Tektronix 465M User Manual

2
The
A
EXT
trigger signal is
applied to J2205.
The
signal
passes through one of
two voltage dividers.
The
A
SOURCE switch
(S2200) determines
which divider
is
selected. In
the EXT
position,
the
A SOURCE
switch
selects
the divider
composed
of
R2205-C2205
and
R2206-
C2206. In the EXT
position
the
selected
divider
attenuates
the input
signal
by
a
factor
of
about
4. In
the EXT
10
position,
the
A SOURCE
selects
the
divider
composed
of
R2203-C2203
and
R2204-C2204.
In
the EXT
^
10
position
the selected
divider
attenuates
the input
signal
by a factor
of
about
40. The
capacitors
in
parallel
with
the divider
re-
sistors provide
correct
voltage
divider
action
at
high
frequencies.
^In the
AC, LF
REJ, and HF
REJ
positions of
the
A
COUPLING
switch
(S2220), the
signal from
the out-
put
of
the selected
voltage
divider
is
coupled
to
the
gate of
02212
through
a capacitor
(C2212). In
the DC position,
the signal
is directly
connected
to the
gate of 02212.
^The
EXT
signal
is applied
to
the
gate of
source-follower
02212.
FET
02214 provides
a
relativety-
constant
current
source
for
02212. Diode
CR2214
com-
pensates
for current
changes
as
temperature
changes
by
slightly
adjusting
the
bias on
02214.
The
signal on the
source of
02212
is applied
to the
base of
emitter
follower
02216. The
signal
on the
emitter
of
02216
is supplied
to
the A
SOURCE
switch.
^To
protect
0221
2 in
the presence
of
high-
amplitude
positive-going
input
signals,
R2203
or R2205
(depending
on
the
A SOURCE
setting)
limits
the gate
cur-
rent
that can
be
drawn
by
02212.
In
the presence
of high-
amplitude
negative-going
signals,
CR2213
becomes
for-
ward
biased.
The
path for
current
flow
is
from
—5
volts
through
R2229,
CR2213,
and R2204
or R2205.
Resistor
R2203
or R2205
limits
the
current
through
R2229
and
CR2213
preventing
the
anode
of
CR2213
from
going
more
negative
than
about
-6
volts.
(d) Trigger
Switching.
Trigger
SOURCE
Switching
selects
the
source
of the
signal
applied
to
the
Trigger
Gen-
rators.
Trigger
COUPLING
Switching
determines
the
band
of
frequencies
supplied
to the
Trigger
Generators.
The
A
and
8 Trigger
Switching
circuits
are
the
same
except
A
SOURCE
has
a
LINE
position
and
B
SOURCE has
a
STARTS
AFTER
DELAY
position.
The LINE
position
supplies
a sample
of
the
power
line
voltage
from
the
Low-
Voltage
Power
Supply
to
the
A Trigger
Generator.
The
STARTS
AFTER
DELAY
position
will
be
discussed
in
the
B Trigger
Generator
description.
Since
both
circuits
are
so
similiar,
only
the A
Trigger
Switching
circuit
will
be dis-
cussed.
J^Two
paths
exist for
the
triggering
signal.
The
high-frequency
signal
components
connect
directly
to input
pins
of
U2260.
The
low-frequency
signal
components
con-
nect
to
pin
19
of
U2260
through
the
A
SOURCE
switch.
AIR
FORCE
T033A1-13<496-1
NAVE
LEX
0969-LP-1
70-0010
Operation
Instructions
Figure
4-3A
shows
a simplified
diagram of
the low-
frequency
signal
path.
Figure
4-3B shows
a simplified
dia-
gram
of
the high-frequency
signal
path.
^Figure
4-4
shows
a simplified
diagram
of
signal flow with
A SOURCE
set
to
NORM
and
A COU-
PLING
set to
AC.
Other
SOURCE
settings
operate
in
a
similar
manner. Each of
the high-frequency
signal
inputs
to
U2260 is internally
connected
to the
base of
an
emitter
follower.
Normally these
emitter
followers
are
prevented
from
conducting
by connecting
the
base
to
—2
volts
through
a
pair
of resistors
(see Figure
4-4).
To
select
a high-
frequency
input,
the junction
of these
resistors
is
connected
to
ground
through the
SOURCE
switch
which
allows
the
emitter in
U2260 to conduct.
For
instance,
to select
the
NORM
trigger
source, the
junction
of R2233
and
R2238
is
grounded
through
the
A SOURCE
switch
(see
Figure 4-4).
_^For
all
A COUPLING
settings
except
HF
REJ,
the
resistor junction
selected
is
connected
to ground
through
the
A COUPLING
switch
(see Figure
4-3B and
Figure
44).
In
the HF REJ
position,
the
selected
resistor
junction
is
disconnected
from
ground
and
pin 4
of
U2260
is
selected
by grounding
the
junction
of
R2243
and
R2242.
Pin
4
must
be selected
even
though
no
signal
is
connected
to
it because
one of
the
emitter followers
within
U2260
must be
selected
for proper
operation
of
U2260.
Since the
high-frequency
signal
path
is
opened
the
only
signal
sup-
plied
to the
A Trigger
Generator
is through
the
low-
frequency
path.
^
For
the
AC and H
F R EJ
positions
of
the
A
COUPLING
switch,
the
low-frequency
signal
is ac
coupled
through
C2226
and
C2227
to pin
19 of
U2260.
In
the
dc
position,
the low-frequency
signal
is
dc
coupled
(C2226
and
C2227
are
bypassed).
In the
LF REJ
position,
the
low-
frequency
signal
is interrupted
and
only
the
high-frequency
signal is
connected
to the
A Trigger
Generator.
(2)
A
Trigger
Generator.
The
A Trigger
Generator
consists
of
U2260
and
associated
circuitry.
Figure
4-5
shows
a simplified
diagram
of
the
A
Trigger
Generator.
(a)
Sequence
of
Events
During
Trigge
r
Gener-
ation.
The
following
discussion
will
follow
the
sequence
of
events
in
the
A Trigger
Generator.
Refer
to Figure
4-5
throughout
the
discussion.
1 During
Holdoff.
Point E
is held HI
by the
holdoff
gate
at pin 17
of
U2260. Point
I
is held HI
by the
complement
sweep
gate
output
at point
L
causing
point
J
to be
LO.
Both of
the arm
latch
inputs
are
LO.
The
output
of
the
arm
latch
(point
K) has
previously
been
reset
to HI
(at the
beginning
of
holdoff
by the
holdoff
signal
applied
to pin
17
of
U2260).
When
point
K is
HI,
pin 14
will be
held
LO
regardless
of
the trigger
signal
input.
The
sweep
gate
latch is
held
off.
4-9

Tektronix 465M Specifications

General

Brand	Tektronix
Model	465M
Category	Test Equipment
Language	English