User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08 Objective Specification System description
Page 57 of 188
1.10 Audio interface
SARA-G300 and SARA-G310 modules do not support audio interface.
The following audio interfaces are provided by SARA-G3 and SARA-U2 series modules:
 SARA-G340 and SARA-G350 modules provide one analog audio interface and one digital audio interface
 SARA-U2 modules provide one digital audio interface
The audio interfaces can be selected and set by the dedicated AT command +USPM (refer to the u-blox AT
Commands Manual [3]): this command allows setting the audio path mode, composed by the uplink audio path
and the downlink audio path.
Each uplink path mode defines the physical input (i.e. the analog or the digital audio input) and the set of
parameters to process the uplink audio signal (uplink gains, uplink digital filters, echo canceller parameters). For
example the “Headset microphone” uplink path uses the differential analog audio input with the default
parameters for the headset profile.
Each downlink path mode defines the physical output (i.e. the analog or the digital audio output) and the set of
parameters to process the downlink audio signal (downlink gains, downlink digital filters and sidetone). For
example the “Mono headset” downlink path uses the differential analog audio output with the default
parameters for the headset profile.
The set of parameters to process the uplink or the downlink audio signal can be changed with dedicated AT
commands for each uplink or downlink path and then stored in two profiles in the non volatile memory (refer to
u-blox AT Commands Manual [3] for Audio parameters tuning commands).
1.10.1 Analog audio interface
SARA-U2 modules do not provide analog audio interface.
1.10.1.1 Uplink path
SARA-G340 / SARA-G350 pins related to the analog audio uplink path are:
 MIC_P / MIC_N: Differential analog audio signal inputs (positive/negative). These two pins are internally
directly connected to the differential input of an integrated Low Noise Amplifier, without any internal series
capacitor for DC blocking. The LNA output is internally connected to the digital processing system by an
integrated sigma-delta analog-to-digital converter
 MIC_BIAS: Supply output for an external microphone. The pin is internally connected to the output of a low
noise LDO linear regulator provided with proper internal bypass capacitor to guarantee stable operation of
the linear regulator
 MIC_GND: Local ground for the external microphone. The pin is internally connected to ground as a sense
line as the reference for the analog audio input
The analog audio input is selected when the parameter <main_uplink> in AT+USPM command is set to
“Headset microphone”, “Handset microphone” or “Hands-free microphone”: the uplink analog path profiles
use the same physical input but have different sets of audio parameters (for more details, refer to u-blox AT
Commands Manual [3], AT+USPM, AT+UMGC, AT+UUBF, AT+UHFP commands).
SARA-G3 series Data Sheet [1] provides the detailed electrical characteristics of the analog audio uplink path.