VPC3230D datasheet(11/78 Pages) MICRONAS

11 / 78 page

ADVANCE INFORMATION

VPC 323xD, VPC 324xD

Micronas

Fig. 2–5: Frequency response of chroma filters

2.3.4. 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 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-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.

Color saturation can be selected once for all color

standards. In PAL/NTSC it is used as reference for the

ACC. In SECAM the necessary gains are calculated

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

color killer operation; they are used for automatic stan-

dard detection as well.

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

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.

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 VPC32xxD

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

PAL/NTSC

SECAM

MHz

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