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
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.
