Datasheet

ADV7188
Rev. A | Page 40 of 112
7
DNR_EN, Digital Noise Reduction Enable, Address 0x4D [5] DNR_TH2 [7:0], DNR Noise Threshold 2,
Address 0xFC [7:0]
0—Bypasses DNR (disables it).
The DNR2 block is positioned after the luma peaking block and
therefore affects the amplified luma signal. It operates in the
same way as the DNR1 block, but has an independent threshold
control, DNR_TH2 [7:0]. This value is an unsigned, 8-bit
number that determines the maximum edge that is interpreted
as noise and therefore blanked from the luma data.
Programming a large value into DNR_TH2 [7:0] causes the
DNR block to interpret even, large transients as noise and
remove them. As a result, the effect on the video data is more
visible. Programming a small value causes only small transients
to be seen as noise and to be removed.
1 (default)—Enables DNR on the luma data.
DNR_TH [7:0], DNR NoiseThreshold, Address 0x50 [7:0]
The DNR1 block is positioned before the luma peaking block.
The DNR_TH [7:0] value is an unsigned, 8-bit number that
determines the maximum edge that is interpreted as noise and
therefore blanked from the luma data. Programming a large
value into DNR_TH [7:0] causes the DNR block to interpret
even, large transients as noise and remove them. As a result, the
effect on the video data is more visible.
Programming a small value causes only small transients to be
seen as noise and to be removed.
COMB FILTERS
The comb filters of the ADV7188 have been greatly improved to
automatically handle video of all types, standards, and levels of
quality. The NTSC and PAL configuration registers allow the
user to customize comb filter operation, depending on which
video standard is detected (by autodetection) or selected (by
manual programming). In addition to the bits listed in this
section, there are other Analog Devices internal controls.
Contact an Analog Devices representative for more information.
The recommended DNR_TH [7:0] setting for A/V inputs is
0x04, and the recommended DNR_TH [7:0] setting for tuner
inputs is 0x0A.
The default value for DNR_TH [7:0] is 0x08, indicating the
threshold for maximum luma edges to be interpreted as noise.
PEAKING_GAIN [7:0], Luma Peaking Gain,
Address 0xFB [7:0]
NTSC Comb Filter Settings
This filter can be manually enabled. The user can boost or
attenuate the mid region of the Y spectrum around 3 MHz. The
peaking filter can visually improve the picture by showing more
definition on the picture details that contain frequency
components around 3 MHz. The default value (0x40) in this
register passes through the luma data unaltered (0 dB response).
A lower value attenuates the signal, and a higher value amplifies
it. A plot of the filter responses is shown in
Figure 24.
Used for NTSC M and NTSC J CVBS inputs.
NSFSEL [1:0], Split Filter Selection NTSC,
Address 0x19 [3:2]
NSFSEL [1:0] selects how much of the overall signal bandwidth
is fed to the combs. A narrow bandwidth split filter results in better
performance on diagonal lines, but more dot crawl in the final
output image. The opposite is true for a wide bandwidth split filter.
15
–20
0
05478-024
FREQUENCY (MHz)
FILTER RESPONSE (dB)
10
5
0
–5
–10
–15
123456
PEAKING GAIN USING BP FILTER
Table 50. NSFSEL [1:0] Function
NSFSEL [1:0] Description
00 (default) Narrow
01 Medium
10 Medium
11 Wide
CTAPSN [1:0], Chroma Comb Taps NTSC,
Address 0x38 [7:6]
Table 51. CTAPSN [1:0] Function
CTAPSN [1:0] Description
00 Do not use
01
NTSC chroma comb adapts three lines (three taps)
to two lines (two taps)
Figure 24. Peaking Filter Responses
10 (default)
NTSC chroma comb adapts five lines (five taps)
to three lines (three taps)
11
NTSC chroma comb adapts five lines (five taps)
to four lines (four taps)