GC5316 Datasheet, PDF (40/75 Pages) Texas Instruments – HIGH-DENSITY DIGITAL DOWNCONVERTER AND UPCONVERTER

GC5316
SLWS154A − JANUARY 2004 − REVISED MARCH 2004
3.1.9 Transmit Sum Chain
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SUM 0
26
SUM 1
To Scale and
Round block
26
SUM 2
26
SUM 3
CDM A
DUC B
CDM A
DUC A
D UCs
2 −10
CDM A
DUC B
CDM A
DUC A
CDM A
DUC B
CDM A
DUC A
Or 1 U MTS Cha nnel
Or 1 U MTS Cha nne l
Or 1 U MTS Cha nne l
D UC 11
DUC 1
D UC 0
Figure 34. Transmit Sum Chain
The transmit sum chain is a daisy-chain of all DUC outputs into four independent composite output streams. Each
DUC output drives four complex adders, each summing the DUC’s contribution into the sum chain.
The DUC output data driving the adders is 21 bits. The sum chain partial sum outputs are 26 bits to allow for word
growth. Each DUC output can contribute to any of the four sum chains, or not, via programmable enable lines. The
output of the last daisy-chained sum is then the composite of all of the 24 CDMA or 12 UMTS channels. One should
always ensure that within a sum chain, there are no DUCs powered down with lower numbers than those that are
active with higher numbers, thus breaking the chain. In other words, if DUCs 3−5 are used and active, DUCs 0−2
must not be powered down.
As shown in the diagram above, each DUC contains a portion of the sumchain. Within the programming for each DUC
one can enable adding results from that DUC signal path(s) to each of the four sum-chains using the parameters
below.
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