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Teilenummer | ACVP2205 |
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Beschreibung | Adaptive Combfilter Video Processor | |
Hersteller | ITT Semiconductors | |
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Gesamt 25 Seiten ACVP 2205
Adaptive Combfilter
Video Processor
Edition August 25, 1992
6251-336-2E
ITT Semiconductors
ACVP 2205
The output signal of the black level expander is charac-
terized as
Yout = K2 (Yin – Yt) + Yin , Yin < Yt
Yout = Yin , Yin ≥ Yt
The tilt point Yt is a function of the dynamic range of the
video signal. Thus the dynamic range determines the tilt
point such that the larger the range, the higher the tilt-
point.
The advantage of this black level expander is, that the
black expansion is performed only if there is a large dy-
namic range in the video signal. Otherwise (Ymin = Ymax)
the expansion to black is zero. Thus the expansion is
performed only when it is most noticeable to the viewer.
Yout
Ymax
k
Ymin
Yt
Yin
Fig. 2–5: Characteristic curve of the black–level–ex-
pander
a) Ymax
Ymin
Yt
b)
Yt
Fig. 2–6: Black–level–expansion
a) luminance input
b) luminance output
6
2.5. Chrominance Channel
The chrominance channel of the ACVP starts with the
chroma filter. The chrominance frequency characteristic
is selectable between a symmetrical or an asymmetrical
response and to broad or narrow bandwidth by the CCU
via IM bus. Asymmetrical response has been provided
for compensation of the IF amplifier’s response. In case
of external video from a video tape recorder or a laser
disk player, the symmetrical filter is recommended.
The automatic color control (ACC) circuit measures the
burst amplitude of the chrominance signal and sets it to
a constant level. The chrominance signal is switched off
by the color killer in case of a weak burst amplitude or
non–synchronism between color subcarrier and the de-
modulator. Additionally this circuit contains the PAL flip–
flop, which is synchronized by the burst. The control
range of the ACC is 36 dB. The reference amplitude is
adjustable in 64 steps via the IM bus. The reference val-
ues for the window of the color killer are adjustable in 2
x 128 steps.
The chrominance signal is demodulated in the decoder.
Outputs are the color difference signals R–Y and B–Y.
The color saturation multiplier adjusts the amplitude of
the color difference signals. Caused by the small band-
width of the color difference signals(max. 1 MHz), they
are transmitted with a quarter of the luminance sampling
rate to the VCU or VDU.
The hue correction is also done in the saturation multipli-
er by rotation of the R–Y and B–Y axles of the chroma
signal.The PAL compensation of the chrominance sig-
nal is part of the combfilter.
The color saturation multiplier works according to the
formula
(R–Y)’ = (R–Y) ⋅ fs ⋅ cos α – (B–Y) ⋅ fs ⋅ sin α
(B–Y)’ = (B–Y) ⋅ fs ⋅ cos α + (R–Y) ⋅ fs ⋅ sin α
where α is the angle of the rotation and fs is the satura-
tion. The resolution of α is 3° per step. The multiplication
of fs ⋅ cos α and fs ⋅ sin α are done in the CCU.
For α = 0, the adjustment range of the color saturation
multiplier is 7 bits (128 steps) corresponding to the fol-
lowing scheme (two’s complement code):
00000000= ×0
0 0 0 1 0 0 0 0 = × 0.125
0 0 1 0 0 0 0 0 = × 0.25
0 1 0 0 0 0 0 0 = × 0.5
0 1 1 0 0 0 0 0 = × 0.75
01111111= ×1
6 Page ACVP 2205
Table 2–8 continued
Parameter
Address
Label
140 DVPK
140 VPK
140 VCOR
140 BWIN
141 BTRE
141 BTLT
141 BAM
Bit No.
(LSB = 0)
6
Default
Setting
0
11–14
0
15
10
9–15
5–8
0–4
0
0
0
0
0
Typical
Operation
Value
0
4
1
0
60
6
7
Function
Disable dyn. vertical peaking for improving vertical
resolution, if adaptive combfilter is active
0 = dyn. vertical peaking enabled
1 = dyn. vertical peaking disabled
Vertical peaking (VPK) is adjustable in 15 steps be-
tween 0 and +6 dB.
VPK
Multiplication Factor
0 0/16
1 1/16
2 2/16
3 3/16
4 4/16
5 5/16
6 6/16
7 7/16
8 8/16
9 9/16
10 10/16
11 11/16
12 12/16
13 13/16
14 14/16
15 15/16
16 16/16
Adjustable coring of vertical peaking
0 = coring off
1 = coring of ”1” LSB
Size of the active video measuring window for the
BLE
0 = 4/3 measuring window
1 = 16/9 measuring window
BLE–Threshold: programmable threshold of the BLE
If the measured luminance value (Ymin) is greater
than 2 ⋅ BTRE, the BLE is automatically disabled.
BLE–Tiltpoint: multiplication factor to adjust the ac-
tive working range and the tiltpoint of the BLE de-
pending on the measured signal difference
BLE–Amount: multiplication factor to adjust the
amount of BLE
Yout
255
BTLT
XT
X
BAM
0 BTRE 255
Fig. 2–9: Black–Level–Expander
12
Yin
12 Page | ||
Seiten | Gesamt 25 Seiten | |
PDF Download | [ ACVP2205 Schematic.PDF ] |
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