GDC21D003 Datasheet, PDF (47/77 Pages) Hynix Semiconductor – VSB Receiver

6.3.10 NTSC Rejection
In the beginning of HDTV broadcasting, it will be
serviced with conventional NTSC broadcasting.
But in case that NTSC broadcasting exists in the
same channel where HDTV broadcasting is on the
air, at the HDTV signal’s point of view NTSC
GDC21D003
signal is interference. This interference is called as
co-channel interference. 3 carrier signals contained
in this co-channel interference can be removed by
using Comb Filter shown in Figure 6.3.15, but
should be checked first if there is co-channel
interference in current channel.
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12 symbol delay
Figure 6.3.15 Comb Filter Block
Figure 6.3.16 is the block diagram of NTSC
Rejection. PN511 signal section contained in Field
Sync helps to get MSE(Mean Square Error).
Difference(error) of input signal and reference
signal generated in Reference Generator is summed
during PN511 signal section and difference(error)
of input signal passed through Comb Filter and
reference signal passed through Comb Filter is
summed during PN511 section. These sums of
signal difference(error) are compared and the
smaller one is selected. The SNR of signal passed
through Comb Filter is decreased to 3dB low.
Therefore, if input signal has no co-channel
interference, the sum of error without passed
through Comb Filter is always smaller than the
other one that Comb Filter isn’t used. But if co-
channel interference exists on channel, even though
the SNR of signal passed through Comb Filter is
3dB low, 3 carriers by co-channel interference are
removed. Therefore the signal passed through
Comb Filter has smaller sum than signal without
passed through Comb Filter and it is output as a
result.
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