Tektronix 454A - Page 68

Ci r c u i t Descr i pt i on- 454zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA ‘ / R 454A
S i gnal

CR201
i n f r om

*

C R202
Channel 1
V er t i cal
CR203
Pr eamp

*
C R 204
Si g n al
i n f r o m
C h a nn el 2
V er t i cal
Pr eam p
11- 1
3- 8
R214
R 210 R220
R213
R223
C
h
a nn el
1
Di ode Gat e
R224
Cur r ent Pat h
R eve r se- B i ase d
Di o d e
F i g .
3- 5
. E f f ect of Di o de Gat es on si gnal pat h ( si mpl i f i ed pat h) . Condi t i ons
shown f or CH 1 posi t i on of t he MODE swi t ch .
V e r t i cal
Si gnal t o
Del ay- Li ne
D r i ve r
St age
CR207- CR208 ar e connect e d t o gr oun d t hr ough R220 ( see

or R 229 . For exam p l e, i f Q225 i s conduct i ng, cur r ent i s
si mpl i f i ed di agr am i n Fi g . 3- 6) . The Channel 1 Di od e Gat e

su pp l i ed t o Q225 t hr ough R229 . The cur r ent
f l ow t hr ough
bl ocks t he si gnal and t he Channel 2 Di ode Gat e
al l ows i t t o

col l ect or r esi st or s R 223 an d R 220
dr o
p
s
t he
CR207- CR208
pass .

cat hode l evel negat i ve so t he
Channel 2 Di o d e Gat e i s
b l ocke d as f or Channel
1
onl y
op er at i on . The si gnal p asses
t hr ough t he Channel 1 Di od e Gat e t o t he Del ay- Li ne Dr i ver
The HORI Z DI SPLAY swi t ch, S1001A, l ocks
t hi s ci r cui t

st age .
i n t he Channel 2 condi t i on
when oper at i ng i n t he § - ¥
mode . Thi s p r ovi d
es
- 12
vol t s
t o
r ever se bi as t he Channel 1
Di ode gat e t hr ough
R214 an d al l ows t he Channel 2 si gnal

The Al t er nat e- t r ace sync
p ul se i s a p pl i e d t o Q234 at t he
t o p ass t o t he Del ay- Li ne Dr i ver st age . The set t i ng of t he

en d of each
sweep . Thi s n egat i ve- goi ng sync p ul se momen-
MODE swi t ch has no ef f ect on ci r cui t op er at i on
i n t he § - ¥

t ar i l y i nt er r u p t s t he cur r ent t hr ough Q234 and
bot h Q215
mo d e ( al so see Hor i zont al Am p l i f i er
d i scussi on) .

an d Q225 ar e t ur ned of f . When Q234
t ur ns
on agai n
af t er
t he al t er nat e- t r ace sync p ul se, t he char ge on
C218 d et er -
mi nes whet her Q215 or Q225 con
d uct s . For exam p l e, when
Sw i t chi ng
MUI t
i
V
i
br at or

0225 was con
d uct i ng, C218 was char ged negat i vel y on t he
ALT . I n t hi s mo d e of o p er at i on, t he Swi t chi ng Mul t i -

CR228 si de t o t he emi t t er l evel of
Q225, an d p osi t i vel y on
vi br at or op er at es as ± b i st abl e mul t i vi br at or
.
I n
t he ALT

t he CR218 si d e . Thi s char ge i s
st or e d whi l e Q234 i s of f an d
p osi t i on of t he MODE swi t ch, - 12
vol t s i s connect ed t o t he

when

cur r ent f l ow t hr ough
Q234 r esumes, t hi s st or ed
emi t t er of
Q234, Al t er nat e Tr ace Swi t chi ng Am p l i f i er

char ge hol ds
t he ano d e of CR228 mor e negat i ve t han
t he
st age, t hr ough
S1001A an d S238A . Q234 i s f or war d bi ase d  ano
d e of CR218 . CR218 i s f or war d bi ased
an d t he emi t t er
t o su pp
l y cur r ent t o t he " on" t r ansi st or i n t he
Swi t chi ng

of Q215 i s pul l e d mor e negat i ve
t han t he emi t t er of Q225
Mul t i vi br at or st age t hr ough R233, R
234, CR234, an d R 219

t o swi t ch t he mul t i vi br at or .
The cond i t i ons d escr i be d p r e-