Proximity sensing electrode design

AN3150

12/25

DocID17048 Rev 3

4

Proximity sensing electrode design

Each application has its specific proximity detection requirement. The design of the

proximity sensing electrode is the result of the performance target requirement integrating

application constraints.

To help proximity sensor integrators, the following chapters provide experimental results that

can be used as guidelines to design the proximity sensing electrodes.

These tests have been performed on STM8T141 or STM8T143. The absolute performance

values like the detection distance, depend on the detection threshold setting or system gain

that are specific to the application.

4.1

Ring, spiral, plain electrode design

The performance results presented in this application note were measured using electrodes

with basic shapes. The differences between these electrodes were obtained by changing

only one parameter at a time in order to clearly show each parameter impact.

The differences between electrodes highlight the influence of:

•

Electrode size with 5 mm, 10 mm, and 20 mm electrodes.

•

Electrode shape with plain, spiral, and loop electrodes.

•

Backside influences with grounded or non conductive electrode backside layers.

The PCB layouts used for these tests are shown in Figure 6.

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Electrodes 1, 4 and 7 include square spiral electrode shape

•

Electrodes 2, 5 and 8 include square loop electrode

•

Electrodes 3, 6 and 9 include full plain square electrode