class-E Power Amplifier Research Articles

High Efficiency Class-E and Compact Doherty Power Amplifiers with Novel Harmonics Termination for Handset Applications

High Efficiency Class-E and Compact Doherty Power Amplifiers with Novel Harmonics Termination for Handset Applications

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.

Theory and Implementation of a Load-Mismatch Protective Class-E PA System

Highly efficient switch-mode class-E power amplifiers (PAs) are sensitive to load impedance variations. For voltage standing wave ratios (VSWRs) up to 10:1, the peak switch voltage and the average switch current can increase by a factor of 1.7 and 2.5, respectively, relative to those under nominal load conditions, imposing serious reliability risks. This paper describes a technique to self-protect class-E PAs to decrease their sensitivity to load variations, relying on the tuning of the switch-tank relative-resonance frequency, implemented by an on-chip switched-capacitor bank (SCB). To validate the technique, load-pull measurements are conducted on a class-E PA implemented in a standard 65-nm CMOS technology, employing an off-chip matching network, augmented with a fully automated self-protective control loop. Under nominal conditions, the PA provides 17.8 dBm at 1.4 GHz into $50\,{\Omega }$ from a 1.2-V supply with 67% efficiency. The proposed self-protective PA can reduce its peak switch voltage below the technology- and switch design-related limit for any load with a VSWR up to 19:1 while not considerably impacting output power and efficiency, which see a maximum degradation of 1.6 dB and 6%, respectively. Furthermore, a class-E PA designed to safely handle $2.5{\times }$ the nominal average switch current can reliably operate for VSWRs up to 19:1 when protected with our technique.

System Linearity-Based Characterization of High-Frequency Multilevel DC–DC Converters forS-Band EER Transmitters

In modern telecommunications systems, the requirements for the amount and speed of transmitted data are increasing rapidly. For better spectral efficiency, complex-type modulations [quadrature amplitude modulation (QAM) and orthogonal frequency-division multiplexing (OFDM)] are used, resulting in high peak-to-average power ratio (PAPR) signals. As a consequence, when conventional linear amplifiers (classes A and AB) are used in transmitters, both prominent linearity and poor efficiency are assured. The efficiency of the transmitters can be significantly improved using some of the popular techniques: Kahn envelope elimination and restoration (EER) principle, envelope tracking (ET) technique, Doherty amplifier, and Chireix’s amplifier. In this article, two different approaches in supplying a 2.4-GHz class-E power amplifier (PA) ( ${S}$ -band) based on the EER technique are analyzed and compared. The consistent part of the EER transmitters is a switched-capacitor-based voltage divider combined with a switching structure—analog multiplexer, in the envelope amplifiers (EAs) and a class-E PA. The analog multiplexer is assisted with a series linear regulator in the first system and a fourth-order ${LC}$ filter in the second system, providing supply modulation for the PA. The systems are compared in terms of efficiency and system linearity using the standard metrics [error vector magnitude (EVM) and adjacent channel power ratio (ACPR)]. Special consideration is devoted to the characterization of how the EAs affect the quality of the RF output signal. It is shown that the tested EER transmitters can reproduce 16-QAM and 64-QAM signals up to 2.5 MHz, manifesting an average efficiency of about 32% with the first transmitter, and 16-QAM signals up to 660 kHz RF bandwidth and average efficiency of 44% with the second transmitter. A software tool that accurately estimates the EA linearity is utilized and successfully tested on both EER transmitters.

Parameter Analysis and Optimization of Class-E Power Amplifier Used in Wireless Power Transfer System

In this paper, a steady-state matrix analysis method is introduced to analyze the output characteristics of the class-E power amplifier used in a wireless power transfer (WPT) system, which takes the inductance resistance, on-resistance and leakage current of metal-oxide-semiconductor field effect transistor (MOSFET) into account so that the results can be closer to the actual value. On this basis, the parameters of the class-E power amplifier are optimized, and the output power is improved under the premise of keeping the efficiency unchanged. Finally, the output characteristics of the amplifier before and after optimization are compared by an experiment, while the B-field strength around the WPT system is studied through simulation. The experimental results verify the correctness and feasibility of the optimization method based on steady-state matrix analysis.

Towards a Miniaturized 3D Receiver WPT System for Capsule Endoscopy.

