Tektronix 454A User Manual

R 797- C R 797 f l ows t h r o u g h CR 702
an d i s suf f i ci ent t o

RE S E T l i g h t . DS792, i s
connect e d i nt o t h e ci r c u i t . T he
aut omat i cal l y swi t c h t h e Swee p Gat e
t unnel d i o d e st age

anode of C R 793 i s al so d
i sconnect e d f r om gr oun d . Now,
bac k i nt o i t s h i g h - vol t age st at e . T h e r esul t i s t h
at t h ezyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ‘

t he condi t i on of Q794 i s d
et er mi ne d by t h e Swee p R eset
Swee p Gener at or ci r cui t i s aut omat i cal l y r et r i gger ed
at t he

M ul t i vi br at or st age . Wh en Q774 i s of f
bef or e t h e RE S E T
en
d
of eac h h ol d of f p er i o d , an d ± f r ee- r u
nni ng sweep i s

bu t t on i s p r esse d , t h e col l ect or l evel of
Q774 i s negat i ve .
p r od uced .
Si nce t h e swee p f r ee- r u ns at t he swee
p r at e of

T h e c u r r ent t h r o u g h R 794- C R 793- R 791
set s t h e base l evel
t h e ‘ Swee p Gener at or
( as sel ect e d by t h e ‘ ¤™œ• / DI V  of
Q794 negat i ve eno u g h t o bi as i t of f . H
owever , w h en t h e
swi t c h ) , ± br i g h t r ef er ence
t r ace i s pr od u ced even at f ast

RE
S
E T
but t on i s p r esse d an d Q774 t u r n s
on, i t s col l ect or
swee p r at es .

goes p osi t i ve .
T h i s p osi t i ve l evel al l ows t h e b ase of 0794
t o
go p osi t i ve al so,
an d i t i s bi ase d on . T h e col l ect or of
Q794
goes negat i ve
an d t he RE S E T l i g h t comes
on . Q794
an
d t h e
Si ngl e
Swee p O p er at i on

