User's Manual

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Note d’étude / Technical document : URDx– OTL 5635.1– 007 / 70 230 Edition 03
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7. AUDIO INTEGRATION
Audio mandatory tests for FTA are in handset mode only so a particular care must be brought to the design of
audio (mechanical integration, gasket, electronic) in this mode.
The audio norms which describe the audio tests are 3GPP TS 26.131 & 3GPP TS 26.132.
7.1 MECHANICAL INTEGRATION AND ACOUSTICS
Particular care to Handset Mode: FTA
• Design of the microphone and speaker gasket (elastomer)
• All receivers and speaker must be completely sealed on front side
• For the speaker mode, the back volume must be completely sealed
• The sealed volume must be as big as possible
• Microphone sensitivity depends on the shape of the device eg. about –40 ±3 dBV/Pa for clamshell
• Pre-amplified microphone
• Foresee a stable and large enough area for the gasket of the artificial ear
• 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
8. RECOMMENDATIONS ON LAYOUT OF MMI BOARD
8.1 GENERAL RECOMMENDATIONS ON LAYOUT
There are many different types of signals in the module which are disturbing each other. Particularly, Audio
signals are very sensitive to external signals as VBAT*.... Therefore it is very important to respect some rules to
avoid disruptions or abnormal behaviour.
Main rules:
Ground:
• A ground plane as complete as possible
• Ground of components has to be connected to the ground layer through many vias not regularly
distributed.
• Top and bottom layer shall have as much as possible of ground planes.
Power supplies
• Plan for power supply signals (VBAT, VGPIO), no loop.
• Suitable power supply (VBAT, VGPIO) track width, thickness.
Clocks
• Clock signals must be shielded between two grounds plans and bordered with ground vias.
Data bus and other signals
• Data bus and commands have to be routed on the same plane, none of the lines of the bus shall be parallel to other
lines