class-E Amplifier Research Articles

A High Efficiency Multi-Mode Outphasing RF Power Amplifier With 31.6 dBm Peak Output Power in 45nm CMOS

A high efficiency multi-mode class-E outphasing RF power amplifier (PA) with a passive combining circuit is presented. The multi-mode PA combines multiple class-E amplifier branches and can work in different configurations. The PA improves efficiency at lower power levels by switching ‘on’ and ‘off’ individual branches in a static or dynamic manner and using Efficiency Enhancement Circuit (EEC). The proposed power amplifier is designed in 45nm CMOS technology. The PA delivers 31.6 dBm peak output power at 2.4 GHz with 49.2% drain efficiency in high power single level mode. With 64-QAM long-term evolution (LTE) signal with 10 MHz and 20 MHz bandwidth, −57 dBc and −53 dBc adjacent channel power ratio (ACPR) are obtained in single level outphasing (SLO) mode after digital pre-distortion (DPD). 25% and 33% average drain efficiency are achieved with LTE signal with 6 dB peak-to-average power ratio (PAPR) in single level outphasing and asymmetric multilevel outphasing (AMO) mode, respectively. The PA satisfies the spectral mask requirement of 802.11g WLAN signal with high margin. Error vector magnitude (EVM) of 1.1% (−39.36 dB) is obtained from the PA in single level outphasing high power mode after DPD with 64-QAM LTE signal with 10 MHz bandwidth.

Analysis and Design of Outphasing Transmitter Using Class-E Power Amplifiers With Shunt Capacitances and Shunt Filters

In this paper, a novel outphasing power amplifier (PA) based on class-E amplifiers with shunt capacitances and shunt filters is proposed. The new design provides high drain efficiency for both peak and back-off power levels. A mathematical model for the class-E power amplifier with shunt capacitance and shunt filter is presented. The proposed model enables derivation of load circuit parameters that provide optimum drain efficiency for the peak and back-off power levels using closed form mathematical expressions. Based on this model, an outphasing power amplifier is designed and subsequently implemented using microstrip transmission lines and a GaN HEMT devices. The fabricated power amplifier prototype is optimized for 2.14 GHz and provides drain efficiency of over 60% for back-off power levels up to 8.5 dB. The amplifier demonstrates a 44.3% drain efficiency for 64QAM OFDM modulated signal with 20 MHz bandwidth. Adjacent channel leakage ratio (ACLR) of −39.5 dB and error vector magnitude (EVM) of 0.9 % were achieved after the application of a memory polynomial linearization algorithm.

An automated design procedure for class-E amplifier

An automated design procedure for class-E amplifier

Stacked Class-E Amplifier

In this article, a novel class-E amplifier topology, based on the functioning principle of the stacked converters, is presented. In this amplifier the available output electric power is determined by the addition of the electric power generated by each of the associated devices. Herein, two MOSFETs connected in series are linked, on the one hand, to a dc voltage source and, on the other hand, to a resonant $LC$ circuit and a resistance charge connected in parallel to the capacitor. Both MOSFETs are driven by a gate-to-source square signal allowing a synchronized commutation, promoting a quasi-resonant amplifier behavior similar to that of the classical class-E amplifier; with the characteristic of being able to manage the double of applied dc voltage amplitude and to supply twice electric power to the same load in comparison with the class-E amplifier. This device is able to distribute the same electric power between both MOSFETs, reducing at almost half the magnitude of applied drain-to-source voltage. As a result, voltage stress of each power switch is reduced in comparison with the typical class-E amplifier. Drain efficiency (DE), power added efficiency, and gain of the proposed device were obtained in function of the applied dc voltage.

Full-Duplex High-Speed Simultaneous Communication Technology for Wireless EV Charging

This letter presents a novel simultaneous wireless power and data transmission (SWPDT) system for wireless electric vehicle (EV) charging. The data carrier is injected and extracted by a plug-and-play toroidal-core inductor. Two data carriers of 5 and 6.25 MHz are adopted to achieve bidirectional and full-duplex communication using frequency-division multiplexing. Differential quadrature phase-shift keying modulation is achieved by a Class-E amplifier in the data transmitter. An analog switch circuit is designed to demodulate the data carrier in the data receiver. The proposed method is verified by a prototype that achieves up to 64 kbps full-duplex data transmission under 3.3 kW power transfer. The bit rate and interference immunity of data transmission are greatly improved compared to the reported SWPDT systems, which makes it possible to realize high-speed simultaneous communication in the kilowatt-level wireless EV charging.

