User's Manual

URD1 – OTL 5696.1– 022 / 72740 Edition 0.4 HILONC- 3GPS APPLICATION NOTE
The sealed back volume must be in compliance with specifications of the speaker supplier.
Pay attention to the design of the speaker gasket (elastomer).
Make sure to leave sufficient space for the artificial ear gasket.
To achieve a more ideal audio input design (microphone part) :
Pay attention to the design of the microphone (elastomer).
All receivers must be completely sealed on the front side.
 Microphone sensitivity depends on the shape of the device but should be in the region of
–
40
±3 dBV/Pa.
Encourage the use of a pre-amplified microphone. If needed, use a pre-amplification stage.
As audio input and output are strongly linked:
Place the microphone and the speaker as far away as possible from one another.
7.2. Electronics and layout
Avoiding Distortion & Burst Noise
 Audio signals must be symmetric (same components on each path).
Differential signals must be routed in parallel.
Audio layer must be surrounded by 2 ground layers.
The link from one component to the ground must be as short as possible.
If possible separate the PCBs of the microphone and speaker.
Reduce the number of electronic components as much as possible (to avoid loss of quality and greater
dispersion).
Audio tracks must be larger than 0.5 mm.
8. Recommendations on customer board layout
8.1. General recommendations on layout
There are many different types of signals in the module which may interfere with each other. Particularly, audio
signals are very sensitive to external signals such as
VBAT
.
Therefore it is very important to follow some basic
guidelines to avoid signal disruption or abnormal behavior.
 Magnetic fields generated by
VBAT
tracks may cause speaker interference and burst noise. In this case,
modify layout of the
VBAT
tracks to reduce the phenomenon.
8.1.1. Ground
 Ensure the ground plane is as complete as possible.
 Grounding of components should be connected to the ground layer through a number of irregularly
distributed vias.
 Top and bottom layer should set aside as much space for the ground plane as possible. Flood remaining
empty surfaces of the layout of those two layers with a ground plane connected to the main ground through as
many vias as possible.
8.1.2. Ground layout guidelines
 Proper grounding is crucial to end-product performance. At least one layer must be a dedicated ground plane.
This ground plane is the common point referenced by all end-product circuits.
In addition to the dedicated ground plane layer, unused space on all PCB layers should be filled with
grounding to provide the most robust grounding possible from layer to layer.
 Bypass capacitors should be connected directly to their surface layer ground fill. Multiple vias should connect
Note d’étude / Technical document :
01/08/20111 - Page 28 / 41