LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 84 of 116
C1-Public
For additional guidelines regarding the design of applications with u-blox 3.0 V GNSS receivers, the
Integration Manual of the selected u-blox GNSS receiver. It is recommended to consider and
implement all the possible measures for proper RF coexistence of the Cellular and the GNSS systems.
2.6.3.2
Guidelines for I2C layout design
The I2C serial interface requires the same considerations regarding electro-magnetic interference as
any other digital interface. Keep the traces short and avoid coupling with RF line or sensitive analog
inputs, since the signals can cause the radiation of some harmonics of the digital data frequency.
2.7
Cellular audio interface
2.7.1
Cellular digital audio interface
2.7.1.1
Guidelines for digital audio circuit design
I2S digital audio interface can be connected to an external digital audio device for voice applications.
Any external digital audio device compliant with the configuration of the digital audio interface of the
LENA-R8 series cellular module can be used. The external digital audio device must provide:
•
The opposite role: host device role, as LENA-R8 series modules act as local device only
•
The same mode and frame format: Normal I2S / long synch mode with
o
data in 2’s complement notation, linear
o
MSB transmitted first
o
data word length = 16-bit (16 clock cycles)
o
frame length = synch signal period: 32 bits (16 x 2 clock cycles)
•
Support for 8 kHz sample rate, i.e. word alignment synch signal frequency
•
The same serial clock frequency: 16 x 2 x 8 kHz
•
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 translator (as TI SN74AVC4T774, providing partial power down
feature so that the digital audio device 3.0 V supply can be also ramped up before
V_INT
1.8 V
supply), using the module
V_INT
output as 1.8 V supply for the voltage translators on module side
An appropriate specific audio application circuit must be implemented and configured according to
the selected external digital audio device or audio codec, and according to the general application
requirements regarding the audio system.
Examples of manufacturers offering compatible audio codec parts are the following:
•
Realtek Semiconductor (as the ALC5616 audio codec)
•
Maxim Integrated (as the MAX9860, MAX9867, MAX9880A audio codecs)
•
Texas Instruments / National Semiconductor
•
Cirrus Logic / Wolfson Microelectronics
•
Nuvoton Technology
•
Asahi Kasei Microdevices
describe an application circuit for the I2S digital audio interface providing basic
voice capability using an external audio voice codec, in particular the Realtek ALC5616 audio codec:
•
DAC and ADC integrated in the external audio codec respectively converts an incoming digital data
stream to analog audio output through a mono amplifier and converts the microphone input signal
to the digital bit stream over the digital audio interface,
•
A digital side-tone mixer integrated in the external audio codec provides loopback of the
microphones/ADC signal to the DAC/headphone output.
