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Reference Guide
*
The input voltage depends of the input micro gain set by AT command. Refer to the AT Commands Interface
Guide at http://www.usr.com/support/3500.
**
Because CMICxP 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 CMICxP and CMICxN inputs.
Refer to the following table for the list of recommended microphone characteristics.
Table 12.
Recommended Microphone Characteristics
Feature
Type
Impedance
Sensitivity
SNR
Frequency response
3.1.2.5.2.
The speaker outputs are connected in differential mode to reject common mode
noise and TDMA noise.
Speaker outputs are connected to internal push-pull amplifiers and may be loaded
down with components between 32 – 150Ω and up to 1nF. These outputs may be
directly connected to a speaker.
The output power may be adjusted by 2dB steps. The gain of the speaker outputs is
internally adjusted and may be tuned using the AT+VGR command. Furthermore,
the digital gain can be adjusted using AT+WDGR. Refer to the AT Commands
Interface Guide at
AT commands.
The following table shows the pin assignments of the speaker output.
Table 13.
Speaker Outputs Pin Description for USR3500
(Sub D
15-pin)
Signal
Pin #
10
CSPK1P
15
CSPK1N
Speaker
http://www.usr.com/support/3500
I/O
I/O Type
O
Analog
O
Analog
Rev 1.0
Values
Electret 2V/0.5 mA
Z = 2kΩ
-40dB to -50dB
> 50dB
Compatible with GSM specifications
for more information about these
Description
Speaker positive output
Speaker negative output
Interfaces
1/27/14
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