ADVANCE INFORMATION
VPC 323xD, VPC 324xD
color killer operation; they are used for automatic stan-
dard detection as well.
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
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.
MHz
PAL/NTSC
dB
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:
MHz
SECAM
Fig. 2–5: Frequency response of chroma filters
PAL B,G,H,I; NTSC M; SECAM; NTSC 44; PAL M;
PAL N; PAL 60
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.
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.
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
For error handling the recognition algorithm delivers
the following status information:
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.
– search active (busy)
– search terminated, but failed
– found standard is disabled
– vertical standard invalid
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
Micronas
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MICRONAS [ MICRONAS ]
