Envelope Tracking Power Supply Research Articles

A Triangular-Wave Current Control for Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply to Achieve High Efficiency

A Triangular-Wave Current Control for Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply to Achieve High Efficiency

An advanced solid-state RF power source maximizing energy efficiency for optimal superconducting RF cavity charging

Abstract This paper outlines an experimental demonstration of an envelope tracking (ET) technique applied to a kilowatt-level single-ended solid-state power amplifier (SSPA), aimed at enhancing the charging efficiency of superconducting radio frequency (SRF) cavities by reducing reflection power while maintaining a high degree of efficiency. The technique is particularly designed for the pulsed operation of the European Spallation Source (ESS) at a nominal frequency of 352 MHz, with a 5% duty cycle and a pulse width of 3.5 ms. The study introduces an optimal charging scheme using a solid-state-based amplifier to maintain high efficiency, allowing for power ramp-up while minimizing reflections from SRF cavities and optimizing SSPA efficiency. A fast envelope tracking power supply (ETPS) system is implemented for the approximately 300 ms charging time required by the SRF cavities at ESS. The ETPS system, demonstrated on a single module as a proof-of-concept with scalability potential to a 400 kW power station, indicates an overall average efficiency of 70% and a 24% energy saving over traditional vacuum-tube based amplifiers. This demonstrates the ET technique’s effectiveness at the kilowatt level for efficient SRF cavity charging with reduced reflection, offering significant efficiency and energy savings.

Boundary Adjustment Hysteresis Current Control for Improving the Efficiency of Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply

Boundary Adjustment Hysteresis Current Control for Improving the Efficiency of Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply

Efficiency Analysis and Design Considerations of a Hysteretic Current Controlled Parallel Hybrid Envelope Tracking Power Supply

This paper presents the realization of an Envelope Tracking Power Supply (ETPS), for a sinusoidal envelope input signal. A parallel hybrid topology is chosen for the implementation. In this topology, a voltage-controlled Class-AB linear amplifier stage and a current-controlled switching converter stage operate in parallel. A hysteretic current control scheme is employed to control the operation of the switching converter. Block-level implementation of the ETPS is done using Simulink 2017b, continuous mode simulation. Simulations are performed using a sinewave input envelope signal = 1.94+ 1.2 sin(ω∙t). The input frequency varied from 1MHz to 60MHz. As the input frequency is increased, the ETPS moves from the linear to the non-linear region of operation. During the transition, the slew rates of the load current and the switching current match at a particular input frequency of 2MHz while the efficiency peaks. The maximum obtained efficiency while tracking the sinewave input signal is 82.3%. The way the efficiency can be optimized by focusing on the matching of the slew rates of load and switching currents is explained. Also, an insight into the study of various circuit parameters and the trade-offs that the designer needs to consider while designing an ETPS, is provided.

A Series-Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply With Two Multilevel Converters Sharing a Voltage-Level Provider

Series-parallel-form switch-linear hybrid envelope tracking power supply is composed of a voltage-controlled linear amplifier (VLA), a voltage-controlled switched-mode converter (VSC) and a current-controlled switched-mode converter. When the VLA adopts a class AB linear amplifier, an additional VSC can be added to be in series with the bottom transistor of the VLA to reduce its voltage drop. In order to reduce the system complexity, this article proposes to employ multiple bidirectional converters to implement the voltage-level provider, for being shared by the two VSCs, which are implemented with multilevel converters. Then, the loss model of the system is established, and based on which, an optimized design of the voltage-level number and voltage-level values of the multilevel converters is presented for improving the overall system efficiency. Finally, a prototype is fabricated aiming for tracking the envelope signal with 10-MHz bandwidth, 9.6–26.4-V output voltage, and 20-W average output power. The measured system efficiency is 78.79%, an improvement by 2.58% with the additional VSC.

