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12
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Model No.: 14LAANZACDC
Version: 1.0
All the color trap in the luminance channel, band pass filtering circuit in the chroma
channel and filter adjuster are controlled by the broadcast system identifying circuit
and I
2
C bus to ensure correct and complete Y /C separation when different-system
signals received. Meanwhile, when Y /C separation signals are input to LA76818A’s
Pin44 and Pin42, the inner I
2
C bus makes the color trap in the luminance channel
and band pass filtering circuit in the chroma channel enter the bypass mode, thus
preventing attenuation to signal to the greatest extent and ensuring sharper and
more vivid pictures.
b) Luminance signal processor
The luminance signal processor includes a luminance delay line, definition control
circuit, coring circuit and contrast /luminance control circuit.
As the bandwidth of channel processing the luminance signal is wider than one
processing the chroma signal, the transmission speed of the luminance signal is
faster than of the chroma signal. It without delay processing, the time when the
luminance signal reaches the CRT is not consistent with that when chroma signal
reaches the CRT, resulting in display luminance and color not coinciding. A
luminance delay line integrated in LA76818A can adjust delay time of the delay
line by the I
2
C bus so that the luminance and chroma signals reach the CRT
synchronously. After delay processed, the luminance signal is sent into the
definition control circuit, coring circuit, black level stretcher and contrast/
luminance control circuit for processing, and then sent into the luminance amplifier
for amplifying and outputting a Y signal to the primary color matrix circuit.
LA76818A is equipped with an aperture compensating circuit to improve definition
of pictures, coring circuit to reduce high frequency noise and black level stretcher to
improve picture quality greatly.
c) Chroma
signal
processor
The chroma signal processor includes an ACC amplifier, killer identification control
circuit, sub-carrier restorer, base band delay circuit, PAL /NTSC demodulator and
color difference matrix /primary color matrix circuit.
The video signals selected out by the video switch are filtered out chroma signals
with luminance element removed by the band pass filter, which are sent to the
chroma signal selector. After selected, the chroma signals are amplified and
chroma-controlled by the ACC circuit, and then output in two ways. One set is sent
chroma demodulator and another set to sub-carrier restorer.
