GC5330IZEV Datasheet, PDF (18/49 Pages) Texas Instruments – Wideband Transmit-Receive Digital Signal Processors

GC5330
GC5337
SLWS226 B – DECEMBER 2010 – REVISED JANUARY 2011
www.ti.com
MUX and SUM (TX Direction)
The MUX and SUM block maps any channel from the DUC to any TX stream for subsequent per-stream
processing.
Crest Factor Reduction (CFR)
The CFR blocks include the CFR function and two interpolate-by-2 filters (referred to here as UC1 and UC2).
The two CFR blocks together can support 1, 2, or 4 TX streams. The CFR function selectively reduces the
peak-to-average ratio (PAR) of wideband digital signals provided in quadrature (I and Q) format, such as those
used in 3G and 4G wireless applications. For example, the CFR function can reduce the PAR of WCDMA Test
Model 1 signals to 5.7 dB, while still meeting all 3GPP requirements for ACLR, composite EVM, and peak code
domain error (PCDE).
The CFR blocks can be configured in eleven different modes, depending on the number of TX streams, the DPD
mode, and the signal sample rates. Relative to previous TI CFR products, the GC533x CFR has enhanced
features such as:
• Constant PAR mode
• Constant input-to-output power mode
• Dynamic PAR target levels for different portions of the time-domain signal
• Up to 25% less latency for certain configurations
• Enhanced CFR performance for narrowband signals
• Automatic (i.e., no host interaction required) CFR coefficient generation for frequency-hopping signals
The UC1 and UC2 blocks can be set to 1× or 2× interpolation and may be used to provide optimum selection of
signal oversampling ratio at CFR. UC1 may be positioned before or after the CFR function, while UC2 is always
at the output of CFR. Since UC2 has only a 40% bandwidth image rejection (90 dB) filter, it is only used if
preceded by UC1, which has an 80% bandwidth image-rejection (90 dB) filter.
Digital Predistortion (DPD)
The DPD blocks include the DPD function, TX equalization, and the envelope tracking (ET) function. The
GC533x supports two modes of operation, depending on signal bandwidth and desired DPD correction capability:
high-performance (HP) mode and high-bandwidth (HB) mode. For 5× DPD expansion bandwidth (fifth-order DPD
correction), the following signal bandwidths and number of streams can be supported.
High-performance DPD mode
1 TX stream at 62 {74} MHz
2 TX streams at 31 {37} MHz each
4 TX streams at 15.5 {18.5} MHz each
This mode provides more extensive nonlinear correction or longer DPD memory and is suitable for the
most-difficult and high-performance DPD requirements.
High-bandwidth DPD mode
1 TX stream at 62 {74} MHz
2 TX streams at 62 {74} MHz each
4 TX streams at 31 {37} MHz each
This mode provides excellent DPD correction for most DPD requirements.
The TX equalizer is a complex equalizer and is configurable from 17 to 34 taps, depending on the DPD mode of
operation. In HP modes, the number of taps may be up to 34. In HB modes, the number of taps may be up to 17.
Contact the TI factory for additional details.
The predistortion correction terms are computed by an external processor (e.g., TI TMS320C6748 DSP) based
on reference-input and PA-feedback data captured in the GC533x capture buffers. The external processor reads
the captured data buffers from the GC533x and writes back the newly computed DPD correction terms on a
continuous basis.
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