ADVANCE INFORMATION
VCT 38xxA
dB
L
a)
max
20
15
10
L
t
5
0
L
min
–5
–10
–15
–20
b)
MHz
0
2
4
6
8
10
L
t
Fig. 2–13: Dynamic peaking frequency response
Fig. 2–12: Black-level expansion
a) luminance input
b) luminance input and output
2.10.3.Dynamic Peaking
Especially with decoded composite signals and notch
filter luminance separation, as input signals, it is nec-
essary to improve the luminance frequency character-
istics. With transparent, high-bandwidth signals, it is
sometimes desirable to soften the image.
In the VCT 38xxA, the luma response is improved by
‘dynamic’ peaking. The algorithm has been optimized
regarding step and frequency response. It adapts to
the amplitude of the high-frequency part. Small AC
amplitudes are processed, while large AC amplitudes
stay nearly unmodified.
The dynamic range can be adjusted from −14 to
+14 dB for small high-frequency signals. There is sep-
arate adjustment for signal overshoot and for signal
undershoot. For large signals, the dynamic range is
limited by a non-linear function that does not create
any visible alias components. The peaking can be
switched over to “softening” by inverting the peaking
term by software.
The center frequency of the peaking filter is switchable
from 2.5 MHz to 3.2 MHz. For S-VHS and for notch filter
color decoding, the total system frequency responses
for both PAL and NTSC are shown in Fig. 2–14.
Transients, produced by the dynamic peaking when
switching video source signals, can be suppressed via
the priority bus.
Micronas
19
MICRONAS [ MICRONAS ]
