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Analog Audio Interface
The WISMO228 supports one microphone input and one speaker output. It also includes an echo
cancellation feature which allows hands free function.
In some cases, ESD protection must be added on the audio interface lines.
Microphone Features
The microphone, MIC, can have either a single‐ended or a differential connection. However, it is
strongly recommended to use a differential connection instead of a single‐ended connection in order
to reject common mode noise and TDMA noise.
When using a single‐ended connection, be sure to have a very good ground plane, very good
filtering as well as shielding in order to avoid any disturbance on the audio path.
The gain of MIC inputs is internally adjusted and can be tuned using AT commands.
The MIC interface already includes suitable biasing for an electret microphone. The electret
microphone can be connected directly on the inputs for easy connection.
AC coupling is also already embedded in the WISMO228.
WA_DEV_W228_PTS_002
Figure 16. DC Equivalent Circuit of MIC
Figure 17. AC Equivalent Circuit of MIC
Rev 001
Product Technical Specification &
Customer Design Guidelines
Page 54 of 108
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