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Advanced Doherty power amplifier design for modern communication systems
2018
Mobile communication technologies are becoming increasingly sophisticated and have experienced rapid evolution over the last few decades, and this is especially true for the base station transmitter. In response to the ever increasing demand in communication traffic and data throughput, largely driven by video based social media platforms, both spectral and power efficient device and systems are needed to fulfil the requirements. In terms of energy consumption, the power amplifier is an important component, and although developing efficient technologies for handset equipment is important, it is the base station element of the communications system that poses the greater challenge, having to deal with many channels simultaneously, resulting in the need to linearly and efficiently amplify highly dynamic phase and amplitude modulated signals possessing very large peak-to-average power ratios, at high power levels. This unique set of challenges has led to continuous research to improve ...
The Doherty Power Amplifier: Review of Recent Solutions and Trends
IEEE Transactions on Microwave Theory and Techniques, 2015
In this work, an extensive review of the most up-todate papers on microwave Doherty power amplifiers is presented. The main applications are discussed, together with the employed semiconductor technologies. The different research trends, all aimed to improve the advantages of the Doherty scheme and to solve its inherent drawbacks, are presented. The first considered topic is the maximization of efficiency and/or linearity, where analog and digital techniques are exploited. Another important trend is the bandwidth enlargement of the Doherty architecture, that involves a large number of papers. Multi-band, multi-mode solutions are also considered, using either fixed or reconfigurable solutions. The final section is dedicated to the most significant Doherty integrated implementation.
High Efficiency Doherty Power Amplifier Historical Aspect and Modern Trends
This overview of the Doherty amplifier covers broadband capabilities of a two-stage amplifier, conventional Doherty architectures, a digitally driven Doherty technique, and the amplifier applied to microwave integrated circuits. ABSTRACT | In modern wireless communication systems, it is very important to realize simultaneously high-efficiency and linear operation of power amplifiers. This paper-overview describes the historical aspect of the Doherty approach to the power-amplifier design introduced in 1936 and modern trends in Doherty amplifier (DA) design techniques using multistage and asymmetric multiway architectures. To increase efficiency over the power backoff range, the switchmode class-E, conventional class-F, or inverse class-F operation mode by controlling the second and third harmonics can be used in the load network. The DA with a series-connected load, and inverted, pushpull, balanced, and parallel Doherty architectures are also described and discussed. Finally, examples of the lumped DA implemented in monolithic microwave integrated circuits, digitally driven Doherty technique, and broadband capability of the two-stage DA are given.
Experimental investigation on efficiency and linearity of microwave Doherty amplifier
2001 IEEE MTT-S International Microwave Sympsoium Digest (Cat. No.01CH37157), 2001
We have investigated the microwave Doherty amplifier, testing for efficiency and linearity. For the experiment, a 1.4GHz Doherty amplifier has been implemented using a silicon LDMOSFET. The Doherty amplifier-I(a combination of a class B carrier amplifier and a class C peaking amplifier) and the Doherty amplifier-II(a combination of a class AB carrier amplifier and a class C peaking amplifier) have been compared with class B and AB amplifiers, respectively, using single-tone, two-tone, and forward-link CDMA signals. It demonstrated the superior performance of Doherty amplifiers. The results provide a topology selection guide of the CDMA base station power amplifier to achieve both linearity and efficiency enhancements.
2005 European Microwave Conference, 2005
We have proposed advanced design methods of Doherty amplifier for high efficiency base station power amplifiers with wide bandwidth. First, we develop Doherty amplifier with uneven power drive which is provided more input power to the peaking cell than the carrier cell for full power operation and appropriate load modulation. Second, we optimize the matching circuits of the carrier and peaking cells individually to enhance the linearity and efficiency. Third, we optimize the bias circuit to solve an asymmetric ACLR(Adjacent Channel Leakage Ratio) characteristics for wideband signals such as WCDMA 4FA. The proposed design methods are applied to implement Doherty amplifier using a MRF5P21180. For a 2.14 GHz WCDMA 4FA signal, the amplifier is optimized at 25 W average output power. The drain efficiency and ACLR measured at the power are 33 % and -41 dBc, which represent about 1.3 % and 3 dB improvements, respectively, compared to the Doherty amplifier with even power drive. Additionally, the PEP of the amplifier is about 180 W, while that of the comparable Doherty amplifier is about 165 W. The difference of ACLR with the bias circuit optimization between lower and upper ACLR is reduced below 2 dB at whole average output power range.
Microwave Doherty Power Amplifier for High Efficiency and Linearity
2006 International Workshop on Integrated Nonlinear Microwave and Millimeter-Wave Circuits, 2006
This paper explains the basic circuit configuration of microwave Doherty amplifier and additional design methods for wide bandwidth and high power applications. This paper also presents the recent experimental results of our group using the uneven power drive. Most of the previous works about microwave Doherty amplifier have employed identical input drives. In this works, two 1:1(2-way) and a 1:2(3-way) Doherty amplifiers are implemented at 2.14GHz center frequency using LDMOS with a peak envelope power of 180 watt and 285 watt, respectively. The 2-way Doherty amplifiers are optimized at 25 watt average output power for high efficiency and linearity and the 3-way Doherty amplifier at 16 watt average output power for high linearity. The amplifiers are tested using WCDMA 4FA signal. The performances of the 2-way Doherty amplifier are compared with that of the comparable class AB amplifier and the Doherty amplifier with even power drive. The performances of the 3-way Doherty amplifier are compared with that of the comparable class AB amplifier. The experimental results show the superior performances of our Doherty amplifiers.
