Panasonic EURO 4 Chassis, Technical Manual

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3DQDVRQLF
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17.7. Display Processor
The Display processor is used to carry out the
conversion from digital (YC
r
C
b
) to digital (RGB).
In the luminance processing path, the luminance
signal passes via a number of control stages such as
the contrast control stage, dynamic peaking circuit
used to enhance the luminance signal, and the black
level expander which is used to enhance the
contrast of the picture by modifying the luma signal.
This is achieved by decreasing the dark portions of
the picture towards black level, however this only
takes place if the dark portion of the signal does not
exceed a fixed level.
The luminance signal is then fed via a brightness
adjustment and soft limiter circuit. The soft limiter
circuit being used to prevent the CRT from being
driven to hard due to high contrast and brightness
levels, which would in turn cause the beam current
to increase causing the CRT to overheat and
produce colouration.
Once the signal has been output from the soft limiter
the luma signal is fed to the matrix circuit for
production of the RGB signals.
In the chrominance processing path the C
r
C
b
signals
are converted from 10.125MHz to 20.25MHz
sampling rate by the interpolator stage before
undergoing Colour Transient Improvement (CTI).
The colour transient improvement stage is used to
sharpen the chrominance rise time, which is
achieved by applying a correction signal that is
calculated by differentiating the colour difference
signals.
The amount of correction is limited
automatically. The C
r
C
b
signals are then input to the
matrix circuit where the luminance signal is added to
the C
r
C
b
signals to produce a digital RGB signal.
After the RGB signals are output from the matrix
circuit, the signals are input to 3 multipliers which are
used to digitally adjust the white drive. The digital