AD7183 datasheet(11/40 Pages) AD

11 / 40 page

REV. 0

ADV7183

–11–

LUMINANCE PROCESSING

Figure 7 shows the luminance data path. The 10-bit data from

the Y ADC is applied to an antialiasing low pass filter that is

designed to band-limit the input video signal such that aliasing

does not occur. This filter dramatically reduces the design on an

external analog antialaising filter; this filter need only remove

components in the input video signal above 22 MHz. The data

then passes through a shaping or notch filter.

When in CVBS mode a notch filter must be used to remove the

unwanted chrominance data that lies around the subcarrier

frequency. A wide variety of programmable notch filters for

both PAL and NTSC are available. The YSFM[4:0] control the

selection of these filters; refer to Figures 8 to 16 for plots of

these filters. If S-video or component mode is selected a notch

filter is not required. The ADV7183 offers 18 possible shaping

filters (SVHS1-18) with a range of low pass filter responses from

0.5 MHz up to 5.75 MHz. The YSFM[4:0] control the selec-

tion of these filters. Please refer to Figures 8 through 16 for

filter plots.

The next stage in the luminance processing path is a peaking

filter; this filter offers a sharpness function on the luminance

path. The degree of sharpness can be selected using YPM[2:0].

If no sharpness is required, this filter can be bypassed.

The luminance 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 128 phases to resample the video, giving 1/128

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 luminance path, before it is applied to an

output formatter block, is a two-line delay store that is used to

compensate for delays in the chroma data path when chroma

comb filter is selected.

ANTI-

ALIASING

LPF

SHAPING

AND

NOTCH

FILTER

PEAKING

FILTER

RESAMPLE

DELAY

LINE

STORES

SYNC

DETECTION

ADC DATA

Figure 7. Luminance Processing Path

FREQUENCY – MHz

–60

–10

–20

–30

–40

–50

SVHS1

SVHS2

SVHS3

SVHS4

SVHS5

SVHS6

SVHS7

SVHS8

SVHS9

SVHS10

SVHS11

SVHS12

SVHS13

SVHS14

SVHS15

SVHS16

SVHS17

SVHS18

Figure 8. Luminance SVHS1–18 Shaping Filter

Responses

FREQUENCY – MHz

1.0

–1.0

2345

0.8

0.2

–0.4

–0.6

–0.8

0.6

0.4

–0.2

Figure 9. Luminance SVHS1–SVHS18 Shaping

Filter Responses (Close-Up)

FREQUENCY – MHz

–60

–10

–20

–30

–40

–50

NTSC WN1

NTSC WN2

NTSC WN3

NTSC NN1

NTSC NN2

NTSC NN3

NTSC WN2

NTSC NN3

NTSC WN1

NTSC NN2

NTSC NN1

NTSC WN3

Figure 10. Luminance NTSC Narrow/Wide Notch

Shaping Filter

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