Tektronix WFM 601i, User Manual

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Measurement Theory
WFM 601i Serial Component Monitor
3–21
composite signal. In a component format, utilizing R–Y and B–Y the errors are
most likely to be in amplitude and timing. The most obvious short coming of
using the color vector display is that there is no convenient method of relating
the color difference signals to the luminance signal, which is the third element of
the component signal necessary for determining color saturation.
Lightning Display
In order to overcome the shortcomings of not being able to plot the color
difference signals against the luminance signal, the lightning display was created.
The three signals are back porch clamped and identically low pass filtered to
provide a common point and identical delay through the system. Next the color
difference signals are line alternated and the luminance signal inverted on
alternate lines.
The B–Y (P
B
) signal is applied concurrently with the positive luminance signal
(Y); the R–Y (P
R
) signal is then applied with the inverted luminance signal. This
provides a display that compares B–Y to Y on the top half of the display and
R–Y to –Y on the lower half of the display. See Figure 3-11.
Y
Y
CY
CY
G
G
M
M
R
R
B
B
CLAMP
POINT
0V
P
R
(R-Y)
P
B
(B-Y)
+ LUMINANCE (Y)
–LUMINANCE (–Y)
BLACK
WHITE
WHITE
Figure 3-11: Construction of the Lightning waveform.
Valuable gain and timing information is recoverable when a graticule is added to
this display. By using an electronic graticule the effects of CRT nonlinearity are
eliminated. The information that we can obtain from this display is color
difference signal accuracy (horizontal displacement of either half of the display),
luminance gain (vertical displacement between the black and white levels),
timing delay between either color difference signal and luminance (bending of