High Bandwidth Series-Form Switch-Linear Hybrid Envelope Tracking Power Supply With Reduced Bandwidth Envelope and Step-Wave Edge Adjustment Methods

The series-form switch-linear hybrid envelope tracking (ET) power supply is constituted by a multilevel converter and a linear amplifier connected in series, featuring high efficiency and wide tracking bandwidth. With the development of wireless communication, the envelope bandwidth of the radio-frequency signal reaches tens of megahertz and even hundreds of megahertz, leading to a high switching loss in the multilevel converter and thus degraded overall efficiency of the ET power supply. To reduce the switching loss and ensure high tracking bandwidth, this article proposes to let the multilevel converter track the reduced bandwidth envelope signal and the linear amplifier track the original one. Then, a step-wave edge adjustment method is proposed to adjust or eliminate the rising and falling edges of the step-wave voltage for further reducing the equivalent switching frequency of the multilevel converter and the voltage across the power device of the linear amplifier. As a result, the switching loss in the multilevel converter and the power loss in the linear amplifier could be reduced, leading to a notably higher overall efficiency. A prototype with 40 MHz tracking bandwidth, 7–27 V output voltage, and 15 W average output power is fabricated and tested in the lab, and the experimental results are provided to verify the effectiveness of the proposed method.

Improved Pulse Edge Independent Distribution Method for High PAPR High Bandwidth Envelope Tracking Power Supply

Envelope tracking (ET) power supply provides the power amplifier (PA) with a dynamic supply voltage that tracks the envelope of the input signal to the PA, and the final PA efficiency can be greatly improved. With the ever-advancing tracking bandwidth, the switching frequencies of ET power supplies are pushed to be very high and even difficult to be implemented. To address this issue, the pulse edge independent distribution (PEID) method has been proposed. Based on the idea of alternatively working by sets, the control pulses for the multilevel converter are broken into independent rising and falling edges, and rematching them with optimized new sequences can achieve a 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n \in N$ </tex-math></inline-formula> ) ratio of the switching frequency over envelope bandwidth. However, each increase of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> by 1 means that a whole set of voltage cells is added, leading to a great increase in system complexity and cost, especially for high peak-to-average power ratio (PAPR) applications. Besides, due to the irregular and aperiodic feature of the real communication envelope, the PEID control logic may suffer from surplus and imbalance in switching frequency reduction. Thus, this article proposes an improved PEID method. Assisted by the digital control platform, the control logic is redesigned, which can realize a balanced distribution of the rising and falling edges for arbitrary envelopes. Moreover, it can extend the domain of the “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> ” to noninteger, achieving a more subtle resolution of PEID. On this basis, an evaluation function is constructed taking into account the efficiency, voltage-cell quantities, and switching frequency. With the desired weighted coefficients, an optimized comprehensive performance can be achieved. A prototype with 2–27-V output voltage range, 10- and 20-MHz tracking bandwidths, and 8.5-dB PAPR is fabricated and tested in the lab. The experimental results validate the proposed method.

Single-Input Relay Charging Switched-Capacitor Topology for High-Bandwidth Envelope Tracking Power Supply

Switching converters are the key parts of envelope tracking (ET) power supplies. To achieve a high tracking bandwidth, the ratio of the switching frequency over the envelope bandwidth is often far larger than 1. The pulse edge independent distribution (PEID) method can reduce this ratio to 1/n (n ϵ N), significantly promoting the high-bandwidth tracking capability. However, multiple isolated voltage sources are required, leading to increased system complexity. Based on the PEID method, this article proposes a switched-capacitor ET power supply, which employs supplementary switches to flexibly link all the switched capacitors so that more charging loops are created and the relay charging mechanism is formed, which can equivalently extend the charging time and achieve more balanced voltage levels between the switched capacitors. Thus, with only one input, all the switched capacitors can maintain a stable and equal voltage and, thus, competently serve as the isolated voltage sources. To verify the proposed configuration and control method, a prototype with 2-27 V output voltage range, 54 W peak output power, and 10 MHz tracking bandwidth has been built and tested. The experimental results validate the proposed scheme.

