Inverse class-F Power Amplifier Research Articles

Design and experimental validation of class-[formula omitted] GaN power amplifier using a compact harmonic control unit

In this paper, we present the design and implementation of an efficient inverse Class-F (Class-F−1) power amplifier (PA) using a compact Harmonic control unit (HCU). The HCU is implemented using a two-transmission line network that precisely controls the second and third harmonic impedances. The small size of the HCU reduces the circuit’s overall layout and enables easy implementation. Tuning lines are utilized to better match the source and load impedances at the input and output. The design is substantiated by a PCB-fabricated prototype over a frequency range of 1 GHz to 2 GHz. For a bandwidth of 600 MHz (1200–1800 MHz), the proposed PA has a measured power-added efficiency (PAE) and output power of over 65% and 40 dBm, respectively.

Reduced Complexity Sequential Digital Predistortion Technique for 5G Applications

Wireless communication infrastructure is a key enabling technology for smart cities. This paper investigates a novel technique to enhance the performance of 5G base stations by addressing the compensation of nonlinear distortions caused by radiofrequency power amplifiers. For this purpose, a sequential digital predistortion approach that uses twin nonlinear two-box structure along with reduced sampling rates in the feedback path is proposed to implement a linearization system. Such a system is shown to have a correction bandwidth that exceeds the bandwidth of the feedback path. This is achieved by synthesizing the predistortion function in two successive characterization iterations. Both characterizations use the same hardware, which has a reduced sampling rate in the feedback path. Hence, the proposed predistorter scheme does not require any additional hardware compared to standard schemes. Moreover, coarse delay alignment is performed while identifying the memory polynomial function in order to further reduce the computational complexity of the proposed system. Experimental results using an inverse Class-F power amplifier demonstrate the ability of the proposed predistorter to achieve a correction bandwidth of 100 MHz with a feedback sampling rate as low as 25 MSa/s.

Analysis of Efficiency-Limiting Factors Resulting from Transistor Current Source on Class-F and Inverse Class-F Power Amplifiers

Analysis of Efficiency-Limiting Factors Resulting from Transistor Current Source on Class-F and Inverse Class-F Power Amplifiers

Optimization design of fragment-type filtering matching network for continuous inverse class-F power amplifier

Optimization design of fragment-type filtering matching network for continuous inverse class-F power amplifier

High Efficiency Continuous Inverse Class-F Power Amplifier with Modified Current Waveform

Abstract Continuous inverse class-F (CICF) is a recent mode of harmonically-tuned RF power amplifiers used to extend the operating bandwidth of the conventional narrowband class-F−1 power amplifier by producing variable set of drain current waveforms and load admittances that give the same operating efficiency. In this work, a new approach of analysis is developed by suggesting some modified drain current waveforms and comparing the resulting theoretical performance characteristics such as drain efficiency and output RF power with the conventional type. It has been shown that the drain current with a truncated square wave shape can better model the actual behavior of the power amplifier, delivering a theoretical efficiency higher by about 8% than the conventional shape. Besides, a simple analytic technique for extracting the device harmonic load impedances for the desired band is also presented. Based on the theoretical analysis, a 6 W power amplifier circuit was designed and simulated to operate within the frequency band 800 – 1000 MHz. Simulation results indicated that a drain efficiency of values between 82% and 86% was obtained across the specified band.

Extended Inverse Class-F Continuum for Designing Broadband Power Amplifier

The impedance space of the continuous inverse class-F power amplifier (PA) is extended in this paper. Traditionally, for extending impedance space, a reactive term is introduced into the current waveform of the continuous inverse class-F PA. In this paper, two reactive terms are introduced into the current and voltage waveforms simultaneously. The proposed method results in an expansive impedance space for designing broadband continuous inverse class-F PAs. For validating the proposed theory, a broadband PA working over 1.2–4.0[Formula: see text]GHz is designed and fabricated. Experimental results indicate that the fabricated broadband PA delivers a saturation power of 40.2–42.8[Formula: see text]dBm and a drain efficiency of 50.7–69%.