On the Optimization of a Class-E Power Amplifier With GaN HEMTs at Megahertz Operation

Class-E power amplifiers have regained academic interest over the past decades due to the introduction of new high-performance wide-bandgap semiconductor devices and the increasing demand for high-efficiency power amplifiers. While these power devices, notably GaN HEMTs, have exceptional performance at megahertz operation, they also display an additional loss component due to $C_{{\rm oss}}$ at this frequency. Unfortunately, the dependence of this loss term on the peak voltage and the device size is the opposite of that of the conduction loss. In this article, we mathematically analyze the operation of a Class-E amplifier to find the optimal input voltage and device sizing where the sum of these two losses is minimized. From this analysis, we have found that the common design approach of maximizing device voltage rating and area to get the best efficiency no longer holds for some operating conditions. Furthermore, we examine the constraints that dictate when this optimization equations can and cannot be used, as well as propose a distributed loss model for the $C_{{\rm oss}}$ loss based on a generalized Steinmetz equation (GSE) to allow this new loss term to be easily simulated. To verify our mathematical analysis and to demonstrate the applications of the proposed GSE-based $C_{{\rm oss}}$ loss model, two design examples are provided. They consist of a choke-input Class-E amplifier at 10 MHz and a variable-resistance Class-E amplifier at 40.68 MHz. The experimental results on these two design examples show good agreements with our analysis.

Methods for assessing the impact of the energy fields of experimental prototypes of contactless charging of implants’ power supply sources on biological objects

Currently existing bioimplants need to be periodically removed from a body to replace a source of energy supply and then reinstall them in a body. It is to a certain degree a threat to the health of the patient and degrades the quality of his life. Developed by the authors contactless charger for transcutaneous energy supply of implantable modules automatically adjusts the power of the electromagnetic field. When implementing the methodology for assessing the impact of the energy fields of experimental prototype of implant power supplies’ contactless charging on biological objects, it was decided to link the transmitting and receiving modules to negative feedback loop, which allows stabilizing the power supplied to the transmitting circuit by the D class amplifier. This solution minimizes the heating of the receiving module, both in the area of the receiving circuit, and in the area of the stabilizer of the charging current of the battery. Thus, in addition to smaller dimensions, the new solution allows optimizing the energy characteristics of the device as a whole.

Singular perturbation‐based model reduction of power electronic circuits

Here, the authors present a model order reduction (MOR) framework based on singular perturbation approximation to accelerate the simulation of high-fidelity power electronic converters. The problem of slow simulation speeds caused due to the wide span of the eigenvalues is mitigated by implementing the proposed framework. The dynamics of the original stiff system is approximated by neglecting the transient contribution of the non-dominant eigenvalues and retaining the steady-state contribution of all the eigenvalues of the system. The model reduction problem has been reformulated to fit the switched nature of these circuits. An error bound for the approximation method has been derived. The method is demonstrated on a DC–DC boost converter and a Class-E amplifier. Significant improvement in speed and reduction in the size of the solution arrays is achieved. It is seen that the reduced-order models are able to replicate the response of the original models and the approximation error is within acceptable limits.

A Class-E Amplifier for a Loosely Coupled Inductive Power Transfer System with Multiple Receivers

We present a method for optimizing the electronic power system for a new type of photobioreactor or photoreactor in general. In the case of photobioreactors, photosynthetic active microorganisms or cells are grown. A novel concept for the illumination of photobioreactors was necessary, as the external illumination of those reactors leads to a limited penetration depth of light. Due to the limited penetration depth, no standard reactors can be use for cultivation, but custom made reactors with very small volume to surface ratio have to be used. This still prevents the technology from a large scale industrial impact. The solution we propose in this paper is an internal illumination via Wireless Light Emitters. This increases the manageable culture volume of photosynthetic active microorganisms or cells. The illumination system is based on floating light emitters, which are powered wirelessly by near field resonant inductive coupling. The floating light emitters are able to illuminate a photobioreactor more homogeneously than external illumination systems do. We designed a class-E amplifier and field coils to produce an intermediate frequency electromagnetic field inside the reactor. An appropriate magnetic flux density was found to be approx. B = 1 mT and the driving frequency is f = 176 kHz. We conducted experiments with a laboratory size photoreactor. The cultivation volume was 30 L containing up to 3000 WLEs. The maximum electric power input was more than 300 W and we calculated an efficiency of up to 76%.

