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Maxim > Design Support > Technical Documents > Application Notes > Basestations/Wireless Infrastructure > APP 4611
Maxim > Design Support > Technical Documents > Application Notes > Communications Circuits > APP 4611
Maxim > Design Support > Technical Documents > Application Notes > Wireless and RF > APP 4611
Keywords: predistorter, RF, WCDMA, modulation, linarization, feed forward, FFD, digital predistortion, DPD, AM,
PM, ACPR, class AB amplifier, phase distortion, gain, compression, EVM, intermodulation, bias, IM3, Rohde &
Schwarz, amptune
APPLICATION NOTE 4611
Tuning the MAX2009/MAX2010 RF Predistorters for
Optimal Performance
By: Ruediger Brodowski
Oct 02, 2009
Abstract:
Linear modulation
schemes like WCDMA allow higher data rates and multiple wireless connections per
carrier, but introduce a high peak-to-average ratio of the carrier signals. Consequently, the amplifier now has to be
largely backed off to meet the limits for adjacent-channel leakage. Since the PA's (power amplifier's) efficiency
decreases the more the PA is backed off, linearization techniques are applied to combine a maximum efficiency
with a minimum of IM (intermodulation). This application note details different techniques for tuning the
MAX2009/MAX2010 analog predistorters while optimizing the ICs' performance.
Introduction
Linear modulation schemes like WCDMA allow higher data rates and multiple
wireless connections per carrier, but they also introduce a high peak-to-
average ratio of the carrier signals. Unlike constant envelope-modulation
schemes where PAs (power amplifiers) can be driven into compression, the
amplifier now has to be largely backed off to meet the limits for adjacent-
channel leakage. Since PA efficiency decreases the more the PA is backed
off, linearization techniques are applied to combine a maximum efficiency with
a minimum of IM (intermodulation).
Well-known linearization technologies, e.g., feed forward (FFW) and digital predistortion (DPD) are expensive and
need considerable space. Consequently, a method is needed that works with few components and is easy to
handle.
The MAX2009/MAX2010 analog RF predistorters, when compared to FFW or DPD, need very few external
components, are easy to adjust, and give a considerable amount of linearization.
The MAX2009/MAX2010 rely on AM-AM and AM-PM curve correction at the RF frequencies to improve IM3 and
ACPR performance. Internally, the chip measures the signal power and distorts the phase and gain predistortion as
a function of the current signal's amplitude. Although AM-AM and AM-PM correction rely on memory-less circuits,
Class AB amplifiers can still benefit from the negative distortion created by the Maxim® parts and significantly
improve performance.
As with all linearization techniques, a good signal-clipping algorithm which reduces the peak-to-average ratio of the
signals before the PA (without exceeding the EMV limits) is helpful for analog predistortion. Using the
MAX2009/MAX2010 together with proper signal clipping is a good combination.
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