ADVANCE INFORMATION
VDP 3108
color distortion and chroma noise is reduced. In the
NTSC combfilter mode, Fig. 2–7 d), the delay line is in
the composite signal path, thus allowing reduction of
cross-color components as well as cross-luminance.
The loss of vertical resolution in the luminance channel
is compensated by adding the vertical detail signal with
removed color information.
CVBS
MHz
8
0
–1
–2
–3
–4
–5
–6
–7
–8
–9
–10
–11
dB
Notch
filter
Chroma
Process.
Y
CrC b
Luma
8
Y
Chroma
Process.
0.01
0.1
1.0
chroma
8
CrC b
Fig. 2–6:
Frequency response of SECAM
deemphasis
a) conventional
CVBS
8
Notch–
filter
b) S-VHS
Y
2.2.5. Burst Detection
In the PAL/NTSC-system the burst is the reference for
the color signal. The phase and magnitude outputs of
the CORDIC are gated with the color key and used for
controlling the phase-lock-loop (APC) of the demodula-
tor and the automatic color control (ACC) in PAL/NTSC.
The ACC has a control range of +30 ... –6 dB.
For SECAM decoding, the frequency of the burst is mea-
sured. Thus, the current chroma carrier frequency can
be identified and is used to control the SECAM proces-
sing. The burst measurements also control the color kill-
er operation; they can be used for automatic standard
detection as well.
2.2.6. Color Killer Operation
The color killer uses the burst–phase, –frequency mea-
surement to identify a PAL/NTSC or SECAM color sig-
nal. For PAL/NTSC the color is switched off (killed) as
long as the color subcarrier PLL is not locked. For SE-
CAM the killer is controlled by the toggle of the burst fre-
quency. The burst amplitude measurement is used to
switch–off the color if the burst amplitude is below a pro-
grammable threshold. Thus color will be killed for very
noisy signals. The color amplitude killer has a program-
mable hysteresis.
2.2.7. Delay Line / Comb Filter
The color decoder uses one fully integrated delay line.
Only active video is stored.
The delay line application depends on the color stan-
dard:
NTSC:
combfilter
or
color compensation
PAL:
color compensation
SECAM:
crossover-switch
In the NTSC compensated mode, Fig. 2–7 c), the color
signal is averaged for two adjacent lines. Thus cross–
MICRONAS INTERMETALL
Chroma
Process.
1H
Delay
CrC b
c) compensated
CVBS
8
1H
Delay
Notch–
filter
Y
Chroma
Process.
CrC b
d) Comb Filter
Fig. 2–7:
NTSC color decoding options
CVBS
8
Notch–
filter
Y
Chroma
Process.
1H
Delay
CrC b
a) conventional
Luma
8
Y
Chroma
8
Chroma
Process.
1H
Delay
CrC b
b) S-VHS
Fig. 2–8:
PAL color decoding options
CVBS
8
Notch–
filter
Y
Chroma
Process.
1H
Delay
MUX
CrC b
Fig. 2–9:
SECAM color decoding
9
MICRONAS [ MICRONAS ]
