ucb1300 NXP Semiconductors, ucb1300 Datasheet - Page 15

• Manufacturer Part Number: ucb1300
• Description: Advanced Modem/audio Analog Front-end
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Product specification
Advanced modem/audio analog front-end
UCB1300
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. The measurement is done with a resistive voltage divider. The internal resistor should be
taken into account to evaluate the settling time of the pressure measurement given the board capacitors connected to
the ADC tap point in pressure mode.
2000 Jun 26
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