VPX 322xE
ADVANCE INFORMATION
dB
2.3. Color Decoder
10
5
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.
0
–5
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.
–10
–15
–20
The output of the color decoder is YC C in a 4:2:2 for-
r
b
3.5
3.75
4
4.25
4.5
4.75
5
MHz
mat.
Fig. 2–4: Freq. response of chroma IF-compensation
2.3.1. IF-Compensation
2.3.2. Demodulator
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:
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.
– 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.
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.
Luma
Notch
Filter
Luma / CVBS
Chroma
Cross-
Switch
1 H Delay
ACC
Lowpass Filter
Phase/Freq.
Demodulator
IF Compensation
DC-Reject
Chroma
MIXER
Color-PLL/Color-ACC
Fig. 2–5: Color decoder
MICRONAS INTERMETALL
11
MICRONAS [ MICRONAS ]
