HP 182C - Horizontal Plug-In

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