Tektronix 2235 - Α TRIGGER GENERATOR; A Schmitt Trigger and TV Trigger Circuit; A Sweep Generator and Logic

Α TRIGGER G ENER ATO R

biased on
and
U
460A an d U 460D are b iase d off . F or t h e
negative
slo p e p osition, t he transistors reverse states to in-
T h
e
Α Trigger Ge n erato r , sh own
on
Diag r am 3, sup p lies

vert t h e comparator ou t pu t p ola r ity .
trigger signals to t he Α Sweep Generato r . Included in t he
Α Trigger Generator circ u it are t h e Ρ - ΡA u to Trigger, A u to
B aseline, and TV Triggering circ u itry .

Α Sc h mitt T r igge r a nd T V Trigge r Circuit
T h is circuitry gen erates α signal t h at drives t h e Α Trigger
L ogic as α fu n ctio n of t he Trigger L evel Comparato r out pu t
sig n al a nd t he ΑTR IGG ER M ode switc hes .
T h
e
Α Trigger L evel Circ u it esta b lis hes voltages at t h e
ends of
t he Α TR IGG ERLEVEL poten tiometer as α function
of t h eΑ TR IGG ER p ush bu tton selection a nd trigge r sig n als

T he out p ut signals from t h e Α Trigger L evel Com p a r ato r
selected by t he Α SO UR C E switc h .

drive Q460 and Q463 . T h ese tra n sistors are co n fig ur ed as α
current mi r ror t h at converts t he d iffe r e n tial ou t p ut to α sin-
gle-ended current to drive am p lifie r U 480C . Slope B alance
In t h eΡ -
Ρ
Auto a
n
d
TV F
ield modes, 0413 is
off
and

p otentiometer R 471 D corrects for d o offsets b etwee
n p
osi-
C
R 414
a
n
d C
R 415
a
r
e reverse biased .
Trigger signals se-

tive and negative slo p e . S
h
u
n
t-feed bac
k amplifier
U 480C
lecte d b y t h e Α SO UR C E switc h a r e applied to p ea k detec-

con verts α curre
n
t
i n
put to α voltage output to drive
t h
e
tors
consisting of Q420-Q422 and 0421-Q423 . T h ese pea k input of t he Sc h mitt Trigger, U 480D, t h ro u g h R
469
. P ositive
detectors trac k do levels a
n
d
h
ave α
h ig h
voltage transfer

feedback for t he Sc h mitt Trigger is p rovi de d by poten tiome-
efficie
n
cy .
T h
e positive- and negative- p ea
k sig n
al levels

ter R 479, and C479 reduces trigger j itter by i n creasing p osi-
stored by
C414
a
n
d C415 are near t
h
e pea
k
levels of
t h
e

tive feedback at h ig h er fre qu e n cies .
T
h e setti ng of
R
479
trigger signal . Am p
lifiers
U 426A a
n
dU
426 B
are configured

determines t h e circuit h ysteresis .
a s voltage
followers wit h transistors 0428
an
d Q429 in t h e
feedbac
k
loo ps .
T h
ese transistors
t h ermally com p ensate for
Q420 and 0421 and level sh ift t h e am p lifier o u t pu ts bac
k
to

Wh en T VF ield is not selected, t h eTV T r ig E nab le line
t h e original do levels of t
h
e
input trigger signals
.
T h
e out
p
ut

connecte d to R 402 and R 473 is L O . T r ansistors 0402 and
of U 426A
will
b e
t h
e positive p ea
k
voltage of
t he in pu t trig-

Q403 are biased off and α L O is p lace d on o n e
i np
ut of
ger
sig n
al and
t h
e out
p
ut of U
426 B will b e t he n egative p eak

U 480A by R 474 . T h is L O in p ut
will
cause U 480A to
i n vert
voltage . Poten tiometers R 434 and R 435 ad j ust for do off-

t h e outpu t from U 480D . W it
h
Q403
off,
α
L
O
will
b e placed
sets
in t h e trigger ci r cuit r y .

on one input of U 480 B by R 405 a nd U 480 B will also act as
an inve r ter . T he Α Trigger sig n al at t h e ou t pu t of U 480
B
is
t h erefore t he same as t he i np u t signal to U 480A
.
In t
h
e
N orm
mode, +8 .6
V is a pp lied to t he j un ctio n of
R 411
and
R 414 . Dio d
e C
R 414 is forwa r d b iased, tur n ing on
Q413 w h ic h forward b iases CR 415 . Input transisto r s Q420

Wh en T V F iel d is selected, t
h
e
TV Trig E
nable
line
is HI .
an
d Q421 are t hen biased off and no trigger signals will

T he outputs of U 480D will d etermi ne t he cond uction states
reac
h
t
h
e
Α Trigger L
evel ci
r
cuit
. T h
e
inputs
and
o u t pu ts of

of 0402 and Q403, and t he
i np
ut of U 480A con
n
ected to
U
426A an d U 426 B will t hen be fixed voltages and indepen-

R 473 will b e HI . T he o u t p ut of U 480A
will
be
L
O and U 480
B
dent of
trigger-sig n al am p litude .

will invert
t
h
e
signal
at
its
ot
h
er
i npu t . Sig n als at t he collec-
tor of Q403 are
filtered
b y
C408, R 405, and C405 to r e j ect
TV
video
information an d average t he T V h orizo n tal-sync
Α Trigge r L evel Com pa r ato ι

p ulses . Setti
ng
t
h
e
trigger-level t h
res
h
old near
t he center of
t
h
e
h
orizontal-sync-pulse
swing
establis
h
es
t h
e
un triggere d
T h e Α Trigger L evel Com p arator com p ares sig n als se-

level . Wh
en t
h
e
T V
vertical-sync bloc
k
occ u rs,
t he
o
u t pu t of
lected by t
h
e
Α T R IGG ER SO
UR
C E switc h to α voltage set

t
h
e
filter
a pp lied to U
480 B p i n 7 rises to α level t h at will
b y
t h
e
Α TR IGG ER LEVEL con trol . P ositive or negative

cause t
h
e Sc
h mitt Trigger circuit
to
switc h . P recise TV fiel d
slope
trigge r ing is selecte d by t he Α T R IGG ER S L O PE

sy
n
c
h
ro
n
ization is obtained as α result of
t h is filtering actio n .
switc
h .

T he Α Trigger signal ou t pu t
will
b e t
h
e
i n
ve
r
se of t
h
e filtered
Α Trigge r L
evel
Ci r cu it
signal ap p earing at U 480 B p
i n 7 .
T h eo r y of O pe r ation-2235 Service
Tra n
sistors U
460 B
and U
460 E com p are t he wi p er volt-
age on
t h eΑT R IGG ER LEVEL control to t he i npu t trigger
sig n al, an d t he transistor wit h t he h ig h er b ase voltage will

Α S
WEEP
G
ENER ATO R A ND L OGIC
conduct more of t he availa b le emitter curre n t . T h e output
collector cur r ents su pp ly emitter cu rrent to two tra n sistor

T h e Α Swee p Ge
n
erato
r
and
L
ogic
circuitry, sh own
on
p airs w h ic h serve as c r oss-wired switc hes t h at are b iased

Diagram 4, produces α li nea
r
voltage
r amp t h
at is
amplified
on or off by t h e ΑTR IGG ER S L O PE switc h . Wh en S464 is

by t he H orizontal Am p lifie
r
to provide
h orizontal
deflectio
n
set to t he p ositive slope position, U 460C and U 460 F are

of t h e crt beam . The Swee p Gene
r
ato
r
circuits also produce