Amplifier Linearization Technique Research Articles

A 26–31 GHz Linearized Wideband CMOS LNA Using Post-Distortion Technique

This paper presents a modified post-distortion (PD) linearization technique for cascode common-gate low noise amplifiers (CG-LNAs) working at high frequencies up to millimeter-wave band. This technique utilizes an auxiliary transistor together with an inter-stage inductor to suppress the third order distortion without degrading gain. The input third order intercept point (IIP3) of the linearized CG-LNA is improved by a factor of up to 12 dB. For demonstration, an mm-wave differential CG-LNA was fabricated based on a 65-nm CMOS process. It achieves 2.4–10.6 dBm IIP3, 9.6–12 dB gain, 5.0–5.45 dB NF over 26–31 GHz and consumes 14.4 mW from a 1.2 V supply.

Band-limited dual-frequency multiplexing technique for GNSS signals

Global navigation satellite systems (GNSSs) usually adopt constant-envelope multiplexing (CEM) techniques to deal with the nonlinear characteristic of high-power amplifiers (HPAs) on satellites. However, almost all the existing navigation signal CEM techniques assume that the bandwidth of the transmitter is large enough when compared to that of navigation signals, which often contradicts reality, especially for the multiplexing of wideband navigation signals such as the signals in the Galileo E5 and BDS-3 B2 bands. Consequently, the constant-envelope characteristic deteriorates severely when the composite signal passes through the filter, which leads to nonlinear distortion and low amplification efficiency. Even if the nonlinear distortion can be mitigated by using amplifier linearization techniques, the actual transmitted signal power still suffers from a high peak-to-average power ratio (PAPR) of the composite signal. In order to address this problem, we present a new band-limited, dual-frequency multiplexing technique. The main premise of this method is to consider the impact of the filter on the navigation signals at first and then introduce the band-limited auxiliary signals to reduce the peak power of the composite signal as much as possible, thereby increasing the actual transmission power of the navigation signals. Simulation results demonstrate that the proposed method has lower PAPR and higher amplification efficiency than existing methods. In addition, implementation of the proposed multiplexing technique is still based on a look-up table, which has little change compared with previous CEM methods, and the complexity of signal generation is affordable.

A Resistive Degeneration Technique for Linearizing Open-Loop Amplifiers

This brief presents a linearization technique for open-loop amplifiers. It utilizes the exponential ${V}{-}{I}$ transfer of MOS transistors in weak-inversion together with a weak form of resistive degeneration. By using a specific relationship between the input transconductance and the source degeneration resistance, the amplifier is shown to have a significant reduction ( $\sim 50\times $ ) in its third-order distortion component. Based on this linearization principle, two amplifier topologies are proposed by implementing the degeneration in (a) pseudo-differential and (b) common-mode configuration. The pseudo-differential degeneration scheme allows the amplifier to achieve more than 80dB linearity for 150mV $_{\text {pp-diff}}$ input swing at the expense of 35% lower power-efficiency. The common-mode degeneration eliminates this power penalty but exhibits ~10dB worse linearity. To ensure an optimal linearity over process variation, a foreground calibration scheme is used to detect the nonlinearity. The nonlinearity correction is done by adjusting the bias current of the amplifier. The proof-of-concept amplifiers are constructed on a stripboard to demonstrate the effectiveness of the proposed linearization technique. With an input signal of 50mV $_{\rm pp{-}diff}$ , the two topologies achieve −105dB and −95dB HD3, respectively, improving the linearity of the state-of-the-art open-loop amplifiers by at least 30dB.

Hysteresis nonlinearity modeling and linearization approach for Envelope Tracking Power Amplifiers in wireless systems

Novel Dual-Input Single-Output (DISO) behavioral modeling and linearization techniques for Envelope Tracking Power Amplifiers (ET PAs) in wireless application are presented in this paper. The proposed modeling approach applies the Hammerstein structure for the Amplitude-to-Phase (AM/PM) conversion. An extension of the Saleh AM/PM model is also proposed to model the static nonlinearity in the ET PA AM/PM conversion. This paper presents a new linearization technique for ET PAs by inverting the proposed ET PA model and using it as a Digital Predistortion (DPD). The measurement results show that both the proposed model and DPD can clearly outperform both the original Saleh model and the DPD based on the Saleh model inversion. Compared to the state-of-the-art behavioral models for ET PAs, the proposed model and DPD can offer an improved complexity-accuracy trade-off thanks to the lower number of coefficients.

