Suggestion For Mechanical Design - Quectel GSM Series Audio Design Manual

4. Reduce power voltage ripple, especially the power supply in audio circuits. A wide layout is used from
power source (like adapter interface, battery connector, or LDO output pin) to audio power supply.
Good antenna matching is also important to reduce power ripple.
5. The filtering capacitors and ESD protection devices should be connected to main digital ground, and
other audio components should use AGND from the module interface. Please be noted that the
AGND pin should not be connected with main digital ground at PCB, or else, it could lead to TDD
noise.
6. Antenna must be stay away from audio components and layout of audio circuit. Keep the distance at
least 5cm from antenna to microphone.
7. Layout of power supply must be stay away from audio and cannot be parallel.

2.6. Suggestion for Mechanical Design

It is important to consider how to suppress echo in the equipment with hands-free function or in an
application which microphone and speaker are very close to each other.
The mechanical structure design has significant impact on echo issue. If it is not properly designed, the
echo suppressing arithmetic in software could not make up echo issue caused by bad mechanical
structure, and even force to redesign.
Echo issue could be generated by several paths as shown in Figure 19.
GSM Module Audo Design Guide
Figure 19：Five Echo Paths
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