DDP 3310B
ADVANCE INFORMATION
2.1.10. Picture Frame Generator
2.1.11. Scan Velocity Modulation
When the picture does not fill the total screen (height
or width too small) it is surrounded with black areas.
These areas (and more) can be colored with the pic-
ture frame generator. Another possibility is the inser-
tion of a vertical and a horizontal stripe into the picture.
This is done by switching over the RGB signal from the
matrix to the signal from the frame color register.
Picture tubes equipped with an appropriate yoke can
use the Scan Velocity Modulation signal to vary the
speed of the electron gun during the entire video scan
line depending on its content. Transitions from dark to
bright will first speed up and then slow down the scan;
vice-versa for the opposite transition (see Fig. 2–6).
The digital RGB input signal for the SVM is converted
to Y in a simple matrix. Then the Y signal is differenti-
ated by a filter of the transfer function 1−Z−N, where N
is programmable from 1 to 6. With a coring some noise
can be suppressed. This is followed by a gain adjust-
ment and an adjustable limiter. The analog output sig-
nal is generated by an 8-bit D/A converter. The signal
delay can be adjusted by ±3.5 clocks in half-clock
steps in respect to the analog RGB output signals.
This is useful to adjust the different group delays of
analog RGB amplifiers to the one for the SVM yoke
current.
The width of each area (left, right, upper, lower) can be
adjusted separately. The generator starts on the right,
respectively lower side of the screen and stops on the
left, respectively upper side of the screen. This means,
it runs during horizontal, respectively vertical fly-
back.The color of the complete border can be stored in
a programmable frame color register. The format is
3×4 bit RGB. The contrast can be adjusted separately.
If the start value for the generator is larger than the
stop value, the picture frame is inserted at the borders.
If the start value is smaller than the stop value a verti-
cal or horizontal stripe is inserted.
Ampl.
Beam
Current
SVM Yoke
Current
t
Fig. 2–6: SVM signal wave form
10
Micronas
MICRONAS [ MICRONAS ]
