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An adaptive algorithm unique to an innovative DPD linearization circuit
In wireless communication systems, achieving a balance between power amplifier (PA) linearity and efficiency is a critical challenge. Engineers are continuously seeking advanced digital predistortion (DPD) techniques that can enhance the performance of wideband RF power amplifiers while maintaining high efficiency. This article explores various digital predistortion methods and introduces an innovative adaptive algorithm designed for improved linearization in modern RF systems.
Volterra-based adaptive DPD technology has emerged as a promising solution to achieve both high linearity and efficiency in RF PAs. By extending the linear operating range of the amplifier and reducing the crest factor, this approach allows for more powerful signal transmission with greater energy efficiency. It also meets the stringent requirements for spectrum efficiency and modulation accuracy. The effectiveness of such techniques is particularly important in next-generation wireless systems where higher bandwidths and complex modulation schemes are becoming the norm.
One notable implementation of this technology is found in Texas Instruments’ GC5322 integrated transmitter solution. This highly integrated application-specific standard product (ASSP), fabricated in a 0.13-micron CMOS process, includes digital up-conversion, crest factor reduction, and digital pre-distortion. Designed to be "modulation-agnostic," it supports a 30 MHz signal bandwidth and offers significant improvements in peak-to-average power ratio (PAR) for 3G signals and adjacent channel power ratio (ACPR) for OFDM systems. It can correct nonlinearities up to order 11 and handle PA storage effects of up to 200 ns, significantly improving ACPR and power efficiency by over 20 dB and 4 times respectively.
With the growing demand for energy-efficient technologies and increasing spectral efficiency needs, power amplifier linearity is becoming a key design consideration for future base stations. Traditional analog and RF-based linearization techniques are being replaced by more efficient and cost-effective digital solutions, especially with the advancement of DSP and ASSP computing power.
The GC5322 transmitter solution integrates DUC, CFR, and DPD into a single chip, supporting a wide range of air interface standards including CDMA2000, WCDMA, TD-SCDMA, WiMAX, and LTE. Its flexibility makes it suitable for various power amplifier topologies, from Class A/B to Doherty amplifiers, and supports signal bandwidths up to 30 MHz.
Non-constant envelope modulation schemes, such as those used in 3G and emerging standards, offer better spectral efficiency but come with higher peak-to-average ratios, which challenge PA efficiency. This leads to increased power consumption and cooling costs in base stations. Efficient linearization techniques like DPD help mitigate these issues, making them essential in today’s wireless infrastructure.
In conclusion, the need for accurate modeling in predistortion schemes is crucial for achieving optimal performance. As RF systems evolve, so too must the models and algorithms used to maintain signal integrity and system efficiency. The next section will delve deeper into the importance of precise predistorter modeling in modern wireless applications.