5.5.4 Active shield or driven shield
Active shield or driven shield. (this name is used in some application notes) drives the shield plane with the same
signal as the electrode.
There are several advantages using Active Shield instead of a grounded shield:
• The parasitic capacitance between the electrode and the shield no longer needs to be charged.
• Protect the touch electrodes from a noise source.
• Increase system stability and performance when a moving metal part is close to the electrode.
Figure 11. Active shield principle
IO4
IO1
IO2
IO3
IO4
IO3
IO2
IO1
Touchkey
group X
Shield
group Y
Rs
key
Cs
key
Rs
shield
Cs
shield
Table 10. Active shield documentation gives a list of documents containing information about the active shield.
Table 10. Active shield documentation
Id
Title Chapters
AN4299
Guidelines to improve conducted noise robustness
on STM32F0/F3/L0/L4 series touch sensing
applications
Active Shield
AN4312
Guidelines for designing touch sensing
applications with surface sensors
Driven shield
AN4316 Tuning a STMTouch-based application Shield adjustment
OLT STM32L4 Online Training Touch sensing controller (TSC)
AN5105
Sensors
AN5105 - Rev 1
page 14/52
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