3.6 CROSSTALK PRECAUTIONS

Adjacent sense traces might require intervening ground

traces in order to reduce capacitive cross bleed if high

sensitivity is required or high values of delta-Cx are

anticipated (for example, from direct human touch to an

electrode connection). In normal touch applications behind

plastic panels this is almost never a problem regardless of

how the electrodes are wired.

Higher values of Rsns will make crosstalk problems worse;

try to keep Rsns to 22K or less if possible.

In general try to keep the QT220 close to the electrodes and

reduce the adjacency of the sense wiring to ground planes

and other signal traces; this will reduce the Cx load, reduce

interference effects, and increase signal gain.

The one and only valid reason to run ground near SNS

traces is to provide crosstalk isolation between traces, and

then only on an as-needed basis.

7

QT220R R1.02/0905