Linear Amplification With Nonlinear Components Research Articles

A review of different structures of power amplifiers to improve linearity and efficiency

<p>This review paper presents a comprehensive study of commonly used power amplifier (PA) structures. In recent years, with the development of modern wireless telecommunications and their dramatic challenges, new requirements are needed. In addition, some applications, like cell phones and tablets for example, need new considerations, especially in terms of power consumption. Also, linearity is another major factor in designing a PA. Furthermore, fabrication technologies such as complementary metal-oxide semiconductor (CMOS), silicon on insulator (SOI), gallium nitride (GaN), gallium arsenide (GaAs), etc., play a crucial role in terms of power consumption. Therefore, it is necessary for PAs to meet these considerations. This paper reviews design considerations, fabrication technologies and common PA structures including envelope tracking (ET), envelope elimination and restoration (EER), Doherty, linear amplification with nonlinear components (LINC), feedback and feedforward linearization techniques with their pros and cons. This review focuses on the significant achievements, techniques, structures and characteristics of each. Also, this review focuses on the significant achievements, techniques, structures and characteristics of each. Also, this paper tries to provide a brief overview of the various methods with the advantages and disadvantages of each. This review paper tries to make readers familiar with common structures so that readers know the advantages and disadvantages of each and choose the desired structure based on their priorities.</p>

Phase-Only Multilevel LINC Architecture for Linearizing Chireix Outphasing Power Amplifiers

This letter presents a distinct approach to linearize Chireix outphasing power amplifiers (PAs), which is leveraging the multilevel linear-amplification-with-nonlinear-components (LINC) concept. The proposed architecture operates only on phase-modulated signals and is therefore compatible with digital-like signal generation and distribution. The analysis of the architecture and a calibration algorithm are presented. The validity of the proposed concept is verified by the implementation of a prototype operating at 3.5 GHz, providing 42 dBm of peak output power. The prototype achieves −40.8 and −39.4 dB adjacent channel leakage ratio (ACLR) and 1.73% and 1.94% error vector magnitude (EVM) for a 64- quadrature amplitude modulation (QAM) modulated signal with 6.5 dB PAPR at 10 and 20 MHz bandwidth (BW), respectively. For an orthogonal frequency-division multiplexing (OFDM) modulated signal with 8.3 dB PAPR at 10 MHz BW, the ACLR and EVM are −40.2 dB and 2.64%, respectively.

Outspacing Planar Phased Arrays for Wireless Communications Infrastructure

The future mobile-data demand, driven by 5G and 6G wireless communications, puts enormous pressure on the required infrastructure. Especially the need for higher data rates and corresponding higher operating frequencies calls for new transmitter concepts with improved power-added efficiencies. Outspacing, which combines outphasing, also known as linear amplification with nonlinear components (LINC), a phased array, and spatial power combining, could be a promising solution for these challenging performance requirements. In this paper, an extended array-level analysis is performed on the efficiency, mutual coupling, and transmit performance of outspacing arrays supported by new performance metrics, since conventional metrics show to be insufficient for analyzing the outspacing concept. The analysis of the concept is performed on two different planar outspacing configurations. The presented outspacing concept with an element spacing of λ 0 / 2 appears to be very suited for applications that require a limited scan range, typically smaller than ±20°. A prototype is realized and characterized for a limited-scan scenario at 2.4 GHz to limit technology-related risks in the verification of the outspacing concept. The outspacing planar array is tested using an over-the-air (OTA) test concept applied in an anechoic test facility. An error vector magnitude below 3%, when transmitting a QAM16 signal, is realized in the main beam of the antenna without the use of calibration. Furthermore, an analysis is done on additional efficiency improvements. The active reflection coefficient, which is strongly related to the mutual coupling between the array elements, appears to have very interesting properties for improving amplifier drain efficiency by active load modulation.

