Pressure sensing apparatus and method

1. An apparatus for 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 apparatus comprising:

a first circuit comprising:

a capacitive touch controller for connection to the plurality of sensing electrodes;

a charge amplifier for connection to each of the plurality of sensing electrodes via an impedance network, the charge amplifier configured to output a first pressure signal corresponding to all of the plurality of sensing electrodes, wherein the first pressure signal is indicative of a pressure acting on the touch panel proximate to the plurality of sensing electrodes;

a second circuit comprising a common electrode charge amplifier 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 the first pressure signal.

2. The apparatus according to claim 1 , wherein the controller is further configured to determine a location at which pressure is applied to the touch panel;

wherein a coefficient used for the weighted difference of the second pressure signal and the first pressure signals depends upon the location.

3. The apparatus according to claim 1 , wherein the controller determines the estimate of the total pressure using equation:

F CE =(1− C CE ) Q CE C CE Q sen

in which F CE is a piezoelectric charge induced on the at least one common electrode, Q CE is a charge measured on the at least one common electrode, Q sen is a sum of charges measured on all of the plurality of sensing electrodes, and C CE is a pre-calibrated constant having a value between zero and unity;

wherein the estimate of the total pressure is based on F CE .

4. The apparatus according to claim 1 , wherein the first circuit is configured to generate, for each sensing electrode of the plurality of sensing electrodes, a capacitance signal indicative of a capacitance of the each sensing electrode;

wherein the controller is configured to determine a location at which pressure is applied to the touch panel based on the capacitance signals.

5. The apparatus according to claim 4 , wherein generating the first pressure signals and the capacitance signals comprises separating single signals received from the plurality of sensing electrodes.

6. The apparatus according to claim 1 , further comprising a differential amplifier configured to receive the first pressure signal and the second pressure signal, and to output a weighted difference of the received first pressure signal and the second pressure signal to the controller;

wherein the controller is configured to determine the estimate of the total pressure based on the weighted difference received from the differential amplifier.

7. A touch panel system comprising:

the apparatus according to claim 1 ; and

the touch panel comprising a layer of piezoelectric material disposed between the plurality of sensing electrodes and the at least one common electrode.

8. An electronic device comprising the touch panel system according to claim 7 .

9. 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 first pressure signals, the first pressure signal based on signals received from all of the plurality of sensing electrodes, and output from a charge amplifier connected to each of the plurality of sensing electrodes via an impedance network, wherein the first pressure signal is indicative of a pressure acting on the touch panel proximate to the plurality of sensing electrodes;

generating, based on signals received from the at least one common electrode by a common electrode charge amplifier, 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 the first pressure signal.

10. The method according to claim 9 , further comprising determining a location at which pressure is applied to the touch panel;

wherein a coefficient used for the weighted difference of the second pressure signal and the first pressure signals-depends upon the location.

11. The method according to claim 9 , wherein determining the estimate of the total pressure applied to the touch panel comprises using the equation:

F CE =(1− C CE ) Q CE −C CE Q sen

in which F CE is a piezoelectric charge induced on the at least one common electrode, Q CE is a charge measured on the at least one common electrode, Q sen is a sum of charges measured on all of the plurality of sensing electrodes and C CE is a pre-calibrated constant having a value between zero and unity;

wherein the estimate of the total pressure is based on F CE .

12. The method according to claim 9 , comprising generating, based on signals received from each sensing electrode of the plurality of sensing electrodes, a capacitance signal indicative of a capacitance of the each sensing electrode;

the method further comprising determining a location at which pressure is applied to the touch panel based on the capacitance signals.

13. The method according to claim 12 , wherein generating the first pressure signal and the capacitance signals comprises separating single signals received from the plurality of sensing electrodes.