VDP3108 Просмотр технического описания (PDF) - Micronas

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VDP3108

Single-Chip Video Processor

Micronas 

ADVANCE INFORMATION

VDP 3108

cutoff R

cutoff G

cutoff B

white drive R or G or B (sequentially).

b) The picture measurement returns

active picture maximum current

active picture minimum current.

The tube measurement is automatically started when

the cutoff blue result register is read. Cutoff control for

RGB requires one field only while a complete white-drive

control requires three fields. If the measurement mode

is set to ’offset check’ a measurement cycle is run with

the cutoff / whitedrive signals set to zero. This allows to

compensate the MADC offset as well as input the leak-

age currents. During cutoff and whitedrive measure-

ments, the average beam current limiter function (ref.

2.5.2.) is switched of and a programmable value is used

for the brightness setting. The start line of the tube mea-

surement can be programmed via I2C bus, the first line

used for the measurement, i.e. measurement of cutoff

red, is 2 lines after the programmed start line.

The picture measurement must be enabled by the con-

trol microprocessor after reading the min./max. result

registers. The measurement is always started at the be-

ginning of active video.

The vertical timing for the picture measurement is pro-

grammable, and may even be a single line. Also the sig-

nal bandwidth is switchable for the picture measure-

ment.

Two horizontal windows are available for the picture

measurement. The large window is active for the entire

active line. Tube measurement is always carried out with

the small window. Measurement windows for picture

and tube measurement are shown in figure 2–23.

tube measurement

picture meas. start

active video

field 1/ 2

ÍÍÍÍ

small window for active picture

ÍÍÍÍÍÍÍÍÍ window for cutoff, white drive

large window for active picture

picture meas. end

Fig. 2–23: Windows for tube and picture measure-

ment

MICRONAS INTERMETALL

2.5.2. Average Beam Current Limiter

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 approximately 2

kHz. The beam current limiter has an automatic offset

adjust that is active two lines before the first cutoff mea-

surement line.

The beam current limiter allows to set a threshold cur-

rent. If the beam current is above the threshold, the ex-

cess current is low pass filtered and used to attenuate

the RGB outputs by adjusting the white drive multipliers

for the internal (digital) RGB signals and the analog con-

trast 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 attenuation is switched off. After

the whitedrive measurement line it takes 3 lines to switch

back to BCL limited drives and brightness.

Typical characteristics of the ABL for different loop gains

are shown in Fig. 2–24; for this example the tube has

been assumed to have a square law characteristic.

drive

Fig. 2–24: Beam current limiter characteristics:

beam current output vs. drive

BCL threshold: 1

2.6. Synchronization and Deflection

The synchronization and deflection processing is distrib-

uted over front end and back end. The video clamping,

horizontal and vertical sync separation and all video re-

lated timing information are processed in the front end.

Most of the processing that runs at the horizontal fre-

quency is programmed on the internal Fast Processor

(FP). Also the values for vertical & East-West deflection

are calculated by the FP software.

The display related synchronization, i.e. generation of

horizontal and vertical drive and synchronization of hori-

zontal and vertical drive to the video timing extracted in

the front end, are implemented in hardware.

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