N27 Hardware User Guide
Chapter 4 Application Interfaces
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Keep a distance greater than 13 mm between ANT and ANT_GNSS in case of EMI jamming to
each other.
On the PCB, keep the RF signals and components far away from high-speed circuits, power
supplies, transformers, great inductors, the clock circuit, etc.
4.4.2 ANT_GNSS Interface
GPS Impedance Control
ANT_GNSS (71st pin) is the GNSS RF interface of N27, which requires a characteristic impedance of
50Ω. Figure 4-21 shows the GNSS structure inside the module.
Figure 4-21 GNSS RF structure
GNSS_ANT
WTR GPS
Interface
N27 module
SAW
LNA
Schematic guidelines:
For the impedance matching circuit between N27 and GNSS antenna, refer to the last section.
PCB layout guidelines
For guidelines of PCB layout between GNSS interface and antenna, refer to design guidelines in
section 4.4.1 "ANT Interface."
50Ω impedance is required for the feeder and PCB traces and the traces should be as short as
possible. The power supply of the active antenna is fed by the 100 nH inductance through the
signal traces.
The common active antenna requires 3.3V to 5V power supply. Though the active antenna is a
low power component, it requires a low-noise LDO to supply power for the antenna through a
100nH inductance.
Keep the GNSS antenna circuit far away from the main antenna circuits on PCB. Otherwise,
these two parts will jam each other, lowing the RF performance.
