Pulse Jitter Measurements - Tektronix 7B51 Instruction Manual

Operating Instructions-Type 7B51
signal does not meet the triggering requirements. If the
condition cannot be remedied with the B Triggering
controls or by increasing the display amplitude (lower
VOL TS/DIV setting), trigger the B sweep externally.
5. Measurement and magnification are as described
above.
Displaying Complex Signals Using Delayed Sweep
Complex signals often consist of a number of individual
events of differing amplitudes. Since the trigger circuits are
sensitive to changes in signal amplitude, a stable display can
normally be obtained only when the sweep is triggered by
the event(s) having the greatest amplitude. However, this
may not produce the desired display of a lower·amplitude
portion which follows the triggering event. The delayed
sweep feature provides a means of delaying the start of the
B sweep by a selected amount following the event which
triggers the A Sweep Generator. Then, the part of the wave-
form which contains the information of interest can be
displayed.
Use the following procedure:
1. Set up the display as given in Delayed Sweep Magnifi-
cation Steps 1 through 6.
2. Time measurements can be made from the display in
the conventional manner. Sweep rate is determined by the
setting of the B TIME/DIV selector.
Example. Fig. 2-14 shows a complex waveform as dis-
played on the CRT. the circled portion of the waveform
cannot be viewed in any greater detail because the sweep is
triggered by the larger amplitude pulses at the start of the
display and a faster sweep rate moves this area of the wave-
form off the viewing area. The second waveform shows the
area of interest magnified 10 times using Delayed Sweep.
The DELAY-TIME MULTIPLIER dial has been adjusted so
the delayed sweep starts just before the area of interest.
Fig. 2·14. Displaying a complex signal using delayed sweep.
2-18
Pulse Jitter Measurements
In some applications it is necessary to measure the
amount of jitter on the leading edge of a pulse or jitter
between pulses.
1. Set up the display as in the above procedure.
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~ ~Jitter
Fig. 2-15. Measuring pulse jitter.
2. Set the B DELAY MODE selector to B STARTS
AFTER DELAY. Slight readjustment of the B Triggering
LEVEL control may be necessary to produce as stable a dis-
playas possible.
3. Pulse jitter is shown by horizontal movement on the
pulse (take into account inherent jitter of Delayed Sweep).
Measure the amount of horizontal movement. Be sure both
VARIABLE controls are set to CAL.
4. Multiply the distance measured in step 3 by the B
TIME/DIV switch setting to obtain pulse jitter in time.
Example. Assume that the horizontal movement is 0.5
divisions (see Fig. 2-15), and the B TIME/DIV switch set-
ting is .5 llS.
Using the formula:
horizontal
Pulse Jitter
=
jitter X
(divisions)
Substituting the given values:
Pulse Jitter
=
0.5 X 0.5 lls
The pulse jitter is 0.25 microseconds.
B TIME/DIV
setting
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