The AB‐C Doherty power amplifier. Part I: Theory

In this article, the complete theoretical analysis of a Doherty amplifier employing a Class AB bias condition for the Main and a Class C one for the Auxiliary devices, respectively, is presented. Starting from the simplified model of an active device, the analysis of the AB‐C Doherty behavior is carried out as a function of the input signal. In particular, the proposed approach is based on the analysis of the output drain current waveforms generated by the two active devices, while assuming a Tuned Load configuration (i.e., short circuit condition) for higher harmonic terminations. A closed form formulation is derived in order to directly design an AB‐C Doherty amplifier, while fully understanding the basis of its physical behavior. Finally, which Doherty parameters can be chosen by the designer or have to be implicitly fixed are discussed and clarified. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Doherty功率放大器的设计与分析

本文介绍了采用Doherty结构来设计高效率功率放大器。载波放大器和峰值放大器分别工作在AB类和C类状态。首先用ADS进行单管AB类和C类功放仿真设计,然后选择合适的延迟线来完成Doherty的整体设计,最终仿真结果显示Doherty功放在功率回退6db的情况下（43dbm）,其PAE达到了51％。     

A systematic design of 1.5–9 GHz high power–high efficiency two‐stage GaAs PHEMT power amplifier

In this article, a systematic design approach for a Class‐A operated wideband power amplifier is presented. The power amplifier structure comprises of two transistors in the cascaded single stage traveling wave amplifier topology. A power amplifier was designed by using the systematic approach and fabricated with 0.25 μm GaAs PHEMT MMIC process. The amplifier has an area of 3.4 × 1.4 mm². Measurement results show that almost flat gain performance is obtained around 15 dB over 1.5–9 GHz operating bandwidth. In most of the band, with the help of a wideband load‐pull matching technique, the amplifier delivers P_o,sat and P_o,1dB of around 30 dBm and 28 dBm where the corresponding power added efficiencies are >50% and >36%, respectively. It is shown that the proposed design approach has the advantage of simple and systematic design flow and it helps to realize step‐by‐step design for the designers. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:615–622, 2014.     

Design scheme for broadband Doherty power amplifier using broadband load combiner

This article proposes a design strategy for broadband Doherty power amplifier (PA) using broadband load combiner. The bandwidth of the Doherty PA based on the proposed combiner using packaged transistor is about 2.5 times the bandwidth of conventional Doherty PA using a quarter‐wave transformer. An easy to implement analytical design methodology has been presented for the proposed load‐combiner while describing the bandwidth enhancement strategy. The design methodology is validated with the design of a broadband Doherty PA based on CREE 10 W packaged GaN high electron mobility transistor devices using the proposed load combiner. Measurement results show more than 45% drain efficiency at 6 dB output power back‐off (OPBO) over 400 MHz frequency range, centred around 1.95 GHz. The peak drain efficiency at saturation is better than 60% over this band of operation. At 6 dB OPBO, the maximum improvement of 18.5% in drain efficiency is achieved as compared to the balanced mode PA. Measurement with single carrier wideband code division multiple access modulated signal shows the average drain efficiency of more than 44% at 36.6 dBm average output power at center frequency of operation. The adjacent channel power ratio is better than ?45 dBc after applying digital predistortion. The circuit is realized with microstrip technology, which can be easily fabricated using conventional printed circuit processes. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:655–674, 2015.     

Broadband Doherty power amplifier with improved band‐pass auxiliary network

In this article, a Doherty power amplifier (DPA) with improved band‐pass auxiliary impedance inverter is proposed for broadband operation. As a wideband DPA solution, the output matching networks of main and auxiliary devices are designed to achieve proper impedance matching at back‐off and peak power by employing a two‐point matching technique without the λ/4 impedance transformer. It is found that the modified band‐pass network has broader bandwidth feature and is compact in form from the comparison with some different topologies of matching networks. So, it is more suitable to be the auxiliary transformer to achieve the broadband configuration of DPA. For validation purpose, a Doherty power amplifier based on two commercially available gallium nitride HEMT (Cree CGH 40010F) devices was designed, fabricated, and measured. Under the drive of continuous wave (CW) signal, the measurement results show that the DPA has a 6‐dB back‐off efficiency of 35% to 48% and a saturated efficiency of 44% to 64% within the frequency band from 1.50 GHz to 2.35 GHz, which is about 44% fractional bandwidth.     