A high efficiency Si LDMOS Doherty power amplifier with optimized linearity
2009 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference (IMOC), 2009
This paper presents a high efficiency uneven UMTS Doherty power amplifier (DPA) based on Si LDMOS technology. An optimum output combining network was designed to enhance the efficiency at backoff power. High efficiency Si LDMOS transistors were used for the DPA design. The designed DPA has a maximum output power of P sat =39.7 dBm (9.4 W). A maximum drain efficiency of η max =54 % (PAE max =40 %) was measured. The efficiency was maintained above η=40 % (PAE =36 %), over 6 dB backoff, and above η=32 % (PAE=30 %), over 9 dB backoff, relative to the maximum (saturated) output power. The designed PA was experimentally optimized to enhance its linearity. For a 1-carrier W-CDMA test signal, an ACPR of -44 dBc was measured at an average output power of P out =30.7 dBm.
Highly efficient 3-stage Doherty power amplifier using gate bias adaption
International Journal of Microwave and Wireless Technologies, 2010
ildu kim, junghwan moon, jungjoon kim, seunghoon jee, junghwan son and bumman kim This paper demonstrates a highly efficient 3-stage Doherty power amplifier (PA) employing an envelope tracking (ET) technique. The '3-stage' Doherty PA is the most efficient architecture for a high peak-to-average power ratio (PAPR) signal among the various Doherty PAs. However, because of the lower peaking biases than those of the 'N-way' Doherty PA, the proper load modulation is hard to be achieved. To get proper modulation, the peaking PAs' gate biases have been adaptively controlled using the ET technique, and the peak power and maximum efficiency characteristic along the backed-off output power region is successfully achieved. By ADS and Matlab simulations, the overall behavior of the 3-stage Doherty PA employing the ET technique has been fully analyzed. To maximize the overall efficiency of the proposed 3-stage Doherty PA, the unit PA has been designed using class F 21 PA. For verification, the amplifier is implemented using 5 W and 10 W PEP LDMOSFETs for the 802.16e mobile world interoperability for microwave access (WiMAX) at 1 GHz with a 8.5 dB PAPR. The measured drain efficiency of the proposed 3-stage Doherty PA is 55.5% at an average output power of 37 dBm, which is a 7.54 dB backed-off output power. The digital feedback predistortion (DFBPD) algorithm has been used to linearize the proposed PA considering the ET technique. After linearization, the 233.15 dB of relative constellation error (RCE) performance is achieved, satisfying the system specification. These results show that the 3-stage Doherty employing the ET technique and saturated PA is the most suitable PA for the highly efficient and linear transmitter.
Broadband Doherty Power Amplifier
In this paper, the transformer-less loadmodulated (TLLM) architecture for designing broadband Doherty amplifiers is presented. In this architecture, the quarter-wave impedance transformers of the Doherty amplifier are not used. As a result, the design will be much more compact and large operational bandwidths can be obtained. The simulation results for an amplifier implemented using this architecture shows that drain efficiency of higher than 47% is obtainable at 6dB power back-off in 1.7-2.8GHz frequency range (50% fractional bandwidth).
IEEE Transactions on Microwave Theory and Techniques, 2000
This paper proposes a new method for extending the bandwidth of Doherty power amplifiers (PAs) in the digital domain. The bandwidth enhancement is achieved through a frequency-selective pre-compensation mechanism that is derived to prevent the efficiency degradation that naturally occurs as the frequency of operation deviates from the center frequency. A methodical analysis of the frequency response of the conventional Doherty PA and that of the proposed Doherty PA is carried out to point out the limitations of the former and demonstrate the capability of the latter in recovering the bandwidth. Over the frequency range spanning from 1.96 to 2.46 GHz, the measured drain efficiency at 6-7-dB output power back-off is higher than 40% for the proposed Doherty PA. Such efficiency performance is achievable only from 2.04 to 2.22 GHz using the conventional Doherty PA. Hence, the bandwidth is enhanced from 180 to 500 MHz, which corresponds to an increase by a factor of 2.8 (i.e., almost triple). By applying the proposed methodology, a Doherty PA that is originally designed at the center frequency of 2.14 GHz for downlink wideband code division multiple access became operative at 1.98-GHz uplink wideband code division multiple access (UL-WCDMA), 2.22-GHz long-term evolution (LTE), and 2.34-GHz worldwide interoperability for microwave access (WiMAX) bands. The average drain efficiencies for UL-WCDMA, LTE, and WiMAX applications, were 40.1%, 44.2%, and 41.4%, respectively, using the proposed Doherty PA, and 37%, 37.3%, and 35.2%, respectively, using the conventional Doherty PA.