A Linearization Technique for Differential OTAs

This brief presents an operational transconductance amplifier (OTA) linearization technique that is applied to a low-noise amplifier (LNA) and an OTA-C filter. Simulations show the effectiveness of the proposed technique on the LNA, whose noise and gain performance remain unaffected while the linearity is significantly improved. Measurements of the 80-MHz fourth order Butterworth OTA-C filter are also presented. It is implemented using six OTAs instead of eight, thus reducing the power consumption and area. The filter is implemented in 65-nm low-power CMOS, with a core area of 0.05 mm $^{\boldsymbol 2}$ and consumes 12.6 mA from 1.2 V supply. The measured in-band noise voltage is below 42 nV/ $\mathbf {\sqrt {Hz}}$ , and the measured third order intercept point improvement using OTA linearization is up to 17 dB in-band and about 3 dB out-of-band. Supply and temperature variation measurements on three samples show that the linearization is effective without a need for bias adjustment.

Power-Scalable Wideband Linearization of Power Amplifiers

In this paper, a wideband RF power amplifier (PA) linearization technique based on the addition of a linearization amplifier (LA) is proposed. The technique is suitable for low-powered and low-cost small cell and fifth-generation (5G) large-scale multi-antenna PA designs since its power and cost overhead does not increase with the input signal bandwidth and because they are scalable with the power range and cost of the PA. In-depth analysis of the proposed technique is provided and its linearization improvement mechanisms are described. As a proof of concept, a prototype LA was designed and fabricated to linearize a broadband 6-W class-AB PA with a center frequency of 850 MHz. When stimulated by a wideband 40-MHz signal, the PA’s adjacent channel leakage ratio (ACLR) was improved by up to 13 dB after the addition of the LA. This enabled the PA to achieve an ACLR of about −45 dBc without the use of any other linearization techniques. Furthermore, significant ACLR improvements were observed for even signals with wider bandwidths up to 160 MHz.

A 5.9-GHz Fully Integrated GaN Frontend Design With Physics-Based RF Compact Model

This paper presents the design of a fully integrated high-efficiency and high-power RF frontend for the IEEE 802.11p standard in GaN HEMT technology. An embedded transmitter/receiver (Tx/Rx) switching scheme and a dual-bias power amplifier linearization technique are used to improve Tx efficiency and linearity. An accurate physics-based nonlinear large-signal device model is developed and used for the design, providing insight into the impact of the behavioral nuances of the GaN HEMTs on RF circuit performance. The fully integrated RF frontend is fabricated in 0.25- $\mu{\hbox{m}}$ GaN-on-SiC technology and occupies only 2 mm $\times$ 1.2 mm. The Tx branch achieves 48.5% drain efficiency at 33.9 dBm, $P{\rm sat}$ with 28-V supply. With orthogonal frequency-division multiplexing modulated signals, it achieves 30% average efficiency at 27.8-dBm output power while meeting the $-$ 25-dB error vector magnitude limit without predistortion. The Rx branch achieves $+$ 22-dBm output third-order intercept point with 3.7-dB noise figure at 12-V supply. The fully integrated high-efficiency and linear RF frontend designed with physics-based RF GaN compact models is demonstrated for the first time for future device-to-device applications.

Development of Wideband Power Amplifier for RF / Microwave Front-End Subsystem

This paper reviews the Wideband Power Amplifier (PA) that has been developed since 1990. Several journals had been discussed in this paper covers few topics such as Characterization of Power Amplifiers, Power Amplifier Architecture and Linearization Technique. Advantages and disadvantages of the technique used had been highlighted as well as the summary of those cases been compiled in the table form for comparison purposes. Power Amplifier is one of the important parts in transmitter. However, when involve transistor as an active device, it is important to ensure that the signals are stabilized and transmitted at higher efficiency. This leads to the proposal of a new design of Wideband Power Amplifier based on the concept of the multiplexer.