高效率的Doherty功率放大器设计

本文采用Doherty技术对高效率的功率放大器进行设计。利用ADS2008对放大器直流偏置,源、负载网络匹配,功率分配器以及功率放大器整体进行设计。观察仿真结果,可以看出补偿线的引入可以极大地提高Doherty结构的功率放大器增益和效率。     

一种基于2．14GHz功率放大器的预失真反馈延迟估计

反馈回路的延迟估计是功率放大器数字预失真技术的前提,本文提出了一种环路延迟估测方法,在考虑信道畸变的同时,降低了运算量。然后基于一款Freescale（MHL21336）2．14GHz的AB类功率放大器,采用无记忆预失真方法和正交记忆多项式预失真方法实验验证,结果表明该环路延迟估计算法能够使无记忆多项式预失真器的单载波WCDMA信号的ACPR（邻近信道功率比）改善近20dB,而对正交记忆多项式预失真方法大约可以改善24dB。     

High‐efficiency transmission‐line inverse Class F power amplifiers for 2‐GHz WCDMA systems

In this article, a novel load‐network solution to implement the transmission‐line inverse Class F power amplifiers for base station WCDMA applications is presented. The theoretical analysis is based on an analytical derivation of the optimum load‐network parameters to control the second and third harmonics at the device output, including the device output parasitic shunt capacitance and series inductance. The transmission‐line inverse Class F LDMOSFET and GaN HEMT power amplifiers using NXP BLF6G22LS‐75 and CREE CGH27060F devices, respectively, were designed and measured. The high‐performance results with the drain efficiency of 70.2% and power gain of 18.0 dB for a 60‐W LDMOSFET power amplifier and with the drain efficiency of 82.3% and power gain of 14.3 dB for a 50‐W GaN HEMT power amplifier were achieved at an operating frequency of 2.14 GHz. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

A simplified adaptive sparse digital pre‐distorter for joint mitigation of frequency‐dependent transmitter impairments

The interplay between the unavoidable various nonlinearities of the direct conversion transmitter, such as local oscillator leakage, power amplifier (PA) nonlinearities, and in‐phase and quadrature (I/Q) branch imbalance, and so forth will degrade the communication system performance seriously. To overcome these nonlinear interactive effects, an accurate adaptive sparse behavioral model is proposed for the joint compensation of the transmitter impairments in this article. First, a three‐input nonlinear joint compensation model, which is composed of the nonlinear frequency‐dependent cross terms between the I and Q branches as well as the magnitudes of the input signal, is developed. Second, to prune the redundant terms and reduce the computational complexity of the full three‐input model, an efficient robust quasi‐newton–based adaptive greedy algorithm is developed. To verify the performance of the proposed method, the different imperfect transmitters based on single‐device GaN Class‐F PA and GaN Doherty PA are used for experimental verification and analysis. Experiment results show that the proposed method can efficiently construct a sparse joint compensation model with improved modeling and distortion mitigation capability than the reported I/Q imbalance model, where nonlinear distortion and I/Q imbalance characteristics in the transmitter can be almost completely removed.     

Frequency reconfigurable RF circuits using photoconducting switches

Designs for a frequency switchable dual‐band branch‐line coupler and a reconfigurable S‐band power amplifier input matching network with photoconducting switches are presented. Frequency switching is achieved by increasing the power of the laser applied to the highly resistive silicon wafer and changing the properties of silicon under optical illumination. The advantages of this approach are high‐speed switching, electromagnetic transparency (no interference), and thermal and electrical isolation between the device and the control circuit. A branch‐line coupler frequency shift of 35% and 10% has been achieved from all switches off to all switches on in lower (900 MHz) and upper (1800 MHz) frequency bands, respectively. Frequency switchable class AB power amplifier with silicon switch in the input matching circuit has obtained the frequency tuning range of 2.5–3.5 GHz with no significant loss in efficiency and linearity. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Analysis and design of a novel concurrent Class B/J continuum power amplifier

