MeiG Smart product technical information
SLM758
Hardware Design Guide
Page 66
the TDD interference of the DCS1800 frequency band is more serious. Therefore, the user can
select the required filter capacitor according to the actual test result, and sometimes even do
not need to paste the filter capacitor.
The GSM antenna is the main source of coupling interference for TDD, so users should pay
attention to keeping the audio trace away from the GSM antenna and VBAT during PCB
layout and routing. The filter capacitor of the audio is preferably placed close to the module
end and placed next to the interface end. The audio output should be routed according to the
differential signal rules.
The conducted interference is mainly caused by the voltage drop of VBAT. If the Audio PA is
directly powered by VBAT, it is easier to hear the “zizi” sound at the SPK output. Therefore, it
is better to connect in parallel with the input of the Audio PA in the schematic design. Some
large capacitance capacitors and series magnetic beads.
The conducted interference is also strongly related to TDD and GND. If GND is not
handled well, many high-frequency interference signals will interfere with MIC and Speaker
through devices such as bypass capacitors, so users should ensure good performance of GND
during PCB design.
5.2.7. Other
The serial port interface of the module should also be kept as short as possible. It is best to
walk in a group when routing, and do not distract the wires.
