User guide

WA_DEV_FEX20_UGD_002 Rev 004 March 08, 2011 44
Fastrack Xtend User Guide
Interfaces
Table 16. Equivalent Circuits of CMIC2
DC Equivalent Circuit
AC Equivalent Circuit
Table 17. 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)
Impedance between
MIC2P and MIC2N
1.3
1.6
2
Working voltage
( MIC2P-MIC2N)
AT+VGT*=3500dB
13.8
mVrms
AT+VGT*=2000dB
77.5
AT+VGT*=700dB
346
Maximum rating voltage
(MIC2P or MIC2N)
Positive
+7.35**
V
Negative
-0.9
* The input voltage depends of the input micro gain set by AT command. Refer to document [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).
** Because MIC2P is internally biased, it is necessary to use a coupling capacitor to connect an audio signal
provided by an active generator. Only a passive microphone can be directly connected to the MIC2P and MIC2N inputs.
Refer to the following table for the list of recommended microphone characteristics.
Table 18. Recommended Microphone Characteristics
Feature
Values
Type
Electret 2V/0.5 mA
Impedance
Z = 2k
Sensitivity
-40dB to -50dB
SNR
> 50dB
Frequency response
Compatible with GSM specifications