Captivate: components opposite to cap touch electrodes

Hi Patrick,

Placing components underneath the electrodes is possible but with some limitations. Ground planes are placed as close as possible to reduce noise but also kept far enough away to minimize parasitic capacitance. A good rule is one-eighth the thickness for separation between traces and ground and one-half the thickness for separation between electrodes and ground. A 25% fill hatch is typical for reducing the parasitic capacitance and can be increased or decreased to improve noise immunity or sensitivity, respectively. Placing components on the same layer as the GND plane reduces the GND plane's effect thereby increasing sensitivity but decreasing noise immunity. In this regard it depends on the location and quantity of the components used. A four-layer board is recommended so that the GND layer can be separated from both the electrode and component layers, as we've successfully done with other customer designs. Best layout Practices are covered in the Design Guide Section of the CapTIvate Technology Guide: software-dl.ti.com/.../ch_design.html

Regards,
Ryan