A new methodology for designing and implementing high-efficiency broadband Class-E power amplifiers (PAs) using high-order low-pass filter-prototype is proposed in this paper. A GaN transistor is used in this work, which is carefully modeled and characterized to prescribe the optimal output impedance for the broadband Class-E operation. A sixth-order low-pass filter-matching network is designed and implemented for the output matching, which provides optimized fundamental and harmonic impedances within an octave bandwidth (L-band). Simulation and experimental results show that an optimal Class-E PA is realized from 1.2 to 2 GHz (50%) with a measured efficiency of 80%-89%, which is the highest reported today for such a bandwidth. An overall PA bandwidth of 0.9-2.2 GHz (84%) is measured with 10-20-W output power, 10-13-dB gain, and 63%-89% efficiency throughout the band. Furthermore, the Class-E PA is characterized through measurements using constant-envelop global system for mobile communications signals, indicating a favorable adjacent channel power ratio from -40 to -50 dBc within the entire bandwidth.

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Design of Highly Efficient Broadband Class-E Power Amplifier Using Synthesized Low-Pass Matching Networks

This paper describes the design approach employed for achieving approximated continuous Class-F power amplifier (PA) modes over wide bandwidths. The importance of the nonlinear device capacitance for wave-shaping the continuous Class-F voltage and current waveforms is highlighted, thus reducing the device sensitivity to second and third harmonic impedance terminations. By identifying the high-efficiency regions on the reactance plane for harmonic band placement, the design can be reduced to a fundamental matching problem. The distributed simplified real frequency technique synthesis algorithm can then be utilized to achieve wideband operation. Using a 10-W Cree GaN HEMT device, greater than 70% efficiency has been measured over a 51% bandwidth from 1.45 to 2.45 GHz, with output powers of 11-16.8 W. The nonlinear PA was then linearized using digital predistortion with 20-MHz long-term evolution and 40-MHz eight-carrier W-CDMA excitation signals, to attain adjacent channel power ratios below -53 and -49 dBc, respectively. To the best of the authors' knowledge, the measured results represent the best performance obtained from a broadband switch-mode PA, and the best linearized switch-mode performance using 20- and 40-MHz modulated signals.

A Simplified Broadband Design Methodology for Linearized High-Efficiency Continuous Class-F Power Amplifiers

A comprehensive method of designing a broadband Doherty power amplifier is presented in this paper. The essential limitations of bandwidth extension of a Doherty power amplifier are discussed based on the proposed structure of the Doherty power amplifier, which also takes the output matching networks of both sub-amplifiers into account. The broadband matching is realized by applying the simplified real frequency technique with the desired frequency-dependent optimum impedances. GaN transistors were selected to implement the circuit structure.

Broadband Doherty Power Amplifier via Real Frequency Technique

In this paper, an extensive review of the most up-to-date papers on microwave Doherty power amplifiers is presented. The main applications are discussed, together with the employed semiconductor technologies. The different research trends, all aimed to improve the advantages of the Doherty scheme and to solve its inherent drawbacks, are presented. The first considered topic is the maximization of efficiency and/or linearity, where analog and digital techniques are exploited. Another important trend is the bandwidth enlargement of the Doherty architecture, that involves a large number of papers. Multi-band, multi-mode solutions are also considered, using either fixed or reconfigurable solutions. The final section is dedicated to the most significant Doherty integrated implementations.

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The Doherty Power Amplifier: Review of Recent Solutions and Trends

A novel methodology for designing high-frequency broadband harmonic-tuned power amplifiers (PAs) is presented in this paper. Specifically, a hybrid PA mode, transferring between continuous inverse Class-F and continuous Class-F, is for the first time employed to design PAs with optimal performance over more than-an-octave bandwidth. A GaN PA is designed and realized based on this mode-transferring operation using a three-stage transmission-line-based low-pass matching network. Simulation and experimental results show that an in-band PA-mode transferring between continuous Class- F-1 and continuous Class-F is successfully performed. The implemented PA achieves a measured 87% bandwidth from 1.3 to 3.3 GHz, while exhibiting a state-of-the-art performance of >;10-dB gain, 60%-84% efficiency, and 10-W output power throughout this band. Furthermore, modulated evaluation is carried out using a 300-kHz bandwidth 16-quadrature amplitude-modulation signal. Good linearity performance is measured with adjacent channel power ratio from -20 to -35 dBc and an error vector magnitude of 4%-9% over the entire bandwidth.

