Daniel Diaz

Multilevel Power Supply for High-Efficiency RF Amplifiers

In radio systems linear power amplifiers (class A, B or AB) are usually used as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has low peak-to-average power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a combination of multilevel converter and linear regulator. The proposed solution can reproduce any signal with maximal spectral component of 2 MHz and give instantaneous maximal power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, it has up to 15% higher efficiency than linear regulator that is used as a conventional solution. Additionally, the algorithm for selection of voltage levels for the multilevel converter is explained, as well.

Dual Active Bridge-Based Battery Charger for Plug-in Hybrid Electric Vehicle With Charging Current Containing Low Frequency Ripple

Manufacturers want high power density for the on-board battery chargers of plug-in hybrid electric vehicles. Wide bandgap devices can be used to shrink other passive components by increasing the switching frequency, but the bulk dc link capacitor of the ac-dc power factor correction stage, becomes one of the major barriers to higher power density, because its volume depends on the ripple power at the double line frequency in a dc current charging system. However, if this double line frequency ripple flows into the battery, the dc link capacitance can be significantly reduced. This charging scheme, named as sinusoidal charging in this paper, is analyzed and implemented based on a two-stage battery charging system, which is comprised of one full bridge ac-dc stage and one dual active bridge dc-dc stage. We further find that converter loss causes ripple power imbalance and bigger dc link capacitance. Therefore, the impact of converter loss on the ripple power balance is analyzed, and a feedback control on the dc link voltage ripple is proposed based on this analysis in order to further reduce the dc link capacitance. The effectiveness of the proposed solutions is verified in both Si-based and GaN-based charging systems.

Multilevel Power Supply for High Efficiency RF Amplifiers

In communication systems, linear power amplifiers (PAs) (class A, B, or AB) are usually used as a solution for the PA stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration technique is used to enhance the efficiency of RF transmitters by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a combination of multilevel converter and linear regulator. The proposed solution can reproduce any signal with maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, it has up to 49% higher efficiency than an ideal linear regulator that is used as a conventional solution. Additionally, the algorithm for the optimization of the voltage levels, for the multilevel converter, is explained as well.

The Ripple Cancellation Technique Applied to a Synchronous Buck Converter to Achieve a Very High Bandwidth and Very High Efficiency Envelope Amplifier

This paper presents a single-stage converter for a high-bandwidth and high-efficiency envelope amplifier. In the proposed application, due to the high peak-to-average-power ratio, high bandwidth, and the power level requirements, the envelope amplifier has low efficiency. Therefore, many efforts have been made to increase the efficiency of the envelope amplifier. To achieve this improvement, the current ripple cancellation technique is applied in this paper to a synchronous buck converter to cancel the output current ripple and to decrease the switching frequency without a reduction in the large signal bandwidth, for open-loop operation and for the envelope elimination and restoration technique. The advantages of the proposed design are presented and validated experimentally. The transfer function of the output filter of the buck converter with a ripple cancellation circuit has been modeled and compared to measurements, showing a good correspondence. Experimental validation is provided at 4 MHz of switching frequency, for dc and for variable output voltage, applying a sinusoidal reference and a 64-QAM signal. Experimental validation of the efficiency improvement is provided, compared to the equivalent design of the conventional buck converter in terms of the output voltage ripple rejection ratio and large signal bandwidth.

Comparison of two different cell topologies for a multilevel power supply to achieve high efficiency envelope amplifier

A solution combining a multilevel converter in series with a linear regulator to obtain an envelope amplifier was presented recently in [1] for EER. Two possible implementations of the multilevel cell are compared. In [1], a two-state topology for the multilevel cell is proposed for the envelope amplifier. The three-state cell topology, proposed in this paper, has two main advantages: less number of cells and inputs and a simpler electrical and physical design. The comparison of the energy handled by each cell topology confirms several advantages of the three-state cell. Considerations to optimize the design of the multilevel converter for both cell topologies and experimental comparison between both cell architectures are enclosed.

