VDP3108B datasheet(16/72 Pages) MICRONAS

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PRELIMINARY DATA SHEET

VDP 31xxB

Micronas

2.8.3. Dynamic Peaking

Especially with decoded composite signals and notch fil-

ter luminance separation, as input signals, it is neces-

sary to improve the luminance frequency characteris-

tics. With transparent, high-bandwidth signals, it is

sometimes desirable to soften the image.

In the VDP 31xxB, the luma response is improved by ‘dy-

namic’ peaking. The algorithm has been optimized re-

garding step and frequency response. It adapts to the

amplitude of the high frequency part. Small AC ampli-

tudes 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 sepa-

rate adjustment for signal overshoot and for signal un-

dershoot. 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 figure 2–16.

Transients, produced by the dynamic peaking when

switching video source signals, can be suppressed via

the priority bus.

Fig. 2–15: Dynamic peaking frequency response

MHz

–5

–10

–15

–20

MHz

–5

–10

–15

–20

MHz

–5

–10

–15

–20

CF= 3.2 MHz

CF= 2.5 MHz

S-VHS

MHz

–5

–10

–15

–20

MHz

–5

–10

–15

–20

CF= 3.2 MHz

CF= 2.5 MHz

PAL/SECAM

MHz

–5

–10

–15

–20

MHz

–5

–10

–15

–20

CF= 2.5 MHz

CF= 3.2 MHz

Fig. 2–16: Total frequency response for peaking filter and S-VHS, PAL, NTSC

NTSC

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