Modeling of a Power Amplifier for Digital Pre-distortion Applications using Simplified Complex Memory Polynomial

With the advent of spectrally efficient wireless communication systems emp loying modulation schemes with varying amplitude of the communication signal, linearization techniques for nonlinear microwave power amplifiers have gained significant interest. The linearization task can be divided into two parts: exact modeling of the power amplifier (PA) to be linearized and development of linearization technique. In this paper PA modeling using simplified complex memory polynomial has been presented. The proposed model has been tested using two-tone method.

Theoretical and Experimental Studies of a Probabilistic-Based Memoryless PA Linearization Technique

This paper studies the performance of a memoryless power amplifier (PA) linearization technique based on a probabilistic approach. This technique employs a nonparametric method to derive a predistorter function, which does not need any parametric modeling and explicit parameter estimation. It only needs to calculate a probabilistic cumulative distribution function (CDF) and a quantile function (an inverse function of the CDF). Histogram and order statistic methods are proposed to perform the calculation. A rigorous analytic formula is derived for the inter-modulation product power (IMPP) of the PA output signal when a finite number of samples as well as a finite number of bins are used to calculate the CDF and the quantile function. The analytic results show that, with the probabilistic-based technique, the IMPP approaches zero as the number of samples approaches infinity and the bin width approaches zero.

Mixed Cartesian feedback for Zero-IF WCDMA transmitter

In this paper, a new adaptive power amplifier (PA) linearization technique is presented. The idea is to consider a classic WCDMA zero-intermediate frequency (Zero-IF) transmitter with a modified Cartesian feedback (CFB) loop. The new transmitter architecture consists of an analog stage including forward I/Q modulator and feedback I/Q demodulator, and a digital stage adjusting the phase rotation around the loop. The whole system consumes 500 and 2.94 mW, respectively, for the analog and the digital part. System level simulation gave a maximum improvement of 35 dBc at 5 MHz from the carrier for the W-CDMA signal.

Low complexity look up table based adaptive digital predistorter with low memory requirements

With the advent of spectrally efficient wireless communication systems employing modulation schemes with varying amplitude of the communication signal, linearization techniques for nonlinear microwave power amplifiers (PAs) have gained significant interest. In this article, a low complexity, direct-learning multilevel lookup table based adaptive digital predistortion technique has been proposed to linearize a PA. A loop delay compensation scheme has been used to achieve a significant reduction in convergence time and an improvement in linearization accuracy in the presence of an unknown loop delay. Compared with the conventional predistorters, the proposed technique shows fast adaptation speed which enables the predistorter to track time-varying PA nonlinearities.

Adaptive Digital Predistortion with Iterative Noise Cancelation for Power Amplifier Linearization

In this paper, we propose a power amplifier linearization technique combined with iterative noise cancelation. This method alleviates the effect of added noises which prevents the predistorter (PD) from estimating the exact characteristics of the power amplifier (PA). To iteratively cancel the noise added in the feedback signal, the output signal of the power amplifier without noise is reconstructed by applying the inverse characteristics of the PD to the predistorted signals. The noise can be revealed by subtracting the reconstructed signals from the feedback signals. Simulation results based on the mean-square error (MSE) and power spectral density (PSD) criteria are presented to evaluate PD performance. The results show that the iterative noise cancelation significantly enhances the MSE performance, which leads to an improvement of the out-of-band power suppression. The performance of the proposed technique is verified by computer simulation and hardware test results.

