Now showing 1 - 10 of 16
  • Publication
    Analysis and Design of Highly Efficient Wideband RF-Input Sequential Load Modulated Balanced Power Amplifier
    The analysis and design of an RF-input sequential load modulated balanced power amplifier (SLMBA) are presented in this article. Unlike the existing LMBAs, in this new configuration, an over-driven class-B amplifier is used as the carrier amplifier while the balanced PA pair is biased in class-C mode to serve as the peaking amplifier. It is illustrated that the sequential operation greatly extends the high-efficiency power range and enables the proposed SLMBA to achieve high back-off efficiency across a wide bandwidth. An RF-input SLMBA at 3.05-3.55-GHz band using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated SLMBA attains a measured 9.5-10.3-dB gain and 42.3-43.7-dBm saturated power. Drain efficiency of 50.9-64.9/ 46.8-60.7/43.2-51.4% is achieved at 6-/8-/10-dB output power back-off within the designed bandwidth. By changing the bias condition of the carrier device, higher than 49.1% drain efficiency can be obtained within the 12.8-dB output power range at 3.3 GHz. When driven by a 40-MHz orthogonal frequency-division multiplexing (OFDM) signal with 8-dB peak-to-average power ratio (PAPR), the proposed SLMBA achieves adjacent channel leakage ratio (ACLR) better than -25 dBc with an average efficiency of 63.2% without digital predistortion (DPD). When excited by a ten-carrier 200-MHz OFDM signal with 10-dB PAPR, the average efficiency can reach 48.2% and -43.9-dBc ACLR can be obtained after DPD.
      968Scopus© Citations 60
  • Publication
    Magnitude-Selective Affine Function Based Digital Predistorter for RF Power Amplifiers in 5G Small-Cell Transmitters
    (IEEE, 2017-06-09) ; ;
    To accommodate small-cell deployment in future 5G wireless communications, a magnitude-selective affine function based digital predistortion model for RF power amplifiers is proposed. This model has a very simple model structure and is easy to implement. Experimental results showed, by employing this model, substantial hardware resource reduction can be achieved without sacrificing performance in comparison with the existing models.
      513Scopus© Citations 17
  • 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.
      670Scopus© Citations 20
  • Publication
    Extend High Efficiency Range of Doherty Power Amplifier by Modifying Characteristic Impedance of Transmission Lines in Load Modulation Network
    A load modulation network with characteristic impedance-modified transmission lines (TLs) is presented in this paper to extend the efficiency range and bandwidth of the Doherty power amplifier (DPA). Characteristic impedance values for designing the proposed DPA with different high efficiency ranges are given and wideband performance can also be achieved. A DPA with 2.55-3.35 GHz bandwidth using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated DPA achieves a measured 9.2-10.4 dB gain and 44.3-45.4 dBm saturated power. 57.9-75.6% and 47.6-58.8 % drain efficiency is achieved at saturation and 8 dB output power back-off (OBO) within the designed bandwidth, respectively. When driven by a 5-carrier 100 MHz OFDM signal with 8 dB peak to average power ratio (PAPR), the proposed DPA achieves adjacent channel leakage ratio (ACLR) of better than -50 dBc after digital pre-distortion with average efficiency of 53.4%, 55.3% and 56.6% at 2.75, 2.95 and 3.15 GHz centre frequencies.
      349Scopus© Citations 10
  • Publication
    Bandwidth Enhancement of Doherty Power Amplifier Using Modified Load Modulation Network
    A novel Doherty power amplifier (DPA) architecture with extended bandwidth is presented in this paper. A modified load modulation network is introduced to provide impedance condition required by the Doherty operation in a wide frequency range. Analytical parameter solutions of the proposed load modulation network and the related load modulation process are presented. A DPA with 2.80-3.55 GHz bandwidth utilizing commercial GaN transistors is implemented. The fabricated DPA attains a measured 9.3-11.1 gain and 43.0-45.0 dBm saturated power. 50.0-60.6% and 66-78% drain efficiency is obtained at 6 dB output power back-off and saturation throughout the designed band, respectively. Moreover, the back-off drain efficiencies are higher than 55% within 700 MHz bandwidth. When driven by a 6-carrier 120 MHz OFDM signal with 7.0 dB peak to average power ratio, the proposed DPA achieves adjacent channel leakage ratio of better than -50 dBc after digital pre-distortion (DPD) at 3.20 GHz with average efficiency of 53.3%.
