PRELIMINARY DATA SHEET
VDP 31xxB
2.9. Analog Back End
Cutoff and white drive current measurement are carried
outduringtheverticalblankinginterval. Theyalwaysuse
the small bandwidth setting. The current range for the
cutoff measurement is set by connecting a sense resis-
tor to the MADC input. For the whitedrive measurement,
the range is set by using another sense resistor and the
range select switch 2 output pin (RSW2). During the ac-
tive picture, the minimum and maximum beam current
is measured. The measurement range can be set by us-
ing the range select switch 1 pin (RSW1) as shown in
Fig. 2–21 and Fig. 2–22. The timing window of this mea-
surement is programmable. The intention is to automati-
cally detect letterbox transmission or to measure the ac-
tual beam current. All control loops are closed via the
external control microprocessor.
The digital RGB signals are converted to analog RGBs
using three video digital to analog converters (DAC) with
10-bit resolution. An analog brightness value is provided
by three additional DACs. The adjustment range is 40%
of the full RGB range.
Controlling the whitedrive/analog brightness and also
the external contrast and brightness adjustments is
done via the Fast Processor, located in the front-end.
2
Control of the cutoff DACs is via I C-bus registers.
Finally cutoff and blanking values are added to the RGB
signals. Cutoff (dark current) is provided by three 9-bit
DACs. The adjustment range is 60% of full scale RGB
range.
beam current
The analog RGB-outputs are current outputs with cur-
rent-sink characteristics. The maximum current drawn
by the output stage is obtained with peak white RGB. An
external half contrast signal can be used to reduce the
output current of the RGB outputs to 50%.
SENSE
A
D
MADC
R2
R3
RSW1
RSW2
2.9.1. CRT Measurement and Control
The display processor is equipped with an 8-bit PDM-
ADC for all measuring purposes. The ADC is connected
to the sense input pin, the input range is 0 to 1.5V. The
bandwidth of the PDM filter can be selected; it is
40/80 kHz for small/large bandwidth setting. The input
impedance is more than 1 MΩ.
R1
Fig. 2–21: MADC Range Switches
CR + IBRM + WDRV·WDR
white
drive
CR + IBRM
cutoff
R
R
R
G
black
ultra black
CG + IBRM
cutoff
G
CB + IBRM
cutoff
B
B
active
measurement
resistor
R1øR2øR3
R1øR3
R1øR2øR3
RSW1=on, RSW2=on
PICTURE MEAS.
R1
RSW2
=on
RSW1=on, RSW2=on
PICTURE MEAS.
TUBE MEASUREMENT
TML
PMSO
PMST
Lines
Fig. 2–22: MADC Measurement Timing
Micronas
21
MICRONAS [ MICRONAS ]
