VCT3834A datasheet(23/172 Pages) MICRONAS

23 / 172 page

ADVANCE INFORMATION

VCT 38xxA

Micronas

2.10.12.Priority Decoder

The priority decoder selects the picture source

depending on the programmed priorities. Up to eight

levels can be selected for OSD and the picture frame –

where 0 is the highest. The video source always has

the lowest priority. A 5-bit information is attached to

each priority (see Table 2–4 on page 34). These bits

are programmable via the I2C bus and have the follow-

ing meanings:

– one of two contrast, brightness and matrix values for

main and side picture

– RGB from video signal or color look-up table

– disable/enable black-level expander

– disable/enable peaking transient suppression when

signal is switched

– disable/enable analog Fast-Blank input

2.10.13.Scan Velocity Modulation

The RGB input signal of the SVM is converted to Y in a

simple matrix. Then the Y signal is differentiated by a

filter of the transfer function 1-Z-N, where N is program-

mable from 1 to 6. With a coring, some noise can be

suppressed. This is followed by a gain adjustment and

an adjustable limiter. The analog output signal is gen-

erated by an 8-bit D/A converter.

The signal delay can be adjusted by

±3.5 clocks in

half-clock steps. For the gain and filter adjustment

there are two parameter sets. The switching between

these two sets is done with the same RGB switch sig-

nal that is used for switching between video-RGB and

OSD-RGB for the RGB outputs (see Fig. 2–17).

Fig. 2–17: SVM Block diagram

2.10.14.Display Phase Shifter

A phase shifter is used to partially compensate the

phase differences between the video source and the

flyback signal. By using the described clock system,

this phase shifter works with an accuracy of approxi-

mately 1 ns. It has a range of 1 clock period which is

equivalent to

±24.7 ns at 20.25 MHz. The large

amount of phase shift (full clock periods) is realized in

the front-end circuit.

Coring

Gain1

Gain2

Limiter

Limit

Delay

RGB Switch

RGB

Matrix and

Shaping

Modulation

Notch

Differen-

tiator

1-Z-Nx

Coring

adjustment

Gain

adjustment

Delay

adjustment

D/A

Converter

Output

VCT3834A Datasheet(PDF) 23 Page - Micronas

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