GDC21D003 Datasheet, PDF(60/77 Page) Hynix Semiconductor

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GDC21D003 Datasheet, PDF (60/77 Pages) Hynix Semiconductor – VSB Receiver

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6.6.1 12 Symbol Intrasegment

Deinterleaver

To help protect the Viterbi decoder against short

burst interference, such as impulse noise or NTSC

co-channel interference, 12-symbol code

intrasegment interleaving is employed in the

transmitter. As shown in figure 6.6.2, the Viterbi

GDC21D003

decoding block uses 12 Viterbi decoders in parallel,

where each Viterbi decoder sees every 12th symbol.

This code interleaving has all the same burst noise

benefits of a 12-symbol interleaver, but also

minimizes the resulting code expansion when the

NTSC rejection comb filter is active (when the

NTSC rejection comb filter is active, the I2C

register8[4](Ncomb) is set to â0â).

Equalized &

Phase Corrected

Symbols

Viterbi Decoder

Viterbi

Decoded

Data

Viterbi Decoder

#10

Viterbi Decoder

#11

Figure 6.6.2 12 Symbol Intrasegment Deinterleaver

6.6.2 Segment Sync Suspension

Before the 8 VSB signals can be processed by the

Viterbi decoder, it is necessary to suspend the

Segment Sync. The presence of the Segment Sync

character in the data stream passed through the

comb filter presents a complication that must be

dealt with, because Segment Sync is not trellis

encoded or precoded. Figure 6.6.3 shows the

technique that has been used. It shows the receiver

processing that consists of the comb filter in the

VSB Synchronizer/Equalizer and Segment Sync

Removal block in this chip. The multiplexer in the

Segment Sync Removal block is normally in the

upper position. This presents data that has been

filtered by the comb filter to the Viterbi Decoder.

However, because of the sync character in the data

stream, the multiplexer selects its lower input

during the 4 symbols that occurs 12 symbols after

the Segment Sync. The effect of this sync removal

is to present to the Viterbi Decoder a signal that

consists of the subtraction of two adjacent data

symbols that come from the same Viterbi Decoder,

one transmitted before and one after the Segment

Sync. The interference introduced by the Segment

Sync symbol is removed in this process, and the

overall channel response seen by the Viterbi

Decoder is the single-delay partial response filter.

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