ADVANCE INFORMATION
VCT 38xxA
2.4. Color Decoder
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.
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.
Notch
Filter
Luma / CVBS
Luma
Chroma
1 H Delay
CrossSwitch
ACC
IF Compensation
Low-pass Filter
Phase/Freq
Demodulator
Mixer
DC-Reject
Chroma
ColorPLL/ColorACC
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
Micronas
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MICRONAS [ MICRONAS ]
