NEO-M8U - Hardware Integration Manual
UBX-15016700 - R07
Product handling
Page 22 of 28
Production Information
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 is hard to
determine whether the chip structures have been damaged by ESD or EOS.
EOS protection measures
☞
For designs with GNSS positioning modules and wireless (e.g. GSM/GPRS) transceivers in close
proximity, ensure sufficient isolation between the wireless and GNSS antennas. If wireless power
output causes the specified maximum power input at the GNSS RF_IN to be exceeded, employ
EOS protection measures to prevent overstress damage.
For robustness, EOS protection measures as shown in Figure 13 are recommended for designs
combining wireless communication transceivers (e.g. GSM, GPRS) and GNSS in the same design or in
close proximity.
Small passive antennas
(<2 dBic
and performance critical)
Passive antennas
(>2 dBic or
performance sufficient)
Active antennas
(without internal filter which
need the module antenna supervisor circuits)
D
RF
_IN
G
N
SS
R
ec
ei
ver
LNA
GPS
Bandpass
Filtler
E
RF
_IN
G
N
SS
Rec
ei
ver
L
GPS
Bandpass
Filtler
F
LNA with appropriate ESD rating
and maximum input power
GNSS Band pass Filter: SAW or
Ceramic with low insertion loss
and appropriate ESD rating
Figure 13: EOS and ESD Precautions
Electromagnetic interference (EMI)
Electromagnetic interference (EMI) is the addition or coupling of energy causing a spontaneous reset
of the GNSS receiver or resulting in unstable performance. In addition to EMI degradation due to self-
jamming (see section 1.5) 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 ) 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 is listed in Table 5.
