Motorola c18, Руководство разработчика

Страница: 37 / 82

98-08901C63-A 29
Hardware Description
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 32
Ω
earpiece. Figure 14 shows the handset
interface with biasing circuitry:
Figure 14. Handset Audio Interface
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 32
Ω
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.
MIC1P
MICBIAS (1.8V)
MSM5100
70-PIN INTERFACE
CONNECTOR
c18
2.2K
61
69
63
67
2.2K
0.1 uF
0.1 uF
E
R
R
EAR1OP
MIC1N
MIC_IN-
EARPIECE-
EAR1ON