WA_DEV_FEX20_UGD_002
Rev 002
April 26, 2010
43
Fastrack Xtend User Guide
Interfaces
5.1.2.4.
Audio Lines Connection
The Fastrack Xtend supports one microphone input and one speaker output.
5.1.2.4.1.
Microphone
The microphone inputs are connected in differential mode to reject common mode noise and TDMA
noise. The microphone inputs have already included biasing for an electrets microphone (0.5mA and
2V) and are ESD protected. This electrets microphone may be directly connected to these inputs
allowing an easy connection to a headset.
The microphone gain can be adjusted by
AT+VGT
and the transmit digital gain can be adjusted by
AT+WDGT
. Refer to [7] Firmware 7.4a
AT Commands Manual (Sierra Wireless Software Suite
2.31)/Firmware 7.4 AT Commands Manual (Sierra Wireless Software Suite 2.30) for more information
about these AT commands.
Table 13: Microphone Pin Description
(Sub D
15-pin)
Pin #
Signal
I/O
I/O Type
Description
4
CMIC2P
I
Analog
Microphone positive input
5
CMIC2N
I
Analog
Microphone negative input
Table 14: Equivalent Circuits of CMIC2
DC Equivalent Circuit
AC Equivalent Circuit
Table 15: Electrical Characteristics of CMIC2
Parameters
Min
Typ
Max
Unit
Internal biasing
DC Characteristics
MIC2+
2
2.1
2.2
V
Output current
0.5
1.5
mA
R2
1650
1900
2150
AC Characteristics
200 Hz<F<4 kHz
Z2 CMIC2P
(CMIC2N=Open)
1.1
1.3
1.6
k
Z2 CMIC2N
(CMIC2P=Open)
Z2 CMIC2P
(CMIC2N=GND)
0.9
1.1
1.4
Z2 CMIC2N
(CMIC2P=GND)