RE S E T l i g h t
r emai n on u nt i l Q774 t u r ns of f agai n
at t
h
e
en d of t h e next
sweep .
Gener al . O p er at i on of
t h e ‘ Sweep Gener at or i n t he
SI N G LE S WEEP p osi t i on of t h
e
‘
S
WEEP
M OD E swi t c h i s
si mi l ar t o o p er at i on i n t h e ot h er mo d es . H
owever , af t er one
swee p h
as
b
een p r o d uce d , t h e Swee p R eset Mu l t i vi b
r at or
st age d oes not
r eset . Al l s u ccee d i ng t r i gger p u l ses ar e l oc k
ed
out unt i l t h e RE
S E T but t on i s p r esse d .
I n t
h
e SI N G LE S WEEP p osi t i on, t h e ‘
S
WEEP M
OD E
swi t c h d i sconnect s
t h e c h ar gi ng c u r r ent f or t h e H ol d
of f
Ca p aci t or .
Now, Q775 r emai ns on w h en i t i s f or war d bi ase d
b y t h e swee p t h r o
u g h C R 760 or C R 761 . W i t h Ÿ 775 on,
C R 702 i s h el d i n i t s
l ow- vol t age st at e t o l oc k out t h
e i n-
comi ng t r i gger pu l ses . T he
ci r cui t r emai ns i n t h i s con d i t i on
u nt i l
r eset by t h e Si ngl e- Swee p R eset
st age .
Si ngl e- Swee p R
eset . T h e Si ngl e- Swee p R eset
st age p r o-
d uces ± p ul se t o r eset t h
e Swee p R eset M ul t i vi b r at or
st age
so anot h er swee p can be pr od
u ce
d
i n t h e SI N G LE S WEEP
mo d
e of o p er at i on . Q u i escent l y, 0784
i s h el d i n con-
d uct i on by
t h e +12 vol t s a p pl i ed t o i t s base
t h
r o
u g h R 781 .
Wh en t h e RE S E T
bu t t on, S783, i s p r esse d , t h e
vol t age at
t h e base of 0784, as d
et er mi ne d by vol t age d i vi d
er
R
781- R 782, i s near zer o vol t s .
Ÿ 784 i s b i ase d of f an d i t s
col l ect or sl owl y goes p osi t i ve t owar d
+12 vol t s . T h i s
p
osi t i ve- goi ng c h ange at t h e col l ect or of
Q784 i s co u p l e d t o
t h e emi t t er
of Q785 t h r o u g h
t h e net wor k
C784- C785- R 784- R 785 . T h
i s net wor k pr event s noi se
or
ext r aneous
p u l ses f r om r eset t i n g
t h e swee p . Wh en t h e
p osi t i ve- goi ng
l evel at t h e emi t t er of Q785
r eac h es a b out +3
vol t s ( base l evel of
0785 set by d i vi d er R 771- R
772- R 773) ,
i t t ur ns on an d i t s col l ect or
r i ses p osi t i ve t o f or war d
bi as
0786 .
T h e col l ect or of Q786 r a p i d l y
goes negat i ve, w h i c h
f or ces Q785 t o
cond u ct even h ar d er . C787-
R 787 di f f er en-
t i at e t h i s negat i ve- goi ng
c h ange at t h e col l ect or
of Ÿ 786
and connect t h e
f ast negat i ve- goi ng pu l se t o t h e
base of
Q774 . Q774 t ur ns
on an
d
Q775 t u r ns of f t o enabl e
t h e
Swee p Gat e t u nnel di o d e, C R 702 .
Now t h e ‘ Swee p
Gen-
er at or can
be t r i gger e d w h en t h
e next t r i gger pu l se i s
r ecei ve d .
Gener al
Ci r cui t Descr i pt i on - 454A/ R 454A
’ T R I GG ER G ENER ATO R
T h e ’ Tr i gger Gener at or
ci r c u i t i s b asi cal l y t h e same as
t h e ‘ Tr i gger Gener at or
ci r cui t . Onl y t h e d i f f er ences
b
et ween t he t wo ci r cui t s ar e d i sc u sse d h
er e .
P
or t i ons of t h e
ci r cui t not d
escr i
b
e d i n t h e f ol l owi ng d i scussi on
o p er at es i n
t h e same manner
as f or t h e ‘ Tr i gger Gener at or
ci r cui t
( cor r es p ond i ng
ci r cui t n u m b er s ar e assi gne d i n
t
h e
800- 899
r ange) . F i g . 3- 14 s h ows ± d
et ai l e d bl oc k d i agr am of t h e ’
Tr i gger Gener at or ci r c u i t . ‘
sc
h
emat i c of t h i s ci r cui t i s
s hown
on
d
i agr am 8 at t h e b ac k of t h i s manu al .
I n p ut Sour ce F
ol l ower
T h
e
I
n p u t So u r ce F ol l ower
st age, Q823, and E
mi t t er
F ol l ower ,
0826, o p er at e i n b
asi cal l y t h e same manner
as
descr i b e d f or t h
e ‘ Tr i gger Gener at or
ci r c u i t . H owever , i n
t h e ’ Tr i gger
Ge n er at or ci r cui t , t h e H
O
R
I Z DI S PL AY
swi t c h , S1001A, bl oc k
s t h e ’ Tr i gger
Gener at or i n p u t
si gnal i n t h e mo d es w h er e
’ t r i gger i ng i s not d
esi r e d . ™· t h e
‘
an
d § -
¥ p osi t i ons of t h e
• Ÿ R ™– DI S PL AY
swi t c h , - 12
vol t s i s
connect e d t h r oug h R 829
t o t h e cat h o d e of C R
828 .
Si nce
t h e cat h o d e of C R 833 i s
connect e d t o
+12
vol t s
t h r oug h R
833, C R 833 i s r ever se
bi ase d an d i t bl oc k s t h
e
t r i gger si gnal .
I n t h e ‘ ™• ¤• • D
UR I N G ’ . ’ ( D EL AY E
D
S WEEP) an d M I X E
D p osi t i ons, ± secon
d swi t c h , ’ S WEEP
M
OD E S835,
det er mi nes w h et h er t h
e t r i gger si gnal i s
b l oc ke d or p asse d t o
t h e Sl o p e Com p
ar at or st age . I f
t h e ’
S
WEEP M OD E swi t c h
i s i n t h e ’ STA R
TS A F T ER D EL AY
TI ME p
osi t i on, t h e t r i gger
si gnal i s bl oc k
ed as i n t h e ‘ or
§ - ¥ p osi t i ons
. H owever , t h
e ’ Swee p
Gener at or ci r c u
i t
f r ee- r uns i n t h
i s p osi t i on as co
n t r ol l e d by anot
h er por t i on
of t h e ’ S WEEP
M OD E swi t c h
l ocat e d i n t h
e ’ Swee p
Gener at or ci r c u i t . I n t he T R I GG
ER A BLE A F T ER D EL
AY
TI ME
posi t i on, - 12 vol t s i s d
i sconnect e d f r om t h e cat h ode
of C R 828
an d connect e d t o t h e
cat h o d e of C R 833 t h r oug
h
R 835 . C R
833 i s now f or war d b i ase d
an d t h e t r i gger si gnal
can pass t o t h e
Sl o p e Com p ar at or st age
t o p r o d uce t h e
t r i gger pu l se .
L am p
Dr i ver . I n t h e SI N G LE S WEEP
mo d e, t h e cat h -

P
ul se
Ampl i f i er
o d e of C R 795 i s
connect e d t o gr oun d t o bl oc k
t h e
i ncomi ng a u t o- gat e pu l se . T he
‘ S WEEP T R I G' D l i g h t ,

T h
e Pu l se Am p l i f i er st age
i n t h e ’ Tr i gger
Gener at or
DS793, i s di sconnect e d f r om t h
e col l ect or of 0794 an d t h e

ci r cui t

o p er at es muc h

t h e same as

i n

t h e ‘ Tr i gger
3- 23

Tektronix 454A Specifications

General

Brand	Tektronix
Model	454A
Category	Test Equipment
Language	English