurality of capacitance values with a second group of the second plurality of capacitance values to obtain a third plurality of capacitance values;   identifying a third subset of the third plurality of capacitance values; and   identifying the first subset and the second subset based on the third subset.   
     
     
         3 . The method of  claim 2 , wherein combining the first group of the first plurality of capacitance values with the second group of the second plurality of capacitance values to obtain the third plurality of capacitance values comprises:
 determining whether a first capacitance value from the first group and a second capacitance value from the second group are greater than a threshold value; and   in response to determining that the first capacitance value and the second capacitance value are greater than the threshold value, combining the first capacitance value to the second capacitance value to obtain a third capacitance value, wherein the third plurality of capacitance values comprises the third capacitance value.   
     
     
         4 . The method of  claim 3 , wherein combining the first group of the first plurality of capacitance values with the second group of the second plurality of capacitance values to obtain the third plurality of capacitance values further comprises:
 determining whether additional capacitance values from one or more of the first plurality of capacitance values, the second plurality of capacitance values or the third plurality of capacitance values are greater than the threshold value; and   in response to determining that the additional capacitance values are greater than the threshold value, combining the first capacitance value to the second capacitance value to obtain a third capacitance value, wherein the third plurality of capacitance values comprises the third capacitance value.   
     
     
         5 . The method of  claim 1 , wherein performing the first scan comprises:
 driving one or more of the second plurality of electrodes along the second axis with a transmit signal; and   measuring a receive signal from the first plurality of electrodes along the first axis.   
     
     
         6 . The method of  claim 1 , wherein performing the second scan comprises:
 driving one or more of the first plurality of electrodes along the first axis with a transmit signal; and   measuring a receive signal from the second plurality of electrodes along the second axis.   
     
     
         7 . The method of  claim 1 , wherein the second scan is performed during a different period of time than the first scan and does not overlap in time with the first scan. 
     
     
         8 . The method of  claim 1 , wherein determining the first coordinate and the second coordinate is further based on a touch position equation, from a plurality of touch position equations comprising at least one of a centroid equation or a linear interpolation equation. 
     
     
         9 . An apparatus comprising:
 a processing device coupled to a capacitive sense array, the processing device configured to:
 perform a first scan of a first plurality of electrodes parallel to a first axis in the capacitive sense array to obtain a first plurality of capacitance values corresponding to a mutual capacitance at electrode intersections of the capacitive sense array; 
 perform a second scan of a second plurality of electrodes parallel to a second axis in the capacitive sense array to obtain a second plurality of capacitance values corresponding to the mutual capacitance at the electrode intersections of the capacitive sense array; 
 identify a first subset of the first plurality of capacitance values and a second subset of the second plurality of capacitance values based on the first scan and the second scan; and 
 determine a first coordinate of a conductive object proximate to the capacitive sense array based on the first subset and a second coordinate of the conductive object based on the second subset. 
   
     
     
         10 . The apparatus of  claim 9 , wherein to identify the first subset and the second subset the processing device is configured to:
 combine a first group of the first plurality of capacitance values with a second group of the second plurality of capacitance values to obtain a third plurality of capacitance values;   identify a third subset of the third plurality of capacitance values; and   identify the first subset and the second subset based on the third subset.   
     
     
         11 . The apparatus of  claim 10 , wherein to combine the first group of the first plurality of capacitance values with the second group of the second plurality of capacitance values the processing device is configured to:
 determine whether a first capacitance value from the first group and a second capacitance value from the second group are greater than a threshold value; and   in response to determining that the first capacitance value and the second capacitance value are greater than the threshold value, combine the first capacitance value to the second capacitance value to obtain a third capacitance value, wherein the third plurality of capacitance values comprises the third capacitance value.   
     
