Baseband Design
confidential ©
Page :
33 / 58
This document is the sole and exclusive property of WAVECOM. Not to be distributed or divulged
without prior written agreement.
WM_PRJ_Q24NG_PTS_002-001 June
2006
A/ Differential connection
Impedance of the microphone input in differential mode:
•
Module ON: R
in
= 10 k
Ω
+/-10 %
•
Module OFF: R
in
>1 M
Ω
+/-10 %
Typical implementation:
L1
L2
C1 C2
C4
C3
MIC1P
MIC1N
VCC
C5
R1
R2
R3
R4
Figure 14: MIC1 inputs (differential connection)
R1 = R4 = from 100 to 330
Ω
.
R2 = R3 = usually between 1 k
Ω
and 3.3 k
Ω
as per the microphone
characteristics.
C1 = 33 pF to 47 pF.
C2 = C3 = C4 = 47 F to 100 pF.
C5 = 47 µF.
L1 = L2 = 100 nH.
R1 and R4 are used as a voltage supply filter with C5.
C1 has to be as close as possible to the microphone. Microphone
manufacturers provide this capacitor directly soldered on the microphone.
C2 has to be very close to the Q24NG connector.
L1, L2, C3 and C4 have to be placed close to the Q24NG connector and
can be removed according to their environment (ground plane, shielding
...etc). The best way is to plan all the components and to remove those
which are not necessary to filter out the TDMA noise on the audio path.
