3DQDVRQLF
33
Chapter
3
EURO 4H Supplement
2.8.
RGB Switching Stage
The digital RGB signal fed from the Tube Control
stage, is input to the RGB Switching Stage. Here the
digital RGB signal is converted to analogue RGB,
before being output from the DDP IC1504.
The digital RGB signal is converted to analogue using
3 digital to analogue converters (DAC), with 10 bit
resolution, here an analogue brightness value is
added to the RGB signal. The brightness value having
an adjustment range of 40% of the full RGB range.
The backend also allows the insertion of external
analogue RGB signals, which in this case is fed from
the
microprocessor,
providing
text
and
OSD
information.
The text/OSD information is input to the DDP IC1504
via pins 31 (R), 32 (G) and 33 (B) with the fast blanking
pulse input via pin 30.
The RGB signal is initially fed to a clamping circuit,
where the signal is independently adjusted for
brightness and contrast. The RGB signal is then
inserted into the main RGB signal path under the
control of the fast blanking pulse. The control of white
drive, brightness and contrast adjustments being
carried out on the RGB signals, using the internal Fast
processor (FP).
In the final stages, before the selected analogue RGB
signal is output, cutoff and blanking values are added.
Cut off is provided by three 9-bit D/A converters, with
a cut off adjustment range of 60% of the full scale RGB
range.
The RGB signals are then finally output via pins 24
(R), 25 (G), 26 (B), where all three signals are fed via
a transistor array which amplifies and buffers the RGB
signals. This operation for the Blue signal being
performed by transistors Q1507, Q1506 and Q1505,
for the Red Q1510, Q1509 and Q1508, while for the
Green Q1513, Q1512 and Q1511 are used. The RGB
signal is then fed to the E-Board via connector F1 pins
6 (G), 7 (B) and 8 (R) where they are then fed directly
to the CRT drive stage located on the Y-Board.
Summary of Contents for EURO 4 Chassis
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