Pressure sensing apparatus and method

Abstract

Apparatus () for processing signals from a touch panel () is described. The touch panel () includes a layer of piezoelectric material () disposed between a plurality of sensing electrodes () and at least one common electrode (). The apparatus () includes a first circuit () for connection to the plurality of sensing electrodes (). The first circuit () is configured to generate a plurality of first pressure signals (). Each first pressure signal () corresponds to one or more sensing electrodes () and is indicative of a pressure acting on the touch panel () proximate to the corresponding one or more sensing electrodes (). The apparatus () also includes a second circuit () for connection to the at least one common electrode (). The second circuit () is configured to generate a second pressure signal () indicative of a total pressure applied to the touch panel (). The apparatus () also includes a controller () configured to determine an external interference signal () based on a weighted sum over the second pressure signal () and the plurality of first pressure signals (). The controller () is also configured to compare the external interference signal () against a pre-calibrated threshold (V). The controller is also configured, in response to the external interference signal () being greater than or equal to the pre-calibrated threshold (V), to output an interference flag (Int) indicating that the first and second pressure signals () are influenced by coupling to one or more external electrical fields.