AK4650 Datasheet, PDF (47/86 Pages) Asahi Kasei Microsystems – 16Bit ΔΣ CODEC with MIC/HP/SPK-AMP & TSC

[AK4650]
■ Pen Pressure Measurement
The touch screen pen pressure can be derived from the measurement of the contact resistance 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 (R_touch) can be calculated using two different methods.
Total resistance of the X-plate sheet (R_xplate) is known
The resistance, R_touch, is calculated from the results of three conversions, X-position, Z₁-Position, and Z₂-Position, using
the following formula:
( ) ^Xposition
R_touch = R_xplate ×
×
Z₂
–1
4096
Z₁
1) The resistances of both the X-plate and Y-plate (R_xplate, R_yplate) are known
The resistance, R_touch, is calculated from the results of three conversions, X-position, Y-Position, and Z₁-Position, using
the following formula:
R_touch = R_xplate ×
X_position
4096
(^×
4096
Z₁
) ( ^{– 1 – Ryplate × 1–}
) ^Yposition
4096
AK4650
ON
YP
AK4650
ON
YP
XP
VREF+
AIN+
ADC
VREF-
AIN-
XN
ON
YN
touch
XP
VREF+
AIN+
ADC
VREF-
AIN-
XN
ON
YN
a) Z1-Position Measurement
Differential Mode
Figure 35. Pen Pressure Measurement
b) Z2-Position Measurement
Differential Mode
touch
MS0502-E-01
- 47 -
2007/04