GC1115 Datasheet, PDF (4/80 Pages) Texas Instruments – Crest Factor Reduction Processor

GC1115
SLWS144 – FEBRUARY 2005
www.ti.com
V_out
7 dB
output PAR
GC1115
provides
6 dB peak
reduction
1 dB Compression Point
(maximum output)
Input Signal
Average Power
(0 dB Point)
13 dB
input PAR
PA efficiency before GC1115:
Avg PA output (10 W )
DC power (125 W) ^{= 8%}
V_in
Figure 2. Reducing the Peak-to-Average Ratio (PAR)
However, since the peak-to-average ratio of CDMA signals is so high, the average power is relatively low,
consequently resulting in a low PA efficiency (output power divided by input power). By decreasing the
peak-to-average ratio, the average power of the peak-reduced signal at the output of the GC1115 can be
increased, decreasing PA back-off thus also increasing PA efficiency.
Figure 3 illustrates that the decrease in PAR can then be used to increase the average signal power while still
keeping the peaks below the PA’s 1 dB compression point. The GC1115 can typically limit the output PAR of
CDMA signals to between 6 dB and 7 dB while still meeting all relevant 3GPP or 3GPP2 requirements. This
decreased PAR enables a 2 dB to 3 dB increase in PA drive, which in turn allows PA manufacturers to achieve 2
dB to 3 dB more PA output power. As PAs represent a significant percentage of the capital equipment cost of
base stations, using a 10 W PA instead of a 20 W PA (for example) significantly decreases base station costs.
V_out
Input Signal
Average Power
6 dB less
PA back −off
7 dB
output PAR
1 dB Compression Point
(maximum output)
Output Signal
Average Power
13 dB
input PAR
PA efficiency after GC1115:
Avg PA power (20 W) _{= 16%}
DC power (125 W)
V_in
Figure 3. Increasing PA Efficiency
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