184.108.40.206 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. It’s characteristic is
controlled by LUBW (subaddress 09H, bit 4) 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 13 to 16. 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 3 to 0). The 16 resulting frequency characteristics can be seen in Fig.17. 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 2 to 0).
Conﬁdential - NDA required
Last edited by H. Lambers