Now showing 1 - 5 of 5
  • Publication
    Broadband radio frequency power amplifiers for 5G wireless communications
    (University College Dublin. School of Electrical and Electronic Engineering, 2021) ;
    Power amplifier (PA) is one of the key components in radio frequency (RF) front-end transceiver and its performance has a critical impact on wireless systems. In the coming fifth-generation (5G) wireless telecommunication system, due to the growing data traffic, there are increasing demands for higher data rate, wider bandwidth and higher spectrum efficiency. Moreover, modulated signals with high peak-to-average power ratio (PAPR) are widely adopted in 5G systems, requiring PAs to provide high power dynamic range. In this thesis, PA design methodologies aiming at performance enhancement with respect to bandwidth, efficiency, linearity and power dynamic range are comprehensively discussed under 5G sub-6 GHz applications. In each topic, both theoretical analysis and circuit verification are provided. Firstly, the broadband solution for maintaining PA's high efficiency is discussed. The broadband continuous mode operation is analyzed. Based on it, a practical design methodology to construct output matching networks for broadband continuous mode PA is proposed. This solution is designed for Monolithic Microwave Integrated Circuit (MMIC) process which enables compact circuit design with high power density. A prototype PA with 0.25 um Gallium Nitride (GaN) MMIC process is implemented. Secondly, in addition to broadband continuous mode PA design, its linearity performance is analyzed. The simulation reveals that the linearity behaviour varies with frequency inside the extended impedance space provided by continuous mode. To unify the linearity in broadband, a circuit level linearity compensation method adopting clipping contours is presented. A design example implemented with 0.25 um GaN HEMT is demonstrated to validate the method. Thirdly, the bandwidth and efficiency performance at output power back-off is investigated. A design methodology for the broadband Doherty power amplifier (DPA) is presented. To extend the bandwidth and output power back-off range simultaneously, a modified load modulation network is proposed. Based on the analysis and case studies, a series of generalized formulas for estimating design parameters are then introduced, offering broadband solution for arbitrary current ratio and power back-off. A prototype DPA is demonstrated and implemented with packaged GaN devices using proposed formulas. The last part proposes another design methodology for enhancing efficiency at output power back-off. A new way of load modulation is realized with a three-stage load modulated power amplifier architecture. This new load modulation mechanism enables flexible output power back-off and efficiency enhancement within large power dynamic range. Under the proposed architecture, the power back-off can be reconfigured without redesigning the circuit.
  • Publication
    Design of Broadband Continuous Mode MMIC Power Amplifiers With Bandwidth Improvement
    This paper presents the design of continuous mode monolithic microwave integrated circuit (MMIC) power amplifiers (PAs) with bandwidth improvement. The output matching network (OMN) satisfying the continuous mode in broadband can be efficiently constructed with LC resonant circuits. The bandwidth can be further improved through generating the new LC unit in OMN with a minimum number of components added possible. Two prototype MMIC PAs are demonstrated with 0.25-µm Gallium Nitride (GaN) MMIC process. The measured drain efficiency is over 39.2% and 38.7% from 4.5 GHz to 6.5 GHz, respectively. When driven by 100-MHz modulated signals, two PAs exhibit great linearity performance with adjacent channel leakage ratio lower than −51.2 dBc and −53.4 dBc with digital predistortion.
      181Scopus© Citations 1
  • 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.
      353Scopus© Citations 2
  • 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.
      314Scopus© Citations 15
  • Publication
    LC resonant circuits based matching networks for continuous mode MMIC power amplifiers
    (Wiley, 2020-12) ;
    This paper presents a practical design methodology to construct output matching networks for broadband continuous mode monolithic microwave integrated circuit (MMIC) power amplifiers (PAs). Unlike conventional harmonic manipulation approaches, combinationsof parallel and series LC resonant circuits are utilized to build the matching networks as it can generate frequency-dependent components and locate the varying impedance of continuous mode. With a proper design, the impedance variation in frequency domain can be mapped to the frequency response of the matching network at the fundamental frequency and the second harmonic simultaneously. Matching network design procedures are demonstrated and results show that the frequency response of the network has verygood approximation with the desired continuous mode conditions. A prototype PA is implemented on 0.25-µm Gallium Nitride (GaN) MMIC process, and tested with both continuous-wave and modulated signals. Measurement results show 50.82%maximum drain efficiency and 8.5 dB gain can be achieved across the operation bandwidth of 5.4 to 6.4 GHz.
      177Scopus© Citations 1