Datasheet

923
SAM9G35 [DATASHEET]
11053E–ATARM–10-Mar-2014
In an ideal world (linear, with no loss through switches), the horizontal position is equal to:
VY
M
/ VDD or VY
P
/ VDD.
The implementation with on-chip power switches is shown in Figure 41-6. The voltage measurement at the output of the
switch compensates for the switches loss.
It is possible to correct for switch loss by performing the operation:
[VY
P
- VX
M
] / [VX
P
- VX
M
].
This requires additional measurements, as shown in Figure 41-6.
Figure 41-6. Touchscreen Switches Implementation
X
P
X
M
Y
M
VDDANA
Y
P
VDDANA
GND
GND
To the ADC
X
P
X
M
Y
P
VDDANA
GND
Switch
Resistor
Switch
Resistor
Y
P
Y
M
X
P
VDDANA
GND
Switch
Resistor
Switch
Resistor
Horizontal Position Detection
Vertical Position Detection
0
1
2
3