UCB1300BE Просмотр технического описания (PDF) - Philips Electronics

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UCB1300BE

Advanced modem/audio analog front-end

Philips Electronics 

Philips Semiconductors

Advanced modem/audio analog front-end

Preliminary specification

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

tsmy

tspx

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.

Vtscbias

Measured resistor

1999 Jul 20

To ADC

Internal resistor (about 1kΩ)

Fig.9 Pressure measurement scheme.

15

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