The optimization, manufacturing, and performance characterization of a miniaturized 3D receiver (RX)-based wireless power transfer (WPT) system fed by a multi-transmitter (multi-TX) array is presented in this study for applications in capsule endoscopy (CE). The 200 mm outer diameter, 35 μm thick printed spiral TX coils of 2.8 g weight, is manufactured on a flexible substrate to enable bendability and portability of the transmitters by the patients. The 8.9 mm diameter—4.8 mm long, miniaturized 3D RX—includes a 4 mm diameter ferrite road to increase power transfer efficiency (PTE) and is dimensionally compatible for insertion into current endoscopic capsules. The multi-TX is activated using a custom-made high-efficiency dual class-E power amplifier operated in subnominal condition. A resulting link and system PTE of 1% and 0.7%, respectively, inside a phantom tissue is demonstrated for the proposed 3D WPT system. The specific absorption rate (SAR) is simulated using the HFSSTM software (15.0) at 0.66 W/kg at 1 MHz operation frequency, which is below the IEEE guidelines for tissue safety. The maximum variation in temperature was also measured as 1.9 °C for the typical duration of the capsule’s travel in the gastrointestinal tract to demonstrate the patients’ tissues safety.

Energy-Efficient Wireless Communications: From Energy Modeling to Performance Evaluation

In this paper, we analyze energy-efficient communications based on an advanced energy consumption model for wireless devices. The developed model captures relationships between transmission power, transceiver distance, modulation order, channel fading, power amplifier (PA) effects, as well as other circuit components in the radio frequency transceiver. Based the developed model, we are able to identify the optimal modulation order in terms of energy-efficiency under different situations (e.g., different transceiver distance, different PA classes and efficiencies, different pulse shape, etc). This provides an important framework for analyzing energy-efficient communications for different wireless systems ranging from cellular networks to wireless Internet of Things.

Generalized Class-E Power Amplifier With Shunt Capacitance and Shunt Filter

This paper presents a generalized analysis of the Class-E power amplifier (PA) with a shunt capacitance and a shunt filter, leading to a revelation of a unique design flexibility that can be exploited either to extend the maximum operating frequency of the PA or to allow the use of larger active devices with higher power handling capability. The proposed PA fulfills zero voltage switching (ZVS) and zero voltage derivative switching (ZVDS) conditions, resulting in a theoretical dc-to-RF efficiency of 100%. Explicit design equations for the load-network parameters are derived, and the analytical results are confirmed by harmonic-balance simulations. Two PA prototypes were constructed with one designed at low frequency and the other at high frequency. The first PA, which employs a MOSFET and a lumped-element load-network, delivered a peak drain efficiency $(\!D\!E)$ of 93.3% and a peak output power of 37 dBm at 1 MHz. The second PA, which employs a GaN HEMT and a transmission-line (TL) load-network to provide the drain of the transistor with the required load impedances at the fundamental frequency as well as even and odd harmonic frequencies, delivered a peak $D\!E$ of 90.2% and a peak output power of 39.8 dBm at 1.37 GHz.

Reconfigurable RF-MEMS-based impedance matching networks for a hybrid RF-MEMS/CMOS class-E power amplifier

Microelectromechanical-systems technology (MEMS) applied to radio frequency (RF) and microwave systems (i.e. RF-MEMS) has recently started to exhibit its market potential in applications centred on telecommunications and consumer segments. As evolution towards the 5G (5th generation of mobile communications) and the Internet of things (IoT) is progressing, more agile, reconfigurable and multi-functional RF passive components and networks will be necessary. In this work, an entirely RF-MEMS-based impedance matching network (IMN) is reported and discussed, taking the global system for mobile communications (GSM) protocol as testing scenario. The mentioned RF-MEMS IMN was designed in order to perform proper impedance conversion between a CMOS class-E power amplifier (PA) and the transmitting/receiving antenna of a GSM system. In the following pages, the RF-MEMS IMN will be discussed in details against its design solution, working principles, as well as electromechanical and RF simulated and measured characteristics.

A Modified Wireless Power Transfer System for Medical Implants

Wireless Power Transfer (WPT) is a promising technique, yet still an experimental solution, to replace batteries in existing implants and overcome the related health complications. However, not all techniques are adequate to meet the safety requirements of medical implants for patients. Ensuring a compromise between a small form factor and a high Power Transfer Efficiency (PTE) for transcutaneous applications still remains a challenge. In this work, we have used a resonant inductive coupling for WPT and a coil geometry optimization approach to address constraints related to maintaining a small form factor and the efficiency of power transfer. Thus, we propose a WPT system for medical implants operating at 13.56 MHz using high-efficiency Complementary Metal Oxide-Semiconductor (CMOS) components and an optimized Printed Circuit Coil (PCC). It is divided into two main circuits, a transmitter circuit located outside the human body and a receiver circuit implanted inside the body. The transmitter circuit was designed with an oscillator, driver and a Class-E power amplifier. Experimental results acquired in the air medium show that the proposed system reaches a power transfer efficiency of 75.1% for 0.5 cm and reaches 5 cm as a maximum transfer distance for 10.67% of the efficiency, all of which holds promise for implementing WPT for medical implants that don’t require further medical intervention, and without taking up a lot of space.