Saturated PAs for High Efficiency: Operation of Saturated Amplifiers Having the Optimum Voltage Waveform to Achieve Maximum Efficiency

High efficiency is a crucial design consideration. This is true not only for power amplifiers (PAs), but also for transmitters such as the Doherty PA and the supply-modulated PA, due to thermal management, reliability, and size [1]-[3] issues. Several PA topologies, e.g., class E, class F, and class F-1, have been proposed to achieve high efficiency [3]-[17]. In the class-E PA, a transistor acts as a switch, which has very low loss. The voltage of the class-E amplifier is supported through the charging and discharging of a transistor's output capacitor, which is parallel with the switch. Because this amplifier tunes all the harmonic components using the LC resonator, it delivers the highest efficiency among the proposed amplifiers. The capacitor's charging step, however, cannot be abrupt; above the theoretical maximum frequency fmax,E, the capacitor cannot be discharged quickly enough to support the ideal waveform [3], [4]. As a result, the efficiency of the class-E PA is significantly degraded at a frequency above fmax,E [3]-[6]. Also, the power density of the class-E amplifier is low because of the low content of the fundamental voltage component.

Efficient ASK Data and Power Transmission by the Class-E With a Switchable Tuned Network

In this paper, we introduce a novel amplitude shift keying modulation technique, suitable for biomedical implants, which works by switching a class-E amplifier between two tuned modes of operation selected by the input data level. Using this technique, transmission of power and data could be accomplished with higher power transfer efficiency compared with the commonly used drain/collector amplitude modulation topology. We also present a practical design methodology covering details of the class-E power amplifier together with its inductive link and the proposed modulator circuit. This methodology can be further utilized in other applications like cochlear implants for which we will compare the performance of both topologies at the same operating conditions. Moreover, we implemented both topologies, and we made various physical measurements at the same inductive link and set-up conditions. Both theoretical and measurement results will justify the advantage of our proposed topology and its overall energy efficiency over a typical one (42% to 30%). Utilizing a carrier frequency of 10 MHz and a modulation index of 10%, our system is able to transmit data at a bit rate of 1 Mbps, while delivering 24-mW power at the nominal coil separation of 6 mm.

A 120 W Class-E Power Module with an Adaptive Power Combiner for a 6.78 MHz Wireless Power Transfer System

In this article, a highly efficient power module is presented with two class-E power amplifiers and an adaptive power combiner for transmitting output powers >100 W at 6.78 MHz in a wireless power transfer system. The losses caused by the combiners and interstage matching circuits or mismatching between the amplifier, and the combiners can significantly reduce the overall efficiency of the power module. To achieve an efficient combination of the output amplifier signals, the adaptive power combiner is proposed based on the consideration of the optimum load impedance characteristics of the power amplifiers. The input impedance of the combiner is designed using series capacitors and resistors between the two input ports of the combiner and the two output signals of the class-E amplifiers at the optimum load condition. The output performances of the proposed module can decrease based on the component mismatch between the two power amplifiers. The proposed power module was implemented on an FR4 PCB, with a 15 mm metal heat sink, and demonstrated an output power of 123.3 W, a power-added efficiency of 85.7%, and a power gain of 25.6 dB at 6.78 MHz. The second harmonic suppression of the module was 37 dBc.

Class-E Amplifiers and Applications at MF, HF, and VHF: Examples and Applications

The class-E amplifier [1], [2], is a member of the switch-mode amplifier family. Switch-mode amplifiers are characterized by their use of transistors, instead of current sources, as switches [3].

Nathan Sokal and the Class-E Amplifier [From the Guest Editor's Desk

The articles in this special issue expand on a session at the 2017 IEEE Microwave Theory and Techniques Society International Microwave Symposium, focuses on Nathan Sokal and the class-E amplifier. It serves both as a memorial to Nat Sokal and an overview of class-E technology. I began interacting and collaborating with Nat in 1973 on RF applications.

