ADVANCE INFORMATION
VDP 313xY
2.11.3.Average Beam Current Limiter
2.11.4.Analog RGB Insertion
The average beam current limiter (BCL) uses the
sense input for the beam current measurement. The
BCL uses a different filter to average the beam current
during the active picture. The filter bandwidth is
approx. 2 kHz. The beam current limiter has an auto-
matic offset adjustment that is active two lines before
the first cutoff measurement line.
The VDP 313xY allows insertion of 2 external analog
RGB signals. Each RGB signal is key-clamped and
inserted into the main RGB by the fast blank switch.
The selected external RGB input is virtually handled as
a priority bus signal. Thus, it can be overlaid or under-
laid to the digital picture. The external RGB signals can
be adjusted independently as regards DC-level (bright-
ness) and magnitude (contrast).
The beam current limiter function is located in the
front-end. The data exchange between the front-end
and the back-end is done via a single-wire serial inter-
face.
Which analog RGB input is selected depends on the
fast blank input signals and the programming of a num-
ber of I2C-bus register settings (see Table 2–2 and Fig.
2–21). Both fast blank inputs must be either active-low
or active-high.
The beam current limiter allows the setting of a thresh-
old current. If the beam current is above the threshold,
the excess current is lowpass filtered and used to
attenuate the RGB outputs by adjusting the whitedrive
multipliers for the internal (digital) RGB signals, and
the analog contrast multipliers for the analog RGB
inputs, respectively. The lower limit of the attenuator is
programmable, thus a minimum contrast can always
be set. During the tube measurement, the ABL attenu-
ation is switched off. After the whitedrive measurement
line it takes 3 lines to switch back to BCL limited drives
and brightness.
All signals for analog RGB insertion (RIN1/2, GIN1/2,
BIN1/2, FBLIN1/2, HCS) must be synchronized to the
horizontal flyback, otherwise a horizontal jitter will be
visible. The VDP 313xY has no means for timing cor-
rection of the analog RGB input signals.
Table 2–2: RGB Input Selection
FBFOH1=0, FBFOH2=0, FBFOL1=0, FBFOL2=0
Typical characteristics of the ABL for different loop
gains are shown in Fig. 2–20; for this example the tube
has been assumed to have square law characteristics.
FBLIN1 FBLIN2 FBPOL FBPRIO
RGB output
Video
0
0
1
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1
0
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1
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1
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1
1
0
0
1
0
1
0
0
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0
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1
1
1
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1
x
x
x
0
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x
RGB input 2
RGB input 1
RGB input 1
RGB input 2
RGB input 1
RGB input 2
RGB input 1
RGB input 2
Video
Fig. 2–20: Beam current limiter characteristics:
beam current output vs. drive
BCL threshold: 1
Micronas
23
MICRONAS [ MICRONAS ]
