NEO-5
-
Hardware
Integration
Manual
Preliminary
Product
Testing
GPS.G5-MS5-08003-A2
u-blox
proprietary
Page 49
Figure 37: MuRata’s NFM21C Feed Through Capacitors
Any
feed
through
capacitor
will
only
achieve
its
specified
performance
if
it
has
a
proper
ground
connection.
If
the
use
of
a
special
feed
through
capacitor
is
not
feasible
for
a
particular
design,
a
simple
capacitor
between
the
signal
line
and
shielding
ground
placed
very
close
to
the
feed
through
of
the
signal
line
will
also
help.
It
has
been
found
that
a
12
pF
SMD
capacitor
works
quite
well
at
the
GPS/GALILEO
frequency
range.
Larger
capacitance
values
will
be
less
efficient.
One
should
keep
in
mind
that
a
feed
through
capacitor
is
basically
a
high
frequency
“short”
between
the
signal
line
and
ground.
If
the
ground
point
that
the
capacitor
is
connected
to
is
not
ideal,
meaning
the
ground
connection
or
plane
has
a
finite
resistance,
noise
will
be
injected
into
the
ground
net.
Therefore,
one
should
try
to
place
any
feed
trough
capacitor
far
away
from
the
most
noise
sensitive
parts
of
the
circuit.
To
emphasize
this
once
again,
one
should
ensure
a
very
good
ground
connection
for
the
feed
through
capacitor.
If
there
is
no
good
ground
connection
available
at
the
point
of
the
feed
through,
or
injection
of
noise
into
the
non-ideal
ground
net
must
be
avoided
totally,
inserting
a
component
with
a
high
resistance
at
high
frequencies
might
be
a
good
alternative.
Ferrite
beads
are
the
components
of
choice
if
a
high
DC
resistance
cannot
be
accepted.
Otherwise,
for
ordinary
signal
lines
one
could
insert
a
1
K
series
resistor,
which
would
then
form
a
low-pass
filter
together
with
the
parasitic
capacitance
of
the
conductor
trace.
See
also
the
MuRata
web
page
for
extensive
discussion
on
EMC
countermeasures.
