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waveform.
In this case, the output waveform is
shifted with respect to the leading edge of the
reference frequency pulse by a time interval cor-
responding to the pulse width.
Divide-by-8 Circuit Waveforms:
Fig. 6 indicates waveform relationships for a basic
divide-by-eight circuit.
are identical
to those
reference frequency of Fig. 6A is supplied to the
Channel 1 input. Fig. 6B indicates the ideal time
relationship between the input pulses and the out-
put pulse.
In an application
where the logic circuitry is
operating at or near its maximum design frequency,
the accumulated rise time effects of the con-
secutive stages produce a built-in time propagation
delay which can be significant in a critical circuit
and must be compensated for. Fig. 6 C indicates
the possible time delay which may be introduced
into a frequency divider circuit. By use of the dual-
trace oscilloscope, the input and output waveforms
can be superimposed ( A D D or S U B ) to determine
the exact amount of propagation delay that occurs.
A . R E F E R E N C E F R E Q U E N C Y P U L S E
( 1 0 0 0 P U L S E S P E R S E C O N D )
B. I D E A L D I V I D E B Y E I G H T O U T P U T
C . P R O P A G A T I O N D E L A Y
E I G H T C I R C U I T
Fig. 6 Waveforms in divide-by-eight circuit
Propagation Delay Time Measurement:
A n example of propagation dealy in a divide-by-
eight circuit w a s given in the previous paragraph.
Significant propagation delay may occur in any cir-
cuit. This oscilloscope has features which simplify
measurement of propagation delay. Fig. 7 shows
the
resultant
waveforms when the
presentation
is
combined
presentation by selecting the A D D or S U B (CH2
P O L A R I T Y
P U L L
INV) position
switch.
In the A D D position the two inputs are
algebraically
added
in
Similarly, in the INV. (pull) position the two inputs
are
algebraically
subtracted.
provides a precise display of the propagation time
(Tp). Using the procedure given for calibrated time
measurement (CAL), Tp can be measured. A more
10
The oscilloscope settings
used in
F i g . 5.
The
T R A I N
IN D I V I D E B Y
dual-trace
into
a
single-trace
of the M O D E
a single-trace
display.
Either
position
precise measurement can be measured. A more
precise measurement can be obtained if the Tp por-
tion of the waveform is expanded horizontally. This
may be done by pulling the X 5 M A G control.
also may be possible to view the desired portion of
the waveform at a faster sweep speed.
C H 1
C H 2
A D D
E X P A N D T H I S P O R T I O N
F O R T I M E M O R E P R E C I S E
M E A S U R E M E N T
S U B
Fig. 7 Using A D D or S U B modes for
propagation time measurement
Digital Circuit Time Delay Measurement:
Since a dual-trace oscilloscope has the capability of
comparing
the
timing of one waveform
another, it is necessity in designing, manufacturing
and servicing digital equipment.
ment, it is common for a larger number of circuits
to be synchronized, or to have a specific time-
relationship to end other. Many of the circuits are
frequency dividers a s previously described, but
waveforms are often time-related in many other
combinations.
In the dynamic state, some of the
waveforms change depending upon the input or
more of operation.
Fig. 8 shows a typical digital
cuicuit and identifies several of the points at which
waveform measurements are appropriate. The a c -
companying Fig. 9 shows the normal waveforms to
be expected at each of these points and their tim-
ing relationship.
The individual waveforms have
limited value unless their timing relationship to one
or more of the other waveforms is known to be cor-
rect. The dual-trace oscilloscope allows this com-
parison to be made. In typical fashion, waveform
No. 3 would be displayed on Channel 1 and
It
with
In digital equip-
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