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from the edges of the PCB. Connect all the GND pins directly to a solid GND plane and make sure that there

is a low impedance path for the return current following the signal and supply traces all the way from start to

the end.

A good practice is to dedicate one of the inner layers to a solid GND plane and one of the inner layers to

supply voltage planes and traces and route all the signals on top and bottom layers of the PCB. This

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 21: Typical 4-layer PCB construction

Overlapping GND layers without

GND stitching vias

Overlapping GND layers with

GND stitching vias shielding the

RF energy

Figure 22: Use of stitching vias to avoid emissions from the edges of the PCB

7.3 BLE121LR-A Layout Guide

For optimal performance of the antenna place the module at the edge of the PCB as shown in the Figure 23.

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 23: Recommended layout for BLE121LR-A