
2004 Jul 22
28
Philips Semiconductors
Product specication
Multistandard video decoder with adaptive
comb lter and component video input
SAA7118
8.1.2.2
Luminance path
The rejection of the chrominance components within the
9-bit CVBS or Y input signal is achieved by subtracting the
remodulated chrominance signal from the CVBS input.
The comb filtered CB-CR components are interpolated
(upsampled) by the low-pass 3 block. Its characteristic is
controlled by LUBW (subaddress 09H, bit D4) to modify
the width of the chrominance ‘notch’ without influencing
the chrominance path. The programmable frequency
characteristics available, in conjunction with the LCBW2 to
LCBW0 settings, can be seen in Figs
14 to
17. It should be
noted that these frequency curves are only valid for
Y-comb disabled filter mode (YCOMB = 0). In comb filter
mode the frequency response is flat. The centre frequency
of the notch is automatically adapted to the chosen colour
standard.
The interpolated CB-CR samples are multiplied by two
time-multiplexed subcarrier signals from the subcarrier
generation block 2. This second DTO is locked to the first
subcarrier generator by an increment delay circuit
matched to the processing delay, which is different for PAL
and NTSC standards according to the chosen comb filter
algorithm. The two modulated signals are finally added to
build the remodulated chrominance signal.
The frequency characteristic of the separated luminance
signal can be further modified by the succeeding
luminance filter block. It can be configured as peaking
(resolution enhancement) or low-pass block by LUFI3 to
LUFI0 (subaddress 09H, bits D3 to D0). The 16 resulting
frequency characteristics can be seen in
Fig.18. The
LUFI3 to LUFI0 settings can be used as a user
programmable sharpness control.
The luminance filter block also contains the adjustable
Y-delay part; programmable by YDEL2 to YDEL0
(subaddress 11H, bits D2 to D0).