Pressure sensing apparatus and method

An apparatus ( 73 ) for processing signals from a touch panel ( 10 ) is described. The touch panel ( 10 ) includes a layer of piezoelectric material ( 16 ) disposed between a number of sensing electrodes ( 14, 20 ) and at least one common electrode ( 15 ). The apparatus ( 73 ) includes a capacitive touch controller ( 69 ) for connection to the sensing electrodes ( 14, 20 ). The apparatus ( 73 ) also includes a switch network ( 74 ) including a number of inputs for connection to some or all of the sensing electrodes ( 14, 20 ), and an output connected to system ground or a common mode voltage (V CM ). The apparatus ( 73 ) also includes a second circuit ( 24, 44 ) for connection to the at least one common electrode ( 15 ) and configured to generate, based on signals received from the at least one common electrode, a second pressure signal ( 30 ) indicative of a total pressure applied to the touch panel ( 10 ). The apparatus ( 73 ) also includes a controller ( 25 ) configured to control the switch network ( 74 ) to couple any connected sensing electrodes ( 14, 20 ) to system ground or the common mode voltage (V CM ) during a pressure measurement period, and to determine an estimate of the total pressure based on the second pressure signal during the pressure measurement period.