Envelope Tracking Power Supply Research Articles

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.

Feed-Forward Scheme Considering Bandwidth Limitation of Operational Amplifiers for Envelope Tracking Power Supply Using Series-Connected Composite Configuration

Wireless communication transmitters have a low efficiency because of the utilization of linear radio frequency (RF) power amplifiers (PAs) while the RF input signal is with a variant envelope. The envelope tracking (ET) technique is a very promising approach to improve the PA efficiency. For this application, this paper proposes an ET power supply consisting of a multilevel converter in series with a linear amplifier, where the multilevel converter provides the most load power with its essential high efficiency, and the linear amplifier, features of high bandwidth, improves the linearity of the output voltage. A feed-forward scheme is proposed to cancel the spikes in the output voltage caused by the step-wave voltage of the multilevel converter. In practical implementation, due to the bandwidth limitation of the operational amplifiers, a frequency-compensation scheme by adding a zero and a stability pole is proposed to extend the effective bandwidth. Furthermore, the output voltage high-frequency spike-elimination scheme using the transfer function matching concept is also proposed, removing the additional spikes at the output side of the ET power supply. A prototype for 300-kHz sine-wave tracking, with a 10–32-V output voltage and 50-W peak output power, is fabricated and tested. The experimental results validate the proposed schemes.

Full Feedforward of the Output Voltage to Improve Efficiency for Envelope-Tracking Power Supply Using Switch-Linear Hybrid Configuration

A synchronous rectification buck converter in parallel with a Class AB linear amplifier is presented in this paper to construct an envelope-tracking (ET) power supply. To eliminate the influences of the output voltage on the linear amplifier output current, a full feedforward of the output-voltage scheme with two feedforward terms is proposed in this paper, which can counteract all the two load admittances of the linear amplifier, respectively, consequently decreasing the linear amplifier output current substantially. An ET power supply prototype with 100-kHz sine-wave tracking, 5-15 V output voltage, and 75-W-peak output power is fabricated and tested in the lab. The experimental results are well in agreement with the theoretical analyses, and the system efficiency is improved significantly.

Feed-Forwarding the Output Voltage to Improve Efficiency for Envelope-Tracking Power Supply Based on a Switch-Linear Hybrid Scheme

Envelope-tracking (ET) technique is one of the most promising methods to improve the efficiency of the modern wireless communication transmitters, which is based on using a high-efficient power supply to provide varying voltage to the RF power amplifier. For this application, this letter adopts an AB-type linear amplifier and a synchronous rectification buck converter connected in parallel at the output to construct the ET power supply. The linear amplifier features of wide bandwidth and makes the output voltage follow the envelope of the transmitted signal; the buck converter features of high efficiency provides most of the load current. An average current control strategy with constant switching frequency is proposed, and it is further improved by feed-forwarding the output voltage to reduce the current of the linear amplifier, leading to higher efficiency. A prototype is built and shown to perform very well, achieving high efficiency and track bandwidth of about 100 kHz.

Architecture of Wideband High-Efficiency Envelope Tracking Power Amplifier for Base Station

This paper proposes new architectures for envelope-tracking power supplies for base stations. (1) The proposed multiphase DC-DC converter circuit uses multiple switching circuits with hysteresis comparators (as well as a voltage follower circuit), each optimized for a different envelope frequency, to realize both high efficiency and wide bandwidth. (2) We also propose the one using interleaved PWM switching circuits. The operation of the circuits, and simulation results, are described.

TEDS Base-Station Power Amplifier Using Low-Noise Envelope Tracking Power Supply

This paper demonstrates a highly linear and efficient TETRA enhanced data service (TEDS) base-station RF power amplifier (RFPA). Based on the well-known combination of an envelope tracking (ET) power supply and a linear class-A/B RFPA, adequate adjacent channel power ratio (ACPR) and wideband noise performance is shown to be enabled only by further incorporating high-bandwidth Cartesian feedback (CFB) and using a low-noise ET power supply. It is demonstrated that CFB loop bandwidth is limited by modulator/demodulator/RF path group delay to around 2 MHz in the considered setup, and that there exists a significant tradeoff between the depth of the ET and open-loop RFPA linearity, as well as overall efficiency. An empirical method for determining the permissible amount of switching ripple on the ET supply is presented, showing very good accuracy. Performance of the prototype RFPA system is verified experimentally with a 9.6-dB peak-to-average 50-kHz 16 quadrature amplitude modulation TEDS carrier, the setup providing 44-dBm (25 W) average RF output power at 400 MHz with 44% dc-to-RF efficiency state-of-the-art ACPR of less than -67 dBc, switching noise artifacts around - 85 dBc, and an overall rms error vector magnitude below 4.5%.

Ultrafast Tracking Power Supply With Fourth-Order Output Filter and Fixed-Frequency Hysteretic Control

A practical solution is presented for the design of a non-isolated dc/dc power converter with very low output ripple voltage and very fast output voltage step response. The converter is intended for use as an envelope tracking power supply for a radio frequency power amplifier (RFPA) in a TETRA enhanced data service (TEDS) base station. A simple and effective fixed-frequency hysteretic control scheme for the converter (buck with fourth-order output filter) is developed and analyzed. The proposed approach is verified experimentally by a 500 W output prototype, capable of delivering any voltage in the range of 10-30 V within 10 mus with 10 mVpp of output ripple and efficiencies in the 88%-95% range.