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ABSTRACT: This paper introduces a method for bandpass cancellation of the quantization noise occurring in high efficiency, envelope pulsed transmitter architectures-or carrier bursting. An equivalent complex baseband model of the proposed system, including the -modulator and cancellation signal generation, is developed. Analysis of the baseband model is performed, leading to analytical expressions of the power amplifier drain efficiency, assuming the use of an ideal class B power amplifier. These expressions are further used to study the impact of key system parameters, i.e. the compensation signal variance and clipping probability, on the class B power amplifier drain efficiency and signal-to-noise ratio. The paper concludes with simulations followed by practical measurements in order to validate the functionality of the method and to evaluate the performance-trend predictions made by the theoretical framework in terms of efficiency and spectral purity.
Circuits and Systems I: Regular Papers, IEEE Transactions on 04/2012; · 1.97 Impact Factor
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ABSTRACT: A new switch-mode power-amplifier (SMPA) topology particularly suitable for energy efficient amplification of RF pulsewidth modulation (RF-PWM) signals is derived. It is analytically shown that high efficiency can be maintained over a wide power dynamic range if the imaginary part of the Class-E load impedance is varied along with the duty cycle (pulsewidth). Using the theory developed, an explicit design procedure is presented that allows practical realization of the proposed topology from the circuit and component specifications. Following the design procedure, and using in-house (Chalmers University, Göteborg, Sweden) SiC varactor diodes to implement the tunable imaginary load impedance, a 2-GHz 10-W peak output power GaN HEMT circuit demonstrator is realized. RF-PWM input signals for characterization of the prototype power amplifier (PA) is generated with a dedicated 65-nm CMOS modulator. The measurements show that a drain efficiency >; 70% can be obtained over an 6.5-dB dynamic range, which verifies the theory presented and demonstrates the feasibility of the proposed PA topology.
IEEE Transactions on Microwave Theory and Techniques 12/2011; · 1.85 Impact Factor
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ABSTRACT: This paper reports the design, implementation, and experimental results of two high efficiency GaN-HEMT power amplifiers (PAs) at 3.5 GHz and 5.5 GHz. A bare-die approach is used to eliminate package parasitics in conjunction with an in-house transistor model that enables investigation of the transistor intrinsic waveforms. With this as a basis, harmonic source-pull/load-pull simulations have been used to design and implement two state-of-the-art highly efficient harmonically tuned PAs. For the 3.5-GHz PA, large-signal measurement results show a PAE of 80%, a power gain of 15.5 dB, and an output power of 7 W, while for the 5.5-GHz PA, 5.6 W output power, 12.5 dB power gain, and 70% PAE are achieved.
Wireless and Microwave Technology Conference (WAMICON), 2011 IEEE 12th Annual; 05/2011
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ABSTRACT: In this article, the design of a high-efficiency harmonically tuned GaN HEMT PA has been presented. The PA presents state-of-the-art measured efficiency and gain performance at 3.5 GHz, demonstrating the success of the dedicated transistor modeling, the bare-die mounting and implementation technique, and the circuit design methodology.
IEEE Microwave Magazine 03/2011; · 2.11 Impact Factor
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ABSTRACT: This paper describes an optimization method for minimization of quantization noise in ΣΔ-based RF transmitters. The aim of the method is to enable the use of reconstruction filters with wider passband, or alternatively, a lower switch-rate. The method uses a general representation of the ΣΔ converters in combination with a differentiable approximation of the quantizer. Based on this, a Monte Carlo-based algorithm is developed around the damped Gauss-Newton iteration. As a result of the suggested algorithm, the residual quantization noise after reconstruction filtering is significantly decreased. Finally, simulations using a bandlimited signal with a Gaussian distribution are used to demonstrate the capabilities of the suggested algorithm when applied with the proposed ΣΔ modulator representation. The resulting performance is compared to several cases of ΣΔ converters designed using traditional methods, demonstrating significant improvements in terms of reduced reconstruction normalized mean square error. This implies that the transmitter efficiency can be improved with minor changes in the modulator implementation.
Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2011; · 1.97 Impact Factor
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ABSTRACT: In this paper, the high potential of varactor-based dynamic load modulation (DLM) techniques for wideband cellular applications is demonstrated. A systematic design procedure is proposed to ensure high-efficiency wideband performance. It incorporates harmonically tuned power amplifier (PA) concepts and tunable matching techniques in an integrated design. A DLM transmitter at 2.65 GHz with a peak output power of 6 W is designed using the proposed procedure. In order to investigate the wideband performance of the implemented demonstrator, WCDMA signals with scaled bandwidths are employed. The signal peak-to-average ratio is 7 dB and the same for all the experiments. For the 38.4-MHz signal, which has a corresponding channel bandwidth of > 40 MHz, an average power added-efficiency (PAE) of 44%, normalized mean square error (NMSE) of -35 dB, and adjacent channel leakage ratio (ACLR) of -43 dBc are measured.