In this paper, a novel concurrent Class B/J continuum mode is presented based on waveform shaping of current and voltage. The behavior characteristics and performances of power amplifiers (PAs) in concurrent dual‐band mode are investigated in detail. According to the analysis of proposed concurrent mode, the optimal load impedances at fundamental, harmonic and intermodulation (IM) frequencies are related to the magnitude ratio of the two carriers. Comparing with concurrent Class‐B mode, two parameters α, β can be configured independently in the proposed concurrent mode, which provides more freedom and flexibility for design without output power and drain efficiency degradation. In order to verify the proposed theory, a 1.9/2.35 GHz dual‐band power amplifier based on proposed concurrent mode is designed, fabricated and measured. Experimental results show that when the PA is driven by two 10 MHz LTE signals concurrently with total 9.2 dB peak‐to‐average power ratio (PAPR), the total average power is 36.0 dBm with 40.6% drain efficiency, which indicates a good concurrent performance.     

Efficiency‐enhanced Doherty power amplifier using Chireix‐like compensation technology

This article presents a novel efficiency‐enhanced Doherty power amplifier (DPA) by using a Chireix‐like compensation technique. This technique introduces a compensation circuit structure at the combiner to offset the phase difference effect of a DPA for enhancing drain efficiency. A DPA based on the proposed structure is fabricated with two 10 W GaN high electron mobility transistor (HEMT) transistors. The fabricated DPA with such proposed compensation structure manifests a measured saturated output power of 43.5 dBm and drain efficiency of 68% to 71% in the frequency range of 3.2 to 3.7 GHz. Forty‐five percent of drain efficiency can be achieved at 6 dB power back‐off. And the adjacent channel leakage ratio (ACLR) is better than ?48.6 dBc with digital predistortion.     

高效率线性功率放大器设计

3G信号的高峰均比和快速的包络变化为基站功率放大器的设计提出了新的挑战。结合Doherty技术与基带多项式预失真技术,设计了一款高效率线性功率放大器。仿真分析得到,放大器在输出为P1dB到回退6dB的范围内,效率超过38.4%。使用码率为3.6864Mcps的CDMA2000信号源测试,在输入功率为38.5dBm时,其输出信号的ACPR达到-45dBc。本设计在线性放大的条件下实现了从P1dB处回退6dB范围的高效率放大器。     

Investigation of load modulated inverse Class‐F power amplifier with extended conduction angle

A novel design space of load modulated (LM) inverse Class‐F power amplifiers (PAs) with extended conduction angle is proposed. The effects of the driven level factor β and the biasing operation factor ρ on the third‐harmonic generation are discussed. The harmonic generation mechanism shows that the knee voltage effects are the source of third‐harmonics for LM inverse Class‐F PAs. The definition of the inverse Class‐F mode is consistently valid under the circumstance of load modulation in a limited output power back‐off (OPBO) range. Meanwhile, the conduction angle θ₀ can be extended from π/2 to a limited value (<110°) to keep the standard waveforms of inverse Class‐F mode and maintain high efficiency. After introducing the “continuous concept” and the second harmonic manipulation method, the mathematical design space of inverse Class‐F PAs with extended conduction angle is derived. Calculation shows that the purely conductive load modulation can enable high back‐off efficiency operation for LM inverse Class‐F PAs. As proof of concept, a demonstrator amplifier is fabricated and measured. The experimental results show that the power added efficiency (PAE) with optimum V_ctrl is improved by 5% over an OPBO range of 6 dB compared with the same PA with fixed V_ctrl.     

Class G approach for low‐voltage,high‐efficiency PA design

Class G power amplifier (PA) design guidelines are presented and experimentally validated, showing the interesting features of the new approach. For the same operating conditions, the Class G amplifier exhibits superior performances if compared to a tuned load one in large signal gain, output power, and third‐order intermodulation (IM3), with a power‐added efficiency (PAE) improvement of 38.5%. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 366–378, 2000.     

