Application Interfaces; Analog Audio Interfaces; Audio Interfaces Design - Quectel EG915U-EU Manual

4

Application Interfaces

4.1. Analog Audio Interfaces

Table 11: Pin Definition of Audio Interfaces
Pin Name
MIC_N
MICBIAS
SPK_P
SPK_N
MIC_P
⚫
AI channels are differential output channels, which can be applied for input of microphone (usually an
electret microphone is used).
⚫
AO channels are differential output channels, which can be applied for output receiver.

4.1.1. Audio Interfaces Design

It is recommended to use the electret microphone with dual built-in capacitors (e.g. 10 pF and 33 pF) for
filtering out RF interference, thus reducing TDD noise. The 33 pF capacitor is applied for filtering out RF
interference when the module is transmitting at EGSM900. Without placing this capacitor, TDD noise
could be heard. The 10 pF capacitor here is used for filtering out RF interference at DCS1800. Please
note that the resonant frequency point of a capacitor largely depends on the material and production
technique. Therefore, customers would have to discuss with their capacitor vendors to choose the most
suitable capacitor for filtering out high-frequency noises.
The filter capacitors on the PCB board should be placed as close to the audio devices or audio interfaces
as possible, and the traces should be as short as possible. they should go through the filter capacitors
before arriving other connection points.
In order to reduce radio or other signal interference, the radio frequency antenna should be far away from
the audio interface and audio traces. The power traces should not be parallel to the audio traces, and
EG915U-EU_Hardware_Design
Pin No. I/O
119 AI
120 PO
121 AO
122 AO
126 AI
LTE Standard Module Series
Description
Microphone analog input (-)
Bias voltage output for microphone
Analog audio differential output (+)
Analog audio differential output (-)
Microphone analog input (+)
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