VPX3225D 查看數據表（PDF） - Micronas

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VPX3225D

Video Pixel Decoders

Micronas 

PRELIMINARY DATA SHEET

VPX 3225D, VPX 3224D

2.2.3. Chrominance Filter

The demodulation is followed by a lowpass filter for the

color difference signals for PAL/NTSC. SECAM requires

a modified lowpass function with bell-filter characteristic.

At the output of the lowpass filter, all luma information is

eliminated.

The lowpass filters are calculated in time multiplex for

the two color signals. Four bandwidth settings (narrow,

normal, broad, wide) are available for each standard.

The filter passband can be shaped with an extra peaking

term at 1.25 MHz. For PAL/NTSC, a wide band chroma

filter can be selected. This filter is intended for high

bandwidth chroma signals; for example, a nonstandard

wide bandwidth S-VHS signal.

dB

0

–10

–20

–30

–40

–50

0

1

2

3

4

5

MHz

PAL/NTSC

dB

0

–10

–20

–30

–40

–50

0

1

2

3

4

5

MHz

SECAM

Fig. 2–5: Frequency response of chroma filters

2.2.4. Frequency Demodulator

The frequency demodulator for demodulating the SE-

CAM signal is implemented as a CORDIC-structure. It

calculates the phase and magnitude of the quadrature

components by coordinate rotation.

The phase output of the CORDIC processor is differen-

tiated to obtain the demodulated frequency. After a pro-

grammable deemphasis filter, the Dr and Db signals are

scaled to standard CrCb amplitudes and fed to the cross-

over-switch.

2.2.5. Burst Detection

In the PAL/NTSC-system, the burst is the reference for

the color signal. The phase and magnitude outputs of

the CORDIC are gated with the color key and used for

controlling the phase-lock-loop (APC) of the demodula-

tor and the automatic color control (ACC) in PAL/NTSC.

The ACC has a control range of +30 ... –6 dB.

For SECAM decoding, the frequency of the burst is mea-

sured. Thus, the current chroma carrier frequency can

be identified and is used to control the SECAM proces-

sing. The burst measurements also control the color kill-

er operation; they can be used for automatic standard

detection as well.

2.2.6. Color Killer Operation

The color killer uses the burst-phase / burst-frequency

measurement to identify a PAL/NTSC or SECAM color

signal. For PAL/NTSC, the color is switched off (killed)

as long as the color subcarrier PLL is not locked. For SE-

CAM, the killer is controlled by the toggle of the burst fre-

quency. The burst amplitude measurement is used to

switch off the color if the burst amplitude is below a pro-

grammable threshold. Thus, color will be killed for very

noisy signals. The color amplitude killer has a program-

mable hysteresis.

2.2.7. PAL Compensation / 1-H Comb Filter

The color decoder uses one fully integrated delay line.

Only active video is stored.

The delay line application depends on the color stan-

dard:

– NTSC: 1-H comb filter or color compensation

– PAL: color compensation

– SECAM: crossover-switch

Micronas

11

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