Power amplifier linearization technique with IQ imbalance and crosstalk compensation for broadband MIMO-OFDM transmitters

The design of predistortion techniques for broadband multiple input multiple output-OFDM (MIMO-OFDM) systems raises several implementation challenges. First, the large bandwidth of the OFDM signal requires the introduction of memory effects in the PD model. In addition, it is usual to consider an imbalanced in-phase and quadrature (IQ) modulator to translate the predistorted baseband signal to RF. Furthermore, the coupling effects, which occur when the MIMO paths are implemented in the same reduced size chipset, cannot be avoided in MIMO transceivers structures. This study proposes a MIMO-PD system that linearizes the power amplifier response and compensates nonlinear crosstalk and IQ imbalance effects for each branch of the multiantenna system. Efficient recursive algorithms are presented to estimate the complete MIMO-PD coefficients. The algorithms avoid the high computational complexity in previous solutions based on least squares estimation. The performance of the proposed MIMO-PD structure is validated by simulations using a two-transmitter antenna MIMO system. Error vector magnitude and adjacent channel power ratio are evaluated showing significant improvement compared with conventional MIMO-PD systems.

Linearization Techniques for CMOS Low Noise Amplifiers: A Tutorial

This tutorial catalogues and analyzes previously reported CMOS low noise amplifier (LNA) linearization techniques. These techniques comprise eight categories: a) feedback; b) harmonic termination; c) optimum biasing; d) feedforward; e) derivative superposition (DS); f) IM2 injection; g) noise/distortion cancellation; and h) post-distortion. This paper also addresses broadband-LNA-linearization issues for emerging reconfigurable multiband/multistandard and wideband transceivers. Furthermore, we highlight the impact of CMOS technology scaling on linearity and outline how to design a linear LNA in a deep submicrometer process. Finally, general design guidelines for high-linearity LNAs are provided.

Some Results of the Analogue Passive Linealizer in a OFDM System

In this paper, starting from the baseband model of a OFDM system, we study through simulation the performance of passivity-based RF power amplifier linearization technique. Obtained result are highly more favourable than reported using more consolidated techniques.

Frequency-Selective I/Q Mismatch Calibration of Wideband Direct-Conversion Transmitters

The current trend in building low-cost yet flexible radio transceivers is to use the so-called direct-conversion principle, which is based on complex (I/Q) up- and down conversions. Such transceivers are, however, sensitive to mismatches between the I and Q branches. These mismatches are unavoidable in any practical implementation, and result in finite attenuation of the mirror frequencies. In addition to the mirror-frequency interference problem, I/Q mismatches can severely compromise the performance of power amplifier linearization techniques based on pre-distortion. The effects of these impairments are becoming more pronounced as higher order modulated waveforms and/or more wideband multichannel signals are used. This brief focuses on digital-signal-processor-based I/Q mismatch calibration in wideband direct-conversion transmitters, assuming the challenging case of frequency-dependent I/Q mismatch. First, a novel widely linear (WL) calibration structure is introduced, suitable for frequency-dependent calibration. Then, two alternative principles for calibration parameter estimation are proposed. The first estimation approach stems from second-order statistics of complex communication signals, while the second technique is based on WL least-squares model fitting. Both estimators are shown by simulations to yield very good calibration performance. The obtainable performance is further assessed using laboratory RF signal measurements.

Effective linearization technique for amplifiers operating close to saturation

The linearization technique that uses simultaneous injection of the second harmonics into the amplifier input and their feedforwarding to the amplifier output is suggested. This technique reduces the third-order intermodulation products in multichannel amplifiers when amplifiers operate closer to saturation. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.

Effects of PAPR reduction on HPA predistortion

There have been many papers concerning about the peak to average power ratio (PAPR) reduction and high power amplifier (HPA) linearization techniques for wireless OFDM communication systems. Few papers, however, make deep analysis on the relation between these two techniques. Based on Saleh's memoryless traveling wave tube amplifier (TWTA) model, computer simulations and analysis in this paper demonstrates that, especially when the HPA is working near or in the saturation region, a predistorter ceases to be in effect. In such cases, PAPR reduction techniques may be resorted to help to improve the adjacent channel interference (ACI), BER performances and HPA efficiency.

Improvement in second harmonics linearization technique for multichannel amplifiers

AbstractA linearization technique that uses the injection of the fundamental signal second harmonics together with the fundamental signals at the amplifier input has been improved in this paper by introducing phase correction of the fundamental signals according to the differences in phases of the second harmonics. As the result, the improvement in third‐order intermodulation power levels is approximately 40 dB for analog and 22 dB for digitally modulated signals for multichannel applications. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 150–153, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11000