Block Diagram; Video Input; Luminance Processing - Tektronix 1725 Instruction Manual

Theory of Operation

BLOCK DIAGRAM

Video Input

Luminance Processing

4–2
The regenerated subcarrier, used for demodulation, is applied directly to the B–Y
(U) Demodulator and delayed by 90° (quadrature phased) for the R–Y (V)
Demodulator.
The B–Y (U) Demodulator drives the Horizontal Output Amplifier; the R–Y (V)
Demodulator drives the Vertical Output Amplifier.
The rear-panel X Y INPUT connector provides an input for audio signals, which
can be displayed as XY signals for stereo comparisons. Identical amplifiers
provide high input impedance and drive the Vertical and Horizontal Output
Amplifiers.
If there is no signal, the Center Dot Blanking circuit blanks the crt to prevent it
from being damaged by the non-deflected center dot.
This description uses the 1725 Block Diagram, which is located at the beginning
of the Diagram section (Section 9). The diagram can be folded out and viewed
while reading this description.
Video signals are applied through identical input amplifiers to normalize gain
and provide impedance matching. An external reference can be used for both
luminance- and chrominance-related functions. If composite video or black burst
is used for the External Reference, no additional processing is required. When
CW Subcarrier is used, the luminance reference is taken from the video input and
the chrominance reference is attenuated from the subcarrier input, through the
External Reference.
The sync signals used by the vectorscope are contained in the luminance
information from the video inputs. The composite video signal through the
Luminance Amplifier drives a sync separator, whose output is used to drive a
Bowes Oscillator that regenerates H Sync. The H Sync also generates Sample
Pulses and the Clamp signals, that activate the Burst Switches, and provide the
line rate control signal for the V Axis Switcher.
1725 PAL/NTSC Vectorscope