User's Manual

HiLo3G-850 User Manual
04 March 2011 - Page 12 / 36
3.2.2 Analog Audio
Analog audio is connected via MIC_N and MIC_P as input and HSET_N and HSET_P as output to the HiLo3G-850.
Please note that external circuitries are mainly needed for the microphone and speaker.
Figure 9: Analog audio connections
3.2.2.1 Microphone Note
Careful attention must be given to the microphone device design because it must not be sensitive to RF disturbances.
If you must have deport microphone out of the board using long wires, extra care must be given to avoid EMC and ESD
effects. It is also the case when your design is ESD sensitive. In those cases, add the following protections to improve your
design.
To ensure proper operation of such sensitive signals, they must be isolated from others by analog grounding on
customer board layouts.
To use an external bias voltage for the microphone, simply use a capacitor of 10μF to prevent this bias voltage from
being re-injected inside the module.
Figure 10: Filter and ESD protection for microphone
3.2.2.2 Note for Speaker
The differential analog output of the HiLo3G-850 is able to drive a 32 Ohms telephone receiver directly. In case there is
a need to drive something different, e.g. an 8 Ohms speaker, an external amplifier is required.
HSET_P, HSET__N tracks must be larger than other tracks: 0.3 mm.
Differential signals have to be routed in parallel.
To use an external audio amplifier connected to a loud-speaker, use serial capacitors of 10nF on the HiLo3G-850 audio
outputs to connect the audio amplifier.
HiLo3G
-850
ESD protection
Mic.
Speaker
MIC
33pF
33pF
Ferrite Bead
Ferrite Bead
+
ESD protection
ESD protection
HiLo3G-850