Rev 1.0
1/27/14
27
27
Reference Guide
Interfaces
*
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
Values
Type
Electret 2V/0.5 mA
Impedance
Z = 2k
Ω
Sensitivity
-40dB to -50dB
SNR
> 50dB
Frequency response
Compatible with GSM specifications
3.1.2.5.2.
Speaker
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 – 150
Ω
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
http://www.usr.com/support/3500
for more information about these
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)
Pin #
Signal
I/O
I/O Type
Description
10
CSPK1P
O
Analog
Speaker positive output
15
CSPK1N
O
Analog
Speaker negative output