VPX 322xE
ADVANCE INFORMATION
2.3.3. Chrominance Filter
2.3.4. Frequency Demodulator
The demodulation is followed by a lowpass filter for the
color difference signals for PAL/NTSC. SECAM requires
amodifiedlowpassfunctionwithbell-filtercharacteristic.
At the output of the lowpass filter, all luma information is
eliminated.
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
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.
scaled to standard C C amplitudesandfedtothecross-
r
b
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.
dB
0
–10
–20
–30
–40
–50
Color saturation can be selected once for all color stan-
dards. In PAL/NTSC, it is used as reference for the ACC.
In SECAM, the necessary gains are calculated automat-
ically.
ForSECAMdecoding, thefrequencyoftheburstismea-
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.
0
1
2
3
4
5
MHz
PAL/NTSC
dB
0
–10
–20
–30
–40
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 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.
–50
0
1
2
3
4
5
MHz
SECAM
Fig. 2–6: Frequency response of chroma filters
12
Micronas
MICRONAS [ MICRONAS ]
