DDP3310B View Datasheet(PDF) - Micronas

Part Name

Description

Manufacturer

DDP3310B

Display and Deflection Processor

Micronas 

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

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