Hysteresis Voltage Prediction Control for Multilevel Converter in the Series-Form Switch-Linear Hybrid Envelope Tracking Power Supply

Switch-linear hybrid (SLH) envelope tracking (ET) power supply can achieve high efficiency and high tracking bandwidth simultaneously, and it has two typical forms, namely, series-form and parallel-form. In the series-form SLH ET power supply, the switched-mode converter is expected to output a continuous-wave voltage which can track the load voltage accurately to enhance the overall efficiency, and the buck converter with hysteresis voltage control (HVC) can be utilized. However, the output voltage of the buck converter will go over the hysteresis voltage boundaries, degrading the linearity and efficiency of the ET power supply. In this article, the hysteresis voltage prediction control (HVPC) is proposed to mitigate the problem in the HVC for buck converter. Moreover, in order to further increase the efficiency, the multilevel converter (MLC) is adopted instead of the buck converter for reducing the switching frequency and the inductor root-mean-square current, and the corresponding HVPC control strategy is also proposed. A prototype of the series-form SLH ET power supply employing the MLC with HVPC aimed at 5-MHz envelope signal is fabricated in the lab. The measured overall efficiency is 77.5%, a 12% efficiency improvement over that using step-wave switched-mode converter.

Switched Capacitor Based High Bandwidth Envelope Tracking Power Supply

The envelope tracking (ET) power supply can output a variable voltage which tracks the envelope of the radio frequency input signal to the power amplifier (PA), and the system efficiency can be significantly improved. To achieve a high tracking bandwidth, the switching frequency of the ET power supply is usually too high. The pulse edge independent distribution (PEID) method has been proposed to reduce the switching frequency to 1/n (n ϵ N) of the tracking bandwidth, but a large number of isolated voltage sources are needed, leading to increased power stage and system complexity. In this letter, a switched capacitor based high bandwidth ET power supply is proposed, which employs optimized charging topologies and mechanisms to stabilize the voltages across the switched capacitors, and thus they can fully replace the isolated voltage sources. Since the proposed configuration is derived from the PEID method, all the features of PEID method are retained. A prototype with 6-26-V output voltage and 20-W peak output power is fabricated and tested with a 1-MHz sine wave and a 5-MHz bandwidth communication envelope. The experimental results validate the proposed configuration.

Current Control Strategies for Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply With Two Switched-Mode Converters to Achieve Optimal Power Allocation

Switch-linear hybrid (SLH) envelope tracking (ET) power supply is one of the mainstream structures for achieving both high efficiency and high bandwidth. When tracking a high bandwidth envelope signal, the overall efficiency of SLH ET power supply with the single switched-mode converter is limited. This paper adopts two switched-mode converters with different tracking bandwidths instead of the single switched-mode converter. The switched-mode converter with low tracking bandwidth is called slow switched-mode converter (SSMC), which aims for providing the low-frequency load current components with low slew rate; while the switched-mode converter with high tracking bandwidth is called fast switched-mode converter (FSMC), which copes with the high-frequency load current components with high slew rate. The rest load current components are processed by the linear amplifier. The class-A linear amplifier is employed for reducing the complexity of the circuits, which works as a voltage regulator that does not sink the load current. The SSMC provides the majority of the load current with low switching frequency. Thus, the switching loss of the SSMC is not high. The FSMC is operated at high switching frequency but provides the minority of the load current, and thus the switching loss of the FSMC is not high. The valley-point current control and peak current control with critical continuous current mode are proposed for the SSMC and FSMC, respectively, achieving the desired power allocation among the SSMC, FSMC, and the linear amplifier. Finally, a prototype is fabricated in the lab aiming for tracking a 10-MHz envelope signal and 20-W average output power. Experimental results are provided to verify the effectiveness of the proposed configuration and its current control strategies. The efficiency of the proposed SLH power supply is 77.0%, a 4.5% efficiency improvement compared with the SLH ET power supply with the single switched-mode converter.

High Bandwidth Envelope Tracking Power Supply With Pulse Edge Independent Distribution Method

Switching-linear hybrid envelope tracking (SLH ET) power supplies can achieve both high efficiency and high bandwidth. However, the switching frequency is often required to be far higher than or at least equal to the envelope bandwidth. With the modulation methods advance, the increasing envelope bandwidth may lead to a too high switching frequency to implement. This paper proposes an SLH ET power supply, consisting of a multilevel converter and a linear amplifier connected in series. Based on the multicell configuration of the multilevel converter, a pulse edge independent distribution method is proposed, which can break the control pulses for the multilevel converter into independent rising and falling edges, and rebuild them with new sequences. It can not only reduce the switching frequency to 1/ n ( n ∊ N ) of the envelope bandwidth but also extend the pulsewidths to provide a more reliable and effective driving for high bandwidth applications. A prototype for 2 MHz sine-wave tracking, with 7–27-V output voltage and 90-W peak output power, is fabricated and tested. It is also verified by a 5- and a 10-MHz bandwidth communication envelope. The experimental results validate the proposed method.