Recollections of Nathan Sokal: The Man, His Work, and the Class-E Amplifier

Recollections of Nathan Sokal: The Man, His Work, and the Class-E Amplifier

Microwave Class-E Power Amplifiers: A Brief Review of Essential Concepts in High-Frequency Class-E PAs and Related Circuits

Since Nathan Sokal's invention of the class-E power amplifier (PA), the vast majority of class-E results have been reported at kilohertz and millihertz frequencies, but the concept is increasingly applied in the ultrahigh-frequency (UHF) [1]-[13], microwave [14]-[20], and even millimeter-wave range [21]. The goal of this article is to briefly review some interesting concepts concerning high-frequency class-E PAs and related circuits. (The article on page 26 of this issue, A History of Switching-Mode Class-E Techniques by Andrei Grebennikov and Frederick H. Raab, provides a historical overview of class-E amplifier development.)

A low-area, 43.5% PAE, 0.9 W, Class-E differential power amplifier in 2.4 GHz for IoT applications

In this study, a new Class-E power amplifier (CEPA) with high efficiency, gain and output power for the Internet of things (IoT) applications is presented. Using cross coupling neutralization and fully differential topology in Class-E power amplifier, led to high-power efficiency, high-power gain and better reverses isolation. Cross coupled pair structure and the tuning LC tank oscillator are employed to decrease THD and power consumption. On the other hand, cross coupled capacitor could improve the performance of our design; and differential topology could cause high power efficiency, while cross coupled neutralization could increase PAE and power gain. The main contribution of this structure is employing cross capacitor intelligently. In this way, the capacitor used is not only contributing in stability enhancement, but also in die size diminishing. The performance and frequency range of the presented PA has appropriated it for IoT applications. The proposed Class-E amplifier can attain 29.5 dbm output power at 2.4GHz with 43.5% and 36dB of PAE and power gain, respectively. Furthermore, the proposed power amplifier can deliver 0.9W to load. These results are verified by post layout simulations of the proposed PA performed by 0.18µm standard CMOS technology.

High-frequency resonant gate driver with isolated class-E amplifier

High-frequency resonant gate driver with isolated class-E amplifier

Stability Analysis of Digital Microwave Power Amplifiers

This paper presents a stability analysis of microwave power amplifiers (PAs) driven by binary pulse trains, as in the case of class-S PAs. First, using a simplified digital PA test bench in class-D configuration, different qualitative behaviors are obtained when varying the pulsewidth, including subharmonic and incommensurable oscillations. The mechanisms affecting the stability properties are studied with a harmonic balance-based formulation, by means of pole-zero identification and bifurcation detection. A sufficiently high number of harmonic components must be considered, together with the Krylov decomposition for an efficient computation of the inverse of the Jacobian matrix. It is demonstrated that, when varying the pulsewidth, the distinct pairs of complex-conjugate poles may shift to the right-hand side of the complex plane and, therefore, lead to different kinds of unstable behavior. This phenomenon is related to the dependence of the critical poles on the average value of the input signal. Boundaries of the various types of unstable behavior are traced in the plane defined by the pulse repetition rate and pulsewidth, using bifurcation detection techniques. All the predicted phenomena have been confirmed experimentally. In a second step, the algorithms derived from the simple class-D circuit are transferred to study the stability of a more complex tri-band class-S amplifier. It has been analyzed versus the input bitrate, obtaining a fully stable behavior that has been validated experimentally.

A Novel Fully Differential CMOS Class-E Power Amplifier with Higher Output Power and Efficiency for IoT Application

The class-E amplifiers are used in many devices which need high efficiency, high gain and low power consumption. These types of power amplifiers could be used in the Internet of Thing gadgets, which are widely developed as portable electronic tools nowadays. In this work we present a novel class-E power amplifier (CEPA) that achieves high power gain and high efficiency simultaneously. These approaches are attained by using fully differential topology in our PA design and employing cross coupling neutralization technique. Power consumption of proposed PA is decreased by using LC tank VCO. On the other hand, high power efficiency is achieved by using differential topology. All components are adjusted to have better performance in IoT applications. The proposed CEPA have 29.5 dBm output power in 2.4 GHz, 36 dB power gain and 43.65% PAE. All of our results are verified by the post layout simulations that perform by 0.18 um standard CMOS technology.