Tektronix 2235 User Manual

T h eo r y of O pe r ation-2235
Service
B uffer Amplifie r an
d Gai n Switc h ing N etwor k

P ara ph ase Am p lifie r
T he B uffer Am p lifier p
resents α h ig h -im pe d ance, low-ca-

T he P araph ase Am p lifier
co
n
verts t h e single-e n ded sig-
pacita nce load to t he signal
from t he H ig h -Im pe d ance Atte n -

nal from t he Gain Switc
h ing N etwork into α differe n tial sig-
u ator a nd α
low
outp
ut
impe
d ance to t h e Gain Switch i ng

ηαΙ for a pp lication
to t he V ertical P ream p lifie r . I n
cluded
i
n
N etwor k . Α dual- p at h amplifier
is use d to com b ine h ig h - d
c

t he ci r cuitry is switc h ing
t
h
at provides extra gain for t h
e
sta b ility wit h h ig h -s p eed p erforman
ce .

2 mV p osition of t he V
O
L
TS/DI V switc h , ad j ustme n ts fo r
am p lifier do b alance, a nd
circuitry fo r t heV aria b le V olts/Div
function . A d ditio n ally, t he C h annel
2 P ara ph ase Am p lifie r
In t he slow p at h , t he input sig
n al is a pp lied to b ot h t he

con tains circ u itry to invert
t
h
e C hann el 2 dis p lay .
gate of source-followe r Q13
and t h e inverting in p ut of U 10
t h ro ugh t h e divide-by-two netwo
rk compose d of R 3 a n dR5 .
Tran sistor Q13 an d emitte r -followe r
Q18 isolate t he i npu t

T h e sig n al from t h e
Gain Switch ing N etwo rk is ap p lied to
sig n al from t h e loa d ing
of t
h
e Gain Switch ing N etwor k . T he

t he b ase of one tr a n sistor in
U 30 . T he ot h er in p ut transistor
divider n etwor k at t h
e output of t h e Am p lifier (1146, 1347, and

is b iased b y t he divider network
com
p
osed of R 30, R 31, and
R 48) is connected to t he ot h
e
r i npu
t of U 10 . Am p lifier U 10

R 33 to α level t h at will p
rod uce α null b etwee n t h e outpu ts of
com p ares t he two divider
voltages and c han ges t he co n duc-

U 30 (no trace sh ift
on
t h
e crt screen ) w hen t he V O L TS/DI V
tion level of current-so u rce
transistor 015 to cor r ect for any

control is switc h ed between
5
mV
and 2 m V . E mitter cur r e n t
error at t h e sou r ce of 013 . Ca p
acito
r
C10 limits t h e ban d -

for t he two in pu t transistors
is su pp lied by R 21, R 22, R 23,
widt h of U 10 so t h at t h
e slow p at h r esp onds o n ly to fre-

and R 25, wit h R 29 se r vi ng
as
t h
e gain-setti ng resistor be-
q uencies b elow 100 kH z .

tween t he two emitters . In t he 2 m Vp
osition, am p lifie r gai n
is i n creased b y closi ng contact
15 of S10 to shunt R 29 wit h
R 26 .
In t h e fast p at h , input signals
are cou p le d t hrough R 6,
C6, 013, and Q18 to t he ci r cuit
output . By ad j usting R 47,
t h e gai n in bot h p at h
s is matc h ed . In p ut offset voltage com-

T he collecto r current t h
roug
h
t h e two in p ut tra n sisto r s
p e n sation fo r U
10 is provided by R 10 to eliminate
trace

serves as emitter curre n t for t h
e
two
d iffe r ential out p ut tran-
sh ifts w he n switc h i ng
betwee
n
V olts/Div settings .

sisto r p airs . B ase-bias
voltages fo r t h e two p airs a r e derived
from t h e d ivider networ k
com p osed of R 39, R 41, R 42,
and
R 43 . M onolit h ic IC U 30 h
as matc
h
e d tra n sistor ch aracte r is
T he Gain
Switch ing N etwor k divides d own
t
h
e B uffer

tics, so t he r atio of curre n
ts
in
t
h
e two diodes connected to
Am p lifier
o u t p ut sig n al for a pp licatio n to t he P
arap
h
ase Am-

p in 11 d etermines t he c u rrent
ratios in t he o u t p ut t r a n sisto r
p lifier
and
h
as an outpu t impedance of
75
Ω for
all V olts/Div

pairs . As V O LTS/DI VV ariable p
otentiometer R 43 is rotated
switc h settings
.
T h
e particular V olts/Div switc h
setting will

from t h e calibrated to
uncalibrated positio n
,
t h e co ndu ctio n
determine w h ic h
co
n
tacts of S10 are closed and t h
erefore

level of t he tra n sistors connected
to R 35 will increase . Since
w h et h er t he P ara
p
h
ase Amplifier will receive α
-
1,
-
2,

t
h
e transistor p air out pu ts are cross-wire
d , t h is i ncreased
4, or
-
10 signal .

co ndu ction will subtract from t he signal p
roduced by t h e
FR
O
M
VER T I CAL INPU T
COUPL I NG
ΗΙ GΗ -Ζ
ATTENUATO R
=1 , =
10,
=1 θ0
--a-
BUFFER A MPL
S LO W PATH
U 10 > Q15
BUFFER A MPL
F AST PATH
ρ13, Q18
FRE
Q UEN CY
GAI
N
B A LANCE
R 47
F ig
ur e 3-1 . B loc kd iag r am of t h e V ertical
Atte nu ato r s .
GA I N
S W I TC H I NG τ0
NE
T
W O RK
VERTICAL
=1 , =Ζ ,

PRE AMP
=4, +10
42 θ 6 -1 θ

Tektronix 2235 Specifications

General

Brand	Tektronix
Model	2235
Category	Test Equipment
Language	English