VPX3214C Просмотр технического описания (PDF) - Micronas
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VPX3214C Datasheet PDF : 80 Pages
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VPX 3220 A, VPX 3216 B, VPX 3214 C
PRELIMINARY DATA SHEET
2.2.3. Chrominance Filter
The demodulation is followed by a lowpass filter for the
color difference signals for PAL/NTSC. SECAM requires
a modified lowpass function with a bell-filter characteris-
tic. At the output of the lowpass filter, all luma information
is eliminated.
The lowpass filters are calculated in time multiplex for
the two color signals. Three bandwidth settings (narrow,
normal, broad) are available for each standard. The filter
passband can be shaped with an extra peaking term at
1.25 MHz.
dB
0
–10
PAL/
NTSC
–20
broad
normal
–30
narrow
–40
–50
0
1
2
3
4
MHz
5
dB
0
–10
SECAM
–20
–30
–40
–50
0
1
2
3
4
MHz
5
Fig. 2–4: Frequency response of chroma filters
2.2.4. Frequency Demodulator
The frequency demodulator for demodulating the
SECAM 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
scaled to standard CrCb amplitudes and fed to the cross-
over-switch.
dB
0
–1
–2
–3
–4
–5
–6
–7
–8
–9
–10
–11
0.01
0.1
MHz
1.0
Fig. 2–5: Frequency response of SECAM
deemphasis
2.2.5. Burst Detection
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.
For SECAM decoding, the frequency of the burst is mea-
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.
8
MICRONAS INTERMETALL
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