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Tektronix T921 User Manual

Tektronix T921
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Circuit
Description-T921/T922/T922R
IX
.
1
SWEEP
AND
HORIZ
AMPL
CIRCUIT
DESCRIPTION
Digital logic
devices
are
used
to
perform
some
of
the
functions
in
this
instrument
.
LO
and
HI
designations
are
used
in
this
circuit
description
to
indicate
the
state
of
the
digital circuit
.
H
I
indicates
the
more
positive
of
the
two
levels
.
The
specific
voltages
which
constitute
a
LO
and
HI
logic state
may
vary
between
individual
devices
.
The
sweep
is
producedby
a
Miller
Integrator
circuit
consisting
of
02242,
02244, and
02246
.
A
sweep
ramp
is
initiated
at
the
collector
of
02246
when
pin
3
of
U2234A
goes
LO
and
is
terminated
when
pin
3
goes
HI
(see
Timing
diagram,
Fig
.
7-2)
.
In
the
NORM
triggering
mode,
pin
2
of
U2212A
is
HI,
allowing
a
positive-going
trigger
signal
at
pin
1
of
U2212A
through
U2212D
and
U2234C
to
cause
pin
3
of
U2234A
to
goLO
.
This
reverse
biases
CR2233
and
CR2234
and
allows
the
timing
capacitor
(selected
by the
SEC/DIV
switch,
S2250)
to
charge,
producing
a
sweep
ramp
at
the
collector
of
02246
.
When
the
sweep
ramp
reaches
about
12
volts,
02274
turns
on
.
This
causes
pin
7
of
U2224A
to
go
LO,
pin
8
of
U2234C
to
go
LO
and
pin
3
of
U2234A
to
go
HI
.
When
pin
3
of
U2234A
goes
HI,
CR2233
and
CR2234
are
forward
biased,
terminating
the
sweep
.
Pin 7
of
U2224A
remains
LO
for
a
length
of time
(holdoff time)
determined
by
C2275,
C2274,
,
R2275,
and
R2279
.
Three
holdoff
times
are
selected
by
the
SEC/DIV
switch
S2250
.
After
the
selected holdoff
time,
pin
7
goes
HI
.
This
allows
the next
trigger
signal
to
switch
pin
3
of
U2234A
LO
and
again
start
the
sweep
.
In
the
AUTO
triggering
mode,
when
no
trigger
signal
occurs
at
pin
11 of
U2224B
for
about
50 ms,
pin
10
of
U2224B
goes
LO,
causing
the
sweep
to
start
after
the
holdoff
time
ends
.
This
allows
the
sweep
to free
run
and
provide a
reference
display
.
When
a
trigger
signal
is
present,
pin
11 of
U222413
goes
HI,
then
LO
(when
trigger
signal
ends),
and
the
time
constant
of
C2226-R2226
prevents
pin
10
from
going
LO
as long as
the
repetition
rate of
the
trigger
signal
is
higher than
about
20
Hz
.
SWEEP
GATE
-
;
PIN 3
U2234
REV
.
BJUL
1977
SWEEP
1982-27
Fig
.
7-2
.
Timing
diagram
:
sweep
generator
and
gate
.
When
pin
3
of
U2234A
goes
HI,
the
current
set
by
R2236,
R2235,
and
R2237
is
sent
to
the
Z
Axis
Amplifier
to
blank the
crt
during
hold-off
.
HORIZONTAL
AMPLIFIER
The
horizontal
amplifier
converts the
single-ended
signal
to
a
push-pull
signal,
which
drives
the
crt
horizontal
deflection
plates
.
The
input
to
the
horizontal
amplifier
comes
from
eitherthesweep
generator
or
the
X
(external
trigger)
input
connector
.
In
the
X-Y
mode,
the
trace
is
shifted
to
the
center
of
the screen by the
current
through
R2184
.
In
the
AUTO
and
NORM
modes,
the
input
to
the
horizontal
amplifier
is
a
linear
ramp
from
the
sweep
generator
.
Transistors
02314,
02326,
and
associated
circuitry,
form an
operational
amplifier
with
a
variable gain
range
of
over 10
to
1
.
The
gain
is
set
by
feedbackelements
R2312, R2323,
and
X1-X10
control,
R2322
.
The
horizontal
POSITION
control,
R2316,
positions
the
crt
display
horizontally
by varying
the
current
into
the
base
of
02314
.
When
the
BEAM
FINDER
switch,
S100B,
is
pressed,
the
dynamic
range
of
02326
is
decreased
.
This
limits
the
horizontal
deflection
to
the
crt
screen area
.
The
BEAM
FINDER
switch
also
limits
the
vertical
deflection
to
the
crt
screen
area
.
Transistors
02332,
02334, 02344, and
assoicated
circuitry,
compose
a
paraphase
amplifier
.
Transistor
02332
is
a low-
impedance
input
for
02334
.
HORIZ
CAL
adjustment
R2332
sets
the
gain
of
the
paraphaseamplifier
.
When
the
current
through
the
collector
of
02334
increases,
the
current
through
the
collectorof
02344
decreases
and
is
180° out
of
phase
with
the
current
at
the
collector
of
02334
.
The
resulting
signal
to
the
crt
deflection
plates
is
a
push-pull
signal
.
Diode,
CR2334,
prevents
02334
from
saturating
when
R2322
is
in
the
X10
position
.
Since
02334
is
a
shunt
feedback
amplifier
and
02344
is
a
common
base
amplifier,
any
noise
in
the 100
V
power
supply
will
appear
as
a
part
of
the
output
.
To
prevent the noise from
appearing
on
the
crt
screen,
an
operational
amplifier,
consisting
of
02354
and
associated
circuitry,
supplies
an
inverted
sample
of
the
power
supply noise
to
the
output
.
Now,
any
noise
in
the
100
volt
power
supply
appears
common
mode
to
the
horizontal
deflection
plates,
preventing
horizontal deflection
of
the
noise
signal
.
Resistor
R2354
provides
feedback
for
the
operational
amplifier
.

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Tektronix T921 Specifications

General IconGeneral
BrandTektronix
ModelT921
CategoryTest Equipment
LanguageEnglish

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