HP 54501A - Automatic Top-Base

When
any
of
the
standard
measurements
are
requested,
the
HP
54501A
first
determines
the
top-base
voltage
levels
at
100%-0%. From
this
information,
it
can
determine
the
other
important
voltage
values
(10%,
90%,
and
50%)
needed to
make
the
measurements.
The
10%
and
90%
voltage
values
are
used
in the
risetime
and
falltime
measurements
as
well
as
in
all
other
edge
measurements.
The
10%
and
90%
values
are
also
used
to
determine
the
50%
value.
The
50% voltage
value
is
used
for
measuring
frequency, period,
pulse
width,
and
duty
cycle.
Automatic
Top-Base
Top-Base
is
the
heart of
most automatic
measurements.
It
is
used
to
determine
Vtop and
Vbase,
the
0%
and
100% voltage
levels
at
the
top
and
the
bottom
of
the
waveform.
From
this
information
the
oscilloscope
can
determine
the
10%,
50%,
and
90%
points,
which
are
also
used
in
most
measurements.
The
top
or
base of
the
waveform
is
not
necessarily
the
maximum
or
minimum
voltage
present on
the
waveform.
Consider
a
pulse
that
has
slight
overshoot.
It
would
be
wrong
to select
the
highest
point
of
the
waveform
as
the
top
since
the
waveform
normally
rests below
the
perturbation.
Top-Base
performs
a
histogram
on
the
waveform
and
finds
the
most
prevalent
point
above and
below
the
waveform
midpoint.
The
most
prevalent
point
is
one
that
represents greater
than
approximately
5%
of
the total
display
points
(501)
and
is
considered
to
be
either
the
top
or
base.
If
no
point
accounts
for
more
than
5%
of
the
total,
then
the
top
is
chosen as
the
absolute
maximum
and
the
base
is
chosen
as
the
absolute
minimum.
EdQG
Definition Both
rising
and
falling
edges
are
defined
as
transitional
edges
that
must
cross
three
thresholds.
A
rising edge
must
cross
the
lower
threshold
in
a
positive
direction
(defining
it
as
a
rising
edge),
cross
the
mid
threshold
(any
number
of
crossings,
both
positive
and
negative
are
permissible)
and
then
cross
the
upper
threshold without
any
crossing
of
the
lower
threshold.
Algorithms
A-2
HP
54501A
Programming