ADV7182 datasheet(27/96 Pages) AD

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Data Sheet

ADV7182

Rev. A | Page 27 of 96

Y Shaping Filter

For input signals in CVBS format, the luma shaping filters play

an essential role in removing the chroma component from a

composite signal. Y/C separation must aim for best possible

crosstalk reduction while still retaining as much bandwidth

(especially on the luma component) as possible. High quality

Y/C separation can be achieved by using the internal comb

filters of the ADV7182. Comb filtering, however, relies on the

frequency relationship of the luma component (multiples of the

video line rate) and the color subcarrier (fSC). For good quality

CVBS signals, this relationship is known; the comb filter algorithms

can be used to separate luma and chroma with high accuracy.

In the case of nonstandard video signals, the frequency relationship

may be disturbed, and the comb filters may not be able to remove

all crosstalk artifacts in the best fashion without the assistance

of the shaping filter block.

An automatic mode is provided that allows the ADV7182 to

evaluate the quality of the incoming video signal and select the

filter responses in accordance with the signal quality and video

standard. YFSM, WYSFMOVR, and WYSFM allow the user to

manually override the automatic decisions in part or in full.

The luma shaping filter has the following control bits.

•

YSFM[4:0] allows the user to manually select a shaping

filter mode (applied to all video signals) or to enable an

automatic selection (depending on video quality and video

standard).

•

WYSFMOVR allows the user to manually override the

WYSFM decision.

•

WYSFM[4:0] allows the user to select a different shaping

filter mode for good quality composite (CVBS), component

(YPrPb), and SVHS (Y/C) input signals.

In automatic mode, the system preserves the maximum possible

bandwidth for good CVBS sources (because they can be successfully

combed) as well as for luma components of YPrPb and Y/C

sources (because they need not be combed). For poor quality

signals, the system selects from a set of proprietary shaping

filter responses that complements comb filter operation to

reduce visual artifacts.

The decisions of the control logic are shown in Figure 17.

YSFM[4:0], Y Shaping Filter Mode, Address 0x17[4:0]

The Y shaping filter mode bits allow the user to select from

a wide range of low-pass and notch filters. When switched in

automatic mode, the filter selection is based on other register

selections, such as detected video standard, as well as properties

extracted from the incoming video itself, such as quality and time

base stability. The automatic selection always selects the widest

possible bandwidth for the video input encountered. (See Table 36.)

The Y-shaping filter mode operates as follows:

•

If the YSFM settings specify a filter (that is, YSFM is set to

values other than 00000 or 00001), the chosen filter is

applied to all video, regardless of its quality.

•

In automatic selection mode, the notch filters are only used

for bad quality video signals. For all other video signals,

wideband filters are used.

WYSFMOVR, Wideband Y Shaping Filter Override,

Address 0x18[7]

Setting the WYSFMOVR bit enables the use of the WYSFM[4:0]

settings for good quality video signals. For more information on

luma shaping filters, see the Y Shaping Filter section and the

flowchart shown in Figure 17.

When WYSFMOVR is set to 0, the shaping filter for good quality

video signals is selected automatically.

Setting WYSFMOVR is set to 1 (default), it enables manual

override via WYSFM[4:0].

Figure 17. YSFM and WYSFM Control Flowchart

AUTO SELECT LUMA

SHAPING FILTER TO

COMPLEMENT COMB

SET YSFM

YSFM IN AUTO MODE?

00000 OR 00001

VIDEO

QUALITY

BAD

GOOD

SELECT WIDEBAND

FILTER AS PER

WYSFM[4:0]

SELECT AUTOMATIC

WIDEBAND FILTER

WYSFMOVR

USE YSFM SELECTED

FILTER REGARDLESS OF

VIDEO QUALITY

YES

ADV7182 Datasheet(PDF) 27 Page - Analog Devices

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