SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
Design-in
Page 156 of 217
2.7.2
Digital audio interface
SARA-G300 and SARA-G310 modules do not provide digital audio interface.
2.7.2.1
Guidelines for digital audio circuit design
The I
2
S digital audio interface of SARA-G3 and SARA-U2 series modules can be connected to an external digital
audio device for voice applications.
Any external digital audio device compliant to the configuration of the digital audio interface of the cellular
module can be used, given that the external digital audio device must provide:
The opposite role: slave for SARA-G3 modules that act as master only; slave or master for SARA-U2 modules
that may act as master or slave
The same mode and frame format: PCM / short alignment or Normal I
2
S mode / long alignment mode with
o
data in 2’s complement notation, linear
o
MSB transmitted first
o
word length = 16-bit
o
frame length = 17-bit or 18-bit in PCM / short alignment mode (16 + 1 or 16 + 2 clock cycles, with
Word Alignment / Synchronization signal set high for 1 clock cycle or 2 clock cycles), or
o
frame length = 32-bit in Normal I
2
S mode / long alignment mode (16 x 2 clock cycles)
The same sample rate and serial clock frequency: as the clock frequency depends on the frame length and
the sample rate, the clock frequency can be
o
17 x <I2S_sample_rate> or 18 x <I2S_sample_rate> in PCM / short alignment mode, or
o
16 x 2 x <I2S_sample_rate> in Normal I
2
S mode / long alignment mode
Compatible voltage levels (1.80 V typ.), otherwise it is recommended to connect the 1.8 V digital audio
interface of the module to the external 3.0 V (or similar) digital audio device by means of appropriate
unidirectional voltage translators (e.g. Texas Instruments SN74AVC4T774 or SN74AVC2T245), using the
module
V_INT
output as 1.8 V supply for the voltage translators on the module side
For the appropriate selection of a compliant external digital audio device, see section 1.10.2 including
subsections 1.10.2.1 and 1.10.2.2. See the +UI2S AT command description in the
u-blox AT Commands
Manual
[3] for further details regarding the capabilities and the possible settings of I
2
S digital audio interface of
SARA-G3 and SARA-U2 series modules.
As in general any external digital audio device compliant to the configuration of the digital audio interface of the
cellular module can be used with SARA-G3 and SARA-U2 series modules, an appropriate specific application
circuit must be implemented and configured according to the particular external digital audio device or audio
codec used and according to the application requirements.
Examples of manufacturers offering compatible audio codec parts, suitable to provide basic analog audio voice
capability on the application device, are the following:
Maxim Integrated (as the MAX9860, MAX9867, MAX9880A audio codecs)
Texas Instruments / National Semiconductor
Cirrus Logic / Wolfson Microelectronics
Nuvoton Technology
Asahi Kasei Microdevices
Realtek Semiconductor
