AK4650 Datasheet, PDF (46/86 Pages) Asahi Kasei Microsystems – 16Bit ΔΣ CODEC with MIC/HP/SPK-AMP & TSC

[AK4650]
■ Pen Position Detection of Touch Screen
The selected touch screen position is detected by the voltage measurement of one axis when the voltage is supplied
between the two terminals of the other axis. At least two A/D conversions are needed to get the two-dimensional (X/Y
axis) position.
ON
XP
ON
XP
VREF+
AIN+
ADC
YP
VREF-
AIN-
XN
ON
VREF+
AIN+
ADC
YP
VREF-
AIN-
XN
YN
YN
ON
a) X-Position Measurement
Differential Mode
b) Y-Position Measurement
Differential Mode
Figure 34. Axis Measurement
The differential mode is generally more accurate than the single-ended mode for the position detection. Since the full
scale of single-ended mode is fixed to the internal (or external) reference voltage, the 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 by the ratio-metric measurement.
However, note that the touch screen driver switch is still ON and the current flows even for the A/D conversion time.
MS0502-E-01
- 46 -
2007/04