Design of a high‐efficiency dual‐band class‐J/J power amplifier considering concurrent‐mode input drive

This article analyses concurrent dual‐band Class‐J/J power amplifiers (PAs) with simultaneous input drive at both bands. Although it is well known that the Class‐J PA has the same performance regarding the efficiency compared with the conventional Class‐B PA, in this article, we show that concurrent‐mode efficiency of Class‐J/J dual‐band power amplifier is higher than the Class‐B/B counterparts much closer to their single‐mode efficiency. Furthermore, it has been explained that the performance of concurrent operation of dual‐band PAs is highly dependent to the design space of PA load reactance at intermodulation terms. We also explore that at intermodulation frequencies the design space includes an efficiency degradation region occurring around a specific impedance, which should be avoided when designing for concurrent operation mode. The dependency of the concurrent‐mode efficiency to the nonlinearity performance of the transistor output capacitance is also considered. A concurrent dual‐band Class‐J/J PA operating at 1.842 and 2.655 GHz bands is implemented, where the harmonic and intermodulation control networks are designed based on closed‐form equations. Measured results reveal that about 60% balanced concurrent‐mode efficiency can be achieved, which outperforms recently reported counterparts. At the lower and upper bands, output powers of 41 and 40.5 dBm and efficiencies of 73.5% and 71.7% are obtained, respectively.     

Hybrid Ku‐band low‐noise amplifier for mobile DBS active phased‐array antennas

In this article we present a two‐stage Ku‐band low‐noise amplifier (LNA) using discrete pHEMT transistors on non‐PTFE substrates for low‐cost direct broadcast satellite (DBS) phased‐array systems (patent pending). The vertical input configuration of the LNA lends itself to direct integration with input port of antenna modules of the phased array, which minimizes preamplification losses. DC decoupling between LNA stages is realized using interdigital microstrip capacitors such that the implementation reduces the number of discrete microwave components and thereby not only reduces the component and assembly costs but also decreases the standard deviation of such crucial parameters of phased‐array systems as the end‐to‐end phase shift of the amplifier and the amplifier gain. Using the proposed printed decoupling capacitors, a cost reduction better than 30% of the original costs has been achieved. Additionally, we present a hybrid design procedure for the complete LNA, including its input and output connectors as well as packaging effects. This method is not based on parameter extraction, but encompasses electromagnetic (EM) field simulator results which are further combined using a high‐level circuit simulator. According to the presented measurement results, the implemented Ku‐band LNA has a noise figure better than 0.9 dB and a gain higher than 20 dB with a gain flatness of 0.3 dB over a 5% bandwidth. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Asymmetrical Doherty power architecture with an integrated driver stage in the auxiliary branch

This contribution presents the analysis, design and characterization of a high gain Doherty power amplifier implementing an integrated Driver stage in the Auxiliary branch. Guidelines and design equations are demonstrated, fulfilling the full integration of the whole new architecture. The development of a microwave monolithic integrated circuit prototype based on TriQuint GaN technology for 7 GHz applications is reported. 10.5 dB of Gain, 38.1 dBm of saturated output power and 42% of efficiency at 7 dB of output back‐off have been demonstrated by experimental results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:498–507, 2014.     

一种高线性度AB类CMOS功率放大器的设计与实现

率放大器作为发射机中最核心的模块之一,如何同时提高其效率和线性度一直是人们研究的热点。文章主要分析了AB类功率放大器中的主要非线性源—栅源电容对电路性能的影响,并且使用了一个PMOS管并联的技术来补偿这种影响,最后利用这种技术,采用JAZZ0.25um RF CMOS工艺实现了一个可应用于2.45GHz WLAN的高效率高线性度的AB类功率放大器,三阶交调(IM3)项为-12dBm,输出功率为26dBm,功率附加效率(PAE)为44%。     

Efficiency enhancement by employing the transistor nonlinear capacitors effects in a 6W hybrid X‐band Class‐J power amplifier

This article presents the design and fabrication of a 6 W X‐band hybrid Class‐J power amplifier (PA) based on a bare die GaN on SiC HEMT by accurate implementing the transistor nonlinear capacitor effects. The transistor input capacitor is precisely modelled and its nonlinearity effects on Class‐J performance is studied for the first time. It is shown that the harmonic generation property of the nonlinear input capacitor, especially at the second harmonic, can be of benefit to shape the transistor gate voltage as a quasi‐half wave sinusoidal waveform and consequently, it can improve the power added efficiency (PAE). A complete 3D thermal model of the power transistor is developed using ANSYS software and it is calibrated based on the thermal measured data. The PA achieves 13 dB average power gain over the frequency range of 8.8‐9.6 GHz. The drain efficiency and PAE are about 67% and 58% at 9.2 GHz, respectively.