HP 83480A User Manual

The Digital Communications
Analysis Menus
Measure Eye Menu
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Extinction ratio...
This function is only available with the HP 83480A, or if the HP 83480K
option is installed in an HP 54750A.
Extinction ratio for an eye diagram is simply the ratio of the logic \high"
level (V
top
or P
top
) to the logic \low" level (V
base
or P
base
). A very high
extinction ratio typically implies that the logic low level is very small. In the
case of an optical transmitter, the logic low level would approach a condition
where the laser is nearly turned o. The accuracy of the extinction ratio
can
be
dominated
by
the
accuracy with
which the
low level
was measured.
This
in
turn
can
be
signicantly aected
by any
noise generated
by the
measurement
system
such
as
O/E
converter
,
DC osets
,or
electrical
osets
in
the
instrument
electronics
.
Thus
the
extinction
ratio
measurement
is
dened
as:
V
top
0
V
dar
k
V
base
0
V
dar
k
V
top
(or
P
top
)
and
V
base
(or
P
base
)
are
determined
from
vertical
histograms
of
the
eye
window
.
The
eye
window
is
the
center of
the
eye
and
is
dened
in
the
Dene
Measure
menu.
The
default
window
boundaries
are
40% and
60%.
Thus
,
the
middle
20%
of
the
eye
is
analyzed to
determine V
top
and
V
base
.
The
window
can
be
adjusted
to
analyze
any
portion
of the
eye (100%
window)
by
adjusting
the
window
boundaries
accordingly
.
The
vertical
histogram
of
the
eye
window
is
used
to
determine
the
most
prevalent high level and the most prevalent low value of the eye.The
histogram is typically bi-modal, and V
top
and V
base
correspond to the means
of the histogram about the most prevalent high and low values.
6-32

HP 83480A Specifications

General

Brand	HP
Model	83480A
Category	Measuring Instruments
Language	English