DocID024663 Rev 2

13/20

AN4299

How to improve noise immunity

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4.2

Active Shield

The Active Shield is an electrode which wraps around the sensor. The goal is to minimize

the parasitic capacitance between the sensor and the ground. To drive the shield electrode,

a channel of a dedicated group with its own Cs can be used.

Figure 6. Active Shield

It is important to check the shied electrode waveform. Cs shield capacitance value and Rs

shield serial resistor value must be adjusted in order to obtain the same signal shape as

sensor electrode waveform (same amplitude, same response time).

Figure 7 below shows the electrode sensor waveform in green and shield electrode

waveform in yellow. Cs shield is adjusted to obtain approximately the same charge level at

the end of the acquisition.