Why do I need a Crest Factor Reduction (CFR) function, in the digital basestation design? What products does TI offer for CFR,
and what product-integration is offered with CFR functions?
Crest Factor Reduction (CFR) or Peak to Average Power Reduction (PAPR) is needed to limit the Peak signal for digital wireless and broadcast signals. The Peak signal limit is not a function of the digital data,
but is based on the high order modulation used for todays transmit systems, multiple carriers transmitted in a common antenna, and multiple digital signals (ie different standards) transmitted on a common antenna.
Power amplifiers are sized to transmit the signal peak associated with the multiple carrier / standard signals. If the Power amplifier sees a lower peak signal level, the PA output power can be smaller for the same rms transmitted power (within signal quality limits).
A general CFR description is provided in the attachment for the GC1115.
TI offers several products that use Crest Factor Reduction (CFR) blocks, some of these products have additional integrated functions:
GC1115 - standalone CFR processor, one or two antenna streams, requires >= 2x oversampled complex data, 1 antenna stream parallel IQ data, can support upto 40Mhz BW, 2 antenna streams interleaved IQ, can support upto 30Mhz BW. The GC1115 has an 32 peak detection cancellers, that are assigned in 4 banks of peak reduction. The GC1115 has additional functions: input decimation, output interpolation, and output gain blocks. The GC1115SEK can be used to run customer signals through, the GC1115 and capture the output digitally, or output to a DAC EVM (usually 5687 or 5688). See the GC1115 datasheet on the TI website for more information (http://focus.ti.com/docs/prod/folders/print/gc1115.html).
GC5325 - this device integrates a CFR block, Resampler, IF translator, Digital Predistortion, Bulk Interpolation and mixer, DAC transmit section, Feedback block, and a capture buffer ( to capture 4K complex samples). The CFR section device has 24 peak detection cancellers that are pooled between 4 banks of peak detection. The GC5325 can support 1 or 2 antenna streams. The bandwidth limits for the GC5325 are based both on CFR and the DPD correction bandwidth. The CFR BW in single antenna is typically < 35Mhz, using the 2x oversampling for CFR. CFR can be operated at reduced performance with an oversampling as low as 1.6x. The GC5325 EVM is scheduled for release 2Q09. Additional information for the GC5325 on the TI website is at: http://focus.ti.com/docs/prod/folders/print/gc5325.html
GC5322 - the GC5322 device, has a GC5325 and included additional DUC and Baseband functions. The CFR section is the same as the GC5325 described above. The added GPP and DUC functionality allow for 1 to 2 wideband carriers, 2 to 4 Wimax10/LTE10 carriers, or 6 to 12 CDMA carriers. Additional information for the GC5322 is on the TI website at http://focus.ti.com/docs/prod/folders/print/gc5322.html, and there is additional material that requires an NDA, contact your local TI High Speed Analog Products Field Application Engineer.
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