ak4650 AKM Semiconductor, Inc., ak4650 Datasheet - Page 46

• Manufacturer Part Number: ak4650
• Description: 16bit 6 Codec With Mic/hp/spk-amp & Tsc
• Manufacturer: AKM Semiconductor, Inc.

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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.
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
ADC
Pen Position Detection of Touch Screen
VREF+
VREF-
a)
X-Position Measurement
Differential Mode
AIN+
AIN-
ON
ON
XP
YP
XN
YN
Figure 34. Axis Measurement
- 46 -
ADC
VREF+
VREF-
b)
Y-Position Measurement
Differential Mode
AIN+
AIN-
ON
ON
XP
YP
XN
YN
[AK4650]
2007/04