Table of Contents
Advertisement
13.
17 Video Switching
Circuit
(see
Fig.
13-53)
•
Buffer 2
and clamp
circuit
1
To
match
the pedestal
level
of the computer
picture
signal
processed
by
DC
coupling
(the
level
at
point
(I)
in Fig.
13-53)
with the
pedestal
level
of an
external
video
signal,
the
DC
level
(deter-
mined by
the
Q241/Q242
damp
circuit)
of
that
external
video
signal
is
adjusted
by
a
video
level
adjustment
control
(VR105)
after
the
signal
has
been
passed
through
the
Q240
buffer (the adjusted
level
being the
level
at
point
(2)
in
Fig.
13-53
(see
Photo.
13-21).
D103
and
D104
are
used
in
temperature
compen-
sation
of
the
Q241/Q242
junction
voltage.
•
Video
switching
circuit
This
circuit
switches the external video
signal
and computer
signal
outputs
in
response
to
the
OVLYF
signal
from
pin
7 of IC104.
When
OVLYF
is
H,
pins
5 and 13
of analog
switch
IC108
are
also
changed
to
H
to
select
the
external
video
signal.
And
when
OVLYF
is
L,
pin
12
of
IC108
is
changed
to
H
to
select
the
computer
signal,
the output
signal
being obtained
from
pin
11
of IC108.
•
Video
amplifier
The
video
amplifier
(Q282/Q281/Q280)
is
a
current input
type of
amplifier
which
amplifies
the
signal
switched
from
the video switching
circuit
to
obtain a
2Vp-p
output
at
the
VIDEO
OUT
terminal
via
R280
(see Fig.
13-53).
•
Video
switching control
signals
P:
PEDESTAL LEVEL
Photo. 13-21
External/internal
video
signal levels
(Pincture synthesis
mode)
(color bar
(external)
(16
color bar
(internal)
Fig.
13-53
V
id
eo
switch
i
ng
ci
rcu
i
t
IIS
Advertisement
Table of Contents