IEEE Transactions on Microwave Theory and Techniques 12/2010; · 1.85 Impact Factor
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ABSTRACT: A band-reconfigurable LDMOS high power amplifier (PA) with state-of-the-art performance is presented. The frequency reconfigurability is implemented by band-switchable matching networks using PIN diodes. The PA provides power-added efficiencies which are higher than 61% and output power levels exceeding 8 W at 0.9 GHz, 1.5 GHz, and 1.9 GHz. The input return loss in all the three bands is better than 12 dB.
Microwave Conference (EuMC), 2010 European; 10/2010
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ABSTRACT: In this paper, the design, implementation, and experimental results of a high-efficiency wideband GaN-HEMT power amplifier are presented. A method based on source-pull/load-pull simulation has been used to find optimum source and load impedances across the bandwidth and then used with a systematic approach to design wideband matching networks. Large-signal measurement results show that, across 1.9-4.3 GHz, 9-11-dB power gain and 57%-72% drain efficiency are obtained while the corresponding power-added efficiency (PAE) is 50%-62%. Moreover, an output power higher than 10 W is maintained over the band. Linearized modulated measurements using a 20-MHz long-term evolution signal with 11.2-dB peak-to-average ratio show an average PAE of 27% and 25%, an adjacent channel leakage ratio of -44 and -42 dBc at 2.5 and 3.5 GHz, respectively.
IEEE Transactions on Microwave Theory and Techniques 08/2010; · 1.85 Impact Factor
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ABSTRACT: In this paper, the efficiency of a GaN HEMT transistor and its intrinsic waveforms are measured at 0.9 GHz and investigated for load- and supply-modulation applications. The results show that both techniques perform equally well for back-off levels ≤ 6.5 dB. At higher back-off levels, the efficiency improvements achieved by supply modulation outperform load modulation. At 10 dB back-off, supply, and load modulation provide a power-added efficiency (PAE) of 68%, and 58%, respectively. Using measured intrinsic waveforms, it is shown that PAE degradations in load modulation can be mainly attributed to parallel losses rather than series losses, which are dominant in supply modulation. The harmonic contents of the intrinsic waveforms, in both techniques, are equally strong in back-off and peak power operations. There is, therefore, a great potential for further efficiency enhancement by circuit-level optimization of harmonic terminations for back-off.
Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
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ABSTRACT: In this paper, a detailed linearization procedure for dynamic load modulation (DLM) transmitter architectures is proposed for the first time. Compared with the conventional single-input/single-output digital predistortion (DPD) approach used with traditional power amplifiers (PAs), the proposed linearization scheme is based on a regular memory DPD in combination with an efficiency-optimized static one-to-two mapping inverse model, which constructs the predistorted input signals to the DLM transmitter. The time-alignment issue, which is very important to this dual-input architecture, is also considered. The proposed technique is demonstrated by a 1-GHz 10-W LDMOS PA that employs a varactor-based tunable matching network. A normalized mean square error of -35 dB, and adjacent channel leakage ratio of -43 dBc is achieved, with an average power-added efficiency of 53% for a single-carrier WCDMA signal with 7-dB peak-to-average ratio. Finally, it is shown that the time-alignment sensitivity is relaxed when the proposed linearization scheme is used. This means that the overall complexity of the transmitter implementation can be reduced.
IEEE Transactions on Microwave Theory and Techniques 05/2010; · 1.85 Impact Factor
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ABSTRACT: This paper presents results for a dynamic load modulation transmitter where an existing 1 GHz LDMOS power amplifier is combined with a varactor based tuneable load network to produce a dramatic efficiency improvement for modulated signals. The transmitter is combined with a dedicated linearization method to achieve an average PAE of 53% for a WCDMA signal at 7 dB PAPR. The results demonstrate the potential of dynamic load modulation for future transmitters combining flexibility and high efficiency at a low cost.
RF Front-ends for Software Defined and Cognitive Radio Solutions (IMWS), 2010 IEEE International Microwave Workshop Series on; 03/2010
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ABSTRACT: This paper presents the design and implementation of an inverse class F power amplifier (PA) using a high power GaN HEMT transistor. For a 3.5 GHz continuous wave (CW) signal, the measurement results show state-of-the-art power-added efficiency (PAE) of 78%, a drain efficiency of 82%, a gain of 12 dB, and an output power of 11 W. Moreover, drain efficiency is maintained over 60% and the output power level is higher than 10 W over 300 MHz bandwidth. To our knowledge, the presented power amplifier represents the highest efficiency for all switching mode PAs that have been reported for high power applications at frequencies above 2 GHz.
