參數(shù)資料
型號(hào): AD7183
廠商: Analog Devices, Inc.
英文描述: Advanced Video Decoder with 10-Bit ADC and Component Input Support
中文描述: 先進(jìn)的視頻解碼器,10位ADC和組件輸入支持
文件頁(yè)數(shù): 13/41頁(yè)
文件大小: 484K
代理商: AD7183
REV. 0
ADV7183
–13–
CHROMINANCE PROCESSING
Figure 17 shows the chrominance data path. The 10-bit data
from the Y ADC (CVBS mode) or the C ADC (S-video) is first
demodulated. The demodulation is achieved by multiplying by
the locally generated quadrature subcarrier, where the sign of
the cos subcarrier is inverted from line to line according to the
PAL switch, and then low pass filtering is applied to removed
components at twice the subcarrier frequency. For NTSC, the
phase of the locally generated subcarrier during color burst is
the same as the phase of the color burst. For PAL, the phase of
the color burst changes from line to line, relative to the phase
during active video, and the phase of the locally generated
subcarrier is the average of these two values.
The chrominance data is then passed through an antialiasing
filter which is a band-pass filter to remove the unwanted lumi-
nance data. This antialaising filter dramatically reduces the
external antialaising filter requirements as it has only to filter
components above 25 MHz. In component mode the demodu-
lation block is bypassed.
The next stage of processing is a shaping filter that can be used
to limit the chrominance bandwidth to between 0.5 MHz
and 3 MHz; the CSFM[2:0] can be used to select these
responses. It should be noted that in CVBS mode a filter of no
greater than 1.5 MHz should be selected, as CVBS video is
typically band-limited to below 1.5 MHz. In S-video mode a
filter of up to 2 MHz can be used. In component mode a filter
of up to 3 MHz can be used as component video has higher
bandwidth than CVBS or S-video.
The chrominance data is then passed through a resampler to
correct for line length variations in the input video. This
resampler is designed to always output 720 pixels per line for
standard PAL or NTSC. The resampler used on the ADV7183
is of very high quality as it uses 64 phases to resample the video,
giving 1/64 pixel resolution. The resampler is controlled by a
sync detection block that calculates line length variations on the
input video.
The final stage in the chrominance path, before it is applied to
an output formatter block, is chroma comb filter.
ANTI-
ALIASING
LPF
SHAPING
LPF
RESAMPLE
CHROMA
COMB
FILTERS
SYNC
DETECTION
U/V
CV/C
27MHz
SINE
ANTI-
ALIASING
LPF
COSINE
13.5MHz
13.5MHz
6.75MHz
SUBCARRIER
RECOVERY
INTERLEAVE
Figure 17. Chrominance Processing Path
FREQUENCY
MHz
0
600
4.0
0.5
A
1.0
1.5
2.0
2.5
3.0
3.5
10
20
30
40
50
SH2 SH3 SH4 SH5
SH6
SH1
Figure 18. Chrominance Shaping Filter Responses
FREQUENCY
MHz
1.0
1.00
4.0
0.5
A
1.0
1.5
2.0
2.5
3.0
3.5
0.8
0.4
0.2
0.6
0.8
0.6
0.2
0
0.4
SH2SH3 SH4SH5
SH1
SH6
Figure 19. Chrominance Shaping Filter Responses
(Close-Up)
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