Effect of losses in an active device and harmonic network on the efficiency of Class F and inverse Class F power amplifiers

High frequency class F and inverse class F power amplifiers obtain high efficiency of dc to ac power conversion, by reducing the overlap of voltage and current waveforms at the output of the active device, to ensure that the power dissipated in the resistance Ron of the active device is minimised. In this paper the active device is modelled as a switch in series with resistance Ron 0 to 5Ω. For ideal switch voltage / current waveforms and equal dc input power for both amplifiers the efficiency of power conversion is compared. To confirm the predicted results ideal lossless load harmonic networks using lumped elements were designed to meet all frequency conditions of the two amplifiers. These networks were done used in Advanced Design System (ADS) software for Ron=0, 2 and 4 Ω. The predicted efficiency for 2Ω and 4 Ω were 80% and 60% and the obtained simulation efficiency were 83.2% and 65.5% for class F amplifier. For the inverse class F amplifier the predicted efficiency was 87.3% and 74.5% and for the simulation results it was 87.26% and 74.4%. Above predicted and simulated results show that the resistance Ron has less effect on the efficiency of inverse class F than for class F amplifier. As lumped elements can not be used at high frequencies they were replaced initially with lossless transmission lines and then by microstrip lines to also investigate also how copper and dielectric losses affect the efficiency of power conversion

The Class-E/F Family of ZVS Switching Amplifiers

A new family of switching amplifiers, each member having some of the features of both class E and inverse F, is introduced. These class-E/F amplifiers have class-E features such as incorporation of the transistor parasitic capacitance into the circuit, exact truly switching time-domain solutions, and allowance for zero-voltage-switching operation. Additionally, some number of harmonics may be tuned in the fashion of inverse class F in order to achieve more desirable voltage and current waveforms for improved performance. Operational waveforms for several implementations are presented, and efficiency estimates are compared to class-E

Continuous Inverse Class-F GaN Power Amplifier with 70% Efficiency over 1.4-2 GHz Bandwidth

This work presents the design and experimental characterization of a wideband continuous inverse class-F power amplifier, covering several bands in the 5G FR1 frequency range, and thus suitable for base station applications. The design spaces of the class-F and inverse class-F in terms of input and output terminations are reviewed and compared, and the design choices relative to an implementation using a packaged device are described. Measurements show a saturated output power of 40 dBm, with corresponding efficiency and gain higher than 70% and 13 dB, respectively, over 1.4-2 GHz. The performance is well in line with the state of the art and is accurately predicted by simulations, proving the effectiveness of the design strategy

Class F And Inverse Class F Power Amplifier Subject To Electrical Stress Effect

This study investigated the Class F and inverse Class F RF power amplifier operating at 5.8 GHz. The major challenging issue in design and implementation of CMOS power transistor is the breakdown voltage especially in sub-micron CMOS technologies. In order to eliminate this problem a Cascode topologies were implemented to reduce the Drain-toSource voltage (stress). A Cascode Class F & Inverse Class F RF power amplifier were designed, and optimized in order to improve efficiency and reliability using 0.18µm CMOS technology process. A 50% decrease in the stress has been achieved in the Cascode class-F and Inverse class F amplifiers. The sensitivity and temperature effect were investigated using BSIM-4 model. Such an amplifier was designed and optimized for a good sensitivity. A substrate bias circuit was implemented to achieve a good sensitivity. Recommendations were made for future advancements for modification and optimization of the class F and inverse class F circuit by the application of other stress reduction strategies, and improvement of the substrate bias circuit for a better sensitivity

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

Assessment of the Performance of Inverse Class-F Power Amplifiers in a Discrete Doherty Architecture

This work presents an assessment, at simulation and experimental levels, of the performance of inverse class-F power amplifiers in a Doherty architecture. Two connectorized amplifier modules, designed for standalone operation, are adopted to construct a quasi-balanced Doherty architecture exploiting 3-dB 90° hybrid couplers at the input and output to demonstrate the concept. The Doherty architecture shows competitive performance at 1.8 GHz, with 43 dBm output power and around 60% efficiency from saturation to 6 dB output power back-off. The performance is in line with the state of the art of integrated load-modulated amplifiers, demonstrating the validity of the approach

Time-Domain Analysis of Optimum Bias Point in Inverse Class-F Power Amplifiers

The optimum bias point for an inverse class-F power amplifier is discussed in this paper from a time-domain point of view. It is shown that the inverse class-F power amplifier should be biased in shallow triode region where the bias current is slightly higher than DC current when driven into compression. Lower bias currents can cause significant efficiency degradation due to peaking in the drain-source voltage. Simulation results show that drain efficiency at 6dB over drive drops from 83.4% to 65.2% when bias current is reduced by 34% from optimum bias current. Moreover, it is shown that if the bias current is too high, then the efficiency under power back off is reduced

Wideband Reconfigurable Harmonically Tuned GaN SSPA for Cognitive Radios

The paper presents the architecture of a wideband reconfigurable harmonically-tuned Gallium Nitrate (GaN) Solid State Power Amplifier (SSPA) for cognitive radios. When interfaced with the physical layer of a cognitive communication system, this amplifier topology offers broadband high efficiency through the use of multiple tuned input/output matching networks. This feature enables the cognitive radio to reconfigure the operating frequency without sacrificing efficiency. This paper additionally presents as a proof-of-concept the design, fabrication, and test results for a GaN inverse class-F type amplifier operating at X-band (8.4 GHz) that achieves a maximum output power of 5.14-W, Power Added Efficiency (PAE) of 38.6, and Drain Efficiency (DE) of 48.9 under continuous wave (CW) operation

Experimental Validation of a Four-Way Outphasing Combiner for Microwave Power Amplification

This letter presents a 2.14 GHz, four-way power combining and outphasing system for high-power amplifiers such as those in radio basestations (RBS). The combiner is ideally lossless, and enables power control through load modulation of the power amplifiers (PAs). A discrete-component power combiner is designed and characterized, and combined with inverse Class-F PAs using GaN HEMT devices to develop a complete PA system. We demonstrate the effectiveness of the system over a range of outphasing control angles. This first-ever microwave implementation of the outphasing system has a peak CW drain efficiency of 68.9%, with efficiency greater than 55% over a 5.5 dB power range. It provides an average modulated efficiency of 57% for a W-CDMA signal with 3.47 dB peak to average power ratio (PAPR) at 42 dBm output power.Massachusetts Institute of Technology. Center for Integrated Circuits and System

Multiband Reconfigurable Harmonically Tuned Gallium Nitride (GaN) Solid-State Power Amplifier (SSPA) for Cognitive Radios

The paper presents the architecture of a wideband reconfigurable harmonically-tuned Gallium Nitride (GaN) Solid State Power Amplifier (SSPA) for cognitive radios. When interfaced with the physical layer of a cognitive communication system, this amplifier topology offers broadband high efficiency through the use of multiple tuned input/output matching networks. This feature enables the cognitive radio to reconfigure the operating frequency without sacrificing efficiency. This paper additionally presents as a proof-of-concept the design, fabrication, and test results for a GaN inverse Class-F type amplifier operating at X-band (8.4 GHz) that achieves a maximum output power of 5.14-W, Power Added Efficiency (PAE) of 38.6 percent, and Drain Efficiency (DE) of 48.9 percent under continuous wave (CW) operation