Table of Contents
Advertisement
Section IV
Paragraphs
4-11
to
20
to the
Schmitt
trigger.
When
the
ramp
(the
positive-
going portion
of
the
sweep
signal)
reaches apredeter-
mined
amplitude,
the
Schmitt
trigger
changes
state,
causing
the
gate
generator
to
turn
off,
terminating
the
main
sweep.
After a
brief
delay
from
the
end
of
the
sweep,
the hold-off circuit
generates a negative
signal
that
switches
the
Schmitt
trigger
back
to
the
pretrigger
state.
This
action
"resets"
the
gate
gen-
erator.
The
next negative pulse
from
the
trigger
generator
"fires" the gate
generator again and
the
cycle repeats.
4-11.
AUTO.
Selecting
AUTO
with
the
SWEEP MODE
switch
activates the auto
circuit.
However,
if
a
trigger signal greater than about
40
Hz
is
present,
the
signal
from
the
trigger
generator
"locks out"
the
auto
circuit.
With
the auto circuit
"locked
out", the
main
sweep
circuit
operates as
it
did
in
NORM.
If
the trig-
ger
signal
drops below 40 Hz, or
is
removed,
the
auto
circuit
turns
on.
It
is
triggered by
the
Schmitt
trig-
ger
at the
same
time
the gate
generator
is
"reset"
and
supplies
the
current
necessary
to
"fire" the gate
generator.
This
action
causes
the
main sweep
circuit
to
free-run
--
its
rate
determined
by
the
sweep
speed.
4-12.
SINGLE.
Setting the
SWEEP MODE
switch
to
SINGLE
disconnects
the hold-off circuit
from
the
Schmitt
trigger.
The
gate
generator
must now
be
"reset" by
depressing
the
RESET
push
button
at the
end
of
each sweep,
manually
switching
the
Schmitt
trigger
to
the
pretrigger
state.
4-13.
CIRCUIT
DETAILS.
4-14.
The
following
paragraphs provide
more
informa-
tion
about
the
main sweep
circuit.
Refer
to
the
sche-
matic
diagram
in
Figures
7-4
and
7-6.
4-15.
NORMAL.
The
trigger signal
is
obtained
from
one
of
three
sources
as
determined by
the
Trigger
Source
Switch, SI
01.
The
external signal
is
obtained
from
a front-panel
BNC
connector;
the
line
signal
from
the
Model
180-series Oscilloscope; and
the in-
ternal signal
from
the
Vertical Plug-In through
the
in-
ternal trigger amplifier,
Q101/Q102.
Voltage divider
R103/R104
attenuates
the
external signal by a factor
of
10
when
EXT-^10
is
selected.
Voltage divider
R1
01/
R102
attenuates the
line
signal
to
10
v
pk-pk.
The
selected trigger signal
is
coupled through
the
Trigger
Coupling switch
SI
02
to
source
follower Q103.
Trigger
Coupling switch S102
selects
between
direct coupling
(DC) capacitive coupling (AC) a
low-pass
filter
(ACS)
and
a high -pass
filter
(ACE).
CR103
protects
Q103
from
excessive
negative
voltage.
Q103
provides ahigh
input
impedance
to
the trigger signal
and
couples
the
signal
to
the
trigger
comparator, Q104/Q105.
4-16.
The
trigger
comparator
switches tunnel diode
CR106
to
a high-voltage
state
at
a selected
point
on
the
trigger
signal.
Setting the
SLOPE
switch
to
+
turns
off
CR104
and
turns
on CR105.
Tunnel
diode
CR106
is
connected through
CR107
to
the collector
of
Q104.
Thepositiveslopeof
the
trigger
signal,
applied
to
the
base
of
Q104, causes
Q1
04
to
eventually conduct
hard enough
to
switch
CR106
to
a high-voltage
state.
The
TRIGGER LEVEL
control
determines
the
base
voltage
of
Q105
and therefore
affects the
bias
on Q104.
Adjusting
the
TRIGGER LEVEL
control
determines
the
voltage
required
to
switch
the
tunnel diode.