LINC Method for MMIC Power Amplifier Linearization

Background: This article proposes the design and implementation of a MMIC (monolithic microwave integrated circuits) Power amplifier using the ED02AH process. Methods: The MMIC ED02AH technology have been developed specifically for microwave applications up to millimeter waves, and for high-speed digital circuits. The use of a single branch of a power amplifier can produce high distortion. In the present paper, the Linear amplification with nonlinear components (LINC) method is introduced and applied as a solution to linearize the power amplifier, it can simultaneously provide high efficiency and high linearity. To validate the proposed approach, the design and characterization of a 5.25 GHz LINC Power Amplifier on MMIC technology is presented. Results: Good results have been achieved, and an improvement of about 37.50 dBc and 59 dBc respectively is obtained for the Δlower C/I and Δupper C/I at 5.25 GHz. Conclusion: As a result of this method, we can reduce the Carrier Power to Third-Order Intermodulation Distortion Power Ratio. Excellent linearization is obtained almost 37.6 dBc for Δlower C/I and 58.8 dBc for Δupper C/I.

Generalized LINC

Achieving a power-efficient and a linear amplification at the same time is a considerable challenge, especially when the signals present large envelope fluctuations, as is the case of orthogonal frequency division multiplexing (OFDM) signals. The linear amplification with nonlinear components (LINC) technique is an alternative where two amplifying branches are combined to obtain a power-efficient amplification. In this work, we propose the generalized LINC, a technique which involves several amplification branches that can be combined either in the transmitter (multi-branch LINC (MB-LINC)) or in the channel (multi-antenna (MA-LINC)), both presenting advantages over conventional LINC schemes. We also study theoretically the nonlinear distortion effects in the generalized LINC techniques, showing that they are comparable to those of conventional LINC.

Improvement of Carrier Power to Third-Order Intermodulation Distortion Power Ratio for a Power Amplifier at 5.25 GHz using LINC Method

Introduction:This paper focuses on improving the power amplifier linearity for wireless communications. The use of a single branch of a power amplifier can produce high distortion with low efficiency.Method:In this paper, the Linear Amplification with Nonlinear Components (LINC) technique is used to improve the linearity and efficiency of the power amplifier. The LINC technique is based on converting the envelope modulation signal into two constant envelope phase-modulated baseband signals. After amplification and combining the resulting signals, the required linear output signal is obtained. To validate the proposed approach, LINC technique is used for linearizing an amplifier based on a GaAs MESFET (described by an artificial neural network Model).Conclusion:Good results have been achieved, and an improvement of about 40.80 dBc and 47.50 dBc respectively is obtained for the Δlower C/I and Δupper C/I at 5.25 GHz.

Efficiency enhancement by reconfigurable matching networks in LINC transmitters

This paper proposes the use of a transmitter based on a linear amplification with nonlinear components (LINC) architecture, in which the reconfigurable matching networks (RMNs) are included. By varying the RMN active cell number, it is possible to change the load impedance at the power amplifier (PA) output, improving the amplifier drain efficiency and therefore the efficiency of the whole system. A long-term evolution (LTE) downlink signal with a bandwidth of 1.4 MHz and a peak-to-average power ratio (PAPR) of 11.48 dB is applied in order to carry out the experiments. Results show that the use of the RMNs in a LINC architecture improves the efficiency at all tested frequencies, especially at 927 MHz reaching an enhancement of 36.50%. Regarding the distortion, the adjacent channel leakage ratio (ACLR) values increase in all cases, with an improvement of 3.5 dB at 958 MHz. Finally, in terms of error vector magnitude (EVM), the proposed architecture offers a value of 1.96% at 927 MHz.