     
         12 . The apparatus of  claim 11  wherein to combine the first group of the first plurality of capacitance values with the second group of the second plurality of capacitance values the processing device is further configured to:
 determine whether additional capacitance values from one or more of the first plurality of capacitance values, the second plurality of capacitance values or the third plurality of capacitance values are greater than the threshold value; and 
 in response to determining that the additional capacitance values are greater than the threshold value, combine the first capacitance value to the second capacitance value to obtain a third capacitance value, wherein the third plurality of capacitance values comprises the third capacitance value. 
 
     
     
         13 . The apparatus of  claim 9 , wherein to perform the first scan, the processing device is configured to:
 drive one or more of the second plurality of electrodes parallel to the second axis with a transmit signal; and   measure a receive signal from the first plurality of electrodes parallel to the first axis.   
     
     
         14 . The apparatus of  claim 9 , wherein to perform the second scan the processing device is configured to:
 drive one or more of the first plurality of electrodes parallel to the first axis with a transmit signal; and   measure a receive signal from the second plurality of electrodes parallel to the second axis.   
     
     
         15 . The apparatus of  claim 9 , wherein the second scan is performed during a different period of time than the first scan and does not overlap in time with the first scan. 
     
     
         16 . The apparatus of  claim 9 , wherein determining the first coordinate and the second coordinate is further based on a touch position equation, from a plurality of touch position equations comprising at least one of a centroid equation or a linear interpolation equation. 
     
     
         17 . An apparatus comprising:
 a touch-sensor device, the touch-sensor device comprising an array of capacitive sense elements, the array comprising a plurality of transmit electrodes and a plurality of receive electrodes;   a transmit selection circuit coupled to the touch-sensor device, the transmit selection circuit to selectively apply a transmit signal to one or more of the transmit electrodes;   a receive selection circuit coupled to the touch-sensor device, the receive selection circuit to selectively measure a signal from one or more of the receive electrodes, wherein the measured signal corresponds to a mutual capacitance value between a transmit electrode and a receive electrode; and   a processing device coupled to the touch-sensor device, the processing device configured to:
 perform a first scan of a first plurality of electrodes aligned with a first axis in the capacitive sense array to measure a first plurality of capacitance values from the receive electrodes aligned with the first axis in the capacitive sense array; 
 switch an orientation of the transmit and receive electrodes; 
 perform a second scan of a second plurality of electrodes aligned with a second axis in the capacitive sense array to measure a second plurality of capacitance values from the receive electrodes aligned with the second axis in the capacitive sense array; and 
 determine a first coordinate of a conductive object proximate to the capacitive sense array based on a first subset of the first plurality of capacitance values and a second coordinate of the conductive object based on a second subset of the second plurality of capacitance values. 
   
     
     
         18 . The apparatus of  claim 9 , wherein to determine the first coordinate and the second coordinate, the processing device is configured to:
 combine a first group of the first plurality of capacitance values with a second group of the second plurality of capacitance values to obtain a third plurality of capacitance values;   identify a third subset of the third plurality of capacitance values; and   identify the first subset and the second subset based on the third subset.   
     
     
         19 . The apparatus of  claim 10 , wherein to combine the first group of the first plurality of capacitance values with the second group of the second plurality of capacitance values the processing device is configured to:
 determine whether a first capacitance value from the first group and a second capacitance value from the second group are greater than a threshold value; and   in response to determining that the first capacitance value and the second capacitance value are greater than the threshold value, combine the first capacitance value to the second capacitance value to obtain a third capacitance value, wherein the third plurality of capacitance values comprises the third capacitance value.   
     
     
         20 . The apparatus of  claim 11  wherein to combine the first group of the first plurality of capacitance values with the second group of the second plurality of capacitance values the processing device is further configured to:
 determining whether additional capacitance values from one or more of the first plurality of capacitance values, the second plurality of capacitance values or the third plurality of capacitance values are greater than the threshold value; and 
 in response to determining that the additional capacitance values are greater than the threshold value, combining the first capacitance value to the second capacitance value to obtain a third capacitance value, wherein the third plurality of capacitance values comprises the third capacitance value.