Tektronix 7B71 Instruction Manual page 30

Circuit
Description--7B71
Out
p
ut Stage
The output of t
h
e slope comparator is applied
t
h
ro
u
g
h
t
h
e Outp
u
t Stage to t
h
e trigger generator circuit. Diodes
C
R
181 an d
C R
182 limit t
h
e push-pull outp
u
t of t
h
e trigger
amp lifier to about one volt
p
ea
k
-to- pea
k
.
Trigger
P
ulse Ge nerator
T
h
e Trigger
Pu
l se Gene
r
ator (see
F
ig . 3-3) shapes t
h
e
o
u
t
p
ut of t
h
e Trigger Am plifie
r
to
p
rovi d e α trigger
p
ulse
wit
h
α fast leading edge . Tunnel
d
iode
V
R304 is
q
uiescently
in its low-voltage state. T
h
e signal from t
h
e Trigger Am pli-
fier switc
h
es it to its
h
ig
h
-voltage state, causi
n
g α
n
egative-
going fast rise p ulse at t
h
e base of Q317 an d α p
ositive-
going
p
ulse at t
h
e
b
ase of Q309 . T
h
e output of t
h
e Trigger
P
ulse Generato
r
at t
h
e collector of Q317 is α
p
ositive-going
fast rise
p
ulse w
h
ic
h
is ap plied to t
h e Sweep Gate Stage .
T
h
e outp ut at t
h
e collector of Q309 is α negative-going
p
ulse w
h
ic
h
is ap
p
lied to t
h
e brig
h
t-line Auto circuit.
VR
304 reverts
b
ac
k
to its low-voltage state w
h
en t
h
e signal
from t
h
e Trigger Am plifier
d
ecreases sufficiently .
VR
304
runs at t
h
e repetitio
n
rate of t
h
e in
p
ut signal .
Sweep Gate Stage
T
h
e Swee p Gate Stage
p roduces α negative-going step to
start t
h
e Swee p Generator an
d
α
p
ositive gate for
u se in t
h
e
oscilloscope .
3-4
TRIGGER G
EN E RATO
R
T
h
e positive-going
p
ulse from t
h
e Trigger
P
ulse Ge
n
er-
ator ena
b
les C
R
319, openi
n
g an add itional current
p
at
h
for
VR
358, t
h
e swee
p
gate tunnel
d
iode .
VR
358 switc
h
es to its
h
ig
h
-voltage state, app lying α
p
ositive signal to t
h
e
b
ase of
Q360 ( part of t
h
e
b
istable sweep gate multivibrator) . T
h
e
collector voltage of Q360
d
ec
r
eases,
p
roducing t
h
e negative-
going step used to enable t
h
e t
h
e Swee
p
Generator.
Wh
e
n
Q360 turns on, emitter-couple d 0368 is turne
d
off to
p
ro-
duce t
h
e positive edge of t
h
e swee
p
gate out
pu
t. T
h
e swee
p
gate multivibrator remains in t
h
is state (Q360 on an d Q368
off) until it is reset by t
h
e swee p reset multivibrator (part
of t
h
e Swee p Generator) at t
h
e en d of t
h e sweep.
At t
h
e en d of t
h
e sweep , t
h
e negative-going loc
k
out gate
from the swee p reset multivibrator is app lied to t
h
e base of
Q326 t
u
rning it off.
E
mitter-cou p le d Q328 is turned on,
ta
k
ing c
u
rrent from t
h
e sweep gate tunnel diode,
VR
358,
an
d
reverting it to its low-voltage state. T
h
is switc
h
es t
h e
swee p gate multivibrator bac
k
to its
q
uiescent state (Q360
off an d Q368 on) . T
h
e ci
r
cuit remains in t
h
is con
d
itio
n
(
VR 358 in its low-voltage state) until t
h
e loc
k
out gate re-
turns to its hig
h
level at t
h
e end of
h
ol doff time .
Triggere d
H
ol doff Stage
T
h
e Triggere
d H
oldoff Stage rearms t
h
e swee p gate TD,
VR
358, at t
h
e end of
h
oldoff time . Duri n
g
h
ol doff time
VR
322 is in its
h
ig
h
-voltage state,
b iasing Q326 off. At t
h e
end of
h oldoff time t
h
e loc
k
out gate from t
h
e swee
p
reset
multivibrator returns to its
h
ig
h
level . This switc
h
es
VR
322
0377
S
WEEP
GATE
EMITTER
FO
L
LO
WER
S
WEEP
GATE
MUL
TI
V
I
BR
ATO
R
0360,Q368
VR
358
T
R
IGG
ERE
D
HO
L
DO F F STAG
E
0326, Q328
VR
322
S273
BR
IG
H
T
L
I
NE A U
TO
Q331, Q338, Q339
0346, 0350
Fig. 3-3. Si m
plifie
d b
loc
k
diagram of t
h
e Trigger Generator circuit .