Crosstalk
(XT) in the electronics industry refers to any condition
by which a signal transmitted on one circuit or channel
of a transmission system creates an undesired effect
in another circuit or channel. Therefore crosstalk
is also referred to as the effect seen on a circuit
from neighboring signals. In integrated circuit design,
crosstalk normally refers to a signal affecting another
nearby signal. Usually the coupling is capacitive,
and to the nearest neighbor, but other forms of coupling
and effects on signal further away are sometimes important,
especially in analog designs.
There
are two types of crosstalk in a transmission:
1.
Far-end crosstalk (FEXT) which is the noise a channel
hears from a neighboring channel. FEXT is the noice
heare on the opposite side of the circuit or when
reference this noise in relationship to an connector
it would be at the other end of the connector.
2.
The second type of crosstalk is Near-end crosstalk
(NEXT). NEXT is the effect a channel might experience
from a nearby channel on the same end of the circuit.
In relationship to connectors this would be on the
same side of the connector.
Many customer ask How we test for each of
these types of crosstalk?
First,
We Inject a signal into a neighboring differential
pair (aggressor) and
listen to the effect it has on our focus differential
pair (victim). Our engineers then run this test with
each of the neighboring circuits and provide the data.
The data is to see how our focus signal may be affected.
In Summary, the test is to see the effects the neighboring
circuits have on a certain circuit in the connector
which is being tested.
As
a rule of thumb, the crosstalk value is around 5%,
If the value is larger for the crosstalk this means
the crosstalk is having a significant effect on signal
performance. Therefore engineers and designers target
crosstalk in the 5% range or lower.
The
shielding of connectors and the plating has sugnificant
influences on crosstalk and therefore these are the
tested carefully by our engineers. The plastic housing
material and desidn are analyized as weil so Crosstalk
has a minimal effect in regards to our connectors.
CAT5,
CAT5e, CAT6 and CAT7 Information