HP 8753D - Page 393

Figure
6-67.
Time
Domain
Low
P
ass
Measurement
of
an
Amplier
Small
Signal
Transient
Response
Interpreting
the
low
pass
step
transmission
response
horizontal axis
. The
low pass
transmission
measurement horizontal
axis displays
the
average
transit
time
through
the
test
device over
the frequency
range
used
in
the
measurement.
The
response
of
the
thru
connection
used in
the calibration
is
a
step
that
reaches
50%
unit
height
at
approximately
time
=
0.
The rise
time
is
determined
by
the
highest
frequency
used
in
the
frequency
domain
measurement.
The
step
is a
unit
high
step
,
which
indicates
no
loss
for
the
thru
calibration.
When
a
device
is
inserted, the
time
axis
indicates
the
propagation
delay
or
electrical
length
of
the
device
.
The
markers
read
the
electrical
delay
in
both
time
and
distance
.
The
distance
can
be
scaled
by
an
appropriate
velocity
factor
as
described
earlier
in
this
section
under
\Time
domain
bandpass
."
Interpreting
the
low
pass
step
transmission
response
vertical
axis
.
In
the
real
format,
the
vertical
axis
displays
the
transmission
response
in
real
units
(for
example
,
volts).
F
or
the
amplier
example
in
Figure
6-67
,
if
the
amplier
input
is
a
step of
1volt,
the output,
2.4
nanoseconds
after
the
step
(indicated
by
marker
1),
is
5.84
volts
.
In
the
log
magnitude
format,
the
amplier
gain
is
the
steady
state
value
displayed
after the
initial
transients
die
out.
Measuring
separate
transmission
paths
through the
test device
using low
pass impulse
mode
.
The
low pass
impulse
mode
can
be
used
to
identify
dierent
transmission
paths
through
a test device
that has a response at frequencies down to dc (or at least has a predictable
response, above
the noise oor
, below 30 kHz). F
or example
, use the low pass impulse mode to
measure the relative transmission
times through a multi-path device such as a power divider
.
Another example is to measure the pulse dispersion through a broadband transmission line
,
such as a ber optic cable
. Both examples are illustrated in Figure 6-68 .
The horizontal and
vertical axes can be interpreted as already described in this section under \Time Domain
Bandpass".
6-126 Application and Operation Concepts