An Analytic Design Approach to Inverse Class-F RF Power Amplifiers

The design of high efficiency inverse class-F (class-F-1) radio frequency (RF) power amplifiers includes extensive measurements to characterize the RF power device by means of the empirical load-pull test setup. This paper presents an alternative characterization approach based on evaluating the load impedances analytically at the desired harmonic frequencies for a high electron mobility transistor (HEMT) in terms of the internal and package elements of the active device. It additionally provides a method for extracting the parasitic elements of the power device as well as determining the optimum load-line resistance using the transistor manufacturer’s large signal model. A new topology for the output matching circuit is also proposed with its synthetic procedure to present the appropriate harmonic load impedances. To verify this methodology, a 900 MHz inverse class-F power amplifier circuit was designed and its performance was tested with the aid of the Keysight ADS software. The simulation results showed an output power of 38 dBm, a power gain of about 13 dB, DC-to-RF efficiency greater than 87%, and an acceptable level of linearity for both GSM and CDMA modulated signals.

Highly efficient broadband continuous inverse Class‐F power amplifier using multistage second harmonic control output matching network

A multistage second harmonic control output matching network is proposed in this article. Through the fundamental and harmonic impedance matching at multiple frequencies in the target band, the accuracy of the fundamental and harmonic impedance of the continuous power amplifier is improved. The efficiency is improved consequently. A highly efficient broadband continuous inverse Class-F power amplifier based on this structure is designed and fabricated using a CGH40010F GaN HEMT packaged device. The measurement results demonstrate that drain efficiency of 71% to 82% and output power of 40.1 to 41.5 dBm is achieved with more than 10 dB gain across 1.35 to 2.35 GHz.

High-Efficiency Low Voltage Inverse Class-F Power Amplifier Design Based on Harmonic Control Network Analysis

A high-efficiency inverse Class-F (Class-F−1) power amplifier (PA) with a low voltage pHEMT is presented in this paper. The design process is based on a novel harmonic control network (HCN), consisting of a bias circuit (BC) and a low pass filter (LPF). The goal is reducing the impact of fundamental frequency reflection on DC supply, elimination of harmonics, improvement of power added efficiency (PAE), shaping the voltage and current waveforms along with enhancing the performance of the PA. The simulation is performed based on the harmonic balance analysis in order of 9. The implemented Class-F−1 PA is simulated and measured at 2.4 GHz. The maximum measured PAE of 76% and the drain efficiency of 82% are achieved, with a low drain voltage of 3 V and 11.2 dB gain under a 16 dBm input power. The proposed PA is fabricated and measurement results validated the simulations.

Simplified First-Pass Design of High-Efficiency Class-F−1 Power Amplifiers Based on Second-Harmonic Minima

This paper investigates the source and implication of efficiency minima that is typically observed during the second-harmonic load–pull of transistor amplifiers. The study starts with the theoretical derivation of time-domain voltage and current waveforms as a function of conduction angle ( $\alpha$ ) at the second-harmonic efficiency minima, where the output power and drain efficiency (DE) are at minimum. Thereafter, this paper unfolds a systematic re-engineering approach that is developed to recover the performance degradation and to exploit the region of efficiency minima in favor of design and implementation of high-efficiency inverse class-F power amplifiers (PAs). Interestingly, the inferences drawn from the in-depth analysis are shown to provide a simplified first-pass design approach that guarantees inverse class-F PA operation without an a priori knowledge of device parasitic elements. Theoretical postulations and simulation results are experimentally validated using an on-wafer active harmonic load–pull and a prototype design using 1.95-mm NXP gallium nitride die at a frequency of 2.6 GHz. The designed PA delivers an output power of 40 dBm with DE of 76% and gain of 12 dB at 3-dB gain compression. The measurement results confirm the theoretical framework reported in this paper.

Investigation of load modulated inverse Class-F power amplifier with extended conduction angle

A novel design space of load modulated (LM) inverse Class-F power amplifiers (PAs) with extended conduction angle is proposed. The effects of the driven level factor β and the biasing operation factor ρ on the third-harmonic generation are discussed. The harmonic generation mechanism shows that the knee voltage effects are the source of third-harmonics for LM inverse Class-F PAs. The definition of the inverse Class-F mode is consistently valid under the circumstance of load modulation in a limited output power back-off (OPBO) range. Meanwhile, the conduction angle θ0 can be extended from π/2 to a limited value (<110°) to keep the standard waveforms of inverse Class-F mode and maintain high efficiency. After introducing the “continuous concept” and the second harmonic manipulation method, the mathematical design space of inverse Class-F PAs with extended conduction angle is derived. Calculation shows that the purely conductive load modulation can enable high back-off efficiency operation for LM inverse Class-F PAs. As proof of concept, a demonstrator amplifier is fabricated and measured. The experimental results show that the power added efficiency (PAE) with optimum Vctrl is improved by 5% over an OPBO range of 6 dB compared with the same PA with fixed Vctrl.

