Tektronix 070-8462-03, Instruction Manual

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Theory of Operation
1735 HD High Definition Waveform Monitor
4–3
is approximately 24 V for a full-scale display, and is dependent on the CRT
vertical deflection sensitivity. When alphanumeric readout is active, a vertical
readout signal drives the vertical deflection amplifier, while the signal from the
vertical limiter is disabled.
The sweep generator consists of a current source, capacitor, and discharge
switch. It is controlled by the microcontroller, producing a linear sweep signal
which is synchronized to the selected sync source.
The horizontal level shift adds an offset to the sweep generator output to provide
horizontal position control. The front-panel horizontal position control is a
backlash potentiometer, which has two ranges of adjustment. When the limits of
the fine adjustment are reached, a coarse adjustment is activated to change the
positioning window of the fine adjustment.
The horizontal limiter is an inverting operational amplifier that outputs a
negative-going ramp. Horizontal magnification is accomplished here by
changing the gain in the feedback loop to provide magnification up to X25. The
horizontal limiter clips the portions of the positioned horizontal sweep signal that
would be off screen, reducing the dynamic range (and power dissipation)
required in the horizontal deflection amplifier. The horizontal limiter also outputs
a signal that turns off the CRT beam during the clipped portions of the sweep.
The paraphase horizontal deflection amplifier has a gain of approximately seven.
It is capacitively loaded by the CRT deflection plates and employs shunt
capacitors to speed charging for high slew rate signals. Full-scale deflection
requires approximately 50 V, depending on the CRT deflection sensitivity. When
alphanumeric readout is active, a horizontal readout signal drives the horizontal
deflection amplifier, while the signal from the horizontal limiter is disabled.
The microcontroller consists of two microprocessors serially connected in a
master-slave relationship. Operating software is contained in EPROM (Erasable/
Programmable Read-Only Memory). The master processor handles all traffic to
and from the front panel, readout enable, and character generation, through
DACs (digital-to-analog converters).
The master processor continuously polls the front-panel switch data for changes.
The front-panel indicators and the NOVRAM (non-volatile random access
memory) are updated to relay current conditions and enable the instrument to
power up again in the same configuration. The slave processor controls line rate
switching of the inputs, sweep generator, line select, and all other remaining
control functions.
Sync is derived from the CH 1A, CH 1B, or EXT SYNC inputs (front-panel
selectable). The sync stripper output follows the negative sync tip, with no
special provision for tri-level sync. The timing relationships for frame and line
sweeps and back porch clamp are determined by table look up from the
LINES/FRAME selection in the menu. In addition, accommodation is made for
remote sync input and enable through the rear-panel REMOTE connector.
Horizontal Deflection
Microcontroller