VDP3108B datasheet(21/72 Pages) MICRONAS

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PRELIMINARY DATA SHEET

VDP 31xxB

Micronas

2.9. Analog Back End

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.

Control of the cutoff DACs is via I2C-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.

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%.

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 M

Ω.

Cutoff and white drive current measurement are carried

out during the vertical blanking interval. They always use

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.

SENSE

RSW1

RSW2

beam current

MADC

Fig. 2–21: MADC Range Switches

ultra black

black

cutoff

white

drive

CR + IBRM

CR + IBRM + WDRV·WDR

TML

CG + IBRM

CB + IBRM

PICTURE MEAS.

TUBE MEASUREMENT

active

measurement

resistor

øR2øR3

RSW1=on, RSW2=on

øR3

RSW2

cutoff

øR2øR3

Fig. 2–22: MADC Measurement Timing

RSW1=on, RSW2=on

PMST

PMSO

=on

Lines

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