CEM600 EVDO Mini PCIE Module Hardware User Guide
Shang Hai YUGE Information Technology co., LTD
Page 15 of 25
Figure 5-5 PCM digital voice application reference design
5.4 AUDIO interface
Table 5-4 AUDIO Interface Definition
Pin
Signal name
I/O properties
High value
Description
1
MIC_P
Analog input
1.8V
Audio input positive end
3
MIC_N
Analog input
1.8V
Audio input negative
5
EAR_P
Analog output
1.8V
Positive audio output
7
EAR_N
Analog output
1.8V
Audio output negative
GND
Ground
The AUDIO interface provides an audio input and output interface in differential mode.
The MIC bias voltage and DC blocking capacitors are already provided inside the module, so
the external design is no longer needed. The road audio output can drive a 32 ohm receiver.
The differential line of the differential audio interface should pay attention to the parallel
equidistance in the PCB design. The length of the trace should be as short as possible. The
filter circuits on both sides should be as symmetrical as possible. The positive and negative
differential signals should be as close as possible. The audio input and audio output need to be
separated to prevent crosstalk, while away from power, RF, antenna and other circuits. In
addition, ESD protection devices are recommended at the MIC, RECEIVER/SPEAKER
interfaces.The reference design of the differential audio input and output interface is as
follows:
