Mitigation of external fields in piezoelectric sensors

A touch panel system comprising:

• a touch panel comprising a layer of piezoelectric material disposed between a plurality of sensing electrodes and at least one common electrode;
• and,
• an apparatus for processing signals from the touch panel, the apparatus comprising:
• a first circuit for connection to the plurality of sensing electrodes and configured to generate a plurality of first pressure signals, wherein 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;
• a second circuit for connection to the at least one common electrode and configured to generate a second pressure signal indicative of a total pressure applied to the touch panel;
• and
• a controller configured to determine an estimate of the total pressure based on a weighted difference of the second pressure signal and a sum over the plurality of first pressure signals.

A method of processing signals from a touch panel, the touch panel comprising a layer of piezoelectric material disposed between a plurality of sensing electrodes and at least one common electrode, the method comprising:

• generating a plurality of first pressure signals, each first pressure signal based on signals received from one or more sensing electrodes, and each first pressure signal indicative of a pressure acting on the touch panel proximate to the corresponding one or more sensing electrodes;
• generating, based on signals received from the at least one common electrode, a second pressure signal indicative of a total pressure applied to the touch panel;
• and
• determining an estimate of the total pressure based on a weighted difference of the second pressure signal and a sum over the plurality of first pressure signals.