A Design Methodology and Analysis for Transformer-Based Class-E Power Amplifier

This paper proposes a new technique and design methodology on a transformer-based Class-E complementary metal-oxide-semiconductor (CMOS) power amplifier (PA) with only one transformer and two capacitors in the load network. An analysis of this amplifier is presented together with an accurate and simple design procedure. The experimental results are in good agreement with the theoretical analysis. The following performance parameters are determined for optimum operation: The current and voltage waveform, the peak value of drain current and drain-to-source voltage, the output power, the efficiency and the component values of the load network are determined to be essential for optimum operation. The measured drain efficiency (DE) and power-added efficiency (PAE) is over 70% with 10-dBm output power at 2.4 GHz, using a 65 nm CMOS process technology.

A Self-Tuned Class-E Power Oscillator

The efficiency and output power of a high- $Q$ Class-E power amplifier (PA) are very sensitive to the values of the circuit components. Any mismatch between the nominal Class-E frequency and the input clock frequency could result in considerable degradation in the efficiency and much change in the output power. In this paper, we present a new self-oscillating Class-E PA, or so-called Class-E power oscillator (PO), whose feedback network is mainly constructed of a low- $Q$ RC circuit. As a result, the phase response of the feedback network is almost flat around the operating frequency, and if the nominal Class-E frequency of the load network changes due to variations in the component values, the phase shift in the feedback network does not change considerably, and therefore, the Class-E operation of the circuit is substantially maintained. We also present a complete design procedure for the proposed Class-E PO. We have built and tested a sample Class-E PO based on the proposed circuit. At $V_{DD}= {\text{4.5}}\,{\text{V}}$ , the measured oscillation frequency, output power, and efficiency of the circuit are 800 kHz, 0.96 W, and 89%, respectively. Simulation and measurement results confirmed that the efficiency and output power of the proposed Class-E PO have small sensitivities to the variations in the component values; therefore, we call the proposed circuit a self-tuned Class-E PO.

Broadband Parallel-Circuit Class-E Amplifier With Second Harmonic Control Circuit

This brief presents the analysis and coherent design method of a high-efficiency broadband parallel-circuit Class-E power amplifier with second harmonic control circuit. The power amplifier’s (PA) broadband characteristic is achieved through analysis of the load network using double reactance compensation technique. Using a high power LDMOS transistor and operated from a 35 V supply voltage, the practical PA exhibits 41.5–44.1 dBm output power and 79%–82.2% drain efficiency over 115–155 MHz frequency range. The measurement results show good agreements with the simulation results and theory.

Rancang Bangun Kombinasi Trafo 1 Ampere CT dan 5 Ampere Engkel Untuk Efisiensi Power Amplifier Class GB (Groudbridge)

Along with the development of technology about audio soundsystems, innovations and new designs about audio are very many, music is an entertainment that is almost every day encountered by people today, Amplifier products that are commonly marketed (finished products) are still very dominated by the outside market country. GB Power Amplifier class (Ground Bridge) is one type of power amplifier that requires a high input voltage in the audio world, the use of a combination of suitable transformers and with the output voltage transformer that is able to meet the required power capacity for the amplifier without having to search for transformer with a high output specification. So a good component selection can make the power amplifier's performance to the maximum.

An MRI Compatible RF MEMs Controlled Wireless Power Transfer System.

In magnetic resonance imaging (MRI), wearable wireless receive coil arrays are a key technology goal. An MRI compatible wireless power transfer (WPT) system will be needed to realize this technology. An MRI WPT system must withstand the extreme electromagnetic environment of the scanner and cannot degrade MRI image quality. Here, a WPT system is developed for operation in MRI scanners using new microelectromechanical RF switch (RF MEMs) technology. The WPT system includes a class-E power amplifier, RF MEMs automated impedance matching, a primary coil array employing RF MEMs power steering, and a flexible secondary coil with class E rectification. To adapt WPT technology to MRI, techniques are developed for operation at high magnetic field, and to mitigate the RF interactions between the scanner and WPT system. A major challenge was the identification and suppression of noise and harmonic interference, by gating, filtering, and rectifier topologies. The system can achieve 63% efficiency while exceeding 13 W delivery over a coil distance of 3.5 cm. For continuous WPT beyond 5W, added filters and full-wave class E rectification lowers harmonic generation at some cost to efficiency, while image SNR reaches about 32% of the ideal. RF-gated WPT, which interrupts power transfer in the MRI signal acquisition interval, achieves SNR performance to within 1 dB of the ideal. With further refinement, the inclusion of WPT technology in MRI scanners appears completely feasible.

