GD32W51x User Manual
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etc. Detecting the change of a system is the key problem and goal in these technologies. The
TSI module is designed to use charge transfer method which detects the capacitive change
of an electrode when touched by or a finger close to it. In order to detect the capacitive change,
TSI performs a charge transfer sequence including several charging, transfer steps. The
number of these steps indicates the capacitance of an electrode. So the application is able to
detect the change of capacitance by monitoring the step number of each transfer sequence.
As shown in
Figure 26-2. Block diagram of Sample pin and Channel Pin
, there are 4 PINs
in one group and each PIN has an analog switch connected to a common point which is the
key component to implement charge transfer. There should be a sample pin and one or more
channel pin(s) configured in one group. In
Figure 26-2. Block diagram of Sample pin and
, PIN0 is a channel pin and PIN1 is a sample pin while PIN2 and PIN3 are unused.
An electrode connecting PIN0 is designed on PCB board. The A sample capacitor C
s
connected to sample pin PIN1 is also required. Now the capacitance of the channel pin PIN0
includes C
x
and the capacitance introduced by the electrode, so capacitance of PIN0
increases when a finger is touching while the capacitance of PIN1 remains unchanged. Thus,
the finger’s touching can be detected if the capacitance of PIN0 can be measured. In TSI
module, a charge-transfer sequence is performed to measure the capacitance of the channel
pin(s) in a group, which will be detailed in next section.
Figure 26-2. Block diagram of Sample pin and Channel Pin
C
X
Electrode
C
S
ASW_0
PIN0
PIN1
ASW_1
ASW_2
PIN2
PIN3
ASW_3
Chip
26.3.3.
Charge transfer sequence
In order to measure the capacitance of a channel pin, charge transfer sequence is performed
in chip. The sequence shown in
Table 26-1. Pin and analog switch state in a charge-
is described based on the connection of
, i.e. PIN0 is channel pin and PIN1 is sample pin.