DDP3310B Datasheet, PDF (15/60 Pages) Micronas – Display and Deflection Processor

ADVANCE INFORMATION
2.2.5. Average Beam Current Limiter
The average beam current limiter (BCL) works on both
the digital YUV input and the inserted analog RGB sig-
nals by using either the sense input or the RSW1 input
for the beam current measurement. The BCL uses a
different filter to average the beam current during the
active picture resulting in a 12-bit resolution. The filter
bandwidth is approximately 4 kHz.
The beam current limiter allows the setting of a thre-
shold current, a gain and an additional time constant. If
the beam current is above the threshold, the excess
current is low-pass filtered with the according gain and
time constant. The result is used to attenuate the RGB
outputs by adjusting the white-drive 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. If the minimum
contrast is reached, the brightness will be decreased
down to a programmable minimum as well. Typical
characteristics of the BCL for different loop gains are
shown in Fig. 2–12; for this example the tube has been
assumed to have square-law characteristics.
gain = 0 %
Threshold
gain = 10 %
gain = 60 %
gain = 90 %
Drive
Fig. 2–12: Beam current limiter characteristics:
beam current output vs. drive
DDP 3310B
Micronas
15