ZED-F9P-Integration Manual
UBX-18010802 - R02
8 Design Page 85 of 114
Advance Information
Pin No Name I/O Description
52 Reserved - Reserved
53 TIMEPULSE O Time pulse
54 Reserved - Reserved
Table 22: ZED-F9P pin assignment
8.2 RF front-end circuit options
It is mandatory that the RF input is fed by an active antenna meeting the requirements for
the ZED-F9P.
The first stages of the signal processing chain are crucial to the overall receiver performance.
When an RF input connector is employed this can provide a conduction path for harmful or
destructive electrical signals. If this is a likely factor the RF input should be protected accordingly.
Additional points on the RF input
What is the expected quality of the signal source (antenna)?
• What is the external active antenna signal power?
• What is the bandwidth and filtering of the external active antenna?
• Does the external antenna and filtering components meet the group delay variation
requirements? This is critical for RTK. Any implementation of a PCB mounted L1/L2 patch
antenna and the required RF components should not be attempted without explicit assistance
of an antenna manufacturer who has experience in achieving the required group delay variation
and bandwidth performance for RTK. u-blox does not have a reference design or recommended
components list to achieve this.
Are destructive RF power levels expected to reach the RF-input? Is interference from wireless
transmitters expected?
• What are the characteristics of these signals (duty cycle, frequency range, power range, spectral
purity)?
• What is the expected GNSS performance under interference conditions?
Is there a risk of RF-input exposure to excessive ESD stress?
• In the field: Is the antenna connector accessible by the user?
• PCB / system assembly: Is there risk that statically charged parts (e.g. patch antennas) may be
discharged through the RF-input?
The following subsections provide several options addressing the various questions above:
In some applications, such as GSM transceivers, interference signals may exceed the
maximum power rating of the LNA_IN input. To avoid device destruction use of external input
protection is mandatory.
During assembly of end-user devices which contain passive patch antennas, an ESD
discharge may occur during production when pre-charged antennas are soldered to the GNSS
receiver board. In such cases, use of external protection in front of LNA_IN is mandatory to
avoid device destruction.
ESD discharge cannot be avoided during assembly and / or field use. Note also that SAW filters are
susceptible to ESD damage.
ESD discharge into the RF input cannot be avoided during assembly or field use with this
circuit. To provide additional robustness an ESD protection diode can be placed at LNA_IN to
GND.
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