LEA-M8S / LEA-M8T - Hardware Integration Manual
UBX-13003140 - R07
Production Information
Hardware description
Page 8 of 31
Electromagnetic interference on I/O lines
Any I/O signal line with a length greater than approximately 3 mm can act as an antenna and may pick up
arbitrary RF signals transferring them as noise into the GNSS receiver. This specifically applies to unshielded lines,
in which the corresponding GND layer is remote or missing entirely, and lines close to the edges of the printed
circuit board.
If, for example, a cellular signal radiates into an unshielded high-impedance line, it is possible to generate noise
in the order of volts and not only distort receiver operation but also damage it permanently.
On the other hand, noise generated at the I/O pins will emit from unshielded I/O lines. Receiver performance
may be degraded when this noise is coupled into the GNSS antenna (see Figure 19).
To avoid interference by improperly shielded lines, it is recommended to use resistors (e.g. R>20
Ω
), ferrite beads
(e.g. BLM15HD102SN1) or inductors (e.g. LQG15HS47NJ02) on the I/O lines in series. These components should
be chosen with care because they will affect also the signal rise times.
Figure 3 shows an example of EMI protection measures on the RX/TX line using a ferrite bead. More information
can be found in section 4.3.
Figure 3: EMI Precautions
TX
RX
G
N
SS
R
ec
ei
ver
FB
FB
BLM15HD102SN1
>10mm
