User's Manual

Bluegiga Technologies Oy
Page 21 of 31
arrangement will make sure that any return current follows the forward current as close as possible and any
loops are minimized.
Layout
• Supply voltage
– If possible use solid power plane
– Make sure that solid GND plane follows the traces all the way
– Do not route supply voltage traces across separated GND regions so that the
path for the return current is cut
• MIC input
– Place LC filtering and DC coupling capacitors symmetrically as close to audio
pins as possible
– Place MIC biasing resistors symmetrically as close to microhone as possible.
– Make sure that the bias trace does not cross separated GND regions (DGND ->
AGND) so that the path for the return current is cut. If this is not possible the do
not separate GND regions but keep one solid GND plane.
– Keep the trace as short as possible
Signals
GND
Power
Signals
Recommended PCB layer configuration
Figure 17: Typical 4-layer PCB construction
Overlapping GND layers without
GND stitching vias
Overlapping GND layers with
GND stitching vias shielding the
RF energy
Figure 18: Use of stitching vias to avoid emissions from the edges of the PCB
6.3 BLE121LR-A Layout Guide
For optimal performance of the antenna place the module at the edge of the PCB as shown in the Figure 19.
Do not place any metal (traces, components, battery etc.) within the clearance area of the antenna. Connect
all the GND pins directly to a solid GND plane. Place the GND vias as close to the GND pins as possible. Use
good layout practices to avoid any excessive noise coupling to signal lines or supply voltage lines. Do not
place plastic or any other dielectric material in touch with the antenna.
Min 17mm
Min 17mm
Metal clearance
area
Board edge
Figure 19: Recommended layout for BLE121LR-A