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13.
16 Composite Video
Signal
Generator
Circuit
(see
Fig.
13-52)
The
two
color
subcarriers
(4.433618MHz)
generated
in
the
color
subcarrier
reproduction
circuit,
and which
are at
a
mutual phase
difference
of 90°
undergo balanced modulation
by
the
R-Y
and
B-Y
signals
in
the
composite
video
signal
generator
circuit,
and
the
carrier
color
signal
is
combined
with
the
Y
signal.
•
Carrier
color
signal
modulator/overlay
elimi-
nator/bias
stabilizer circuit
Since the
IC107
pin
4 and
6
inputs are
DC
coupled with the
R-Y
and
B-Y
signals,
the
DC
level
will
vary
due
to
variations in
the
VDP
and
buffers.
For
this
reason,
the
bias
voltage applied to
IC107
can
be
varied
by
VR106
(carrier
suppression
adjustment
control) to
ensure
that
IC107
(balanced
modulator)
is
properly balanced.
The
outputs
from
pins
1
and
9
are
mixed by
R269/R270
for
carrier
color
signal
modulated
by
IC107
to obtain the
X
part
of the
PAL
system composite video
signal in
equation
(1).
(See Photo.
13-19
and
Photo.
13-20.)
Equation
(1)
PAL
composite video
signal
=
Y
+_
(B—
Y)/2.03
cos
usd
±(R—
Y)/1.14
sin
usd
=
Yj"
+ 0.49(B-Y)
cos
usci
!
;
±0.88(R—
Y)
sin
usd
!
X
part
The
matrix
circuit
R-Y
and
B-Y
Q203/Q202
buffer
outputs appear
as
shown
in
Photo.
13-13
(computer
mode) and
Photo,
13-14
(synthesis
mode).
In synthesis
mode
the
picture synthesis
flag
BUFFERS
3.4
111
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