GC1115
www.ti.com
SLWS144–FEBRUARY 2005
Crest Factor Reduction Processor
FEATURES
APPLICATIONS
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3GPP (W-CDMA) Base Stations
3GPP2 (cdma2000) Base Stations
CDMA Multi-Carrier Power Amps (MCPAs)
CFR Reduction of OFDM, HSDPA Signals
Two-Channel Transmit Diversity Applications
Operates with TI DAC5687 (500 Msps)
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Significantly Reduces Signal Peaks to ≥ 6 dB
PAR
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One 20-MHz or 2 Independent 10-MHz
Channels
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Programmable Output PAR Down to 6 dB
Programmable Cancellation Pulse Coefs
Meets 3GPP TS 25.141 Down to 6 dB PAR
Meets cdma2000 C.S0010 Down to 6 dB PAR
256-ball PBGA Package, 17 × 17 mm
1.2-V Core, 3.3 V I/O
DESCRIPTION
The GC1115 is a flexible, programmable, wideband crest factor reduction (CFR) processor with a maximum
composite bandwidth of 20 MHz. The GC1115 selectively reduces the peak-to-average ratio (PAR) of wideband
digital signals provided in quadrature (I & Q) format, such as those used in third-generation (3G) code division
multiple access (CDMA) wireless applications. By reducing the PAR of digital signals, the efficiency of follow-on
power amplifiers (PAs) is improved, the D/A converter requirements are eased, and the out-of-band spectral
regrowth caused by simple hard limiting is eliminated.
By including the GC1115, manufacturers of 3G BTS equipment can realize significant savings on power amplifier
costs. The GC1115 meets multi-carrier 3G performance standards (PCDE, composite EVM, and ACLR) at PAR
levels down to 6 dB. The GC1115 integrates easily into the transmit signal chain, between a digital upconverter
such as the Texas Instruments GC5016 or GC5316 and a high-quality D/A converter, such as the Texas
Instruments DAC5675 or DAC5687.
The GC1115 uses four cascaded stages of peak detection and cancellation (PDC) to remove over-threshold
peaks from the input signal. Each PDC stage can be independently programmed with detection target peak
levels and cancellation pulse coefficients. A pool of 32 cancellation pulse generators can be flexibly assigned in
groups of 4 to any PDC stage. Spectrally shaped cancellation pulses are designed using any of the widely
available FIR filter design programs, such as those from Matlab™, ADS™, etc. Cancellation pulses are designed
to match the user’s carrier frequency allocation. Cancellation pulse energy is bandlimited and thus is only added
within allocated carrier bands. The GC1115’s peak cancellation algorithm does not affect the signal’s ACLR.
Input sampling rates to 130 Msamp/sec are supported, in either parallel or multiplexed I/Q modes, and in either
twos complement or unsigned format. Output sampling rates to 130 Msamp/sec are supported in either parallel
or multiplexed I/Q modes, and in either twos complement or unsigned format. A special one-channel output
mode uses both GC1115 output ports to carry odd/even real output samples. The GC1115 includes an
interpolator that increases the output sampling rate by 2x or 4x and optionally modulates the output signal to the
fs/4 center frequency. Dual on-chip RAM banks provide either time-domain snapshots or long-term
histogramming of the internal peak cancellation signal chain at five user-selected points, enabling real-time
monitoring of the CCDF function. A power level meter monitors either the GC1115 input or output power level.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Copyright © 2005, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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