      627Scopus© Citations 47
  • Publication
    On-Demand Real-Time Optimizable Dynamic Model Sizing for Digital Predistortion of Broadband RF Power Amplifiers
    (IEEE, 2020-07) ;
    © 1963-2012 IEEE. In this article, we present a dynamic model sizing approach for digital predistortion (DPD) of broadband radio-frequency power amplifiers. By employing a novel model structure adaptation algorithm, the DPD model structure can be adaptively adjusted during its real-time deployment to keep the optimum size and complexity under different operation conditions. Power consumption of DPD can be reduced by on-demand automatic model structure adaptation instead of reusing the same model structure for all power levels and band allocations. To realize dynamic model sizing, the adaptation algorithm explores new potential terms based on prior knowledge of the model structure and prunes the DPD model with a stepwise backward regression method. Experimental results show that the algorithm can quickly find the optimum model structure when the operation condition changes. During the adaptation, it can also maintain robust linearization performance with a relatively low computational complexity and thus demonstrates itself as a suitable solution to the linearization of future broadband wireless systems.
      386Scopus© Citations 20
  • Publication
    Digital Suppression of Transmitter Leakage in FDD RF Transceivers: Aliasing Elimination and Model Selection
    (IEEE, 2017-12-07) ; ;
    The transmitter (TX)-induced interference due to power amplifier nonlinearities poses severe desensitization problems to the receiver chain in frequency-division duplexing transceivers. Due to nonlinear signal process involved, a high sampling rate is normally required in the existing digital suppression approaches, which can result in high cost and high power consumption in wideband systems. In this paper, a new digital suppression model is proposed to cancel the TX leakage at baseband with a low sampling rate. The cancellation model is based on the modified decomposed vector rotation model. With the addition of cross-Term products, the enhanced model is capable of eliminating the aliasing effect arising from the reduced sampling rate. Theoretical analysis of aliasing elimination is presented, and the algorithm is subsequently verified by both simulation and experiment results, confirming the effectiveness and feasibility of the proposed cancellation technique for TX leakage suppression. Compared with conventional solutions, the new approach uses much less hardware resource and consumes much lower power while achieving comparable performance.
      513Scopus© Citations 7
  • Publication
    Broadband RF-Input Continuous-Mode Load-Modulated Balanced Power Amplifier With Input Phase Adjustment
    This article presents the theory and design methodology of broadband RF-input continuous-mode load-modulated balanced power amplifier (CM-LMBA) by introducing the CM output-matching networks in the LMBA architecture. It is illustrated that the CM impedance condition can be achieved by properly adjusting the phase difference between the different PA branches in the proposed CM-LMBA during the entire load modulation process. An RF-input CM-LMBA with 1.45-2.45-GHz bandwidth using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated CM-LMBA attains a measured 11.2-13.4-dB gain and around 40-W saturated power. Power-added efficiency (PAE) of 46.4%-56.5% and 43.2%-50.3% is achieved at 6- and 8-dB output power back-offs throughout the designed band. When driven by a 100-MHz OFDM signal with an 8-dB peak-to-average power ratio (PAPR), the proposed CM-LMBA achieves better than -46-dBc adjacent channel leakage ratio (ACLR) and higher than 45% average PAE after digital predistortion at 1.8 and 2.1 GHz.
      710Scopus© Citations 51
  • Publication
    Real-Time Single Channel Over-the-Air Data Acquisition for Digital Predistortion of 5G Massive MIMO Wireless Transmitters
    In this paper, a single channel over-the-air (OTA) data acquisition approach for real-time calibration of digital predistorter in multiple-input multiple-output transmitters is proposed. By using the data acquired from the far-field OTA tests, the output of each power amplifier (PA) can be virtually reconstructed and thus the linearization reference at the main beam direction can be accurately estimated. Digital predistortion (DPD) can therefore be effectively constructed without direct measurement at PA output. Experimental results demonstrate that the proposed scheme can accurately estimate far-field main beam data and the proposed DPD can achieve excellent linearization performance.
      439Scopus© Citations 15
  • Publication
    Digital Suppression of Transmitter Leakage in FDD RF Transceivers With an Enhanced Low-Sampling Rate Behavioral Model
    With continuously increasing of signal bandwidth, the transmitter leakage issue in frequency division duplexer (FDD) transceivers becomes severer. In this letter, an enhanced behavioral model is proposed to suppress FDD transmitter leakage at a low-sampling rate. The theoretical analysis is provided to explain the operation principle of the proposed model. The experimental results show that the proposed model can effectively increase the accuracy of generating sideband replica and thus improve the suppression performance.
      374Scopus© Citations 4