SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26 System description
Page 69 of 217
1.10.1.2 Downlink path
SARA-G340 / SARA-G350 pins related to the analog audio downlink path are:
SPK_P / SPK_N: Differential analog audio signal output (positive/negative). These two pins are directly
connected internally to the differential output of a low power audio amplifier, for which the input is
connected internally to the digital processing system by to an integrated digital-to-analog converter.
The analog audio output is selected when the parameter <main_downlink> in AT+USPM command is set to
“Normal earpiece”, “Mono headset” or “Loudspeaker”: the downlink analog path profiles use the same
physical output but have different sets of audio parameters (for more details, see the u-blox AT Commands
Manual [3], AT+USPM, AT+USGC, AT+UDBF, AT+USTN commands).
The differential analog audio output of SARA-G340 and SARA-G350 modules (SPK_P / SPK_N) is able to directly
drive loads with resistance rating greater than 14 : it can be directly connected to a headset earpiece or
handset earpiece but cannot directly drive a 8 or 4 loudspeaker for the hands-free mode.
The SARA-G3 series Data Sheet [1] provides the detailed electrical characteristics of the analog audio downlink
path.
Warning: excessive sound pressure from headphones can cause hearing loss.
1.10.1.3 Headset mode
Headset mode is the default audio operating mode of the modules. The headset profile is configured when the
uplink audio path is set to “Headset microphone” and the downlink audio path is set to “Mono headset” (see
the u-blox AT Commands Manual [3]: AT+USPM command: <main_uplink>, <main_downlink> parameters).
1.10.1.4 Handset mode
The handset profile is configured when the uplink audio path is set to “Handset microphone” and the downlink
audio path is set to “Normal earpiece” (see the u-blox AT commands manual [3]: AT+USPM command:
<main_uplink>, <main_downlink> parameters).
1.10.1.5 Hands-free mode
The hands-free profile is configured when the uplink audio path is set to “Hands-free microphone” and the
downlink audio path is set to “Loudspeaker” (see the u-blox AT commands manual [3]: AT+USPM command:
<main_uplink>, <main_downlink> parameters).
Hands-free functionality is implemented using appropriate digital signal processing algorithms for voice-band
handling (echo canceller and automatic gain control), managed via software (see the u-blox AT commands
manual [3], AT+UHFP command).
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