Adaptive digital baseband predistortion for RF power amplifier linearization (original) (raw)
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A Convergence-Free Predistortion Technique for Adaptive Linearisation of RF Power Amplifiers
Analog Integrated Circuits and Signal Processing, 2004
Adaptive digital baseband predistortion is a well-known linearisation technique for removing intermodulation products that radio frequency power amplifiers (PAs) introduce. This paper proposes a new baseband predistortion method that is based on a non-iterative, fast adaptation algorithm without convergence restrictions. The response of the PA in a batch of training magnitude stimuli is used for the computation of the predistortion gain. The latter is directly extracted in rectangular form without prior transformations and AM/AM and AM/PM non-linearities sequential estimation. The influence of the gain table size and the imperfections of the modulator and demodulator in the method's performance are examined. Experimental measurements of an in-house prototype show a linearity improvement of about 25 dB.
2012
This paper presents an overview of different Digital Predistortion (DPD) techniques used in microwave Power Amplifier (PA) linearization. Different DPD approaches are considered with both static and dynamic (memory effects) behavioral models. The most suitable solutions for facing the new challenges to linearize high-bandwidth amplifiers are discussed, which is demanded by most of the new telecommunications standards and emergent technologies.
Adaptive Digital Predistortion for Power Amplifier Linearization
2016
The new radio communication systems move toward the use of non-constant envelops modulations and toward the application of spread spectrum techniques. The modulated output envelops of such signals are strongly dynamic and so, the influence of the nonlinearities of the transmitters are not negligible. A solution consists of correcting the amplifier while associating with it a linearization device so that the whole amplifier-linearizer system behaves in a quasi-linear manner up to practically the power of saturation. The main part is dedicated to the study of a new adaptive digital predistorter that can be applied to wide band signals used in third generation systems. After a state of the art of the predistortion system a new technique or improvement of adaptation techniques are proposed and estimated by simulation. The influence of the main sources of imperfections on the system is analyzed. The work also compares the complexity of the different approaches of predistortion by LUT, po...
On firm ground for highly-developed nonlinear modeling theories, the Digital predistortion (DPD) is a practice of compensating the basic nonlinear distortion caused by power amplifiers (PAs). After nearly 30 years of extensive studies, it has become the most popular and mature technology utilized for linearization of commercial transmitters. However, in the context of rapid development of high-speed wireless communications and the application of various digital technologies, the design and implementation of DPD have been confronted with various new challenges. The DPD involves almost all the aspects for a frontend design, thus implementation of actual DPD system is not an easy task. This report provides a comprehensive overview of important aspects for DPD design and considers mostly parasitical issues that can be found useful to develop a DPD system successfully.
2006
This paper investigates the robustness of the digital predistortion function synthesis process applied to linearize a highly non linear RF power amplifier. For this purpose, a 100-watts peak power amplifier designed for UMTS applications biased in deep class AB is used. Two approaches have been compared: the polynomial curve fitting of the measured AM/AM and AM/PM characteristics and the look-up tables synthesis using the smoothed versions of these same non linear curves. The polynomial based fitting presents badly conditioned matrices that make this approach unpractical for the considered non linearity shape particularly for DSP implementation of the synthesis procedure. The accuracy of both approaches was assessed by measuring the adjacent channel power ratio at the output of the power amplifier under a 2carriers W-CDMA signal. The look-up tables approach based on the averaging technique showed better correction capabilities than the polynomial based fitting.
Digital Predistorter is a cost-effective solution to compensate for the nonlinear distortions appearing in the RF power amplifiers (PAs). The indirect learning scheme is widely implemented because of its flexibility to eliminate the requirement for building a closed-loop real time system, which dramatically reduces the complexity for measurement setup. However, such scheme is sensitive to the measurement noise that may cause biasing in the coefficients estimation. To minimize the influence of measurement noise and simultaneously enable the open-loop implementation, we propose a predistortion technique that first model the PA and then generates predistorted signal iteratively through a feedback configured structure to avoid using the noisy signal when performing the inverse model estimation. Unlike the indirect learning which estimates the postinverse of the PA, our predistortion is based on the preinverse of the PA. Both simulations and measurements show that utilizing the proposed predistortion can obtain adjacent channel power ratio (ACPR) improvement in wideband code division multiple access (WCDMA) signal test compared with the conventional memory polynomial predistortion based on indirect learning.
Frequency-Selective Predistortion Linearization of RF Power Amplifiers
IEEE Transactions on Microwave Theory and Techniques, 2000
This paper presents a frequency-selective RF vector predistortion linearization system for RF multicarrier power amplifiers (PAs) affected by strong differential memory effects. Differential memory effects can be revealed in two-tone experiment by the divergence for increasing tone-spacing of the vector Volterra coefficients associated with the lower and upper intermodulations tones. Using large-signal vector measurement with a large-singal network analyzer, a class-AB LDMOS RF PA is demonstrated to exhibit a strong differential memory effect for modulation bandwidth above 0.3 MHz. New frequency-selective RF and baseband predistortion linearization algorithms are proposed to separately address the linearization requirements of the interband and inband intermodulation products of both the lower and upper sidebands. Theoretical verification of the algorithms are demonstrated with MATLAB simulations using a Volterra/Wiener PA model with memory effects. The baseband linearization algorithm is next implemented in a field-programmable gate array and experimentally investigated for the linearization of the class-AB LDMOS PA for two carrier wideband code-division multiple-access signals. The ability of the algorithm to selectively linearize the two interband and four inband intermodulation products is demonstrated. Adjacent channel leakage ratio of up to 45 dBc for inband and interband are demonstrated experimentally at twice the typical fractional bandwidth.