Now showing 1 - 10 of 78
  • Publication
    Dual-loop Model Extraction for Digital Predistortion of Wideband RF Power Amplifiers
    (IEEE, 2011-09) ;
    A dual-loop parameter characterization structure is proposed in order to improve the accuracy of the model extraction in digital predistortion systems. In this concept, a model reference loop is used in conjunction with a model inverse structure for fine tuning the model parameters. This model extraction process does not increase much of the complexity of system implementation but experimental results show that linearization performance can be significantly improved by employing the proposed structure for wideband RF power amplifiers.
      463Scopus© Citations 29
  • Publication
    Pattern Sensing Based Digital Predistortion of RF Power Amplifiers under Dynamical Signal Transmission
    In this paper, a pattern sensing based digital predistortion (DPD) technique for radio frequency (RF) power amplifiers (PAs) under dynamical signal transmission is proposed. Unlike conventional methods where real time re-calibration is required, this approach utilizes a low resolution amplitude-modulation to amplitude-modulation (AM/AM) pattern to sense PA characteristics and then quickly select proper DPD coefficients to linearize the PA. Experimental results show that the proposed method can provide an efficient a nd effective w ay to deal with complex dynamic signal transmission scenarios and maintain very good linearization performance, which is very suitable for future 5G applications.
      206Scopus© Citations 2
  • Publication
    Three-Stage Load Modulated Power Amplifier With Efficiency Enhancement at Power Back-Off
    This article presents the analysis and design of a three-stage load modulated power amplifier (PA), in which three amplifiers, each with different biasing, are connected to a four-port coupler. It is illustrated that, by properly configuring current relationships between the three amplifiers, this new load modulated PA can provide flexible output power back-off (OBO) and achieve high efficiency within a large OBO range. A detailed theoretical analysis and design methodology are given. In this architecture, the OBO level can be adjusted by simply setting bias conditions of the relevant amplifiers that correspond to the current relationships. Therefore, after circuit fabrication, the OBO range can still be reconfigured without redesigning the circuit. To validate the proposed approach, a prototype operating at 3.45 GHz is demonstrated and implemented with gallium nitride (GaN) transistors. The measured saturated output power reaches 45 dBm with 70.1% drain efficiency. At 6-/8-/10-dB OBO, the fabricated PA can provide up to 62.1%/53.8%/47.3% drain efficiency, respectively. When driven by a 60-MHz 9-dB peak-to-average power ratio (PAPR) long-term evolution (LTE) signal, the PA provides 34-dBm average output power with 44.3% average efficiency. Moreover, measurement results prove that the PA can offer efficiency enhancement when the OBO is reconfigured to 8 or 12 dB after fabrication.
      494Scopus© Citations 14
  • Publication
    Complexity-Reduced Model Adaptation for Digital Predistortion of RF Power Amplifiers With Pretraining-Based Feature Extraction
    In this article, we present a new method to reduce the model adaptation complexity for digital predistortion (DPD) of radio frequency (RF) power amplifiers (PAs) under varying operating conditions, using pretrained transformation of model coefficients. Experimental studies show that the PA behavior variations can be effectively tracked using a small number of ``transformed'' coefficients, even with large deviations in its output characteristics. Based on this discovery, to avoid reextracting all the original coefficients every time when the operating condition changes, we propose to conduct a one-time off-line pretraining stage to extract the common features of PA behaviors under different operating conditions first. The online model adaptation process will then only need to identify a small number of transformed coefficients, which can result in a drastic reduction in the computational complexity of the model adaptation process. The proposed solution is validated by experimental results considering varying signal bandwidth and output power levels on a high-efficiency gallium-nitride Doherty PA, where the computational complexity is significantly reduced and the system performance is not compromised.
      647Scopus© Citations 20
  • Publication
    Decomposed Vector Rotation-Based Behavioral Modeling for Digital Predistortion of RF Power Amplifiers
    (IEEE, 2015-01-14)
    A new behavioral model for digital predistortion of radio frequency (RF) power amplifiers (PAs) is proposed in this paper. It is derived from a modified form of the canonical piecewise-linear (CPWL) functions using a decomposed vector rotation (DVR) technique. In this model, the nonlinear basis function is constructed from piecewise vector decomposition, which is completely different from that used in the conventional Volterra series. Theoretical analysis has shown that this model is much more flexible in modeling RF PAs with non-Volterra-like behavior, and experimental results confirmed that the new model can produce excellent performance with a relatively small number of coefficients when compared to conventional models.
