Now showing 1 - 10 of 16
  • 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.
      223Scopus© Citations 15
  • 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.
      506Scopus© Citations 27
  • 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.
      428Scopus© Citations 13
  • 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.
      301Scopus© Citations 4
  • Publication
    OTA-Based Data Acquisition and Signal Separation for Digital Predistortion of Multi-User MIMO Transmitters in 5G
    In this paper, a non-interruptive over-the-air (OTA) data acquisition method is presented to characterize system nonlinearity and calibrate digital predistortion (DPD) in multi-user (MU) multiple-input multiple-output (MIMO) transmitters with low hardware complexity. Based on a unified system model for fully-digital and hybrid MU-MIMO transmitters, the requirements and difficulties of data acquisition for MU-MIMO DPD are outlined first. A versatile OTA data acquisition technique, featuring a multi-observation forward modelling procedure, is thereby developed to obtain power amplifier (PA) output without interrupting the operation of the MIMO transmitters. By using this method, the output of each PA can be reconstructed instead of directly measuring each PA's output, even when the output signals of PAs are correlated. DPD can therefore be effectively constructed to mitigate the distortion. Experimental results demonstrate that the proposed approach can accurately estimate each PA output and linearize all PAs in the array.
      216Scopus© Citations 4
  • Publication
    Multiband Dual-Mode Doherty Power Amplifier Employing Phase Periodic Matching Network and Reciprocal Gate Bias for 5G Applications
    This article presents a novel method to design the multiband Doherty power amplifier (DPA). It is illustrated that phase periodic matching networks (PPMNs) can be used as multiband impedance inverters, off-set elements, and phase compensators to realize multiband DPAs. Moreover, the number of Doherty operation bands can be further increased by employing the reciprocal gate biases. A six-band dual-mode DPA with 1.8-2.2-/3.9-4.3-GHz operation bands in Mode I and 1.52-1.72-/2.38-2.53-/3.67-3.82-/4.53-4.68-GHz operation bands in Mode II using commercial GaN transistors is designed and implemented to validate the proposed method. The fabricated DPA achieves 8.7-13.5-dB gain and 39.6-41.5-dBm peak output power at all the designed bands. Drain efficiency of 49.2%-54.5% and 42.2%-56.7% is measured at a 6-dB output back-off in Mode I and Mode II, respectively. When stimulated by a five-carrier 100-MHz OFDM signal with a 7.7-dB peak-to-average power ratio (PAPR), adjacent channel power ratio (ACPR) of better than -48.9 dBc can be obtained by the proposed DPA after digital predistortion with 35.5%-50.1% average drain efficiency at 1.65/1.95/2.45/3.75/4.1/4.6 GHz, respectively.
      369Scopus© Citations 18
  • Publication
    Sampling Rate Reduction for Digital Predistortion of Broadband RF Power Amplifiers
    In this article, we present a novel technique to build digital predistorters that can linearize broadband power amplifiers (PAs) using reduced sampling rates. In contrast to conventional digital predistortion (DPD) where oversampling is necessary to avoid aliasing effect, the proposed method cancels the aliasing distortion using a sliced multistage cancellation scheme. A large reduction of sampling rate can be achieved in digital implementation of DPD, significantly reducing power consumption and implementation cost. Experimental results show that a DPD with a sampling rate of merely 1.5x, instead of 5x, signal bandwidth, can still produce satisfactory performance within the linearization bandwidth but consume only one-third of power, compared with that using the conventional approaches. The proposed technique provides a promising solution for the next-generation 5G systems, where large signal bandwidths are required.
      632Scopus© Citations 21
  • Publication
    Mixture of Experts Approach for Behavioral Modeling of RF Power Amplifiers
    Piece-wise (PW) behavioral models are commonly adopted when modeling RF power amplifiers (PAs) that exhibit strong amplitude dependent nonlinear distortion characteristics. In this paper, we consider a new PW model for PAs based on the mixture of experts (ME) approach. We first introduce the ME framework theory while also extend it such that it can be applied to model complex baseband signals and nonlinearities. Then, we show how the ME model allows overcoming some of the intrinsic shortcomings that existing PW behavioral models commonly exhibit, which translates into improved modeling accuracy. The proposed solution is validated with extensive RF measurements on a load modulated balanced PA at 2.1 GHz, excited by a 320 MHz OFDM signal, and is benchmarked against several state-of-the art PW models.
      119Scopus© Citations 2
  • 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.
      186Scopus© Citations 9
  • 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.
      353Scopus© Citations 7