Tektronix 2235 User Manual

Wh en t he Χ - Υ mo de is not selected, Q756 is biased on

and Q829 wit h t h e portion t hr oug h Q829 d riving t he s hunt
a nd t he Χ
-Axis sig n
al is s
hun
te d to gro und .

fee db ack out p ut amplifier consisting of 0835, Q840, and
Q845 . The bias level of Q825 t h e r efo r e d etermi n es t h e
amount of emitter c urr e n t available to Q829 . F eed bac k -r e-
H orizontal O u t p u t Am p lifier

sistor R 841 esta b lis hes t he transresistance gain w h ic h co n -
T he H orizontal Output Am p lifier p r ovides final amplifica-

verts t he i n put cu rre n t to o u t pu t voltage . E mitter-followe r
Qg35 is do cou p led to Q840, and fo r low-speed sig n als
tio n of t
h
e
h
o
r izo n
tal
sig n
al to d
rive
t
h
e
h
orizo n tal crt d eflec-

0845 acts as α cu r rent source . F ast tr a n sitio ns cou p le
tion plates .

t h roug h C845, providing additional cur r en t gai n t hr o ugh
Q845 for fast voltage swings at t h e outp ut of t he Amplifier .
Sig n als fr om t he (+)and(-) swee p outputs of U 760 are
used to drive two sh unt-feedbac k amplifiers . Due to t he
feedbac
k , t h
e
input im p
edance of t
h
ese am
p lifiers
is low .
T h
e base voltages of Q770 and Q780 are at
n
ea
r ly
t
h
e same
do
level
due to forward-biased diodes C
R
765 a
n
d C
R
768
b etween t
h
e two emitters .
Transistors
Q770, Q775, and Q779 fo
r m
α cascode-feed-
bac
k
am
p lifier
fo
r driving t h
e
rig h t
crt
h orizontal
deflection
plate wit h R 775 setting amplifier
gain and C775
providing
h ig h -fre quency com p ensation . F or low-speed sig n als, Q779
serves as α cu rre n t so u rce for Q775, and at h ig h sweep
rates, t he ram p is cou p led t h ro ugh C779 to t h e emitter of
0779 .
T h
is provides additional pull-up output cu
rr
e
n
t to
drive t h
e crt at
h ig h
sweep rates .
T h
e
amplifier consisting
of
0780, 0785, and Q789 drives
t h
e
left crt h orizontal
deflec-
tion
plate in t h
e same ma
n
ne
r
as desc
r i
bed a b ove
wit h
ze-
ner diode
VR 782 level
s
h ifting
t
h
e collecto
r signal
of Q780 .
T he
BEAM
F I N D f u nctio n is imp lemented w h
en S390 is
push e d in to disco n nect t he cat h o de of C R 764 from t h
e
-8 .6
V
sup p
ly . T h
e voltage on
t h
e cat
h
ode of
VR 764
goes
positive, causi
n g
C
R
780 and C
R 770
to b e
forwa
rd b iase d .
Current
from R 764
causes
t h
e output commo
n -mo
de volt-
age of t he two s hun t-fee
db
ack
am
p lifiers
to be s
h ifted
nega-
tive to reduce t he availa b le voltage swin g
at
t h
e
crt p
lates .
T h is p r eve n ts t h e trace from b ei ng d eflected off-scree n
h
orizo
n tally .
Z-AXIS AMPL I F I ER
Th
eo
r y
of O pe r atio n -2235 Service
E xternal Ζ -Axis i np
ut voltages establis h p roportional i n-
pu t currents t hr o u g h R 822
and
R
823, and Am p lifie r sen sitiv-
ity is
determined b y t he transresista nce gain of t h e
s h un t-fee db
ac
k amplifier
. Diode C R 823 pr otects t he Ζ -Axis
Am p lifier if excessive signal
levels a
r
ea pp lie d to t he ΕΧΤ Ζ
AXIS I NPU T connector .
T he intensity of t h e crt display i n t he Α , Β ,
and
Alt H ori-
zontal
modes is determined b y t he I NT EN SITY controls and
associate d circuitry . Th
e
Α I NT EN SITY
potentiomete
r
co
n -
trols t h e b
ase voltage of Q804 to determi
n
e t
h
e amo un t of
emitter
current
t h
at
will flow
t
hr
oug
h
t
h
e tra n sistor and
t h erefore t h e level of t he Ζ -Axis signal . L i k
ewise
t h
e
Β
IN-
TENSITY p otentiomete r will con trol t he b ase voltage
of
Q814
and
t h
e
intensity
of t
h
e
Β
an d
Alt
Swee pd is p lays .
Wh en only t he Α Sweep is displayed, Q586 and CR 583
are biased off . T he current t h roug h R 818, as set by t h e
Α I NT EN SITY p otentiometer, will flow t hr o u g h CR 818 a nd
Q825 to fix t h e voltage level at t heΖ -Axis Amplifier outpu t .
F or α Β -only d is p lay, Q586 is biased on to reverse b ias
C R 818 and p reve n t Α -i n te n sity cur r ent from reac h i ng Q825 .
C u rrent dete r mined b y t h e b ase voltage of 0814 will flow
t hrough CR 817 to Q825 and d ete r mi ne t he Β Swee p inten-
sity . F or an alternating Α and Β display, Q586 will be b iased
off w hen t he Α Swee p is d is p laye d . D u ring t h e portion of t h e
Α Sweep in w h ic h t he Β Swee p r un s, current from R 816 is
allowed to flow t h roug h CR 816 b y t he Β Ζ -Axis L ogic circuit
to p rovide an i n te n sified zone .
T h eΖ -Axis Am p lifier, sh own on Diagram 7, co n trols t he

