EVA-M8E - Hardware Integration Manual
UBX-15028542 - R05
Contents
Page 23 of 44
Production Information
2.13.3
Electrical Overstress (EOS)
Electrical Overstress (EOS) usually describes situations when the maximum input power exceeds the
maximum specified ratings. EOS failure can happen if RF emitters are close to a GNSS receiver or its
antenna. EOS causes damage to the chip structures.
If the
RF_IN
is damaged by EOS, it’s hard to determine whether the chip structures have been
damaged by ESD or EOS.
2.13.4
EOS protection measures
EOS protection measures as shown in Figure 7 are recommended for any designs combining wireless
communication transceivers (e.g. GSM, GPRS) and GNSS in the same design or in close proximity.
Passive antennas
Active Antennas
(without internal filter which need the
module antenna supervisor circuits)
C
D
LNA with appropriate ESD rating
and maximum input power.
Figure 7: EOS and ESD Precautions
2.13.5
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 [1] 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 [5].
2.13.5.1
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.
2.13.5.2
Increasing interference immunity
Interference signals come from in-band and out-band frequency sources.
2.13.5.3
In-band interference
With in-band interference, the signal frequency is very close to the GPS frequency of 1575 MHz (see
Figure 8). Such interference signals are typically caused by harmonics from displays, micro-controller,
bus systems, etc.
