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4-5.
CHROMA SIGNAL PLAYBACK SYSTEM
PB chroma
PB chroma
(4.43MHz) ~~
(732kHz)
4
PB chroma
(4.43 MHz)
=
ofa
4-43MHz
BPF
4-5-1,
Playback Chroma BPF
The Y-FM, AFM and ATF signals are removed from the
playback RF signal, thus extracting the playback. chroma
signal.
BUFFER
PB
PILOT
PB
FM
AUDIO
PB CHROMA
C signal
(after the crosstaik
is canceled)
{COMB block
formed by
CXAIZ07AR
'ond
CXL1506M
—
Fig. 4-45.
Chroma signal playback system block diagram
1121
CXA1208R
Fig. 4-46.
Playback chroma BPF
4-23
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"4-5-2.
ACC Circuit
: - The ACC
circuit has the following two functions during
playback:
4. Elimination of level fluctuations of the playback chroma
signal.
2.
Elimination of playback chroma
signal level differences
between channels caused by video head sensitivity
differences.
Playback chroma signal
(4-43 MHz)
4.43MHz
BPF
Playback chroma signal
(732kHz)
Chroma crosstalk canceler
including CXA1207AR, CXL1506M
Playback chroma signal
(4.43MHz)
Ic124
CXA1208R
Fig. 4-47.
ACC circult
After playback chroma
processing, the playback chroma
signal (4.43 MHz) is input to the ACC control circuit. This is
to prevent faulty operation of the ACC due to crosstalk and
noise components.
The ACC
control circuit controls the
ACC amplifier by detecting the burst signal section of the
input playback chroma signal (4.43 MHz) in order to keep
the burst_signal level of the playback chroma signal (4.43
MHz) constant.
'In
addition,
compensation
for
video
head
sensitivity
differences js performed by switching over the smoothing
capacitor by means of the RF SW.
Note: The ACC
smoothing
capacitor is built into 1C121
(CXA1208R).
;
[High-speed ACC circuit]
Chroma
signal levels
make
large fluctuations
in short
intervals during variable speed playback
(during picture
search, for example, there are three or four large jevel
fluctuations per field).
Consequently,
level changes cannot be followed with an
ACC loop gain equal to that of the ordinary playback mode.
This is solved by using the JOG H signal input to Pin @ of
IC121
(CXA1208R)
during variable
speed
playback
to
switch among loop gain for the ACC circuit.
4-24
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