respect to its sync pulse. These pulse parameters are shown
in figure 3-2. Specific setups for each mode are given in
paragraph 3.3.
3.2.1
White Marks
When first becoming familiar with the 801, the white mark
settings are handy. The white mark settings for the front
panel switches will always give a 5k to 50
kHz
sync signal
when power is on. The same settings will give 50% duty
time, TTL, ECL, ECL and
5Os2
OUT pulses; the LOWER
LEVEL/UPPER LEVEL control may need adjusting to ob-
serve the
501sz
OUT on an oscilloscope. Once the output is
observed, each control can be adjusted and observed until
the desired result is obtained.
3.2.2
Pulse Width, Transition and Delay
Narrow duty cycle pulses require the NORMAL OUTPUT
while greater than 70% duty cycle pulses require the COMP
OUTPUT setting. Pulse width plus trailing edge time plus
delay time settings should not exceed the period time. (See
figure 3-2.) The sum of width, trailing edge and delay actu-
ally must be somewhat less than period time by an amount
that depends upon the period time selected. Therefore,
when the sum of the desired width, trailing edge and delay
time exceeds 70% of the period time, the pulse should be
observed to make sure it is as desired.
The 50% duty time width setting
(
‘L
)
is meant to be used
in continuous mode. Other modes result in the following
default conditions.
Mode Selected
output
TRIG
I-I
A triggered
10
ns pulse
CONT
DBLX
A continuous output of paired
10
ns pulses
TRIG
DBL\
A triggered output of paired 10 ns pulses
GATE
DBL’L
A gated output of paired 10 ns pulses
3.2.4
Output Terminations
Only
5OQ
RG58U
cable should be used to connect the 801
to the circuit under test. A
5OQ
2W load should be used at
the circuit end of the cable for maximum pulse fidelity.
The
5Oa terminations should always be used on the SYNC
and TTL outputs and
5OQ
Thevenin loads should be used
on the ECL outputs.
3.2.5
Nonlinear and Reactive Loads
Both nonlinear and reactive loads will cause pulse distortion.
Reactive loads driven with fast transitions cause voltage
spikes that can damage the 801 output amplifier. If it is
necessary to drive reactive loads directly, the instrument
must be protected against these voltage spikes.
3.2.6
Duty Cycle
Always use the lowest range possible for both delay and
width functions. This will reduce the recovery time of the
one-shots and extend the maximum duty cycle of the 801
to its fullest capability.
3.2.7
Output Mixing
The outputs of two 801’s may be mixed using the following
network.
)
MIXED OUTPUT
FROM
FIRST 801
OUTPUT
20.5a 20.5a
FROM
SECOND 801
OUTPUT
3.2.3
ECL
Termination
Maximum output from either generator is limited to 6 volts.
Figure 3-3 shows a
5.2/0volt
5052
ECL termination. Similar
5Oa terminations can be made for ECL circuits with other
voltage arrangements.
801
-5.2V
ECL
ECL CIRCUIT
3 FT RG58U COAX
j
OR EQUIVALENT
-
Figure 3-3. ECL Termination
3.2.8
Precise Output Levels
Many times when testing a circuit it is desirable to lock the
output of the generator at either the high or low level. A
precise measurement of this level may then be obtained
using a DVM.
The external width
mode is useful for this purpose.
Set the
MODE to EXT WIDTH, TRIGGER to
fl
and TRIGGER
LEVEL maximum cw. The output will now be locked to
the
lower
level. Switching the trigger to
fi
will lock it to
the upper level.
3-4
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