
ASAHI KASEI
[AK4183]
The differential mode position detection is typically more accurate than the single-ended mode.  As the full scale of single-ended 
mode is fixed to the VCC, input voltage may exceed the full-scale reference voltage.  This problem does not occur in differential 
mode.  In addition to this, the differential mode is less influenced by power supply voltage variation due to the ratio-metric 
measurement.   
 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 that 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 that 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)] 
VCC
MS0500-E-00 
 2006/04 
7
XN-Driver SWON
YN 
VREF+ 
VREF- 
ADC 
AIN+ 
AIN- 
XP 
YP 
XN 
YP-Driver SW ON
a) Z1-Position Measurement 
Rtouch
XN-Driver SW ON
YN 
VREF+
VREF-
ADC
AIN+ 
AIN- 
XP 
YP 
XN 
YP-Driver SW ON
b) Z2-Position Measurement  
Rtouch
VCC
Figure 3 Pen Pressure Measurements