Ring-type Magnitude Modulation for LINC: a pragmatic approach to the efficiency challenge

This paper considers the use of the linear amplification with nonlinear components (LINC) technique for the power amplification of spectrally compact offset quadrature phase shift keying (OQPSK) signals allowing the use of highly efficient, low cost, and strongly nonlinear high power amplifiers (HPAs). However, the performance of the LINC signal separation and power combining procedures decreases with the rise of the signal’s peak-to-average power ratio (PAPR). A new ring-type magnitude modulation (RMM) method is proposed for OQPSK signals that limits both its maximum and minimum complex envelope excursions avoiding zero crossings, without spreading the transmitted signal’s spectrum. The performance results show that band-limited OQPSK signals whose envelope has low fluctuations produce LINC components with a narrower spectrum, with a considerable impact on the LINC transmitter regardless of the type of combiner chosen: when using a passive/matched combiner, the transmitter’s power efficiency is significantly increased without spreading the combined signal’s spectrum; for the highly efficient non-linear Chireix combiner, there is a reduction of the amount of spectral leakage produced by nonlinearly combining the LINC signal components. Finally, an iterative decoding scheme is also proposed, which employs estimates of the received symbols’ RMM coefficients to compensate the RMM distortion.

Maximum likelihood detection for coded combinerless LINC-OFDM systems

Owning to the high peak-to-average power ratio problem, the power efficiency of orthogonal-frequency-division-multiplexing (OFDM) systems is usually low. It deteriorates in millimeter wave systems in which the design of an efficient linear power amplifier is much more challenging. The linear-amplification-with-nonlinear-component (LINC) technique can serve as a remedy, decomposing the input signal into two constant-envelop component signals followed by high-efficient nonlinear amplifiers. However, the power combiner, a key component used to combine the amplified signals, is difficult to implement. Combinerless LINC systems employ two transmit antennas such that two component signals can be naturally combined at the receiver. Unfortunately, the performance of combinerless LINC-OFDM systems is seriously degraded if difference, even small, exists between the two channels. The maximum likelihood (ML) receiver can effectively solve the problem; however, its computational complexity is prohibitedly high. We propose a coded combinerless LINC-OFDM system, including a convolutional encoder and a list Viterbi algorithm (LVA) decoder, to solve the problem. The LVA can provide a small number of candidates for the ML detector, dramatically reducing the required computational complexity. We also utilize an enhanced zero-forcing equalizer such that the soft-demapping operation can be effectively conducted. Finally, we propose a simple iterative interference cancellation scheme to further enhance the performance. Simulations show that the proposed combinerless LINC-OFDM system can outperform the conventional OFDM while the consumed power is much lower.

Design of high efficient 3-level LINC transmitter using a 9-point finite difference method

An efficiency of linear amplification with nonlinear components (LINC) system is degraded due to the low efficiency of a power combiner for high peak-to-average power ratio signals such as long-term evolution signal. A multi-level LINC system can be used to improve the performance of the conventional LINC system. In this paper, a novel 9-point finite difference method to determine the optimal threshold values for 3-level LINC system is suggested. Instead of solving the complicated differential equation, the proposed method can extract optimal threshold values efficiently by numerical method. The 3-level LINC system adopting the proposed scheme and dynamic biasing significantly improves the power efficiency and linear performance simultaneously. The proposed system is verified by comparing the performance of the 3-level system with those of the conventional and 2-level LINC systems.

Mismatch Calibration in LINC Power Amplifiers Using Modified Gradient Algorithm

One of the power amplifiers linearization technique is linear amplification with nonlinear components (LINC).The effects of phase and gain imbalances between two signal branches in LINC transmitters have been analyzed in this paper. Then a feedback path has been added to compensate this mismatches, using two complex gain in each path.This complex gains are controlled in a way to calibrate any gain and phase mismatches between two path using Modified Gradient Algorithm (MGA) adaptively. The main advantages of this algorithm over other algorithms are zero residual error and fast convergence time. In the proposedarchitecture power amplifiers in each path are modeled as a complex gain which its phase and amplitude depend on input signal level. Many simulations have been performed to validate the proposed self calibrating LINC transmitter. Simulation results have confirmed the analyticalpredictions. According to simulation results the proposed structure has around 40 dB/Hz improvement in the first adjacent channel of the output signal spectrum.

