VCT3834A datasheet(13/172 Pages) MICRONAS

13 / 172 page

ADVANCE INFORMATION

VCT 38xxA

Micronas

2.4. Color Decoder

In this block, the standard luma/chroma separation and

multi-standard color demodulation is carried out. The

color demodulation uses an asynchronous clock, thus

allowing a unified architecture for all color standards.

A block diagram of the color decoder is shown in Fig.

2–3. The luma as well as the chroma processing, is

shown here. The color decoder provides also some

special modes, e.g. wide band chroma format which is

intended for S-VHS wide bandwidth chroma.

If the adaptive comb filter is used for luma chroma sep-

aration, the color decoder uses the S-VHS mode pro-

cessing. The output of the color decoder is YCrCb in a

4:2:2 format.

Fig. 2–3: Color decoder

2.4.1. IF-Compensation

With off-air or mistuned reception, any attenuation at

higher frequencies or asymmetry around the color

subcarrier is compensated. Four different settings of

the IF-compensation are possible:

– flat (no compensation)

– 6 dB/octave

– 12 dB/octave

– 10 dB/MHz

The last setting gives a very large boost to high fre-

quencies. It is provided for SECAM signals that are

decoded using a SAW filter specified originally for the

PAL standard.

Fig. 2–4: Frequency response of chroma IF-com-

pensation

ColorPLL/ColorACC

1 H Delay

CrossSwitch

Notch

Filter

Luma / CVBS

Luma

Chroma

Mixer

Low-pass Filter

Phase/Freq

Demodulator

ACC

Chroma

IF Compensation

DC-Reject

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