Touch Sensing Having Increased Immunity to the Presence of a Fluid Layer
In certain embodiments, a touch sensitive device includes a cover panel, a plurality of drive electrodes positioned below the cover panel, a plurality of sense electrodes positioned below the cover panel, and a controller. The controller includes a signal generator operable to supply a drive signal to a particular drive electrode of the plurality of drive electrodes. The controller further includes measurement circuits associated with each of the plurality of sense electrodes, each measurement circuit being operable to generate a signal corresponding to the charge transfer between the particular drive electrode and a corresponding sense electrode. The drive signal supplied by the signal generator has a frequency that reduces the charge transfer caused by a fluid layer located on the cover panel to an amount falling below a threshold corresponding to the point at which the controller determines that a touch is present.
1 . A touch sensitive device, comprising
a cover panel;
a plurality of drive electrodes positioned below the cover panel;
a plurality of sense electrodes positioned below the cover panel; and
a controller comprising:
a signal generator operable to supply a drive signal to a particular drive electrode of the plurality of drive electrodes; and
measurement circuits associated with each of the plurality of sense electrodes, each measurement circuit operable to generate a signal corresponding to the charge transfer between the particular drive electrode and a corresponding sense electrode;
wherein the drive signal has a frequency that reduces the charge transfer caused by a fluid layer located on the cover panel to an amount falling below a threshold corresponding to the point at which the controller determines that a touch is present.
2 . The touch sensitive device of claim 1 , wherein the sense electrodes are separated from the drive electrodes by a dielectric layer.
3 . The touch sensitive device of claim 1 , wherein:
the fluid layer comprises water; and
the drive signal has a frequency in the range of 3 MHz to 5 MHz.
4 . The touch sensitive device of claim 1 , wherein the drive signal comprises a sinusoidal waveform.
5 . The touch sensitive device of claim 1 , wherein the drive signal comprises a square waveform.
6 . The touch sensitive device of claim 1 , wherein the drive signal comprises a. waveform containing the frequency.
7 . The touch sensitive device of claim 1 , wherein the threshold comprises a minimum difference between a stored historical average value of the signal generated by the measurement circuit corresponding to a particular sense electrode and a current value of the signal generated by the measurement circuit corresponding to a particular sense electrode.
8 . A touch sensitive device, comprising
a cover panel;
a plurality of electrodes positioned below the cover panel; and
a controller operable to supply a drive signal to a particular electrode of the plurality of electrodes, the drive signal having a frequency corresponding to a frequency-dependent permittivity of a particular fluid.
9 . The touch sensitive device of claim 8 , wherein the drive signal has a frequency in the range of 1 MHz to 10 MHz.
10 . The touch sensitive device of claim 8 , wherein:
the particular fluid comprises water; and
the drive signal has a frequency in the range of 3 MHz to 5 MHz.
11 . The touch sensitive device of claim 8 , wherein the drive signal comprises a sinusoidal waveform.
11 . The touch sensitive device of claim 8 , wherein the drive signal comprises a square waveform.
12 . The touch sensitive device of claim 8 , wherein the drive signal comprises a waveform containing the frequency.
13 . A method, comprising
supplying a drive signal to a particular drive electrode of a plurality of drive electrodes of a touch sensitive device;
generating, using a measurement circuit associated with each of a plurality of sense electrodes of the touch sensitive device, a plurality of signals, each signal corresponding to the charge transfer between the particular drive electrode and one of the plurality of sense electrodes; and
determining if each of the plurality of exceeds a threshold value;
wherein the supplied drive signal has a frequency that reduces the charge transfer caused by a fluid layer located on a cover panel of a touch sensitive device to an amount less than the threshold.
14 . The method of claim 13 , wherein:
the fluid layer comprises water; and
the drive signal has a frequency in the range of 3 MHz to 5 MHz.
15 . The method of claim 13 , wherein the drive signal comprises a sinusoidal waveform.
16 . The method of claim 13 , wherein the drive signal comprises a square waveform.
17 . The method of claim 13 , wherein the drive signal comprises a waveform containing the frequency.
18 . The method of claim 13 , wherein the threshold comprises a minimum difference between a stored historical average value of the signal generated by the measurement circuit corresponding to a particular sense electrode and a current value of the signal generated by the measurement circuit corresponding to a particular sense electrode.