Capacitive Sensing Solutions from
In this section, we are going to cover the Silicon Labs Capacitive Sensing solutions.
What are we measuring?
Capacitance measurement techniques
Relaxation oscillator operation
CapSense system considerations
Tools to aid in capacitive sensing development
Where to learn more
We are going to cover Capacitive Sensing technology starting with an overview of
how CapSense works. Next we will cover how the technology is implemented in
the C8051F900 family and the different pad topologies. We will also cover some of
the tools available for the technology.
What Are We Measuring?
If two metal plates are placed with a gap between them and a voltage is applied to one of
the plates, an electric field will exist between the plates
Any two conductive objects can be used for the plates of the capacitor
When using capacitive sensing for touch applications the capacitor is typically formed by
a PCB element and the conductive object in proximity
Area — capacitance is directly proportional to the area of the plates
Dielectric — capacitance is directly proportional to the relative permittivity of the material
between the plates (air, glass, plastic, etc.)
Distance — capacitance is indirectly proportional to the distance between the two plates
The capacitance of a parallel-plate capacitor is given by:
Є0 is the permittivity of free space
Єr is the relative permittivity of the dielectric material
A is the area of the plates
D is the distance between the plates
When using capacitive sensing for touch applications the PCB trace typically acts as
one plate of the capacitor. When a conductive object (such as a finger for touch
sensing) comes into proximity it acts as the other plate and air is the dielectric. As
the object moves closer to the pad the capacitance changes based on the equ