User's Manual

page 27/35
Note d’étude / Technical document : URD1– OTL 5665.1– 002 / 70 884 Edition 03
Document Sagem Communications Reproduction et divulgation interdites
Sagem Communications document. Reproduction and disclosure prohibited
To get a better audio output design (speaker part) :

The speaker must be completely sealed on front side.

The front aperture must be compliant with speaker supplier’s specifications

The back volume must be completely sealed.

The sealed back volume must be compliant with speaker supplier’s specifications

Take care of the design of the speaker gasket (elastomer).

Foresee a stable and large enough area for the gasket of the artificial ear.
To get a better audio input design (microphone part) :

Take care of the design of the microphone (elastomer).

All receivers must be completely sealed on front side.

Microphone sensitivity depends on the shape of the device eg. about –40 ±3 dBV/Pa for clamshell.

Promote the use of pre-amplified microphone. If needed, use a pre-amplification stage.
As audio input and ouput are strongly linked :

Place the microphone and the speaker as far as possible from one another.
7.2 ELECTRONICS AND LAYOUT
Avoid Distortion & Burst noise

Audio signals must be symmetric (same components on each path).

Differential signals must be routed 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 PCB of the microphone and the one of the speaker.

Reduce as much as possible the number of electronics components (loss of quality, more dispersion).

Audio tracks must be larger than 0.5 mm.