LISA-U2 series - System integration manual
UBX-13001118 - R27
Design-In
Page 118 of 183
C1-Public
forced low, and during the module power-on sequence (at least for 3 seconds after the start-up
event), to avoid latch-up of circuits and enable a clean boot of the module.
All unused pins can be left floating on the application board except the
PWR_ON
pin (must be
connected to
V_BCKP
by a pull-up resistor) and
RSVD
pin number 5 (must be connected to
GND).
2.1.2
Layout checklist
The following are the most important points for a simple layout check:
Check the 50
nominal characteristic impedance of the RF transmission line connected to the
ANT
pad (main RF input/output) and to the
ANT_DIV
pad (RF input for Rx diversity).
Follow the recommendations of the antenna producer for correct antenna installation and
deployment (PCB layout and matching circuitry).
Ensure no coupling occurs with other noisy or sensitive signals (e.g. SIM signals).
The
VCC
line should be as wide and as short as possible.
Provide the suggested series ferrite bead and bypass capacitors close to the
VCC
pins
implementing the recommended layout and placement, especially if the application device
integrates an internal antenna.
Route the
VCC
supply line away from sensitive analog signals.
The high-power audio outputs lines on the application board must be wide enough to minimize
series resistance.
Ensure proper grounding.
Conside
r “No
-
routing” areas for the Data Module footprint.
Optimize placement for minimum length of RF line and closer path from the DC source for
VCC
.
Design the
USB_D+ / USB_D-
connection as 90
differential pair, with 30
common mode
impedance.
Keep routing short and minimize parasitic capacitance on the SPI lines to preserve signal
integrity.
Keep routing short and minimize parasitic capacitance on
CODEC_CLK
line to preserve signal
integrity.
2.1.3
Antenna checklist
Antenna should have 50
impedance, VSWR less than 3:1 (recommended 2:1) on operating
bands in deployment geographical area.
Follow the recommendations of the antenna producer for correct antenna installation and
deployment (PCB layout and matching circuitry).
Follow the additional guidelines for products marked with the FCC logo (United States only)
reported in section
The antenna connected to the
ANT
pad should have built-in DC resistor to ground to get proper
antenna detection functionality.
The antenna for the Rx diversity connected to the
ANT_DIV
pin should be carefully separated
from the main Tx/Rx antenna connected to the
ANT
pin: the distance between the two antennas
should be at least greater than half a wavelength of the lowest used frequency (i.e. distance
greater than ~20 cm, for 2G/3G low bands) to distinguish between different multipath channels,
for proper spatial diversity implementation.
