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from 90 per cent to 10 per cent of its maximum
value
in the
direction
of decreasing
collector
current.
TURN-OFF
TIME:
The
time
between
the
end
of the input pulse
and the time when the output
pulse
has
decreased
to
10
per
cent
of
its
maximum
amplitude.
This
term
is
the
sum
of the storage time and fall time.
SETTING
UP A DISPLAY
CLASS-A OPERATION
Preliminary Considerations
Although the Type R Plug-In Unit willoperate
in any Tektronix oscilloscope of the 530, 540,
550 or 580
series,
the oscilloscope you should
use
will
depend
on
how
fast
a risetime
you
are interested
in observing.
Table
1 on
Page
1-1
lists
the risetime
specifications
of com-
binations
of
presently
available
non-rack-
mounted
oscilloscopes
and the Type R Plug-In
Unit.
Two
of
these oscilloscopes,
Types
532
and
536,
are not suitable for displaying
very
fast
pulses
because
they
do
not
incorporate
a signal delay line.
In
the
procedure
that
follows, a Type 541A
or
Type 545A is
used to demonstrate
the full
high-frequency capabilities of the Type R Plug-
In Unit.
The
first
display
to
be
presented
will
be
the
"Class
A"
pulse
characteristics
of
a
low-power, p-n-p transistor such as the 2N109.
Most
audio-type,
low-power
p-n-p
transistors
will give similar performance.
Before
setting up the controls,
consider the
limitation
of the
transistor
you
have
selected
for test with respect to its collector dissipation.
Since the output of the " R"
unit is ac coupled,
we
have
no
indication
of
average
collector
current
or
voltage
for
"Class
A"
operation
without
making
external
connections.
To
keep
the
display
simple
and still prevent
possible
damage
to
the
transistor
under
test, a good
way to start the display is to first set the front-
panel
controls
so
that
the
transistor
under
test
is cut off.
Then
you
can change
the bias
until
you
obtain
a display
which
is
suitable
for
the discussion
which
follows.
Such
is the
procedure described in the following paragraphs.
Set Type
R controls
as follows:
COLLECTOR
SOURCE
VOLTS
P-N-P, 5 volts
AA
Operating Instructions - Type R
TRIGGER
DOUBLE
COLLECTOR CURRENT,
1 (100 9)
MA/CM
PULSE VOLTS
minus, .05
PULSE VOLTS,
CALIBRATED
VARIABLE
(red knob)
BIAS VOLTS, (black knob)
0
BIAS VOLTS, (red knob)
Xl
SERIES
RESISTOR
1K
Set Oscilloscope controls as follows:
TRIGGERING
LEVEL
Clockwise
STABILITY
Clockwise
TRIGGERING
MODE
AC FAST (AC
LF
REJECT)
TRIGGER SLOPE
EXT, +
Sweep rate
10 wsec/cm
Connect
the
+TRIGGER
OUT
cable
from
the
"R"
Unit
to the TRIGGER
INPUT
of the
oscilloscope.
Connect
the
transistor
to
be
tested
and
an
external
resistor
to
the
Test
Board.
Then
attach
the
Test
Board
to
the
front
panel
of
the
"R"
Unit
and
turn
the
oscilloscope power switch to ON.
Adjust
the
appropriate
controls
for
a mod-
erately
bright
horizontal
trace
which
passes
through
the
line
that
is
one
major
division
below
the center
of the graticule.
Slowly turn
the
black,
BIAS
VOLTS
knob
from
0
to
a
negative
voltage
until
you
obtain
two
traces
which
are
separated
by
2
cm
(two
major
divisions).
Then
turn
the
STABILITY
knob
counterclockwise
until
you
reach
a point
a
little beyond
where
the trace disappears.
Now
turn
the TRIGGERING
LEVEL
control
toward
zero until astable, double-trace display appears,
such as the one shown in Fig. 2-5. The response
of the
audio
transistor
as it is used to present
this
display
is
quite
slow,
and
not
all
the
pulse-response
characteristics
previously
discussed will be present.
Note that the drawing
of
this
display
(Fig.
2-5)
is
quite
different
2-3
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