LEA-5, NEO-5, TIM-5H - Hardware Integration Manual
GPS.G5-MS5-09027-A2
Released
Design-in
Page 48 of 68
segment (>3mm) connected to the GPS receiver can effectively act as antenna and 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 GPS 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 (BLM15HD102SN1)
into any unshielded PCB lines connected to the GPS receiver. Place the resistor as close as possible to the GPS
receiver pin.
Example of EMI protection measures on the RX/TX line using a ferrite bead:
TX
RX
G
P
S
R
e
c
e
iv
e
r
FB
FB
BLM15HD102SN1
>10mm
Figure 40: EMI Precautions
VCC can be protected using a feed thru capacitor. For electromagnetic compatibility (EMC) of the RF_IN pin refer
to section 2.7.5
2.7.7
GSM applications
GSM uses power levels up to 2W (+33dBm). The absolute maximum power input at the GPS receiver is
-5dBm
for Antaris-4 and u-blox 5 GPS receivers.
2.7.7.1
Isolation between GPS and GSM antenna
For GSM applications plan a minimum isolation of 40dB. In a handheld type design an isolation of approximately
20dB Can be reached with careful placement of the antennas, but this isn‖t sufficient. In such applications an
additional input filter is needed on the GPS 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.
2.7.7.2
Increasing jamming immunity
Jamming signals come from in-band and out-band frequency sources.
2.7.7.3
In-band jamming
With in-band jamming the signal frequency is very close to the GPS frequency of 1575 MHz (see Figure 41). Such
jamming signals are typically caused by harmonics from displays, micro-controller, bus systems, etc.