Усилители мощности инверсного класса F – эффективное средство улучшения энергетических характеристик радиопередатчиков

This paper describes energy characteristics of inverse class-F power amplifier with limited quantity of harmonics and defines load characteristics for this type of amplifiers. As a result of the research, allowed ranges of parameter values for class and scheme are defined, where high energy characteristics are saved.

Extended Continuous Inverse Class-F Power Amplifiers With Class-AB Bias Conditions

In this letter, the operation of continuous inverse Class-F (Class-F−1) mode with Class-AB bias conditions is modeled. The extended waveform expression of intrinsic drain current is derived for continuous Class-F−1 power amplifiers (PAs) biased above pinchoff point. Based on the modified current and voltage waveform formulas, the delivered power and efficiency performance is analyzed as a function of conduction angle. Moreover, the design space of fundamental and harmonic load admittances is generalized for any conduction angle between $\pi $ and $2\pi $ . For experimental verification, a broadband PA is implemented with a 6-W LDMOS device. Under a Class-AB bias condition, the fabricated PA exhibits more than 70% power added efficiency and 38-dBm output power with a fractional bandwidth of 62% from 500 to 950 MHz.

On Optimal Truncated Biharmonic Current Waveforms for Class-F and Inverse Class-F Power Amplifiers

In this paper, two-parameter families of periodic current waveforms for class-F and inverse class-F power amplifiers (PAs) are considered. These waveforms are obtained by truncating cosine waveforms composed of dc component and fundamental and either second(k=2)or third(k=3)harmonic. In each period, waveforms are truncated to become zero outside of a prescribed interval (so-called conduction angle). The considered families of waveforms include both discontinuous and continuous waveforms. Fourier series expansion of truncated waveform contains an infinite number of harmonics, although a number of harmonics may be missing. Taking into account common assumptions that for class-F PA the third(n=3)harmonic is missing in current waveform and for inverse class-F PA the second(n=2)harmonic is missing in current waveform, we consider the following four cases: (i)n=k=3,(ii)n=3,k=2,(iii)n=k=2,and (iv)n=2,k=3.We show that, in each of these cases, current waveform enabling maximal efficiency (optimal waveform) of class-F and inverse class-F PA is continuous for all conduction angles of practical interest. Furthermore, we provide closed-form expressions for parameters of optimal current waveforms and maximal efficiency of class-F (inverse class-F) PA in terms of conduction angle only. Two case studies of practical interest for PA design, involving suboptimal current waveforms, along with the results of nonlinear simulation of inverse class-F PA, are also presented.

Design of broadband inverse class-F power amplifier based on resistive-reactive series of inverse continuous modes

Design of broadband inverse class-F power amplifier based on resistive-reactive series of inverse continuous modes

Integrated Inverse Class-F Silicon Power Amplifiers for High Power Efficiency at Microwave and mm-Wave

This paper presents two 2-stage inverse class-F power amplifiers (PAs) at 24 GHz and 38 GHz, integrated in $0.13~\mu \text {m}$ SiGe BiCMOS technology. The PAs are composed of an inverse class-F output stage proceeded by a class-AB driving amplifier. An inter-stage matching network between the driver and output stage delivers an optimal inter-stage power to the output stage with a maximum PAE in the driver amplifier. The output stage’s load network based on multi-resonance LC resonators terminates harmonic impedance explicitly up to the third of the fundamental signal. By leveraging a native low capacitive reactance, the class- $\text {F}^{\mathrm {-1}}$ load network shapes a quasi-rectangular current waveform that effectively contains up to the fifth harmonic spectral component. A high impedance control is limited up to the second harmonic, shaping a half-sinusoid voltage peaking induced by DC, fundamental, and the second harmonic voltage spectra. The 24 GHz PA achieves 50% peak PAE, 16 dBm $\text {OP}_{\mathrm {-1dB}}$ , 18 dBm $\text {P}_{\mathrm {sat}}$ , and 19 dB saturated power gain with 2.3 V supply voltage at 24 GHz. The 24 GHz PA can maintain >45% PAE over 23.5–25.5 GHz and 1.5–2.4 V supply voltage range, manifesting a PAE robustness to the frequency and supply variations. For 38 GHz PA, measurements show 38.5% peak PAE, 15 dBm $\text {OP}_{\mathrm {-1dB}}$ , 17 dBm $\text {P}_{\mathrm {sat}}$ with 15 dB of saturated power gain at the $\text {OP}_{\mathrm {-1dB}}$ point when 2.4 V supply voltage is applied. The 38 GHz PA can sustain >35% PAE over 36–39 GHz and 1.5–2.5 V supply variation. The PAs also are tested under the input of band-limited signals modulated by various modulation schemes including 8-PSK, QAM, 16-QAM, 64-QAM, and 128-QAM, and test results are presented in this paper. The chip size is $0.95\times 0.6$ mm2 for 24 GHz PA and $0.93\times 0.55$ mm2 for 38 GHz PA, including all pads.

