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VPX322XE Datasheet(PDF) 11 Page - Micronas |
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VPX322XE Datasheet(HTML) 11 Page - Micronas |
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11 / 92 page  ADVANCE INFORMATION VPX 322xE 11 Micronas 2.3. Color Decoder In this block, the standard luma/chroma separation and multi-standard color demodulation is carried out. The color demodulation uses an asynchronous clock, thus allowing a unified architecture for all color standards. A block diagram of the color decoder is shown in Fig. 2–5. The luma, as well as the chroma processing, is shown here. The color decoder also provides several special modes; for example, wide band chroma format which is intended for S-VHS wide bandwidth chroma. The output of the color decoder is YCrCb in a 4:2:2 for- mat. 2.3.1. IF-Compensation With off-air or mistuned reception, any attenuation at higher frequencies or asymmetry around the color sub- carrier is compensated. Four different settings of the IF- compensation are possible: – flat (no compensation) – 6 dB /octave – 12 dB /octave – 10 dB/MHz The last setting gives a very large boost to high frequen- cies. It is provided for SECAM signals that are decoded using a SAW filter specified originally for the PAL stan- dard. Fig. 2–4: Freq. response of chroma IF-compensation dB MHz 10 3.5 3.75 4 4.25 4.5 5 0 –10 –15 –20 –5 5 4.75 2.3.2. Demodulator The entire signal (which might still contain luma) is now quadrature-mixed to the baseband. The mixing frequen- cy is equal to the subcarrier for PAL and NTSC, thus achieving the chroma demodulation. For SECAM, the mixing frequency is 4.286 MHz giving the quadrature baseband components of the FM modulated chroma. After the mixer, a lowpass filter selects the chroma com- ponents; a downsampling stage converts the color dif- ference signals to a multiplexed half rate data stream. The subcarrier frequency in the demodulator is gener- ated by direct digital synthesis; therefore, substandards such as PAL 3.58 or NTSC 4.43 can also be demodu- lated. Chroma IF Compensation DC-Reject MIXER Lowpass Filter Phase/Freq. ACC Color-PLL / Color-ACC 1 H Delay Cross- Notch Filter Demodulator Luma / CVBS Luma Chroma Fig. 2–5: Color decoder Switch |
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