Switch-linear Hybrid Envelope Tracking Power 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

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.

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.

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.

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.

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.

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.

Series–Parallel-Form Switch-Linear Hybrid Envelope-Tracking Power Supply to Achieve High Efficiency

Envelope tracking (ET) techniques have been used to improve the efficiency of power amplifiers in wireless communication systems. The switch-linear hybrid (SLH) ET power supply, which features both wide tracking bandwidth and high efficiency, has received a great deal of attention. In both series- and parallel-form SLH ET power supply, the power loss of the linear amplifier is relatively high. This paper proposes a series–parallel form for the SLH ET power supply, which includes two switched-mode converters and one linear amplifier, to reduce both the output voltage swing and output current of the linear amplifier, thus reducing the power loss of the linear amplifier. A current prediction control scheme is proposed to remove the current sensor in the switched-mode converter, achieving accurate control for high-frequency current. A prototype is built for 5 MHz wideband code division multiple access envelope signal tracking and 40 W peak output power. The tested efficiency of the proposed configuration is 80.4%, which is much higher than that of the series-form SLH ET power supply.

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%.

High-Efficiency Switch-Linear-Hybrid Envelope-Tracking Power Supply With Step-Wave Approach

Featuring high bandwidth and high efficiency, the switch-linear hybrid envelope tracking (SLH-ET) power supply has been gaining considerable attentions. This paper proposes a new configuration for SLH-ET power supply, which consists of a switching-mode converter with a step-wave approach and a linear amplifier connected in parallel. The switches in the switching-mode converter are operated only one time in every tracking period, leading to reduced switching loss and, thus, a higher efficiency. The number of the voltage levels and the voltage difference between the adjacent steps are analyzed in terms of the voltage synthesis accuracy and voltage total harmonic distortion. A full feedforward of the output voltage scheme is adopted to make the switching-mode converter provide the most load power and the linear amplifier only provide the ripple current that resulted by the switching-mode converter. Thus, the overall efficiency is improved. A prototype is built aiming for 300-kHz sine-wave tracking, with a 10–26-V output voltage and a 50-W peak output power. The experimental results show that the proposed configuration can obtain higher efficiency as well as high tracking bandwidth.