Microwave Conference, 2009. EuMC 2009. European; 11/2009
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ABSTRACT: A time alignment algorithm is proposed for a dynamic load modulation transmitter architecture. The effect of time mismatch between the RF input and baseband control signal is investigated by experiments, and it is shown that unsynchronized signals can result in severe distortion of the output signal. In this paper, cross correlation and sinc interpolation techniques are applied to estimate and compensate for the sub-sample delay between the RF signal path and the baseband control signal path in the measurement system. The performance of the dynamic load modulation transmitter architecture with accurate time alignment is shown by experimental results. The measurement shows that, the efficiency is greatly affected by time alignment and the spectral regrowth is suppressed by more than 10 dB.
Microwave Conference, 2009. EuMC 2009. European; 11/2009
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ABSTRACT: A 10-W LDMOS harmonically tuned power amplifier at 1 GHz with state-of-the-art power-added efficiency of 80% is presented. The fundamental and second-harmonic load impedances are optimized for maximum efficiency while other harmonics are blocked by a low-pass load network. A simplified model of the transistor specialized for harmonically tuned and switched mode operations is proposed and used for the design. Good agreement between simulations and measurements is observed, indicating high accuracy of the model and design approach for these particular applications.
IEEE Transactions on Microwave Theory and Techniques 08/2009; · 1.85 Impact Factor
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ABSTRACT: In this paper we describe a novel method for selective bandpass cancellation of the quantization-noise that occurs in pulsed transmitter architectures, where the signal is partially or completely quantized. A carrier bursting transmitter architecture, where the amplitude part is quantized and then recombined with a phase-modulated RF carrier, is used as a general example to demonstrate the principles of the method proposed. Measurements on a high efficiency 10 W LDMOS PA working at 1 GHz are used to verify the theoretical results.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: In this paper, the results of dynamic load modulation on a high power amplifier is shown with experiments. A simple static nonlinear model is used as an inverse model, and by dynamically controlling both the input signal to the power amplifier and the load impedance, high efficiency operation of the power amplifier is achieved. The modulated measurements show the feasibility of dynamic load modulation for practical high power, high frequency applications.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: A dynamic load modulation characterization method is presented. The method gives insight into the device operation under dynamic load modulation conditions. The presented method is based on an active injection load-pull system. The load impedance is dynamically controlled to follow an optimum trajectory, resulting in higher efficiency in back-off operation. On-wafer measurements at 2.14 GHz using a LDMOS device are used to demonstrate the method. The measured results show excellent agreement between static characterization and dynamic measurements.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: In this paper, the design of varactor-based tunable matching networks for dynamic load modulation of high power amplifiers (PAs) is presented. Design guidelines to overcome the common breakdown, and tunability problems of the varactors for high power applications are proposed. Based on the guidelines, using commercially available abrupt junction silicon varactors, a tunable matching network is built and measured. The matching network is then used for load modulation of a 1-GHz 7-W class-E LDMOS PA. Static measurements of the load modulated PA show that the power-added efficiency of the PA is improved by an absolute value of 10% at 10-dB backoff. This promising result proves, for the first time, the feasibility of load modulation techniques for high-power applications in the gigahertz frequency range.
IEEE Transactions on Microwave Theory and Techniques 06/2009; · 1.85 Impact Factor
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ABSTRACT: In-phase/quadrature (I/Q) imbalance is one of the main sources of distortion in RF modulators. In this paper, a dual-input nonlinear model based on a real-valued Volterra series is proposed for compensation of the nonlinear frequency-dependent I/Q imbalance. First, different sources of distortion are identified from experimental measurements, then a dual-input nonlinear I/Q imbalance model is developed. Further, the inverse model is used for I/Q imbalance compensation. Finally, the performance of the I/Q imbalance compensator is evaluated with both simulations and experiments. In comparison with previously published results, the proposed I/Q imbalance compensator shows significantly improved performance. Thus, we prove that a complete nonlinear I/Q imbalance compensation can minimize the effects of the RF modulator in high-performance digital communication systems.
IEEE Transactions on Microwave Theory and Techniques 04/2009; · 1.85 Impact Factor
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ABSTRACT: This paper focuses on modeling and compensation of both linear and nonlinear distortions in RF I/Q modulators using a dual-input Volterra series-based modeling approach. Moreover, dual-input memory polynomial and dual-input dynamic deviation reduction-based Volterra series models are proposed. The proposed models are evaluated by digital pre-compensation of a high performance I/Q modulator with a wideband input signal. The results show that the proposed dual-input models efficiently compensate for distortion in the I/Q modulator and may therefore greatly improve performance in modern communication systems.
Radio and Wireless Symposium, 2009. RWS '09. IEEE; 02/2009
