Tektronix 7000 Series Manual page 14

Σ
ph
ase s
h
ift
Ph
ase s
h
ift is critical in areas li
k
e servo,
RF
or
d
igital system d
esign . T
h
e most
common met ho
d
of meas uri ng p hase
shift is to
u
se an oscillosco
p
e in the
Χ-Υ or
d
elaye
d
swee
p
mo
d
e. Α more
accurate meth o
d
of measuring
p
h ase is
with
t
he 7D15 . To determi ne phase, the
time betwee
n
t
he same voltage level on
t he lea
d
ing an
d
lagging sig n als is
measure
d
and d ivided by α conversion
factor (Time/Degree) .
For exam
p
le, if the perio
d
of th e signal
(as meas u re
d
with
t
h e 7D15) is 2 its
(5 MHz), the Time/Degree conversion
factor is : 2 μs/360 degree = 5.55 ns/
d
e-
gree . If th e time interval
b
etween
t
he
two phases is meas u red at 50 ns, th e
phase
d
ifference is th us : 50 ns/5 .55
ns/
d
egree=9 .09
d
egree of
p
h ase s hift.
F
ig . 12 s
h
ows t
h
e e
q
ui
p
ment set
up
for
t
h
e measurement of t
h
e p
h
ase s
h ift of
α 5 MH z signal .
L
i k e the
p
revious
p
ro
p
a-
gation d elay meas
u
rement, o
n
e signal
is a pp
lied to eac
h
trigger in
p
ut to t
h
e
7D15 . Again the SO UR C E
I
NPUT Β
p
us hbutton is
p
resse
d
to enable b ot h
in
p u t connectors. Bot h
t
he chann el Α
a n
d
Β TR IGGER LEVEL controls are
set to PRESET, w h ic h means the trig-
ger circuits will trigger on th e zero
crossover
p
oint.
Trigger arming is not re quire
d
for this
measurement. M erely trigger the sco
p
e
on the negative goi ng slo
p
e of ch annel
1 . This assures that the
p
seudo gate
d
is
p
lay is on the CRT. The
p
seu
d
o gate
dis
p
lay in
d
icates t h at th e measurement
is being made
b
etwee n t
he two zero
crossover
p
oints . In t h is case, the time
measure
d is 75 .60 n s for ph
ase s
h
ift of
75 .6 ns/5 .55 n s/ d
egree=13 .8
d
egrees .
This metho
d
of meas uring
p
h ase sh ift
can be use
d
for si ngles h ot or re
p
etitive
sign als, wit h accuracies of 0.125° an
d
0.075°, res
p ectively at 35 kH z. Several
factors affect t h is accuracy :
1 . Am
p
litu
d
e of th e two signals-It is
more
d
ifficult for the 7D15 trigger cir-
cuits to
d
etect the zero crossover p
oint
on low am
p
litu
d
e signals.
2.
R
elative am
p
litu
d e of the two signals
-I d
eally bot
h
signals s
h
o
u
l
d
be t
h
e
same am
p
lit
ud
e .
Cloc k
In
p
ut
7TTL
Gates i n
Series
L
ea
d
ing
Ph
ase
I
11
C H 1
L
aggi n g Ph ase
Delaye
d
Cloc k
7Α 18 Ι 7D15 Ι 7 Β 53 Α
C H Α & Β
D LY'D T R IG
C H 2 ςΗ Α A RM C Fi Β
IN
Ι
ο
7DIs
Out
p
ut
M
o
d
e . . . . . . . . . . . . . . . . . . . . . . . . . . Tim Α- Β
Ave
r
g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Χ1000
Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
π5
Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
N
o
rm
Ti
m
e
B
ase
Displayed Wavefor m . . . . . . . . . .
P
se udo Gate Main Ti m e/Div . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trigger
L
evel . . . . . . . . . . . . . . . 50% A mp lit ud e Delayed Ti m e/Div . . . . . . . . . . . . . . . . . . . . . . . . .
Slo p e Α & Β . . . . . . . . . . . . . . . . . . . . . . . . . . + Triggering . .
Cou
p
l Α & Β . . . . . . . . . . . . . . . . . . . . . . . . . . DC
Delaye
d
Trig . . . . . . . . . .
Run
s After Dly Time
So
ur
ce . . . . . . . . . . . . . . . . . . . . . . . . . . . Input Β
V
e
r
tical Am
p
lifie
r
M
ai nframe
Dis p lay
M
ode . . . . . . . . . . . . . . . . . . . . Alternate
Vertical
M
od e . . . . . . . . . . . . . . . . . . . Alte r nate
Trigger So u rce . . . . . . . . . . . . . . . . . . . . . . C h 1
T r igge r Sou r ce . . . . . . . . . . . . . . . . . . . . . . . L
eft Volts/Div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
F
ig . 11 .
Eq
ui p ment setu p for p
ro pagation
d
elay measurement.
F
ig . 12 .
Eq
uipment setup for p h
ase s
h
ift measurement .
7603
7 Α18 Ι 7D15 Ι 7 Β 53 Α
ο
Delaye
d
Swee
p
Gate
Out
M
ai nfr ame
7 ρης V e r tical
M
o d e . . . . . . . . . . . . . . . . . . . Alte r nate
M
o
d
e . . . . . . . . . . . . . . . . . . . . . . . . . . Ti
m
Α - ιΒ
Trigger
So
u
rce . . . . . . . . . . . . . . . . . . . . . . .
L
eft
Averg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1000 Χ
Ti m e
B
ase
Cloc k . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 π s
M
ai n Ti m e/Div .
Gate
. . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . .
N
o
rm I
r
igge
r
ing
- . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dis
p
laye
d W
aveform
P
se
ud
o Gate . . . . . . . . . .
T
r
igge
r L
evel . . . . . . . . . . . . . . . . . . . . . .
Pr
eset
V
e
r
tical A
mp
lifier
Slope Α & Β . . . . . . . . . . . . . . . . . . . . . . . . . . . + Dis
p
lay
M
o
d
e . . . . . . . . . . . . . . . . . . . . . . A L
T
CουρΙ Α & Β . . . . . . . . . . . . . . . . . . . . . .
.
. . .
AC Trigge
r
So
ur
ce . . . . . . . . . . . . . . . . . . . . . . C h
1
So
ur
ce . . . . . . . . . . . . . . . . . . . . . . . . . . .I
n
put Β
V
olts/Div . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .