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componentes Descripción

Fabricante

VCT38XXA

Video/Controller/Teletext IC Family

Micronas 

VCT 38xxA

ADVANCE INFORMATION

2.4.9. Luminance Notch Filter

If a composite video signal is applied, the color infor-

mation is suppressed by a programmable notch filter.

The position of the filter center frequency depends on

the subcarrier frequency for PAL/NTSC. For SECAM,

the notch is directly controlled by the chroma carrier

frequency. This considerably reduces the cross-lumi-

nance. The frequency responses for all three systems

are shown in Fig. 2–9.

dB

10

0

–10

–20

–30

–40

0

2

4

6

8

MHz

10

PAL/NTSC notch filter

dB

10

0

–10

–20

–30

–40

0

2

4

6

8

SECAM notch filter

Fig. 2–9: Frequency responses of the luma

notch filter for PAL, NTSC, SECAM

MHz

10

2.4.10.Skew Filtering

The system clock is free-running and not locked to the

TV line frequency. Therefore, the ADC sampling pat-

tern is not orthogonal. The decoded YCrCb signals are

converted to an orthogonal sampling raster by the

skew filters, which are part of the scaler block.

The skew filters allow the application of a group delay

to the input signals without introducing waveform or

frequency response distortion.

The amount of phase shift of this filter is controlled by

the horizontal PLL1. The accuracy of the filters is 1/32

clocks for luminance and 1/4 clocks for chroma. Thus

the 4:2:2 YCrCb data is in an orthogonal pixel format

even in the case of nonstandard input signals such as

VCR.

2.5. Horizontal Scaler

The 4:2:2 YCrCb signal from the color decoder is pro-

cessed by the horizontal scaler. The scaler block

allows a linear or nonlinear horizontal scaling of the

input video signal in the range of 0.25 to 4. Nonlinear

scaling, also called “Panoramavision”, provides a geo-

metrical distortion of the input picture. It is used to fit a

picture with 4:3 format on a 16:9 screen by stretching

the picture geometry at the borders. Also, the inverse

effect can be produced by the scaler. A summary of

scaler modes is given in Table 2–1.

The scaler contains a programmable decimation filter,

a 1-line FIFO memory, and a programmable interpola-

tion filter. The scaler input filter is also used for pixel

skew correction (see Section 2.4.10. on page 16). The

decimator/interpolator structure allows optimal use of

the FIFO memory. The controlling of the scaler is done

by the internal Fast Processor.

Table 2–1: Scaler modes

Mode

Scale Description

Factor

Compression 0.75

4:3 → 16:9 linear

4:3 source displayed on

a 16:9 tube,

with side panels

Panorama

4:3 →16:9

non-

linear

compr

4:3 source displayed on

a 16:9 tube,

Borders distorted

Zoom

4:3 → 4:3

1.33

linear

Letterbox source (PAL+)

displayed on a 4:3 tube,

vertical overscan with

cropping of side panels

Panorama

4:3 → 4:3

non-

linear

zoom

Letterbox source (PAL+)

displayed on a 4:3 tube,

vertical overscan, bor-

ders distorted, no crop-

ping

2.6. Black-line Detector

In case of a letterbox format input video, e.g. Cinema-

scope, PAL+ etc., black areas at the upper and lower

part of the picture are visible. It is suitable to remove or

reduce these areas by a vertical zoom and/or shift

operation.

The VCT 38xxA supports this feature by a letterbox

detector. The circuitry detects black video lines by

measuring the signal amplitude during active video.

For every field the number of black lines at the upper

and lower part of the picture are measured, compared

to the previous measurement and the minima are

stored in the I2C-register BLKLIN. To adjust the picture

16

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