High‐efficiency series–parallel form hybrid envelope‐tracking power supply based on the optimised power losses

To achieve high efficiency, an optimised method of the series-parallel form (SPF) hybrid envelope tracking power supply based on hysteresis current control is proposed in this Letter. The SPF hybrid power modulator is constituted by one linear regulator and two switched-mode converters which include one multilevel converter and one buck converter. Based upon the equivalent average current slew rate matching theory and accurate power loss model analysed in this Letter, the voltage distribution of the multilevel converter is optimised. For verification, a prototype is fabricated aiming for tracking the 10-MHz LTE envelope signal with the efficiency of 83%, 26.9 W average output power, and 67.6 W maximum output power.

Elimination of the Interaction of the Converters in Switch-Linear Hybrid Envelope Tracking Power Supplies

As a combination of the switched-mode converter and linear amplifier, the switch-linear hybrid (SLH) envelope tracking (ET) power supply can achieve high efficiency and high tracking bandwidth simultaneously, and it can be classified into three types, namely, series-form, parallel-form, and series–parallel-form. In the SLH ET power supply, interaction may occur between the converters, and as a result, the controlled variable will deviate from its target. In this paper, the interaction in the series-form SLH ET power supply with different structures is analyzed first from the aspects of control and parasitic capacitances, and the feedforward control scheme and/or filter is adopted to eliminate the interaction. Then, for the parallel-form SLH ET power supply, four current control methods are introduced and compared from the current tracking and disturbance-rejection performances, and the method for suppressing the disturbance is presented. Since series–parallel-form SLH ET power supply contains at least three converters, the interaction is more complex. On the basis of the analysis of the series-form and parallel-form SLH ET power supplies, the interaction between the converters in series–parallel-form SLH ET power supply is analyzed and followed by the corresponding elimination method. Finally, one series-form, and one parallel-form SLH ET power supplies are implemented in the lab, and the experimental results verify the theoretical analysis.

Analysis of Systematic Losses in Hybrid Envelope Tracking Modulators

This paper presents a comprehensive analysis of the intrinsic losses in hybrid envelope tracking power supply modulators used in envelope tracking power amplifier systems. The losses are computed entirely symbolically in terms of system parameters and a single design parameter. Resulting formulations are used to provide design insight into optimum biasing to minimize losses in a hybrid configuration, and establish the theoretical upper bound of achievable efficiency. To illustrate the value of this analysis, a Rayleigh distributed waveform is used to evaluate the performance of the hybrid modulator to describe OFDM and other complex modulation schemes. This paper demonstrates that the common convention of biasing the linear converter’s output stage to have zero average current is generally suboptimal from a loss perspective, and establishes how efficiency can be improved without modifying the underlying circuit topology. These findings are validated with a series of simulations modeling a hybrid modulator implemented in a 180-nm CMOS process. This paper derives for the first time, the intrinsic theoretical losses in the hybrid envelope modulator configuration.

Hysteresis Current Control for Multilevel Converter in Parallel-Form Switch-Linear Hybrid Envelope Tracking Power Supply

Parallel-form switch-linear hybrid (SLH) envelope tracking (ET) power supply is constituted by a linear amplifier and a switched-mode converter connected in parallel. The switched-mode converter is usually implemented by a buck converter with hysteresis current control. However, the slew rates of the load current and the inductor current of the buck converter cannot match well when the slew rate of the load current has a wide variation range. The unmatched slew rates will lead to a high switching frequency of the buck converter or a large loss of the linear amplifier, which degrades the overall efficiency. In this paper, a multilevel converter is adopted to replace the buck converter in the parallel-form SLH ET power supply, and the hysteresis current control scheme is proposed for the multilevel converter to dynamically adjust its inductor current slew rate to approach that of the load current to improve the overall efficiency. The optimal design for the efficiency-related parameters including the inductor, the current hysteresis, and the number and values of the voltage levels in the multilevel converter is given. A prototype of the parallel-form SLH ET power supply with hysteresis current controlled multilevel converter is fabricated and tested in the lab. The measured overall efficiency is 79.4% when tracking the envelope of wideband code division multiple access signal with 5 MHz bandwidth and outputs 18 W average power, and a 3.8% efficiency improvement is achieved over that with the hysteresis current controlled buck converter.

