ZOE-M8 series - Hardware integration manual
UBX-16030136 - R09
Design-in
Page 13 of 34
Production information
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The external LNA (U1) must be placed close to the passive antenna to achieve the best
performance.
If power save mode is used and the minimum current consumption has to be achieved, 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.6, can
be placed in front of the LNA to GND.
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If the 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. This means that a series ferrite bead
FB1 and a decoupling capacitor to GND must be used (see section A.7).
2.5.2
Improved jamming immunity
If strong out-band jammers are close to the GNSS antenna (for example, a GSM antenna), GNSS
performance can be degraded or the maximum input power of the ZOE-M8 GNSS SiPs RF input can
be exceeded. In that case, the SAW filter (F1) must be put in front of the external LNA (U1).
It should be noted that the insertion loss of the SAW filter (F1) directly affects the system noise figure
and hence the system performance.
Figure 6: Circuit for improved jamming immunity
2.5.3
Active antenna
In case an active antenna is used, the active antenna supply circuit must be added just in front of the
SiPs RF-input.
Figure 7: Active antenna supply circuit
