LISA-C2 series and FW75-C200 - System Integration Manual
UBX-13000620 - R21
Early Production Information
System description
Page 39 of 103
connections and set to high impedance during module power down mode, when external reset is forced
low, and during power-on sequence.
LISA-C200: Pay special attention when using voltage level shifter connections. V_INT (1.8 V) is
provided to support biasing of level shifter ASICs. A problem can result with certain level shifter
interface buffers, which can back feed voltage to the V_INT line preventing the modem from
powering off and/or resetting properly. The back feed voltage typically comes from a host output
through the level shifter and out either from the level shifter VCC pin connected to V_INT or to
the modem DDC input lines though an internal protection diode with modem. With modem
VCC = 0 V, a measured voltage can range from 0.3 to 1.0 V on the V_INT, preventing modem from
ever resetting or powering up or down properly.
1.11
Audio Interface (LISA-C200)
LISA-C200 module provides analog and digital audio interfaces:
•
One differential analog audio input (microphone input)
•
One differential analog audio output (speaker output)
•
One 4-wire I2S digital audio interface: input and output
Audio signal routing can be controlled by the dedicated AT cUSPM
For LISA-C200 refer to u-blox C2 series 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).
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).
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 the non-volatile memory. (Refer to relevant
u-blox AT Commands Manual for Audio parameters tuning commands.)
Figure 21: The modem's internal audio paths
1.11.1
Analog Audio interface – LISA-C200
Detailed electrical characteristics of the differential analog audio input can be found in the LISA-C200 series
Data Sheet [1].
Mic
LNA
Gain
ADC
Filters
Echo Canceler Block
Input
Gain
EC
Output
Gain
AF
Limit
NLPP
Gain
NLPP
Limit
Filter
DAC
Filter
Mic
Speaker
CodecSTGain
CodecRxGain
CodecTxGain
TX
AAGC
TX
PCM
Filter
(UBF)
RX
PCM
Filter
(UBF)
RX
AAGC
Modem Module
TX
Processin
g and
Interface
RX
Processin
g and
Interface
Rx Volume
Tx Volume
PCM Uplink
PCM Downlink