Envelope Amplifier Based on Switching Capacitors for High-Efficiency RF Amplifiers

Modern transmitters usually have to amplify and transmit signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, linear power amplifiers (class A, B, or AB) are usually used as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration technique is used to enhance the efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class E) with a highly efficient envelope amplifier in order to obtain a linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a multilevel converter in series with a linear regulator. The multilevel converter is implemented by employing voltage dividers based on switching capacitors. The implemented envelope amplifier can reproduce any signal with a maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, the implemented prototypes have up to 20% higher efficiency than linear regulators used as a conventional solution.

Dynamic Analysis of a Boost Converter With Ripple Cancellation Network by Model-Reduction Techniques

The boost topology with ripple cancellation network allows input and output current ripples attenuation, which means the suppression of the input filter and a high reduction of the output filter. However, to achieve the ripple cancellation, the complexity and the number of components of the converter need to be increased as compared with the conventional boost. A detailed analysis is developed to specify the advantages and disadvantages of this topology. This paper presents the averaged model that derives the complex transfer function of the topology. The theoretical transfer function is obtained. Due to the complexity of the seventh-order transfer function that is obtained, a simplified second-order transfer function is calculated to simplify control design calculations. A comparison between the analyzed topology and a conventional boost in terms of weight and losses is carried out. To estimate the current ripple calculation, it is proposed to use the ripple theorem, which allows an estimation of the efficiency of the cancellation network using the averaged model. A prototype to validate ripple cancellation and the dynamic analysis is developed. Measured waveforms and Bode plots are enclosed. Current ripple cancellation at the input and output in both conduction modes of the converter is also validated.

Efficient and Linear Power Amplifier Based on Envelope Elimination and Restoration

This letter describes a power amplifier (PA) with high linearity based on the envelope elimination and restoration (EER) technique. PAs based on this technique are composed of a highly efficient nonlinear PA (class E) that performs phase modulation and a wide bandwidth envelope amplifier that supplies the nonlinear PA and has to inject the envelope through power supply modulation. The design of the envelope amplifier is a complicated task due to the tradeoff between demanded high efficiency and very wide bandwidth. In order to obtain a reasonably high efficiency and very wide bandwidth, a solution based on the multilevel converter in series with a linear regulator is proposed. It provides up to 100 W of peak power and tracks sine waves up to 2 MHz. The class E amplifier has been optimized for high-efficiency (near 85%) and high-frequency (120 MHz) operation. The experimental results presented in this letter validate the proposed solutions for the envelope and phase amplifier, demonstrate that the implemented EER PA can handle up to 100 W of peak power, and highlight its high linearity (around 40 dB of attenuation of the intermodulation products) and high efficiency (up to 25% less power losses than an ideal class B amplifier).

Three-Level Cell Topology for a Multilevel Power Supply to Achieve High Efficiency Envelope Amplifier

This paper presents an envelope amplifier solution for envelope elimination and restoration (EER), that consists of a series combination of a switch-mode power supply (SMPS), based on three-level voltage cells and a linear regulator. This cell topology offers several advantages over a previously presented envelope amplifier based on a different multilevel topology (two-level voltage cells). The topology of the multilevel converter affects to the whole design of the envelope amplifier and a comparison between both design alternatives regarding the size, complexity and the efficiency of the solution is done. Both envelope amplifier solutions have a bandwidth of 2 MHz with an instantaneous maximum power of 50 W. It is also analyzed the linearity of the three-level cell solution, with critical importance in the EER technique implementation. Additionally, considerations to optimize the design of the envelope amplifier and experimental comparison between both cell topologies are included.

High efficiency power amplifier for high frequency radio transmitters

Modern transmitters usually have to amplify and transmit complex communication signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, linear power amplifiers (class A, B or AB) are usually employed as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents solutions for the power supply that acts as the envelope amplifier and class E amplifier that is used as a nonlinear amplifier. The envelope amplifier is implemented as a multilevel converter in series with a linear regulator and can provide up to 100 W of peak power and reproduce sine wave of 2 MHz, while the implemented class E amplifier operates at 120 MHz with an efficiency near to 90%. The envelope amplifier and class E amplifier have been integrated in order to implement the Kahns technique transmitter and series of experiments have been conducted in order to characterize the implemented transmitter.