AK4673 Datasheet, PDF (71/107 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/HP-AMP and Touch Screen Controller

[AK4673]
■ The Pen Pressure Measurement
The touch screen pen pressure can be derived from the measurement of the contact resistor between two plates. The
contact resistance depends on the size of the depressed area and the pressure. The area of the spot is proportional to the
contact resistance. This resistance (Rtouch) can be calculated using two different methods.
The first method is applied when the total resistance of the X-plate sheet is already known. The resistance, Rtouch, is
calculated from the results of three conversions, X-position, Z1-Position, and Z2-Position, and then using the following
formula:
Rtouch = (Rxplate) * (Xposition/4096) * [(Z2/Z1) – 1]
The second method is applied when both the resistances of the X-plate and Y-plate are known. The resistance, Rtouch, is
calculated from the results of three conversions, X-position, Y-Position, and Z1-Position, and then using the following
formula:
Rtouch = (Rxplate*Xposition/4096)*[(4096/Z1) – 1] – Ryplate*[1 – (Yposition/4096)]
TSVDD
YP-Driver SW ON
YP
TSVDD
YP-Driver SW ON
YP
XP
VREF+
AIN+
ADC
VREF-
AIN-
XN
XN-Driver SWON
YN
Rtouch
XP
VREF+
AIN+
ADC
VREF-
AIN-
XN
XN-Driver SW ON
YN
a) Z1-Position Measurement
b) Z2-Position Measurement
Figure 64 Pen Pressure Measurements
Rtouch
MS0670-E-00
- 71 -
2007/09