DocID17048 Rev 3

5/25

AN3150

Capacitive sensing overview

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Capacitive sensing overview

1.1

Capacitive sensing system equivalent circuit

To better understand the behavior of a proximity sensor, we need to consider Figure 1 as

the basic equivalent circuit of a single electrode sensor. It contains two signal references:

ground and earth.

Figure 1. Equivalent capacitive circuit of a surface capacitive sensor

Ground is the application reference voltage, while earth represents the surrounding potential

at the voltage of the user’s body. Usually, this is the equipotential of the earth prong, the

third terminal on power outlets.

the source of the useful signal and the variable part of the capacitance. It is referred to as

the earth potential.

capacitances between the electrodes and the application ground that are not impacted by

the finger or body proximity. The sensing device input pin capacitance and the stray

greatly from one application to another and influences considerably the sensitivity of the

capacitive sensor.

ai17440V2

Application

Electrode

Earth

Application ground