Series combination of a switched dc-dc converter and a linear regulator for high frequency RF envelope amplifier

Classical linear amplifiers such as A, AB and B offer very good linearity suitable for RF power amplifiers. However, its inherent low efficiency limits its use especially in base-stations that manage tens or hundreds of Watts. The use of linearization techniques such as Envelope Elimination and Restoration (EER) allow an increase of efficiency keeping good linearity. This technique requires a very fast dc-dc power converter to provide variable voltage supply to the power amplifier. In this paper, several alternatives are analyzed to implement the envelope amplifier based on a cascade association of a switched dc-dc converter and a linear regulator. A simplified version of this approach is also suitable to operate with Envelope Tracking technique

Envelope tracking of a radio frequency amplifier for Long Term Evolution using a three-level class-G modulator

In this contribution, efficiency enhancement of a radio frequency (RF) power amplifier (PA) for Long Term Evolution (LTE) base stations using envelope tracking is investigated. The dynamically adapted drain bias voltage is provided by a three-level class-G modulator. The potential of this bias modulator is demonstrated with a class AB PA built in gallium nitride (GaN) technology with an operation frequency of 2.75 GHz, a maximum output power of 41 dBm and a peak power-added efficiency (PAE) of 60%. When driven by an LTE signal with a bandwidth of 20 MHz, overall system efficiency can be increased from 17% with a constant supply voltage up to 29% with envelope tracking. This is accompanied by a reduction of linearity. Adjacent channel leakage ratio (ACLR) decreases by 10 dB in the first and by 18 dB in the second adjacent channel, respectively. Error vector magnitude (EVM) increases from 9% up to 29%

High Efficiency Power Amplifier Based on Envelope Elimination and Restoration Technique

Due to complex envelope and phase modulation employed in modern transmitters it is necessary to use power amplifiers that have high linearity. Linear power amplifiers (classes A, B and AB) are commonly used, but they suffer from low efficiency especially if the transmitted signal has high peak to average power ratio (PAPR). Kahn's technique based on envelope elimination and restoration (EER) is based on idea that high efficiency power supply (envelope amplifier) could be used to modulate the envelope of high efficient non linear power amplifiers (classes D or E). This paper presents solutions for power amplifier that performs envelope modulation and class E amplifier that is used as a non linear amplifier. The envelope amplifier is implemented as a multilevel converter in series with linear regulator and can provide up to 100 W of instantaneous power and reproduce 2 MHz sine wave. The implemented Class E amplifier can operate at 120 MHz with efficiency near to 85%. The envelope amplifier and class E amplifier have been integrated and efficiency and linearity of the implemented transmitter has been measured and presente

Envelope Amplifier for RF Amplifier based on Multilevel Converter

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 low peakto-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 amplifierThis 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 wel

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

Comparación entre dos Arquitecturas para la Implementación de un Convertidor Multinivel para un Amplificación de Envolvente de Alta Eficiencia

Recientemente ha sido presentada una solución que combina un convertidor multinivel en serie con un regulador lineal para obtener un amplificador de envolvente. Este convertidor se emplea para la mejora de la eficiencia en amplificadores de RF mediante la implementación de la técnica de eliminación y restauración de envolvente (EER). La solución propuesta puede reproducir cualquier señal con componentes espectrales de hasta 2 MHz con una potencia instantánea máxima de salida de 50 W. En este artículo se presenta una importante modificación del convertidor multinivel basada en una arquitectura de celda de tres estados. Se presenta una comparación entre estas dos posibles implementaciones de la celda multinivel. La topología de celda de tres estados tiene varias ventajas sobre la de dos estados: menor número de celdas y entradas de tensión y un diseño físico y eléctrico más sencillo. Se ha realizado una comparación de la energía manejada por cada topología de celda para diferentes señales de entrada. Se analiza su influencia en la eficiencia de cada topología de celda y en la optimización del diseño del amplificador de envolvente para ambas topologías. Adicionalmente se ha construido un prototipo para validar los estudios teóricos presentados y poder comparar más detalladamente ambas solucione

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 for EER. Two possible implementations of the multilevel cell are compared. In, 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

Comparison of Two Multilevel Architectures for Envelope Amplifier

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 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 compares two solutions for the envelope amplifier based on a combination of multilevel converter and linear regulator. The solutions are compared regarding their efficiency, size and weight. Both solutions can reproduce any signal with maximal spectral component of 1 MHz and give instantaneous maximal power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, the implemented prototypes have up to 19% higher efficiency than linear regulator that is used as a conventional solution

Two-Phase DC-DC Buck Converter for Power Amplifier Modulation

This thesis presents the theory, design, layout and a proposal for measurement set up of a synchronous DC-DC buck converter. This converter will be used as the supply modulator of power amplifier of mobile phones. The design is done using 45nm CMOS technology. Pmos and nmos switches are synchronously turns on and off for DC voltage conversion. Second order LC type filter is used to filter out the ac component from output. Two phase interleaving is done to reduce the output ripple voltage. Pulse Width Modulation (PWM) method is used for generating the control signal. Several techniques like dead time control mechanism, reduced gate drive voltage for switches are applied for improving the efficiency of the converter. The operating voltage range of the converter is 3.3-4.2V and it can produce 0.5-3V output voltage with 2W of maximum output power. It has maximum load current of 700mA. The switching frequency of the converter can be varied from 10MHz to 100MHz. The ripple voltage is less than 10mV for 50MHz switching frequency. The converter shows good results in terms of power density and simulated efficiency which are 1.65W/mm2 and 88.5%

The design of a multilevel envelope tracking amplifier based on a multiphase buck converter

Envelope Tracking (ET) and Envelope Elimination and Restoration (EER) are techniques that have gained in importance in the last decade in order to obtain highly efficient Radio Frequency Power Amplifier (RFPA) that transmits signals with high Peak to Average Power Ratio (PAPR). In this work a multilevel multiphase buck converter is presented as a solution for the envelope amplifier used in ET and EER. The presented multiphase buck converter generates multilevel voltage using “node” duty cycles and non-linear control. In this way the multilevel is implemented using only one simple power stage. However, the complexity of the multilevel converter implementation has been shifted from complicated power topologies to complicated digital control. Detailed discussion regarding the influence of the design parameters (switching frequency, output filter, time resolution of the digital control) on the performance of the proposed envelope amplifier is presented. The design of the output filter is conducted fulfilling the constraints of the envelope slew rate and minimum driver pulse that can be reproduced. In the cases when these two constraints cannot be fulfilled, they may be relieved by the modified control that is presented and experimentally validated. Finally, in order to validate the concept, a prototype has been designed and integrated with a nonlinear class F amplifier. Efficiency measurements showed that by employing EER it is possible to save up to 15% of power losses, comparing to the case when it is supplied by a constant voltage. Additionally, Adjacent Channel Power Ratio (ACPR) has been measured. The obtained results showed the value higher than 30dB for signals up to 5 MHz of bandwidth, without using predistortion technique