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3.9.5 Audio Design
The audio quality delivered by module is highly affected by the application audio design, particularly when
using the analog audio interface. Therefore, special care must be taken when designing the module audio
interface. Improper design and implementation of the audio interface will result in poor audio quality.
Poor audio quality is a result of electrical interference, or noises, from circuits surrounding the audio
interface. There are several possible sources for the audio noise:
Transients and losses on the power supply
EMI from antenna radiations
Digital logic switching noise
Most of the audio noise originates from the GSM transmit burst current surges (217 Hz TDMA buzz),
which appear on the main power supply lines and antenna, but also indirectly penetrate the internal
application's supplies and signals. The noises are transferred into the module 's audio circuits through the
microphone input signals and then are amplified by the module 's internal audio amplifiers.
To minimize the audio noise and improve the audio performance the microphone and speaker signals
must be designed with sufficient protection from surrounding noises.
The following guidelines should be followed to achieve best audio performance:
1.
Keep the audio circuits away from the antenna.
2.
Use RF filtering capacitors on the audio signals.
3.
The audio signals should not be routed adjacent to digital signals.
4.
Isolate the audio signals by a surrounding ground plane or shields.
3.10 Controls and Indicators Interface
The module incorporates several interface signals for controlling and monitoring the module's operation.
The following paragraph describes these signals and their operation.
Pin No.
13
38
37
G510 Hardware User Manual
Signal Name
VDD
LPG
EMERG_RST
Description
LDO power output Illustrating module start up
Module work status indicator
Emergency Reset
Page 29 of 42
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