ADV7181B
Rev. B | Page 28 of 100
The filter plots in Figure 11 show the S-VHS 1 (narrowest) to
S-VHS 18 (widest) shaping filter settings. Figure 13 shows the
PAL notch filter responses. The NTSC-compatible notches are
shown in Figure 14.
0
–10
–20
–30
–40
–50
–60
–70
0
10
8
6
4
2
12
FREQUENCY (MHz)
COMBINED Y ANTIALIAS, S-VHS LOW-PASS FILTERS,
Y RESAMPLE
AMP
LITUDE
(dB)
04984-011
Figure 11. Y S-VHS Combined Responses
0
–20
–40
–60
–80
–100
–120
0
10
8
6
4
2
12
FREQUENCY (MHz)
AMP
L
ITUDE
(dB)
COMBINED Y ANTIALIAS, CCIR MODE SHAPING FILTER,
Y RESAMPLE
04984-012
Figure 12. Y S-VHS 18 Extra Wideband Filter (CCIR 601 Compliant)
0
–10
–20
–30
–40
–50
–60
–70
0
10
8
6
4
2
12
FREQUENCY (MHz)
COMBINED Y ANTIALIAS, PAL NOTCH FILTERS,
Y RESAMPLE
AMP
L
ITUDE
(dB)
04984-013
Figure 13. Pal Notch Filter Response
0
–10
–20
–30
–40
–50
–60
–70
0
10
8
6
4
2
12
FREQUENCY (MHz)
COMBINED Y ANTIALIAS, NTSC NOTCH FILTERS,
Y RESAMPLE
A
M
PLITU
D
E (
d
B
)
04984-014
Figure 14. NTSC Notch Filter Response
CHROMA FILTER
Data from the digital fine clamp block is processed by three sets
of filters. The data format at this point is CVBS for CVBS
inputs, chroma only for Y/C, or U/V interleaved for YPrPb
input formats.
•
Chroma Antialias Filter (CAA). The ADV7181B over-
samples the CVBS by a factor of 2 and the Chroma/PrPb
by a factor of 4. A decimating filter (CAA) is used to
preserve the active video band and to remove any out-of-
band components. The CAA filter has a fixed response.
•
Chroma Shaping Filters (CSH). The shaping filter block
(CSH) can be programmed to perform a variety of low-
pass responses. It can be used to selectively reduce the
bandwidth of the chroma signal for scaling or compression.
•
Digital Resampling Filter. This block is used to allow
dynamic resampling of the video signal to alter parameters
such as the time base of a line of video. Fundamentally, the
resampler is a set of low-pass filters. The actual response is
chosen by the system without user intervention.
The plots in Figure 15 show the overall response of all filters
together.
