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reserved.
FIBOCOM SC138-
NA
Series Hardware Guide
63/88
Pin Name
Pin No. I/O
Description
Remarks
input+
default, and grounding
Audio interface design considerations:
1)
There is a MIC bias circuit in the SC138 module, so no external addition is required.
2)
SPK is equipped with Class-D power amplifier, so no external power amplifier is allowed. It is
recommended to connect an 8 Ω loudspeaker. The route width should meet the requirements of
rated power. If an external audio power amplifier is required, select the earphone output as the input
source of the external power amplifier. For double-ended input, use two channels. For single-ended
input, the channel can be configured by software.
3)
The earphone reference ground has already been grounded in the module. It is recommended that
the external circuit does not need to be grounded, and a resistor can be reserved.
4)
It is recommended to use a 32 Ω impedance device for the handset.
5)
To reduce noise and improve audio quality, the suggestions are shown in the following:
The audio PCB route should be as far away as possible from antennas and high-frequency
digital signals.
The LC filter circuit is reserved in the audio circuit to reduce EMI.
Audio route needs to be shielded.
3.19.2
Microphone Circuit Design
M odule
M IC _N
M IC _P
33
pF
33
pF
1
0
0
pF
