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4. VI DEO SIG NAL PROCESSING
4-1 . INPUT/OUTPUT SWITCHING
Signals are input to the video signal processing circuit by
the following three routes.
(1 ) Camera block
: Camera luminance signal
Camera chroma signal
(2) S terminal
: Separated luminance signal(S Y)
Separated chroma signal
(3) External terminals : Composite video signal
Of these, the S terminal and the external terminals are used
for both input and output (PAL is output only).
Furthermore, when a cable is connected to the S terminal,
the system gives priority for both input and output to the S
terminal.
(CAM C and S C: IC1 52)
First, during input, the CAM Y (date character insertion) or
S Y which is selected by means of the CAM/LI NE control
signal from analogue switch IC151 (IC1 52 for the chroma
signal) is input to Pin @ of IC1 01 .
In contrast, the VIDEO signals are input to Pin @ of IC1 01 .
At this time, either Q 1 501 , Q 1 502 or Q1 503 is turned ON,
so that R1 501 and R1 502
+
output resistances.
(S C: R1 520
R1 521 )
In addition, Q 1 502 and Q1 503 are O FF when the S terminal
is connected with a cable, so that the signal at the S
terminal side can be given priority.
+
During output, Q1 501 is turned OFF and then R1 501 and
R1 502
R1 503 operate as the input resistances.
4-2. H i8/NORMAL RECORDING AND PLAYBACK
Various switching operations are carried out for recording
and playback in both H i8 and normal modes.
(1 ) Time constant for main emphasis and de-emphasis
(2) Deviation/sync chip frequency
(3) W/D clip level
(4) RF EQ characteristics
(5) Luminance signal band
Each of these is controlled by the H i8 OUT signal which is
output from the microprocessor.
However, as part of the video signal processing, discrim
ination is carried out during playback by the Hi8 DET which
is built into IC1 81 , and the results of this are sent to the
microprocessor.
(CAM Y)
(CAM C)
(S C)
(VIDEO)
+
R1 503 each operate as the
4-3. Hi8 DISCRIMINATION
During playback, it is necessary to determine whether the
signals being recorded are in Hi8 or normal mode. This is
called "Hi8 Discrimination," and is performed by IC1 81 by
the following method.
First, the playback FM luminance signal which has been
controlled to a uniform level by the RF AGC of IC1 01 is
input to Pin @ of IC1 81 . Then , after it passes through the
limiter inside the IC, it is amplified by 4.2 MHz and 9.8 M Hz
tank circuits. Both levels are then compared, and if the 9.8
MHz component is larger, it is determined that the mode is
Hi8 mode, whereas if the 4.2 MHz component is larger,
then the mode is normal mode. If the result of this
determination is Hi8 mode, then Pin @ becomes High.
4-4. LUMINANCE SIGNAL RECORDING SYSTEM
The CAM Y (S Y) signal is input to Pin @ and the VIDEO
signal is input to Pin @ of IC1 01 respectively. Both signals
are switched by the serial signal which has been input to
Pin @) of IC1 01 and then corrected to a uniform level by the
AGC, after which one is sent to the LINE OUT and the other
is sent to the recording system.
EE
4-4-1 .
System
The signals which have passed through the AGC first have
the on-screen display characters added, after which they
are output from Pin @ . One is sent to the Y/C mix circuit
before being sent to the VF block, while the other is output
via Pin @ to LI N E OUT.
At this time, because the termi nal is used for both input and
output, the problem that occurs with the EE system is with
the CAM Y signal only. Because the CAM Y signal is
compatible with Hi8, it has a broad range, and so if it is
mixed as it is with the CAM C signal inside the IC, dot
interference will occur when the signal is input to the
counter this, the 4.43 M Hz component is suppressed by the
TRAP.
4-4-2. Recording System
The other signal which passes through the AGC is input to
the Y/C separation circuit. However, the CAM Y and S Y
signals do not pass through the Y/C separation circuit, but
are instead output directly to Pin (j) . The cut-off frequency
of the LPF and the ON/OFF condition of the TRAP are
switched by the luminance signal which is output from Pin (])
in accordance with whether the signal is Hi8 or normal
mode, after which the l uminance signal is input to Pin ® .
The signal which is input to Pin @ passes through the
sub-emphasis and main emphasis circuits, after which it is
clipped to a uniform level by the W/D clip. It is then input to
the modulator. Here, the deviation/sync-tip frequency is
switched in accordance with whether the mode is Hi8 or
normal mode, and then the FM luminance signal is output
from Pin @ to the RF signal p rocessing IC (IC1 81 ).
At IC1 81 , the sound distortion which occurs when the lower
sideband of the luminance signal intrudes into the AFM
band and the cross colour which occurs when it intrudes
into the chroma band is prevented by means of the OTL
recording system. The FM luminance signal which has
passed through the OTL circuit is then output from Pin @ of
IC1 81 to Pin CD of the recording system amplifier IC (IC1 91 ).
- 4-25 -
TV.
To
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