Theory of Operation
1710J-Series Waveform Monitors
5–3
The composite sync output of the sync stripper times a programmed logic array
(PLA) that controls the horizontal and vertical sync generators. The sync
generator H and V trigger outputs synchronize the sweep generator. If calibrator
is selected, the cal drive signal from the microprocessor provides the sweep
generator triggering signal.
The ramp signal, output by the sweep generator, drives the mag amplifier, which
provides three gain ranges: X1 (un-magnified sweep), X10 (1
m
s/div. in two line
sweep), and X25 (to display the full vertical interval in two field sweep, while
providing 0.2
m
s/div. sweep rate in 1 line sweep). The horizontal positioning
offset voltage is input to the mag amplifier to ensure sufficient range to position
any part of the display onto the graticule.
When the RGB Parade display is enabled, the sweep is shortened. The RGB
staircase produces three short ramps per sweep that are displayed in sequence.
The output of the mag amplifier drives the horizontal output amplifier, which
matches impedances and normalizes gain (approximately 100 V for a 10 cm
sweep length) to drive the CRT horizontal deflection plates.
The Z-Axis control uses the blanking signal (unblanking) and the intensity
voltage to unblank the CRT during sweep time. When the sweep is magnified its
off-screen portion is blanked to increase the on-off contrast ratio. The focus
amplifier, which is controlled by the front-panel FOCUS control, provides a
voltage to the CRT focus ring.
The CRT is of the Post Acceleration type, which requires a relatively high
potential difference between the cathode and post anode. The boost in second
anode voltage is provided by an encapsulated 4X multiplier. Trace rotation
provides compensation for the magnetic field surrounding the CRT.
Vertical Input, Diagram 1
The video signal is input to the waveform monitor through amplifiers that can be
clamped at back porch time. Once buffered by the input amplifiers, whose gain is
–1, a channel switch selects the input to be filtered, drive the picture monitor
output, serve as the internal sync source, and eventually be displayed on the
CRT.
When an external reference (sync) source is used, the composite signal is input
through an ac-coupled amplifier, which also has a gain of –1. Selection of the
sync source is accomplished by a switch that is made up of a common base pair
and switching diodes. A clamped sync stripper is used to remove active video
information and regenerate a composite sync signal for use by time related
monitor circuits.
CRT, Unblanking, and
High Voltage
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