2.3
Signal tracks
•
Routing should be done in the inner layers of the PCB. For example use layer 2 for
the signals and layer 3 for the supply lines.
•
Traces should have a ground area above and under the line. If this is not possible
make sure that the return path is short by other means (for example using a
ground line next to the signal line).
•
Avoid long parallel lines close to each other.
•
When using two signal vias close to each other, block the direct coupling path with
ground vias.
•
Avoid crossings. Examples:
o
A signal line in layer 2 crossing a supply line in layer 3 is not recommended.
o
A signal crossing a gap in a ground area is not recommended. By doing that
a return current coming back in a ground has to find a path by circling
around the gap and this results in a loop.
2.4
Filtering
Always use high-Q components!
Use filtering especially on supply lines. A special care should be taken to filter RF
frequencies at 2441 MHz.
You should make pads for two bypass capacitors near the 3V3 pin of the module. One
capacitor is from 10 nF to 100 nF. The other one is meant to filter the RF and it is initially
Not Placed. This capacitor is only used in the case of problems. The value is from 5 pF to
100 pF. The value varies from design to design and it must be found out experimentally.
You should also place one series inductor in the supply trace. The value of the inductor is
expected to be from 10 nH to 100 nH.
Signal lines too can pick up noise, interfere with each other or pick up RF. Filtering can
help in case of problems.
The following figures show some ideas for the designs.
7
Содержание WT11-A
Страница 1: ...WT11 A D e s i g n G u i d e V e r s i o n 1 1 F r i d a y S e p t e m b e r 3 0 2 0 0 5 ...
Страница 8: ...Figure 2 Filtering the supply lines L1 C6 C21 and L2 C4 C14 Figure 3 UART 8 ...
Страница 9: ...Figure 4 USB Figure 5 An example of a good power supply design Figure 6 Audio design for WT11 9 ...
