saa4996h NXP Semiconductors, saa4996h Datasheet - Page 21

• Manufacturer Part Number: saa4996h
• Description: Motion Adaptive Colour Plus And Control Ic Macpacic For Palplus
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.13
The PALplus system has two modes of operation.
These are called film mode, which is only used with film
sources, and camera mode which is applied for normal
50 Hz interlaced video sources. The motion detector is
only necessary in the camera mode because, in the
film mode, the two fields of a frame are sampled from the
same picture of the film.
The chrominance motion detector has two input branches
(see Fig.10). One input branch is the intra frame average
of the actual frame, the other input branch is the intra
frame average signal of the previous frame. This signal is
delivered by the field memory FM4.
Subtraction of the two intra frame average signals
generates the chrominance inter frame difference.
PAL averaging eliminates phase errors. This PAL
averaging can be switched off when the PAL delay line in
the colour decoder is active.
A look-up table (LUT) generates the motion signal from the
chrominance signal. A comparator generates a
chrominance control switch signal (CS). A horizontal
interpolation filter interpolates a 16 MHz motion signal.
The motion high-pass luminance control signal M_YL is
provided by another LUT.
7.14
The IRXR block diagram is illustrated in Fig.10.
The MACP algorithm requires good stability of the
sampling clock between both fields, because samples
from both fields will be combined, in order to suppress
cross-colour and cross-luminance. Investigations with
currently used sync/clock circuitry have shown that the
stability of these clocks is not as good as it should be for
perfect performance of the MACP algorithm.
When a MACP signal is received the colour subcarrier trap
in the TDA9144 is bypassed and the input signal of the
SAA4996H still contains the modulated colour component.
The MACP technique always processes corresponding
lines of two successive fields (having an offset of
312 lines). These lines will have the same high-frequency
luminance information (YH) and inverted colour
information due to the phase/line relationship in PAL.
With an ideal sampling grid, the two inverted colour signals
will be cancelled completely by addition so that no
cross-luminance (XL) remains in the resulting picture.
1996 Oct 28
Motion Adaptive Colour Plus And Control
IC (MACPACIC) for PALplus
Chrominance motion detection
Intelligent residual cross-luminance reduction
(IRXR)
21
When the sampling grid is not optimum (e.g. shifted a little
in one field with respect to the other field), the cancellation
of both modulated colour signals will not be complete and
some residual XL will remain. The amount of residual XL
is proportional to the amplitude of the modulated colour
signal and to the following formula;
The timing error is determined by the type of circuitry used
for the sync/clock generation and by the amount of
noise/disturbance in the input signal (more
noise/disturbance generally leads to larger timing errors).
The intelligent residual cross-luminance reduction (IRXR)
tries to cancel this residual cross-luminance (XL), by
reducing the amount of YH depending of the amplitude of
the modulated colour signal.
The saturation indication signal (SD) is generated by the
intra frame average signal of the actual frame with the help
of a look-up table (LUT). A horizontal interpolation filter
interpolates a 16 MHz saturation detection signal SD.
Another LUT transforms the SD signal into the signal
SD_YL, which determines the amount of YH to be
reduced. Different characteristics curves of the LUT can
be selected either via SNERT (SEL_SD_YL) or
automatically depending on the measured noise value
(SelSdYl), see Fig.11 and Table 4.
The IRXR function can be disabled or enabled via SNERT
by the EN_IRXR bit.
The output signal YL is generated from the three YH
reduction signals SD_YL, M_YL and NM_YL.
This combination is performed with a minimum detection
circuit. The amount of YH that is allowed is the lowest of
the three input signals. Whenever one input signal
indicates a reason to reduce the YH, this should be
performed independently of the other input signals.
In the event of film mode the signals NM_YL (Fig.12 and
Table 5) and M_YL are over-written with the value 4.
Motion detector processing is not active for these signals
in the film mode. Such film overriding is not allowed for the
SD_YL signal, because the residual XL can occur in the
film mode as well as in the camera mode.
sin
f_sc timing_error
Preliminary specification
SAA4996H