Vertical
System
3
-10
The 2mV range is achieved through an extra amplifier stage UlO0.
The
input
signal is amplified to the level required
by
the
pre-amplifier chip. The
2mV amplifier UlO0 is operated via relay K100
and
reduces the
bandwidth
to±10
MHz.
Vertical channel selection is accomplished with logic signal
CH1
EN
on
the
VENABLE
input
of
the pre-amplifier chip U101.
Differential ground referenced trigger output signals are available
on
U101.
The + output provides the signal for the digital storage circuit and
the
- output signal is applied to the trigger circuit.
Storage Pick-off Amplifier U102
The trigger output
of
the pre-amplifier is about 60 m V P-P
per
division. This
amplitude is insufficient to drive
the
aid converter located on the processor
board (A15). The
input
sensitivity
of
the aid converter is ± 200 mV/divi-
sion.
The
storage pick off circuit amplifies this signal to
the
required level.
In digital store mode a vertical range of 10.24 divisions is represented
by
voltage range of
+1
V
to-1
Vat
the input
of
the
aid converter. Positioning
of
the
vertical signal
in
store mode is accomplished via
the
storage
pick
off
amplifier U102.
The amplitude of
the
output signal of the storage pick off amplifier
is
limited to about +1.2 V and - 1.2 V to prevent overloading
of
the
aid
con-
verter.
DC
Balance
The
input
buffer Q100 and the 2m V amplifier exhibit a
de
offset voltage
which causes the trace to shift
when
the vertical amplifier is switched to a
different
VOL
TS/DIV setting.
The
offset
depends
on
the specific character-
istics
of
the components used.
The
offset
can
be compensated
with
an
internal calibration routine which automatically minimizes the trace shift.
The
compensation voltage ranges between +2.5 V and - 2.5
V.
Transistor Q103 provides level shifting and converts
the
C1
BAL
voltage to
a small offset voltage for QlO0A. QlO0A has been biased more negatively
than Q100B to be able to compensate positive
and
negative offsets.
Probe Coding
Resistor R111
provides+
5 Volts to
the
probe coding ring on the
BNC
input
connector. With a suitable probe connected to the
input
BNC connector the
+ 5 Volt will be divided by R 111
and
the internal probe coding resistor of
the probe.
The
resulting voltage depends on
the
attenuation factor of
the
probe. This voltage is measured
and
the deflection factor displayed
by
the
CRT
read out is corrected.
Theory
of
Operation
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