ZED-F9T - Integration Manual
as described here. This will also be affected by the voltage level of the antenna bias supply
due to power dissipation. The current limit capability of the antenna bias supply needs
to be considered. In the case where the module supplies the voltage via VCC_RF, a higher
value resistor will be needed to ensure the module supply inductor is protected. The current
should be limited to below 150 mA at the module supply voltage under shorting conditions.
In this case a value of 17 Ω or more is required at a module supply of 3V to limit short circuit
current to 150 mA. The DC resistance of the bias-t inductor is assumed to be 1-2 Ω and the
module internal feed inductor is assumed to be 1.2 Ω.
If the VCC_RF voltage does not match with the supply voltage of the active antenna, use a filtered
external supply.
The power dissipation in the resistor and inductor needs to be taken into account based on
the supply voltage and short circuit current. The bias-t inductor current capability and the
bias resistor value need to be calculated as shown above. The supply voltage for the bias-t
and its current capability is part of the calculation.
Figure 35: ZED-F9T external voltage antenna bias
4.5 EOS/ESD precautions
When integrating GNSS receivers into wireless systems, careful consideration must be given to
electromagnetic and voltage susceptibility issues. Wireless systems include components which
can produce Electrostatic Discharge (ESD), Electrical Overstress (EOS) and Electro-Magnetic
Interference (EMI). CMOS devices are more sensitive to such influences because their failure
mechanism is defined by the applied voltage, whereas bipolar semiconductors are more susceptible
to thermal overstress. The following design guidelines are provided to help in designing robust yet
cost effective solutions.
To avoid overstress damage during production or in the field it is essential to observe strict
EOS/ESD/EMI handling and protection measures.
To prevent overstress damage at the RF_IN of your receiver, never exceed the maximum
input power as specified in the u-blox ZED-F9T Data sheet [
1
].
4.5.1 ESD protection measures
GNSS receivers are sensitive to Electrostatic Discharge (ESD). Special precautions are
required when handling. Most defects caused by ESD can be prevented by following strict
ESD protection rules for production and handling. When implementing passive antenna
patches or external antenna connection points, then additional ESD measures as shown in
the figure below can also avoid failures in the field.
UBX-19005590 - R01
4 Design
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