3DQDVRQLF
24
Chapter
3
EURO 4H Supplement
2.2.2. Adaptive Comb Filter
The digital CVBS signal fed from the previous
front-end stage is fed to the 4H adaptive comb filter
stage which is
used to produce high-quality
luminance/chrominance separation for PAL or NTSC
signals. The comb filter improves the luminance
resolution by allowing the full 5MHz bandwidth to be
processed even during colour transmissions. Without
the use of a comb filter, the luminance resolution is
limited to about 3.8MHz.
Where an S-VHS signal or SECAM signal are input
then the comb filter is switched off. In this case the
signals are fed via the delay lines directly to the colour
decoder stage. This also applies where the comb filter
is switched off via software control.
2.2.3. Colour Decoder
In the colour decoder stage standard luminance and
chrominance separation and multi-standard colour
demodulation is carried out. The colour demodulator
uses an asynchronous clock, thus allowing unified
architecture for all colour standards.
The colour decoder also provides some special
modes such as wide band chrominance format which
is intended for S-VHS wide bandwidth chrominance.
If the adaptive comb filter of the VPC3215C IC1501
is used for luminance chrominance separation, the
colour decoder uses the S-VHS processing mode.
The output of the colour decoder is YC
r
C
b
in a 4:2:2
format.
2.3.
Scaler Stage
The luminance and chrominance signals output from
the colour decoder are fed to the following scaler and
Skew filter stages.
2.3.1. Skew Filter
The skew filter is used to ensure that the signal being
processed is at the same timing as the system clock.
As there is no way for the VPC IC1501 to know
whether the signal that it is processing is a standard
signal or a non-standard signal, e.g. VCR input, the
system clock is free running.
The skew filter which is controlled by an internal
Horizontal Phase Lock Loop1 (PLL1), produces a
phase shift which ensures that the system clock and
source signal are at the same timing.
The luminance and chrominance signals are then fed
to the Horizontal scaler.
Summary of Contents for EURO 4 Chassis
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