ZOE-M8B - System Integration Manual
UBX-17045131 - R04
Contents
Page 19 of 42
Production Information
2.5.1
Passive Antenna
ZOE-M8B GNSS SiP is optimized to work with passive antennas. The internal SAW filter inside
followed by an LNA is a good solution for most applications from jamming and performance point of
view.
Figure 13: Typical circuit with passive antennas
Where best performance has to be achieved and no jamming sources are there, an additional external
LNA (U1) can be placed close to the antenna.
Figure 14: Circuit for best performance
The LNA (U1) can be selected to deliver the performance needed by the application in terms of:
•
Noise figure (sensitivity)
•
Selectivity and linearity (Robustness against jamming)
•
Robustness against RF power and ESD
☞
The external LNA (U1) must be placed close to the passive antenna to get best performance.
If Power Save Mode is used and the minimum current consumption has to be achieved, then the
external LNA should also be turned off. The
LNA_EN
pin can be used to turn off the external LNA.
ESD discharge into the RF input cannot always be avoided during assembly and / or field use with this
approach! To provide additional robustness an ESD protection diode, as listed in Appendix A.5, can be
placed in front of the LNA to GND.
☞
If VCC supply is also used to supply the external LNA, make sure some good filtering is in place for
the external LNA supply because of the noise on the VCC. Means a series ferrite bead FB1, see
section A.6, and a decoupling capacitor to GND has to be used.
2.5.2
Active Antenna
In case an active antenna is used, the active antenna supply circuit has to be added just in front of the
SiP RF input.
