AN2869 datasheet(40/43 Pages) STMICROELECTRONICS

40 / 43 page

Projected sensor design

AN2869

40/43

Doc ID 15298 Rev 6

Figure 35.

Potential false key detection

Avoiding false detection

Follow these recommendations to avoid false touchkey detection:

●

The Tx and Rx tracks should never cross each other; but if they do, it must be at a right

angle.

●

When the Rx and Tx tracks go in the same direction and to places that are close

together, it is better to separate them with a ground which has to be more than twice

the width of each signal track.

●

To further reduce the coupling between the Tx and Rx tracks, the Tx signal can run

under the ground, in this case even if Rx is near the ground, coupling should not

happen.

●

If the Rx track is behind the Tx track from a user point of view, the user cannot modify

the electrical field. Obviously, if Rx and Tx signals are too far apart, there will be no

interaction.

Furthermore, you can consider these general guidelines:

●

The Tx and Rx tracks must be as thin as possible.

●

The Rx tracks must be as far as possible from the touchkey.

●

When there are several touchkeys, it is better to keep all the Tx tracks together and all

the Rx tracks together, which greatly reduces any false touchkey detection.

MS18994V1

Panel

Rx trace

Tx trace

PCB

AN2869 데이터시트(PDF) 40 Page - STMicroelectronics