X-band inverse class-F GaN internally-matched power amplifier**Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA016801).

An X-band inverse class-F power amplifier is realized by a 1-mm AlGaN/GaN high electron mobility transistor (HEMT). The intrinsic and parasitic components inside the transistor, especially output capacitor Cds, influence the harmonic impedance heavily at the X-band, so compensation design is used for meeting the harmonic condition of inverse class-F on the current source plane. Experiment results show that, in the continuous-wave mode, the power amplifier achieves 61.7% power added efficiency (PAE), which is 16.3% higher than the class-AB power amplifier realized by the same kind of HEMT. To the best of our knowledge, this is the first inverse class-F GaN internally-matched power amplifier, and the PAE is quite high at the X-band.

Improved modeling of GaN HEMTs for predicting thermal and trapping-induced-kink effects

In this paper, an improved modeling approach has been developed and validated for GaN high electron mobility transistors (HEMTs). The proposed analytical model accurately simulates the drain current and its inherent trapping and thermal effects. Genetic-algorithm-based procedure is developed to automatically find the fitting parameters of the model. The developed modeling technique is implemented on a packaged GaN-on-Si HEMT and validated by DC and small-/large-signal RF measurements. The model is also employed for designing and realizing a switch-mode inverse class-F power amplifier. The amplifier simulations showed a very good agreement with RF large-signal measurements.

Highly Efficient Broadband Continuous Inverse Class-F Power Amplifier Design Using Modified Elliptic Low-Pass Filtering Matching Network

This paper proposes a design approach for a broadband and high-efficiency continuous inverse Class-F ( ${\text {CCF}}^{-1}$ ) power amplifier (PA) based on a modified elliptic low-pass filtering (LPF) matching network (MN). From theoretical and practical perspectives, the importance of a swift impedance transition from the higher end of the fundamental frequency band to the lower end of the second harmonic band is discussed, when designing a broadband single-mode PA. After being compared with widely used Chebyshev LPF MNs, a modified elliptic LPF MN, which provides a sharp roll-off, is utilized to provide the required rapid transition. A step-by-step design procedure of the proposed modified elliptic LPF MN is presented. Experimental results show that a high-efficiency ${\text {CCF}}^{-1}$ PA is realized from 1.35 to 2.5 GHz (fractional bandwidth = 60%) with measured drain efficiency of 68%–82% and output power of 41.1–42.5 dBm. When stimulated by a 20-MHz LTE signal with an average output power of approximately 34.5 dBm, the proposed PA, combined with digital pre-distortion, achieved adjacent channel leakage ratios (ACLRs) below $-{\text {45 dBc}}$ , with average efficiency (AE) ranging from 37% to 45.8%. Similar performance is measured when the proposed PA is driven by a dual-band dual-mode modulated signal with a 100-MHz instantaneous bandwidth at a center frequency of 2.14 GHz.

High-Efficiency Power Amplifier Using an Active Second-Harmonic Injection Technique Under Optimized Third-Harmonic Termination

This brief presents an active second-harmonic injection technique to improve the efficiency and bandwidth for high-efficiency power amplifiers (PAs). An optimum third-harmonic termination condition was examined for higher efficiency after the second-harmonic injection using a multiharmonic load-pull simulation. It was determined that the optimum third-harmonic termination is the same as that of the inverse class-F PA. Based on this result, a high-efficiency PA with an optimized third-harmonic termination for the second-harmonic injection was designed for a center frequency of 1 GHz as a main amplifier. The overall system requires an auxiliary second-harmonic amplifier and a diplexer between the main and auxiliary PAs. The PA with an optimized third-harmonic termination for the second-harmonic injection was implemented using a 10-W GaN high-electron-mobility transistor for both the main and auxiliary power stages. Compared with the PA without second-harmonic injection, the bandwidth with a power-added efficiency of more than 80% is extended from 60 (960-1020 MHz) to 180 MHz (880-1060 MHz) after the second-harmonic injection.