VCT 38xxA
ADVANCE INFORMATION
2.4.9. Luminance Notch Filter
2.5. Horizontal Scaler
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.
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.
dB
10
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.
0
–10
–20
–30
–40
MHz
Table 2–1: Scaler modes
0
2
4
6
8
10
PAL/NTSC notch filter
Mode
Scale
Description
Factor
dB
10
Compression 0.75
4:3 source displayed on
a 16:9 tube,
4:3 → 16:9
linear
0
with side panels
–10
Panorama
4:3 →16:9
non-
linear
compr
4:3 source displayed on
a 16:9 tube,
Borders distorted
–20
–30
–40
Zoom
4:3 → 4:3
1.33
linear
Letterbox source (PAL+)
displayed on a 4:3 tube,
vertical overscan with
cropping of side panels
MHz
0
2
4
6
8
10
SECAM notch filter
Fig. 2–9: Frequency responses of the luma
notch filter for PAL, NTSC, SECAM
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
2.4.10.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.
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 skew filters allow the application of a group delay
to the input signals without introducing waveform or
frequency response distortion.
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
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.
16
Micronas
MICRONAS [ MICRONAS ]
