AN851 Datasheet, PDF (10/25 Pages) Silicon Laboratories – Si468X SCHEMATICS AND LAYOUT GUIDE

AN851
ferrites should be placed on each signal conductor in the cable. The ferrite is used to isolate the signal conductors
from the shield/ground. The choice of the ferrite is dependent upon the type of signal on each individual conductor.
If the conductor is used to carry power, then a ferrite with a large dc current carrying capability should be used.
Likewise, if the conductor is used to carry high frequency analog signals, make sure that the ferrite does not filter
the high frequency.
Table 4. Cable Antenna BOM
Ref Designator
Description
Note
L1
IND, SM, 120 nH, MURATA
L2
IND, SM, 36 nH, MURATA
C13
AC coupling cap, SM, 0402, X7R,
100 pF
F1
Shunt Ferrite bead, SM, 0603, Rated dc current> max expected ground
470, 1 A, Murata,
return current.
BLM18PG471SN1J
F2
Series Ferrite bead, various types. For power signals, make sure the rated
Recommended ferrite for power dc current> max expected ground return
lines:
current.
FERRITEBEAD, SM, 0603, For all other signals, make sure ferrite
470, 1 A, Murata,
does not block/filter the high frequency
BLM18PG471SN1J
component of the signals.
Recommended ferrite for signals:
FERRITEBEAD, SM, 0603, 2.5k,
50mA Murata, BLM18BD252DN1D
4.2.3. Cable Antenna Layout
Place the chip as close to the cable antenna as possible. This will minimize the trace length going to the cable
antenna which will minimize the parasitic capacitance. Place the shunt ferrite for the ground return current as close
to the cable as possible. Putting the shunt ferrite for the ground return current close to the cable ensures that the
ground return current has minimal loop which will reduce noise coupling. The series ferrites should be put as close
as possible to the cable. This will minimize the parasitic capacitance seen by the VHFI pin.
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Rev. 0.2