VPX3225D 查看數據表（PDF） - Micronas

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VPX3225D

Video Pixel Decoders

Micronas 

VPX 3225D, VPX 3224D

PRELIMINARY DATA SHEET

2.2. Color Decoder

In this block, the standard luma/chroma separation and

multi-standard color demodulation is carried out. The

color demodulation uses an asynchronous clock, thus

allowing a unified architecture for all color standards.

A block diagram of the color decoder is shown in Fig.

2–4. The luma, as well as the chroma processing, is

shown here. The color decoder also provides several

special modes; for example, wide band chroma format

which is intended for S-VHS wide bandwidth chroma.

The output of the color decoder is YCrCb in a 4:2:2 for-

mat.

2.2.1. IF-Compensation

With off-air or mistuned reception, any attenuation at

higher frequencies or asymmetry around the color sub-

carrier is compensated. Four different settings of the IF-

compensation are possible:

– flat (no compensation)

– 6 dB /octave

– 12 dB /octave

– 10 dB/MHz

The last setting gives a very large boost to high frequen-

cies. It is provided for SECAM signals that are decoded

using a SAW filter specified originally for the PAL stan-

dard.

dB

10

5

0

–5

–10

–15

–20

3.5

3.75

4

4.25

4.5

4.75

5 MHz

Fig. 2–3: Freq. response of chroma IF-compensation

2.2.2. Demodulator

The entire signal (which might still contain luma) is now

quadrature-mixed to the baseband. The mixing frequen-

cy is equal to the subcarrier for PAL and NTSC, thus

achieving the chroma demodulation. For SECAM, the

mixing frequency is 4.286 MHz giving the quadrature

baseband components of the FM modulated chroma.

After the mixer, a lowpass filter selects the chroma com-

ponents; a downsampling stage converts the color dif-

ference signals to a multiplexed half rate data stream.

The subcarrier frequency in the demodulator is gener-

ated by direct digital synthesis; therefore, substandards

such as PAL 3.58 or NTSC 4.43 can also be demodu-

lated.

Luma / CVBS

Chroma

Fig. 2–4: Color decoder

10

1 H Delay

Notch

Filter

Cross-

Switch

Luma

Chroma

IF Compensation

DC-Reject

MIXER

Lowpass Filter

Phase/Freq.

Demodulator

ACC

Color-PLL / Color-ACC

Micronas

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