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Design of Broadband Highly Efficient Harmonic-Tuned Power Amplifier Using In-Band Continuous Class- ${\hbox{F}}^{-1}/{\hbox{F}}$ Mode Transferring

A new Doherty amplifier configuration with an intrinsically broadband characteristic is presented based on the synthesis of key ideas derived from the analyses of the load modulation concept and the conventional Doherty amplifier. Important building blocks to implement the proposed Doherty amplifier structure are outlined, which include the quasi-lumped quarter-wave transmission line, as well as the Klopfenstein taper for broadband impedance matching. A 90-W GaN broadband Doherty amplifier was designed and fabricated and achieved an average peak output power of 49.9 dBm, an average gain of 15.3 dB, and average peak and 6-dB back-off efficiencies of 67.3% and 60.6%, respectively, from 700 to 1000 MHz (35.3% bandwidth). The amplifier is shown to be highly linearizable when driven with 20-MHz WCDMA and long-term evolution signals, achieving adjacent channel power ratio of better than -48 dBc after digital predistortion.

A Modified Doherty Configuration for Broadband Amplification Using Symmetrical Devices

A comprehensive approach for designing broadband and highly efficient power amplifier based on optimal impedance analysis and simplified real frequency technique (SRFT) is presented. Upon determining the impedances for highest efficiency across the bandwidth of interest, the SRFT is used to obtain the optimal matching topology and element values. The effectiveness of this design technique is illustrated using a commercially available 45W GaN device which achieved an average drain efficiency of 63% from 1.9 GHz to 2.9 GHz (∼42%) with an average output power and gain of 45.8 dBm and 10.8 dB respectively. The PA with DPD yielded ACPR below −50dBc when driven with WCDMA and LTE at 2.14 and 2.6 GHz respectively

Design of a broadband and highly efficient 45W GaN power amplifier via simplified real frequency technique

In this paper, we present a mixed-technology extended Doherty amplifier using asymmetrical voltage biasing with an LDMOS main device and a GaN auxiliary device to improve the power utilization factor of the amplifier. Moreover, in contrast to previous work, the amplifier can achieve reconfigurable back-off power ranges and an extended bandwidth without using a mixed-signal setup. The analysis also highlights the relationship between power utilization and the range of the reconfigurable back-off power level. Finally, we demonstrate that the proposed amplifier can be optimally configured for a given modulated signal to obtain the highest average efficiency. A 180-W mixed-technology prototype Doherty amplifier measured peak and back-off efficiencies greater than 50% when configured for 6, 8, and 10 dB of back-off power level at 790, 870, and 960 MHz under continuous-wave stimulus. The amplifier is highly linearizable when driven with 20-MHz long-term evolution and WCDMA signals, achieving adjacent channel power ratio of better than ${-}{\hbox{50}}$ dBc after digital pre-distortion linearization.

A Mixed-Technology Asymmetrically Biased Extended and Reconfigurable Doherty Amplifier With Improved Power Utilization Factor

A modified Doherty combining scheme is proposed that eases the impedance matching requirement and enables excellent AM/AM, AM/PM, and wide bandwidth in practical designs A 350 W, 790 to 960 MHz symmetrical LDMOS Doherty amplifier measured 20 to 21 dB gain as well as peak and back-off efficiencies of 56% to 61% and 48% to 50% respectively across the band The amplifier achieved excellent linearization results when driven with wideband 20 and 50 MHz WCDMA signals and a 35 MHz GMSK signal

A 350 W, 790 to 960 MHz wideband LDMOS doherty amplifier using a modified combining scheme

In this paper, the nonlinearity generation mechanisms causing AM/AM and AM/PM in GaN power amplifier are analyzed from a circuit perspective. The nonlinear device transconductance is found to be the primary source of slow compression in GaN PA's AM/AM characteristic, while the nonlinear input capacitance is the primary source of AM/PM distortion. Using two 800 MHz GaN PAs, we show that matching networks optimized for linearity can minimize a PA's nonlinear distortions and memory effects.

David Yu-Ting Wu

Papers

A Modified Doherty Configuration for Broadband Amplification Using Symmetrical Devices

Design of a broadband and highly efficient 45W GaN power amplifier via simplified real frequency technique

A Mixed-Technology Asymmetrically Biased Extended and Reconfigurable Doherty Amplifier With Improved Power Utilization Factor

A 350 W, 790 to 960 MHz wideband LDMOS doherty amplifier using a modified combining scheme

Linearity of GaN HEMT RF power amplifiers - a circuit perspective