High Bandwidth and Compact Envelope Tracking Power Supply Utilizing Switched Capacitor Topology

The envelope tracking (ET) power supply has emerged to improve the efficiency of the power amplifier (PA) by supplying a variable voltage that tracks the envelope of the input signal to the PA. Represented by 5G, the future wireless communication technologies are characterized by higher envelope bandwidth and lower base station profile, which puts demanding requirements on ET power supply design. This paper investigates the key features of the switched capacitor topology and the pulse edge independent distribution (PEID) method, and then incorporates them into a unitary ET power supply. Comparing with the regular switched capacitor converter, this ET power supply can only involve minor changes in basic topology, which maintains a compact structure and preserves the merits of the original system being easy to drive. Besides, the corresponding control logic and control sequences are optimally redesigned, which can reduce the switching frequency to 1/n (n ∈ N) of the tracking bandwidth and extend the possible too narrow control pulses. To verify the proposed high bandwidth and compact ET power supply, a prototype with 6-26-V output voltage and 21-W peak output power is fabricated. The experiments are carried out by tracking a 1-MHz sine wave and a 5-MHz bandwidth real communication envelope, the results of which validate the proposed configuration and control scheme.

Research progress on envelope tracking power supply modulation technology

Research progress on envelope tracking power supply modulation technology

Quasi-Interleaved Current Control for Switch-Linear Hybrid Envelope-Tracking Power Supply

An envelope-tracking (ET) technique can greatly enhance the efficiency of the power amplifier in wireless communication system. Among the structures of the ET power supply, the switch-linear hybrid (SLH) structure can obtain both high-tracking bandwidth and high efficiency. An implementation of series–parallel-form SLH ET power supply is proposed in this paper, which includes one multilevel converter, one linear amplifier, and two buck converters. The two buck converters adopt current sensor-less prediction control and are operated at critical conduction mode (CRM). In order to ensure the operation of CRM and provide as much load current as possible, a quasi-interleaved current control scheme is proposed for the two buck converters. Moreover, a peak current restriction method is proposed to prevent the output current of the two interleaved buck converters from excessively exceeding the load current, avoiding the increase of the power loss in the linear amplifier. Finally, a prototype is fabricated with the specifications as 5-MHz tracking bandwidth, 9.6–26.4-V output voltage, and 20-W average output power. The overall measured efficiency is 81.0%, and the normalized-mean-square error is 0.28% when tracking the envelope of wideband code division multiple access signal.

A Review of Envelope Tracking Power Supply for Mobile Communication Systems

In modern mobile communication systems, spectral efficient modulation formats have been widely used, which results in the envelope of the radio frequency (RF) signal is variable and having large peak to average power ratio (PAPR). In order to amplify the RF signal without distortion, the linear power amplifier (LPA) is adopted, which is less efficient when powered by constant voltage. Three popular techniques, i.e., Doherty, envelope elimination and restoration (EER), and envelope tracking (ET) techniques, to greatly improve the efficiency of the power amplifiers are analyzed and compared in this paper, and it is shown that the ET technique is the most suitable for future mobile communication systems. In the ET systems, the ET power supply is the key equipment, which dominates the system efficiency. With the development of the mobile communication systems, the bandwidth and the PAPR of the envelope signals are increasing rapidly, which pose severe challenges on the design of the ET power supply. This paper summarizes and sorts the ET power supplies in the literatures, and a detailed comparison is presented to guide the selection of ET power supplies for different applications. Finally, the methods, including soft-switching, slow envelope, and band separation are proposed for further increasing the efficiency of the ET power supply.