An energy-efficient and ultra-low-voltage power oscillator in CMOS 65 nm

In a direct modulation scheme and particularly in portable and wireless sensor network applications, the oscillator limits the transmitter efficiency therefore, the oscillator efficiency is critical and high-efficiency and high-power oscillators are increasingly required. This paper presents a high-efficiency and ultra-low-voltage power oscillator that operates at 2.4 GHz and is implemented in 65 nm CMOS technology. The power oscillator is a self-oscillating class-E power amplifier (PA) that utilizes a positive feedback system. A class-E PA is selected due to its high efficiency. The power oscillator has an optimized power consumption and output power, where a 2.4 mW power consumption is achieved under a 0.4 V power supply. The proposed oscillator demonstrates a maximum output power of $$-0.45$$ dBm and a peak efficiency of 37.5%. The oscillator is tunable between 1.66 and 2.78 GHz. The oscillator is robust to a $$\pm\,15\%$$ frequency deviation from a 2.44 GHz nominal frequency due to process, voltage, temperature variation.

A Multiresonant Gate Driver for High-Frequency Resonant Converters

This paper presents the design and implementation of a high-frequency/very high frequency (VHF) multiresonant gate drive circuit. The design procedure outlined here is greatly simplified compared with other VHF self-oscillating multiresonant gate drivers presented in previous works. The proposed circuit can reduce the long start-up time required in a self-oscillating resonant gate drive circuit and utilize the fast transient capability of VHF converters better. We demonstrate a prototype resonant gate driver, which reduces up to 60% of the gate-driving power in a 20-MHz 32-W Class-E power amplifier using a Si MOSFET. The proposed technique could also drive a high-voltage rated SiC MOSFET at 30 MHz with a slew rate of 2.5 V/ns at the gate, while an integrated hard-switching gate driver only provides a slew rate of 1.8-V/ns and is five times less efficient than the proposed resonant gate driver.

Co-design of on-chip loop antenna and differential class-E power amplifier at 2.4 GHz for biotelemetry applications

Degradation in gain and efficiency of on-chip antennas limit the communication range of RF transmitters integrated with on-chip antennas below 10 GHz to few centimeters. In this paper, a novel strategy of co-design of fully integrated differential class-E power amplifier and on-chip loop antenna at 2.4 GHz is proposed to increase communication range and save chip area. In the co-design strategy, inductor used for harmonic rejection and matching in the power amplifier is replaced with a parallel capacitance network for harmonic rejection and a modified two turn on-chip loop antenna is used for matching load impedance of power amplifier. From the post-layout simulation results using Cadence Virtuoso, power amplifier has maximum power added efficiency(PAE) of 50.7%, and output power of 17 dBm. On-chip antenna, simulated in Advanced Design System(ADS) has a gain of −19.9 dBi and efficiency of 0.48%. The transmitter designed in UMC 180-nm technology has a higher computed communication range of 1.5 m and is suitable for biotelemetry applications such as patient monitoring.

Striving for Efficiency: A 475-kHz High-Efficiency Two-Stage Class-E Power Amplifier

This article presents the design and validation for the high-efficiency class-E power amplifier (PA) that won first place in the high-efficiency PA for 475 kHz Student Design Competition held during the 2018 IEEE Microwave Theory and Techniques Society International Microwave Symposium (IMS 2018) in Philadelphia, Pennsylvania. Participants were required to implement and evaluate their own PAs. The team that achieved the highest drain efficiency while satisfying the conditions of the competition rules was the winner.

Implementation of a Dual Wireless Power Transfer and Rotation Monitoring System for Prosthetic Hands

This article presents the design, manufacture and test of an inductively coupled wireless power transfer (WPT) system used as a power source for prosthetic hands. Prosthetic hands are the most common artificial limbs among the physically disabled population. Limited storage capacity of the battery places severe limitations regarding the continuous use of this device. A WPT link is therefore proposed to supply power to such devices. The WPT system consists of a transmitter circuit (class-E power amplifier) and WPT coils along with commercially available receiver circuit and multiple motors. Assessment of the unwanted heating of the human tissue due to wireless power transfer was simulated using the commercial electromagnetic simulator ANSYS HFSS™. Results were experimentally validated by measuring in real-time temperature variations inside a phantom mimicking the properties of human muscle. Monitoring and control the rotation of the prosthetic hand was also demonstrated utilizing rotation-dependent wireless power transfer parameters. The WPT scheme proposed serves therefore the dual property of providing power to the prosthetic limb whilst monitoring the wrist rotation.