Sierra Wireless WISMO218 - Manual (Page 52)

WA_DEV_W218_PTS_002 Rev 005 Page 52 of 109
Product Technical Specification &
Customer Design Guidelines
Application
Microphone
The following subsections define different microphone configuration examples.
Microphone Differential Connection Example
When a differential connection of MIC is used, it is necessary to add a 2.2K resistor from MICN to
GND in order to have proper bias of the microphone.
Figure 15. Example of MIC Input Differential Connection with LC Filter
Note: Audio quality can be very good without L1, L2, C2, C3 and C4 depending on the design. But if
there is EMI perturbation, this filter can reduce the TDMA noise. This filter (L1, L2, C2, C3 and C4) is
not mandatory. If not used, the capacitor must be removed and the coil replaced by a 0 resistor as
the shown in the following schematic.