Toshiba TLP-711U Manuel de formation technique - Page 22
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5-2. RGB Signal Process Section
The RGB signal process section mainly performs the
following processes.
( 1 )
RGB input signal switching
( 2 )
Sync signal separation and polarity identification
( 3 )
Audio signal switching and volume control
( 4 )
Clamp process for A/D converter
Table 5-2-1 and 5-2-2 show the main functions of the IC.
5-2-1. RGB Input Signal Switching Process Section
One of the two system input signals of RGB1 and RGB2
selected in the menu is switched by QB001, QB002 and
QB003 (MAX4158ESA) and fed to three buffers of
QB004, QB007 and QB008.
QB004 (MAX497) is an output buffer (75 ohm drive),
QB007 is a low pass filter buffer and QB008 is an
interface buffer for digital PC board. The QB008 also
switches the signal passed through the low pass filter and
the output signals sent from QB001, QB002 and QB003
and feeds them as required.
5-2-2. Sync Signal Processing Section
The HD and VD signals in one of two system inputs
selected in the menu are switched at QB006 (74ACT244F)
and feed the next stage. QB010 (M52347FP) performs
the polarity identification and sync separation of the sync
s i g n a l .
Table 5-2-1 PB8432-1
QB001
R signal input switching
QB002
G signal input switching
QB003
B signal input switching
RGB amplifier for monitor output
QB004
(75 ohm drive)
Sync signal switching and buffer for
QB006
output
QB007
Buffer for low pass filter
QB008
RGB switching and buffer (75 ohm drive)
QB010
Sync separation IC
QB013
Audio signal selection SW
QB026
Electronic volume for audio
The HD and VD signals sync-separated are sent to the
digital PC board (PB8430) and the polarity information
of the sync signal is converted into I
(M62329FP) and then the data are sent to the digital PC
board (PB8430).
5-2-3. Audio Signal Switching and Volume Control
Three audio system lines of RGB1, RGB2 and video
signals are switched by QB013. The output from QB013
is divided in two signals and one develops as a signal for
output terminal and the other is sent to QB026 (elec-
tronic volume) after adding L and R for monaural signal.
5-2-4. Clamp Circuit
Either the RGB signals developed from QB008 or those
from the video process circuit are selected by QD701,
QD801 and QD901 (MAX4121). Each signal developed
from QD701, QD801 and QD901 is clamped to obtain
1.5V pedestal level by the clamp ICs of QD702, QD802,
QD902: (EL4093CS) respectively.
In this case, the output signal amplitude is set to obtain
twice as much as its input.
Table 5-2-2 PB8430
Q D 7 0 1
R signal selection SW
Q D 8 0 1
G signal selection SW
Q D 9 0 1
B signal selection SW
Q D 7 0 2
Clamp IC (R signal)
Q D 8 0 2
Clamp IC (G signal)
Q D 9 0 2
Clamp IC (B signal)
5-3
2
C data by QB011