Wh
en C H O P VER TICA L M OD E is selecte d , t h e C h op
crt i n te n sity level via several in p ut-signal
sou
r
ces .
T
he effect

B la nk signal is applied to t h e collector of 0825 t hrough
of t h ese in p ut signals is eit h er to i n crease
or dec
r
ease
tr
ace

CR 824 during t he display-switc h i ng time . Sig n al cu r rent is
intensity or to completely b la nk p ortions
of
t h
e dis p lay .
T h
e

shunted away from C R 825, and t h e forwa r d b ias of 0829
Ζ -Drive signal current as determi ned b y t h
e
Α
and
ΒΖ -Axis

increases to t h e b la nk i ng level . Wh en blan k ed, t he out pu t of
Switc h ing L ogic and t he i npu t cu rrent from t he ΕΧΤ Ζ AXIS

t h e Ζ -Axis Am p lifie r d r ops to α level t h at reduces t he crt
I NPU T connector (if i n use) are su mme d at t h e emitter of

beam c u rre n t below viewing i n tensity during t he c h op
common-base amplifie r 0825 and t h
ereby dete
r min
e t
h
e

switc h ing t r a n sitio n .
collecto r cur r en t of t he stage . T h is transisto r pr ovi des α
low-
impedance termi n atio n for t h e in p ut signals and isolates t he
signal sources fr om followi ng stages of t he Ζ -Axis Am p lifier .

F or an Χ - Υ d is p lay, CR 818, C R 817, and CR 816 a r e r e-
verse biased . T he Χ signal is L O to reverse b ias C R 551
and allow current in R 820 to flow t h roug h CR 820 . T h e crt
Common- base transistor
Q829 esta b lis hes α constant

intensity is t hen controlled by t h eΑ I NT EN SITY pote n tiome-
cu r rent t h ro ugh R
832
. T h
is cur
r
e
n
t is d ivided between Q825

ter w h ic h sets t he cu rre n t i n R 820 t h ro u g h 0804 .

Tektronix 2235 Specifications

General

Brand	Tektronix
Model	2235
Category	Test Equipment
Language	English