Microphone differential connection example, Figure 15, Figure 16 – Sierra Wireless AIRPRIME WISMO218 User Manual
Page 50
WA_DEV_W218_PTS_002
Rev 006
April 29, 2010
50
Product Technical Specification &
Customer Design Guidelines
Interfaces
3.10.4.1.1. 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
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.
Figure 16.
Example of MIC Input Differential Connection without LC Filter
The capacitor C1 is highly recommended to eliminate TDMA noise. Note that C1 must be close to the
microphone.