EVA-8M and EVA-M8 series - Hardware Integration Manual
UBX-16010593 - R06
Design-in
Page 27 of 47
Early Production Information
LNA with appropriate ESD
rating and maximum input
power.
Figure 7: EOS and ESD Precautions
2.13.5
Electromagnetic interference (EMI)
Electromagnetic interference (EMI) is the addition or coupling of energy, which causes a spontaneous
reset of the GNSS receiver or results in unstable performance. In addition to EMI degradation due to
self-jamming (see section 2.3.4), any electronic device near the GNSS receiver can emit noise that can
lead to EMI disturbances or damage.
The following elements are critical regarding EMI:
•
Unshielded connectors (e.g. pin rows etc.)
•
Weakly shielded lines on PCB (e.g. on top or bottom layer and especially at the border of a PCB)
•
Weak GND concept (e.g. small and/or long ground line connections)
EMI protection measures are recommended when RF emitting devices are near the GNSS receiver. To
minimize the effect of EMI a robust grounding concept is essential. To achieve electromagnetic
robustness follow the standard EMI suppression techniques.
http://www.murata.com/products/emc/knowhow/index.html
http://www.murata.com/products/emc/knowhow/pdf/4to5e.pdf
Improved EMI protection can be achieved by inserting a resistor or better yet a ferrite bead or an
inductor (see Table 16) into any unshielded PCB lines connected to the GNSS receiver. Place the
resistor as close as possible to the GNSS receiver pin.
Alternatively, feed-thru capacitors with good GND connection can be used to protect e.g. the
VCC
supply pin against EMI. A selection of feed-thru capacitors are listed in Table 24.
Intended use
☞
In order to mitigate any performance degradation of a radio equipment under EMC disturbance,
system integration shall adopt appropriate EMC design practice and not contain cables over three
meters on signal and supply ports.
2.13.6
Applications with cellular modules
GSM terminals transmit power levels up to 2 W (+33 dBm) peak, 3G and LTE up to 250 mW
continuous. Consult the corresponding product data sheet in Related documents for the absolute
maximum power input at the GNSS receiver. Make sure that absolute maximum input power level of
the GNSS receiver is not exceeded.
☞
See the GPS Implementation and Aiding Features in u-blox wireless modules [6].
2.13.6.1
Isolation between GNSS and GSM antenna
In a handheld type design, an isolation of approximately 20 dB can be reached with careful placement
of the antennas. If such isolation can’t be achieved, e.g. in the case of an integrated GSM/GNSS
antenna, an additional input filter is needed on the GNSS side to block the high energy emitted by the
GSM transmitter. Examples of these kinds of filters would be the SAW Filters from Epcos (B9444 or
B7839) or Murata.
2.13.6.2
Increasing interference immunity
Interference signals come from in-band and out-band frequency sources.
