Hybrid 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

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.

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‐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.

Optimized Design of the Multilevel Converter in Series-Form Switch-Linear Hybrid Envelope-Tracking Power Supply

In modern radio communications, the envelope of radio frequency (RF) signal features with large peak-to-average power ratio. This necessitates the adoption of linear power amplifiers (PAs). In order to achieve a high efficiency for linear PAs, envelope-tracking (ET) technique is employed, which provides PAs with a supply voltage that tracks the envelope of the transmitted RF signal instead of a constant voltage. This paper focuses on the series-form switch-linear hybrid ET power supply, where the switching-mode converter uses a multilevel converter. The method to select the setting voltages under the premise of ensuring the linearity of output voltage is presented. In addition, the values and number of the voltage levels of the multilevel converter are optimized using a precise loss model based on the probability density function of the envelope signal. Besides, the pulse-blank method is proposed to improve the system efficiency further. Finally, a prototype is built aiming for tracking the envelope signal of wideband code division multiple access, with 5-MHz bandwidth, 12–27 V output voltage, 4 W average, and 10 W peak output power. The experimental results show that the output voltage of the ET power supply tracks the reference accurately and the system efficiency can reach 76%.