      687Scopus© Citations 137
  • Publication
    Optimized Low-Complexity Implementation of Least Squares-Based Model Extraction for Digital Predistortion of RF Power Amplifiers
    (IEEE, 2012-03) ;
    Least squares (LS) estimation is widely used in model extraction of digital predistortion for RF power amplifiers. In order to reduce computational complexity and implementation cost, it is desirable to use a small number of training samples in the model parameter estimation. However, due to strong correlations between data samples in a real transmit signal, the ill-conditioning problem becomes severe in standard LS, which often leads to large errors occurring in model extraction. Using a short training sequence can also cause mismatch between the statistical properties of the training data and the actual signal that the amplifier transmits, which could degrade the linearization performance of the digital predistorter. In this paper, we propose first to use a 1-bit ridge regression algorithm to eliminate the ill-conditioning problem in the LS estimation and then use root-mean-squares based coefficients weighting and averaging approach to reduce the errors caused by the statistical mismatch. Experimental results show that the proposed approach can produce excellent model extraction accuracy with only a very small number of training samples, which dramatically reduces the computational complexity and the system implementation cost.
      781Scopus© Citations 93
  • Publication
    Enhancing Bandwidth and Back-Off Range of Doherty Power Amplifier With Modified Load Modulation Network
    This article presents a novel methodology for designing a broadband Doherty power amplifier (DPA) with extended output power back-off (OBO) range. A modified load modulation network (LMN) is proposed to enhance the OBO range and the bandwidth of the DPA simultaneously. Analysis is conducted to explore the relationship between the proposed LMN parameters and the broadband performance under various OBO levels. Generalized design formulas of the LMN parameters are then introduced to offer the broadband solution for arbitrary current ratios and OBO levels. An asymmetric DPA is demonstrated and implemented with gallium nitride (GaN) transistors using the proposed approach. The fabricated DPA operates from 1.4 to 2.5 GHz with 9-dB OBO range. The measured drain efficiency reaches 61%-75.5% at saturation and 44.6%-54.6% at 9-dB OBO within the operating bandwidth. When driven by a 60-MHz modulated signal with 9-dB peak-to-average power ratio (PAPR), the fabricated DPA attains 47.4%-53.5% average drain efficiency and better than -45.5-dBc adjacent channel leakage ratio (ACLR) after digital predistortion.
      478Scopus© Citations 30
  • Publication
    A 2.0–2.5 GHz frequency-selectable oscillator for digital predistortion model identification of RF power amplifiers
    (IEEE, 2017-04-21) ;
    This paper presents the design of a frequency selectable oscillator used as part of a new data acquisition architecture for digital predistortion (DPD) of RF power amplifiers (PAs). The proposed architecture aims to alleviate the requirement of high sampling rate analog-to-digital-converters (ADCs) in the data acquisition loop. The oscillator utilizes switchable capacitors with a digital control scheme and is capable of operating between 2.0 GHz and 2.5 GHz with an approximate frequency step size of 512 kHz.
      381Scopus© Citations 1
  • Publication
    Peak-to-average power ratio reduction of SFBC MIMO-OFDM signals using unused tones
    Multiple input multiple output techniques combined with orthogonal frequency division multiplexing (MIMO-OFDM) provide a promising approach for wireless systems. However, a serious drawback of the OFDM system is the high peak-toaverage power ratio (PAPR), which may severely affect the power efficiency of RF power amplifiers. In this paper, we propose a simple method to reduce the PAPR of MIMO-OFDM signals based on the use of unused subcarriers. Instead of processing the signals at each transmitter separately, a peak cancelling signal is generated at one antenna and is then applied to all the others with only simple modifications. Simulation has shown that a minimum 2 dB reduction in PAPR can be achieved for all transmit signals using this approach. As the signal processing is nearly all done at a single transmitter, repetition of the operations at each transmitter is avoided, and therefore the overall cost of the system can be significantly reduced.
      204Scopus© Citations 3
  • Publication
    Broadband Fully Integrated GaN Power Amplifier With Embedded Minimum Inductor Bandpass Filter and AM-PM Compensation
    In this paper, we present a design technique for broadband linearized fully integrated GaN power amplifiers (PAs). The minimum inductor bandpass filter structure is used as the output matching network to achieve low loss and high out-of-band attenuation. Two parallel transistors with unbalanced gate biases are used to mitigate nonlinearity of their transconductance and input capacitance, and consequently, compensate AM-PM distortion of the PA. A fully integrated GaN PA prototype provides 35.1–38.9 dBm output power and 40-55% power-added efficiency (PAE) in 2.0–4.0 GHz. For a 64-QAM signal with 8-dB peak-to-average power ratio (PAPR) and 100-MHz bandwidth at 2.4 GHz, average output power of 32.7 dBm and average PAE of 31% are measured with −30.2 dB error vector magnitude (EVM).
      796Scopus© Citations 10