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7-1
7. VIDEO CIRCUIT
7-1. Circuit Component
The video circuit performs selection of input signals,
video signal (NTSC, PAL, SECAM) demodulation to
RGB signals, RGB input signal amplification and audio
signal amplification.
Fig. 7-1-1 shows the block diagram.
7-1-1. Input Signal SW Section
<Video input section>
All the video and audio signals entered are sent to the
input SW IC (except for RGB signals). In the input SW
IC, the signals are switched corresponding to the
composite, Y/C and color modes (NTSC, PAL SECAM
and BLACK & WHITE) respectively. Processing routes
for the composite video signals are changed depending
on the color modes (NTSC, PAL, SECAM and BLACK &
WHITE). Y/C signals, SECAM and Black & White
signals are supplied to the video color process IC in the
next stage passing through the input SW IC. NTSC, PAL
and 4.43 NTSC color signals only are separated into the
luminance Y signal and color C signal by the digital
comb filter and then enter the input SW IC again as the
Y/C signals.
In the cases other than described above, when the power
is on or the input switching occurs, the signals are
supplied to the video/color process IC as a composite
video signal passing through the input SW IC.
<RGB input section>
The RGB signals entered are divided in two systems; the
internal signal process and external output systems.
The signals for the external output system enter 75 ohm
driver IC and then enter D-sub 15 pin for output. The
RGB signals for internal signal process system enter the
mute IC. When the video signal is selected, the RGB
signals are muted by the mute IC output.
7-1-2. Video Demodulation Section
In the video demodulation section, the composite video
signal and Y/C signals are demodulated into the RGB
signals.
In the video/color process IC, the color demodulation is
carried out corresponding to the color mode of the video
signal entered. The applicable color modes are NTSC,
4.43 NTSC, PAL and SECAM.
The mode identification is automatically carried out by
the video/color process IC.
When the power turns on and the input is switched, the
composite video signal passing through the input SW IC
enters and the color mode is determined. The micropro-
cessor detects the result of color mode determination and
sets a corresponding color mode. The color difference
signal demodulated by the video/color process IC is
developed after processed its phase and signal level via
1H delay IC.
The luminance signal enters the picture quality correc-
tion IC and the color difference signal enters the RGB
demodulation IC via the delay line for matching with
the luminance signal.
In the RGB demodulation IC, the gamma correction,
color adjustment, etc. are carried out as well as the
luminance color difference signal is demodulated to the
RGB signals.
7-1-3. RGB Signal Amplification Section
In the RGB signal amplification section, the RGB input
signals and the video signal demodulated to the RGB
signals are switched and the contrast and brightness
adjustments are carried out. Further, the gain adjustment
for each RGB signal is also carried out.
The sync signals of the RGB signals correspond to
HD,VD, composite sync (CS) and SYNC ON G signals.
7-1-4. Audio Signal Amplification Section
The audio signal inputs of the video and RGB inputs
correspond to L and R stereo input. After switching the
input, the signal develops at the audio terminal through
the output buffer circuit. After L and R signals are mixed,
the sound volume control IC controls its level, thus
controlled signal is amplified to the sufficient level to
drive the speaker by the audio output IC, and then sent
to the speaker.