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3.7.1
Handset Interface
This differential interface is intended for handset-like applications. The c18 module contains all biasing circuitry. Therefore, no
external components are needed, except for an active condenser microphone and a 32Ω earpiece. Figure 14 shows the handset
interface with biasing circuitry:
The microphone bias source provides 1.8V DC bias (typical), 1 mA. MIC_IN lines should be routed together and kept as short
as possible, in order to minimize noise pickup.
The output power for the differential earpiece output is typically 35 mW for a full-scale +3dBm0 sine wave into a 32Ω speaker.
The integrator should connect the earpiece speaker through two resistors (with a value of R) for safety compliance, as shown in
the figure above.
The resistors purpose is to limit the maximum sound level that can be created by the speaker. The value of R depends on the
type of earpiece and its mounting. A value between 0 and tens of Ohms can be expected.
98-08901C63-A
70-PIN INTERFACE
CONNECTOR
MIC_IN+
61
63
MIC_IN-
EARPIECE+
R
69
R
67
EARPIECE-
Figure 14. Handset Audio Interface
c18
2.2K
0.1 uF
0.1 uF
2.2K
Hardware Description
MSM5100
MICBIAS (1.8V)
MIC1P
MIC1N
EAR1OP
EAR1ON
29
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