Philips Semiconductors
Product specification
Advanced modem/audio analog front-end
UCB1200
PRESSURE MEASUREMENT
The pressure used to press the touch screen can be determined. In fact the contact resistance between the X and Y plate
is measured, which is a good indication of the size of the pressed spot and the applied pressure. A soft stylus, e.g. a
finger, leads to a rather large contact area between the two plates when a large pressure is applied. A hard stylus, e.g.
a pen, leads to less variation in measured contact resistance since the contact area is rather small.
Vtscbias
ipressure
tspx
tsmy
tspy
tsmx
Fig.9 Touch screen setup for pressure measurement.
One plate is biased at one or both terminals during this pressure measurement, whereas the other plate is grounded,
again on one or both terminals. The current flowing through the touch screen is a direct indication for the resistance
between both plates. A compensation for the series resistance, formed by the touch screen plates itself will improve the
accuracy of this measurement.
1998 Jul 22
14
NXP [ NXP ]