Diodes
Model 1821A
CR109
and CRllOprotect
Q104and QlOSfrom
reverse
breakdown, base
to
emitter.
4-17. Setting
the
SLOPE
switch
to
-
turns
off
CR105
and
turns
on
CR104.
Tunnel
diode
CRl
06
is
connected
through
CR108
to the
collector
of
Q105.
The
trigger
signal
is
coupled through
Q104
to
the
emitter
of
Q1
05.
Eventually
the negative
slope
of
the
trigger signal turns
on Q105 hard enough
to
switch
CR106
to
ahigh-voltage
state.
Since
the
TRIGGER
LEVEL
control
determines
the bias
on Q105,
it
also
determines
the voltage
re-
quired
to
switch
the tunnel diode.
4-18.
The
negative-going rectangular
wave
produced
by
CR106
is
differentiated
by
C118
and
the
emitter
circuit
of
Q107.
The
resulting signal
is
coupled
to
Q108.
Since
Q108
is
biased below
cut-off,
only the
positive
pulses are amplified and
inverted.
The
fast-
rise negative
pulses
from
the collector of
Q108
are
coupled
to
the auto circuit
"locking
it
out"
and
to
the
tunnel
diode,
CR201
(Figure
8-6).
The
current pro-
vided by
the
first
negative pulse,
combined
with
the
current
from Q204
is
sufficient to
switch
CR201
to
a
high-voltage
state.
After
the
trigger pulse ends, the
current
from Q204
alone
is
sufficient to
keep
CR201
in this
high-voltage
state.
The
negative signal
pro-
duced
by
CR201
is
amplified
and
inverted
byQ201
and
Q202.
Diodes
CR202
through
CR204
keep Q201
from
saturating.
The
negative signal
at
the collector of
Q202
is
coupled
to
three places:
(1)
to
PI
pin 14
and
through
the
Model
180-series Oscilloscope
to
the
rear
panel,
(2)
to
S502
as
an
intensity signal
to
unblank
the
CRT,
and
(3)
to
the
Miller integrator
circuit
where
it
opens diode switch
CR211/CR215.
4-19.
When
the
diode switch opens,
the
timing capaci-
tor (C501
through C510) begins charging through
the
timing
resistor (R502
through
R510)
to
the negative
voltage
on
the
wiper
of
R235.
The
TIME/DIV
switch
determines
the
slope
of
the
negative-going
ramp
at
the
gate
of
Q207
in
two ways:
(1)
by
selecting various
RC
time
constants; (2)by selectingthe
base
voltage
on
Q206
which determines
the
charging
voltage
at
R235.
The
VERNIER
control,
R235,
adjusts
the
charging
voltage
between
the calibrated steps
of
the
TIME/DIV
control.
The
positive-going
linear
ramp
at the
out-
put
of
the
Miller integrator
is
coupled
to
PI
pin
11
and
through
the
Model
180-series Oscilloscope
to
a rear-
panel connector,
to
R460
to
arm
the
delayed
sweep
circuit,
and
to
S502
for
horizontal
deflection.
4-20.
The
positive-going
ramp
is
also picked
off
the
wiper
of
R251 andapplied
to
CR216.
As
the
ramp
goes
positive,
CR216
turns
on and connects
the
ramp
to
the
base
of
Q205.
The
ramp
continues going positive
until
it
reaches
the
upper
hysteresis
limit
of
the
Schmitt
trigger,
when Q205
turns
on,
turning
Q204
off.
The
current
from Q204
through
CR201
is
removed, and
the
tunnel diode
switches
to
a low-voltage
state.
The
negative gate ends;
the
diode switch
(CR211/CR215)
closes
and terminates
the
ramp. Disconnect
diode
CR216
opens
when
the
ramp
ends,
disconnecting
the
sweep
voltage
from
the
Schmitt
trigger.
The
base
voltage
of
Q205
returns
to
a quiescent
level
and
the
Schmitt
trig-
ger
remains
in this
new
state.
CR201
is
now
in
a
"no-trigger" condition
and incoming
negative trigger
pulses
have no
effect.
4-2
02591-3
Advertisement
Table of Contents
