CapSense Technology
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
11
The capacitive sensor pads of a sensor board are formed by the PCB traces. The most common PCB format is a two-
layer board with sensor pads and a hatched ground plane (see
) on the top, and the electrical components
on the bottom. The ground plane is also provided in the bottom layer surrounding the electrical components. The
electrical components include the CapSense controller and associated parts that convert the sensor capacitance into
digital raw counts.
shows a cross-sectional view of a two-layer board stack-up. The four-layer design is an
option when the board area must be minimized. PCB layout plays a very important role in CapSense system
performance. Best practices are discussed in the device-specific
Figure 2-3. Two-Layer Stack-Up of a CapSense Board
2.1.1.1 Ground Plane
In general, a proper ground plane on the PCB reduces both RF emissions and interference. However, solid grounds
near CapSense sensors, or traces connecting these sensors to the PSoC pins, increase the parasitic capacitance of
the sensors. The increase in parasitic capacitance is unwanted as it reduces the sensitivity. It is thus recommended
that you use hatched ground planes surrounding the sensor and on the bottom layer of the PCB, below the sensors,
as
shows. Typical hatching for the ground fill is 7-mil line, 45 mil spacing on the top layer, and 7-mil line, and
70-mil spacing on the bottom layer. The same hatch-fill on the top layer is driven with shield signal when liquid tolerance
is required. Refer to
Figure 2-4. Ground Fill on a PCB