A Hybrid Polar-LINC CMOS Power Amplifier With Transmission Line Transformer Combiner

This paper demonstrates the implementation of a hybrid polar linear amplification with nonlinear components (LINC) power amplifier (PA) that uses the combination of polar and LINC schemes. The hybrid polar-LINC operation is based on the idea of representing envelope information with the combination of the two schemes. The high bandwidth burden of a supply modulator in a polar transmitter can be effectively relieved, and the back-off efficiency of a LINC transmitter is improved. The implementation is accomplished with a CMOS PA and a CMOS supply modulator. The designed PA includes a class-E amplifier and the proposed output combiner, which is based on a transmission line transformer with isolation resistors. Since the combiner keeps the operating condition of PAs intact regardless of the phase differences, out-phased signals for LINC can be linearly combined. The implemented hybrid polar-LINC architecture, including the PA and a supply modulator, has a 28.5-dBm maximum linear power and 29.6% efficiency without any pre-distortions.

Behavioral Modeling and Design of Predistortion for Wireless Transmitters with Multi-Branch RF Power Amplifier

In this paper, behavioral modeling approach and predistortion design methods are proposed for wireless transmitters with multi-branch radio frequency (RF) power amplifiers (PAs). Multi -branch RF PA architectures are studied such as balanced RF PA systems and linear amplification with nonlinear component (LINC) systems. Conventional behavioral modeling using single input and single output data cannot extract the behaviors of RF PAs in each branch. The behavioral modeling method using separated input signals and weighted input identification is proposed to extract accurate behavioral models for each branch. A decentralized predistortion structure that consists of multi-branch memory polynomial architecture predistortion components is proposed. The proposed behavioral modeling method is used for the design of decentralized predistortion using indirect learning method. The performances of proposed modeling and predistortion method are evaluated by comparing the normalized mean square error (NMSE) values with conventional single-branch behavioral modeling and predistortion. The input signal is 10MHz long-term evolution (LTE) signal. The results show that the proposed behavioral modeling and decentralized predistortion architecture are suitable for wireless transmitters with multi-branch RF PAs.

Adaptive bias LINC transmitter design using EDA software for power efficiency improvement

In this article, a novel adaptive bias LInear amplification with Nonlinear Components (LINC) transmitter is introduced and analyzed. Predistortion is applied to the baseband signal and the bias of the high-efficiency power amplifier is adaptively changed according to the envelope distribution of the baseband signal and the power amplifier itself. This novel transmitter can simultaneously achieve high average efficiency and linearity even with a high peak to average ratio signal. A comprehensive simulation framework has been developed using EDA software to validate this adaptive bias scheme with 16, 32, and 64 quadrature amplitude modulation signals. The simulation results show that this novel scheme can help in improving the average overall efficiency of the LINC transmitter by 15% while sustaining expected linearity. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

An Outphasing Scheme for Reducing Spectral Regrowth of Multi-Tone Signal in LINC Transmitter

This paper suggests an outphasing scheme to reduce adjacent channel spectral regrowth triggered by the gain and phase mismatch between two signal paths in linear amplification with nonlinear component (LINC) systems. The error vector magnitude and power spectral density of the output signal considering path mismatch are described analytically using path mismatch factor. An outphasing scheme is proposed to reduce the spectral regrowth. The proposed outphasing scheme reshapes the phases of the separated signals in LINC systems to reduce the changes of the phases. Its performance is verified by performing simulations with multi-tone signals. The result shows that the scheme can reduce the spectral regrowth of the multi-tone signals significantly compared to the conventional outphasing scheme for LINC systems with path imbalance.

Efficient Digital Compensation Technique for Path Imbalances in LINC Transmitters Using Complex Gain and Linear Model

In this paper, a simple and efficient design scheme for digital compensation of path imbalances in linear amplification with nonlinear component (LINC) transmitters is proposed to reduce signal distortion. For the LINC transmitters including path imbalances, an error vector magnitude (EVM) is analyzed and an optimal complex gain that minimizes the EVM is extracted. In addition, a straight-forward compensation scheme for the path imbalances is proposed using a least square method for complex gains of each radio frequency path. The effectiveness of the proposed method is compared with the other digital compensation methods. A LINC transmitter with multi-level quadrature amplitude modulation input signals is experimented to verify the performance of the suggested scheme. The proposed compensator can reduce the EVM and the adjacent channel power ratio of the output signals less than 2% and 45dBc, respectively.

