VPC3230D Просмотр технического описания (PDF) - Micronas

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VPC3230D

Comb Filter Video Processor

Micronas 

PRELIMINARY DATA SHEET

VPC 323xD

color killer operation; they are used for automatic stan-

dB

dard detection as well.

PAL/NTSC

dB

2.3.6. 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

SECAM, the killer is controlled by the toggle of the

MHz

burst frequency. The burst amplitude measurement is

used to switch off the color if the burst amplitude is

below a programmable threshold. Thus, color will be

killed for very noisy signals. The color amplitude killer

has a programmable hysteresis.

SECAM

MHz

Fig. 2–5: Frequency response of chroma filters

2.3.4. Frequency Demodulator

The frequency demodulator for demodulating the

SECAM signal is implemented as a CORDIC-struc-

ture. It calculates the phase and magnitude of the

quadrature components by coordinate rotation.

The phase output of the CORDIC processor is differ-

entiated to obtain the demodulated frequency. After

the deemphasis filter, the Dr and Db signals are scaled

to standard CrCb amplitudes and fed to the cross-

over-switch.

2.3.5. Burst Detection / Saturation Control

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-locked loop (APC) of the demodu-

lator and the automatic color control (ACC) in PAL/

NTSC.

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

Color saturation is adjustable independently of the

color standard. In PAL/NTSC it is used as reference for

the ACC. In SECAM the necessary gains are calcu-

lated automatically.

For SECAM decoding, the frequency of the burst is

measured. Thus, the current chroma carrier frequency

can be identified and is used to control the SECAM

processing. The burst measurements also control the

2.3.7. Automatic Standard Recognition

The burst-frequency measurement is also used for

automatic standard recognition (together with the sta-

tus of horizontal and vertical locking) thus allowing a

completely independent search of the line and color

standard of the input signal. The following standards

can be distinguished:

PAL B,G,H,I; NTSC M; SECAM; NTSC 44; PAL M;

PAL N; PAL 60

For a preselection of allowed standards, the recogni-

tion can be enabled/disabled via I2C bus for each stan-

dard separately.

If at least one standard is enabled, the VPC 323xD

checks regularly the horizontal and vertical locking of

the input signal and the state of the color killer. If an

error exists for several adjacent fields a new standard

search is started. Depending on the measured line

number and burst frequency the current standard is

selected.

For error handling, the recognition algorithm delivers

the following status information:

– search active (busy)

– search terminated, but failed

– found standard is disabled

– vertical standard invalid

– no color found

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