User's Manual

Preliminary
Rev
0.6
December 10, 2010
17
Product Specification RF Circuit Routing Constraints
Poor routing Correct routing
The yellow traces cross the RF trace. There is no signal around the RF path.
Figure 3. RF routing examples
• Fill the area around the RF traces with ground and ground vias to connect inner ground layers
for isolation.
• Cut out ground fill under RF signal pads to reduce stray capacitance losses.
• Avoid routing RF traces with sharp corners. A smooth radius is recommended.
• The ground reference plane should be a solid continuous plane under the trace.
• The coplanar clearance (G, below) from the trace to the ground should be at least the trace
width (W) and at least twice the height (H). This reduces the parasitic capacitance, which
potentially alters the trace impedance and increases the losses. Note the figure below shows
several internal ground layers cutout, which may not be necessary for every application.
Figure 4. Coplanar clearance example
Figure 5. Antenna microstrip routing example