Propagation D e l a y T i m e M e a s u r e m e n t :
A n example of propagation delay in a divide-by-
eight circuit w a s given in the previous paragraph.
Significant propagation delay may occur in any cir-
cuit with several consecutive stages. This os-
cilloscope has features which simplify measure-
ment of propagation delay time. F i g . 7 shows the
resultant waveforms when the dual-trace presenta-
tion is combined into a single-trace presentation by
selecting the A D D position of the MODE switch.
With C H 2 PULL. INVERT switch in the normal posi-
tion (pushed in) the two inputs are algebraically
added in a single-trace display. Similarly, in the in-
verted position (pulled out) the two inputs are
algebraically subtracted. Either position provides a
precise display of the propagation time (Tp). Using
procedures given for calibrated time measurement.
Fig. 7 Using A D D mode propagation
time measurement
Tp can be measured. A more precise measurement
can be obtained if the Tp portion of the waveform is
expanded horizontally. This may be done by pulling
the X 1 0 M A G control. It also may be possible to
view the desired portion of the waveform at a faster
sweep speed.
Digital Circuit Time Delay Measurement:
A dual-trace oscilloscope is a necessity in design-
ing, manufacturing and servicing digital equip-
ment. A dual-trace oscilloscope permits easy com-
parison of time relationships between t w o
waveforms. In digital equipment, it is common for
a large number of circuits to be synchronized, or to
have a specific time relationship to each other.
Many of the circuits are frequency dividers as
priviously described, but waveforms are of ten
time-related in many other combinations. In the
dynamic state, some of the waveforms change,
depending upon the input or more mode of opera-
tion.
Ffg. 8 shows a typical digital circuit and identifies
several of the points at which waveform measure-
ment are appropriate. The accompanying
Fig.
8
shows the normal waveforms to be expected at
each of these points and their timing relationships.
The individual waveforms have limited value unless
their timing relationship to one or more of the other
waveforms is known to be correct. The dual-trace
oscilloscope allows this comparison to be made. In
typical fashion, waveform No. 3 would be displayed
on C H 1 and waveform No. 4 through No. 8 and No.
10, would be displayed on C H 2 although other tim-
ing comparisons may be desired. Waveforms No.
11 through No. 13 would probably be displayed on
C H 2 .
In the family of time-related waveforms shown in
Fig. 9,
waveform No. 8 or No. 10 is excellent sync
source for viewing all of the waveforms; there is
but one triggering pulse per frame. For con-
venience, external sync, any of the waveforms may
be displayed without readjustment of the sync con-
trols.
With No. 8 or No. 10 used as external triggering
source, any of the waveforms may be displayed
without readjustment of the T R I G L E V E L control.
Waveforms No. 4 through No. 7 should not be used
as the triggering source because they do not con-
tain a triggering pulse at the start of the frame. It
would not be necessary to view the entire
waveforms as shown in
Fig. 9
in all cases. In fact,
there are many times when a closer examination of
a portion of the waveforms would be appropriate.
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
11
A REFERENCE FREQUENCY PULSE TRAIN
(1000 PULSES PER SECOND)
B
IDEAL DIVIDE BY EIGHT OUTPUT
C PROPAGATION DELAY IN DIVIDE BY EIGHT CIRCUIT
Fig. 6 Waveforms in divide-by-eight circuit
CH2 P O L A R I T Y
N O R M A L
CH2 P O L A R I T Y
I N V E R T