An Amplitude and Phase Mismatches Calibration Technique for the LINC Transmitter With Unbalanced Phase Control

The linear amplifier with nonlinear components (LINC) is highly efficient because it uses a highly efficient nonlinear power amplifier (PA). However, the linearity performance of the LINC system is easily degraded by amplitude and phase mismatches between the two paths. In this paper, we propose a novel mismatch calibration technique for the LINC system that calibrates both phase and amplitude mismatches with only phase control. The technique detects mismatches between two paths without any iteration using predefined five test vector signals. In addition, this technique corrects the path mismatches using unbalanced phase control. Therefore, the proposed scheme does not require additional amplitude mismatch control blocks such as dc/dc converters or low drop output regulators (LDO). The linearity performance of the proposed LINC system is measured with 7-MHz bandwidth orthogonal frequency-division multiplexing (OFDM) signals. According to the measurement results, the proposed technique significantly enhances linearity. The measurement results also shows that the proposed LINC system satisfies the error vector magnitude (EVM) requirement for a 16-state quadratic amplitude modulation (QAM) signal (-24 dB) and a 64-QAM signal (-31 dB) up to 3.8- and 2.35-dB amplitude mismatches, respectively, with any phase mismatch.

A Sub-mW All-Digital Signal Component Separator With Branch Mismatch Compensation for OFDM LINC Transmitters

Linear amplification with nonlinear components (LINC) is an attractive technique for achieving linear amplification with high efficiency. This paper presents a sub-mW all-digital signal component separator (SCS) design for OFDM LINC transmitters, including a phase calculator and a digital-control phase shifter (DCPS) pair. In addition, a digital mismatch compensation scheme is proposed and integrated into the SCS to reduce the design complexity of the power amplifier. This chip is manufactured in a 90 nm standard CMOS process with an active area of 0.06 mm2. The DCPS can generate phase-modulated signals at 100 MHz with 8-bit resolution and RMS error 9.33 ps (0.34°). The phase calculation can be performed at a maximum speed of 50 MHz using a 0.5 V supply voltage, resulting in a 73.88% power reduction. Comparing to state-of-the-art, the power consumption of the overall SCS is only 949.5 μW which minimizes the power overhead for an LINC transmitter. This SCS with the branch mismatch compensation provides a 0.02 dB gain and 0.15° phase fine-tune resolution without adding additional front-end circuits. Considering 1 dB gain and 10° phase mismatch, the system EVM of - 29.81 dB and ACPR of - 34.56 dB can still be achieved for 5 MHz bandwidth 64-QAM OFDM signals.

Modified LINC transmitter using efficient parallel amplification scheme

A modified linear amplification with nonlinear component (LINC) transmitter is presented using a novel power combination scheme.By using multiple LINC sections in parallel with a compact adaptive power combining network, the output power of power amplifiers can be boosted, together with obtaining higher efficiency over a large power back-off region. Compared to existing designs, no gate bias adaptation is needed and efficiency can be further improved. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26086

Editorial: RF/Microwave Communication Subsystems for Emerging Wireless Technologies

This paper covers selected topics related to active components are included. An integrated voltage controlled oscillator; low loss microelectromechanical systems (MEMS) switches and switch networks integrated with GaAs monolithic microwave integrated circuits (MMIC), low-noise amplifiers (LNA) are then presented. The next paper presents a two stage class-AB CMOS power amplifier with improved stability for enhanced data rates for GSM evolution (GSM-EDGE) applications, which additionally includes a study on the efficiency improvement obtained by implementing an envelope tracking architecture. Finally, the section concludes with a paper on the application of digital signal processing techniques in transmitter architectures such as polar, envelope tracking and linear amplification with nonlinear components (LINC), aiming to guarantee increased efficiency.