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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
3.3.2.1.3 Main Microphone Inputs (MIC2)
The MIC2 inputs are differential inputs. They already include the
convenient biasing for an electret microphone (0.5 mA and 2 Volts). This
electret microphone can be directly connected on these inputs.
The impedance of the microphone 2 has to be around 2 k
Ω
. These inputs
are the standard inputs for a handset design while MIC1 inputs can be
connected to an external headset or a hands-free kit.
Typical implementation:
L1
L2
C1
C2
C4
C3
MIC2P
MIC2N
Figure 13: Example of main microphone MIC2 implementation
(differential connection)
C1 = 33 pF to 47 pF
C2 = C3 = C4 = 47 pF to 100 pF
L1 = L2 = 100 nH
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 near the Q24NG connector and may
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.
3.3.2.1.4 Auxiliary Microphone Inputs (MIC1)
The MIC1 inputs are differential and they do not include internal bias. To
use these inputs with an electret microphone, bias has to be generated
outside the Q24NG according to the characteristic of this electret
microphone. These inputs are the standard inputs used for an external
headset or a hands-free kit.
Warning:
For AC coupling, serial capacitors in the microphone input are already
embedded in the Q24NG.
