Recommended speaker characteristics, Recommended filtering components, Figure 21 – Sierra Wireless AIRPRIME WISMO218 User Manual
Page 54: Microphone
WA_DEV_W218_PTS_002
Rev 006
April 29, 2010
54
Product Technical Specification &
Customer Design Guidelines
Interfaces
The capacitors have to be soldered in parallel to the microphone:
CM
Figure 21.
Microphone
3.10.5.3. Recommended Speaker Characteristics
Type of speakers: Electro-magnetic /10mW
Impedance: 8
for hands-free
Impedance: 32
for heads kit
Sensitivity: 110dB SPL min
Receiver frequency response is compatible with the GSM specifications.
3.10.5.4. Recommended Filtering Components
When designing a GSM application, it is important to select the right audio filtering components.
The strongest noise, called TDMA, is mainly due to the demodulation of the GSM900 and DCS1800
signal: A burst is produced every 4.615ms; where the frequency of the TDMA signal is equal to
216.7Hz plus harmonics.
The TDMA noise can be suppressed by filtering the RF signal using the right decoupling components.
The types of filtering components are:
RF decoupling inductors
RF decoupling capacitors
A good “Chip S-Parameter” simulator is proposed by Murata. Refer to
for more details.
Using different Murata components, we could see that the value, the package and the current rating
can have different decoupling effects.