Z87200 Datasheet, PDF (18/54 Pages) Zilog, Inc. – Spread-Spectrum Transceiver

Z87200
Spread-Spectrum Transceiver
FUNCTIONAL BLOCKS (Continued)
Zilog
Figure 7. PN Matched Filter
Power Detector
The complex output of the PN Matched Filter is fed into a
Power Detector which, for every cycle of the internal base-
band sampling clock, computes the magnitude of the vec-
tor of the I and Q channel correlation sums,
I²(K)+Q²(k), where the magnitude is approximated as
Max{Abs(I),Abs(Q)} + 1/2 Min{Abs(I), Abs(Q)}.
This 10-bit value represents the power level of the corre-
lated signal during each chip period and is used in the
Symbol Tracking Processor.
Symbol Tracking Processor
The output of the Power Detector Block represents the sig-
nal power during each chip period. Ideally, this output will
have a high peak value once per symbol (that is, once per
PN code cycle) when the code sequence of the received
signal in the PN Matched Filter is the same as (and is
aligned in time with) the reference PN code used in the PN
Matched Filter. At that instant, the I and Q channel outputs
of the PN Matched Filter are, theoretically, the optimally
despread I and Q symbols.
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DS96WRL0400