Horizontal Plug-In - HP 182C Operating And Service Manual

Theory
Model 182C
4-59.
SWEEP GATE
OUTPUT
AMPLIFIERS.
4-60.
The
output
amplifiers are
four emitter
followers,
A8Q1-A8Q4. They
provide
Isolated
outputs of time
base
sampling
or
TOR
generated
signals to rear-panel
connec-
tors.
The
Operating and
Service
Manual
for the
plug-ln will
provide information on the characteristics of the
output
signals.
4-61.
The
four time base
signal inputs
to
these ampli-
fiers
are
the
main sweep, delayed sweep,
main
gate
and
delayed
gate.
The
emitter -followers convert
the high
impedance
inputs
to
low impedance outputs and
isolate
the time base
signals
from
external
equipment.
4-62.
HORIZONTAL
AMPLIFIER.
4-63.
The
inputs to the horizontal amplifier
are
an
in-
ternal
sweep
signal
from
the
horizontal plug-in
or
an
external
signal
applied to the
HORIZONTAL EXT
INPUT
jack.
Positioning the
HORIZONTAL
DISPLAY
to
INT
grounds
the input of the preamplifier and disconnects the
external
signal
preamplifier
from
the
output
amplifier.
The
internal
sweep
signal
Is
connected through
the
HORIZONTAL DISPLAY
switch to the
output
amplifier.
464. Selecting
HORIZONTAL
DISPLAY EXT
discon-
nects the internal
sweep
signal
and connects
the
external
signal
through the preamplifier to the output
amplifier.
With
EXT
selected,
the amplitude
of
the
signal
from
the
preamplifier
is
adjustable
by
rotating
the
EXT VERNIER
control.
When
the control
is
in
the
CAL
detent
position
the
output amplitude
of the preamplifier
is
determined
by the input amplitude.
4-65.
The
selected
signal
is
applied to the
output
amplifier
and
summed
with
a current established by the
HORIZON-
TAL
POSITION
control.
A HORIZONTAL MAGNIFIER
allows the gain
to
be increased by a factor
of
10 (X10)
or to be directly related to the amplitude of the input
signal
(XI).
The
resulting current
is
converted
to
a
differential signal, amplified,
and
applied to the horizontal
deflection plates of the
CRT.
4-66.
Refer to the schematic of the
horizontal amplifier
for
the
more
detailed
explanation
which
follows.
4-67.
An
external
signal
applied to The preamplifier
is
coupled through
a 3:1 divider
composed
of
A5R5
and
A5R6
to
A5Q1. The
output
of
A5Q2
is
coupled through
the
HORIZONTAL EXT VERNIER
and
the
HORIZON-
TAL
DISPLAY
switch.
The
high
input
impedance
of
A5Q1
in
conjunction
with the voltage
divider
and
A6R4
provides
a
1
megohm
load to the external
circuit.
Transistor
A5Q2
is
an emitter follower.
It
supplies a cur-
rent
to
A5Q3
which
is
determined by
A5R1S
and
the
EXT VERNIER
control.
4-68.
The
bandwidth
of the preamplifier
is
decreased
when
the
Phase/Bandwidth
switch
is
placed
in
die Phase
position.
This
is
accomplished by
connecting
A5C11
and
A5C12
into the
circuit.
The
decreased bandwidth and
phase
shift
compensates
for the
signal
time delay
in
the
vertical amplifier
plug-in. This allows
more
accurate
X-Y
phase measurements
to be made.
4-69.
A
vernier balance
adjustment
A5R11
is
used
to
es-
tablish a
zero input voltage reference
level.
This
eliminates
horizontal dc
shift as
the
EXT VERNIER
control
Is
rotated.
The
EXT VERNIER
provides a range of control
of the deflection factor
when
an
EXT
INPUT
signal
is
used for horizontal deflection.
It
has
sufficient
range to
change
the deflection factor by
at least
1
0.
4-70.
The
input
signal
to
A5Q3
is
summed
in
the
low
impedance
emitter
circuit
with
a
current established
by
the
HORIZONTAL
POSITION
controls.
A
fine
and
coarse
positioning
is
provided.
Both
controls
operate from
a
single
control,
and
are
mechanically
interconnected.
Rotating the control
first
provides fine positioning.
When
the
limit
of
available rotation of the fine
position poten-
tiometer
has
been
reached, the coarse
positioning
potentiometer becomes
effective.
4-71.
The
output of
A5Q3
is
coupled through
emitter-
follower
ASQ4
to
differential amplifier
A5Q5
and A5Q7.
The
low impedance
necessary to drive
A5Q5
is
provided
by
A5Q4,
and
A5Q6
maintains
a similar
low impedance
voltage source for
A5Q7.
4-72.
The
position of the
MAGNIFIER
switch
A5S4
selects either
of
two
values of emitter degeneration
between
A5Q5
and
A5Q7
and
controls the
gain.
As
degeneration
decreases, gain
increases.
Two
gain
levels are
provided,
XI
and X10. Each
has an adjustable element
to
provide for calibration of the
gain.
With
XI
magnification
selected,
A5R46
is
used
to
set
the gain.
With
X10
magnification selected
A5R44
sets
the
gain.
The
emitter
potentials of
A5Q5
and
A5Q7
are balanced
by A5R49.
This prevents horizontal dc
shift as
the
MAGNIFIER
control
is
switched
between
ranges.
4-73. Thedifferential
signal at
the collectors of
A5Q5
and
A5Q7
is
applied to current-fed operational
amplifiers
A5Q11/A5Q12/A5Q13
and
A5Q8/A5Q9/A5Q10.
The
amplifier
low frequency
gain
is
very
stable
because of
the large
negative
feedback employed, and
the high
frequency feedback
for each
side
of the amplifier
is
separ-
ately adjustable. High frequency feedback from
the
col-
lectors
of
A5Q12/A5Q13
to
the base of
A5Q11
is
controlled by
A5C28;
high
frequency feedback
from
the
collectors of
A5Q9/A5Q10
to the base of
A5Q8
is
con-
trolled
by A5C21,
Capacitor
A5C24
adjusts the
ratio
of
feedback
for each
side
of the
amplifier.
The
output of the
amplifiers
is
a voltage
which
is
connected to the horizontal
deflection plates of the CRT.
46