RF power amplifier modeling using polynomials with IIR bases functions

The nonlinearity of power amplifiers is one of the principal reasons degrading the transmission quality in the wireless communication systems comprising the single-carrier frequency-division multiple access (SC-FDMA) utilised for the up-link in the LTE system. In this letter, we analysed and predicted the nonlinearity of SC-FDMA signals in spectrum respect. Owing to the nonlinearity of radio frequency (RF) power amplifiers, an analytic model is established on the basis of a third-order intercept point (), which is fit for weakly nonlinear systems and devices. The research results confirm that the spectrum regrowth with RF power amplifier is specified and measured efficiently. This sort of design inherits the advantages of orthogonal frequency division multiplexing (OFDM) and is of great help for both designing RF power amplifiers and further improving the spectrum regrowth with pre-distortion outside channels, extended to other wireless systems based on SC-FDMA modulation.

Most existing behavioral models of the radio frequency (RF) power amplifiers assume that power amplifiers are memoryless devices. But in broadband communication systems, memory effects of the RF power amplifiers are significantly observed. The traditional memoryless models can no longer accurately depict the input-output relationship of power amplifiers. This paper investigates power amplifiers memory effects and a pre-distortion method is proposed for linearizing RF power amplifiers with memory effects. A valid behavioral model based on the Volterra series is suggested to treat memory effects. Since the characteristics of amplifiers change during transmission time, a recursive least squares algorithm with size- fixed observation matrices is developed to update the parameters of the proposed power amplifiers model. The identification algorithm can decrease computational complexity and data storage space and facilitate real-time online identification. Simultaneously, the pre-distortion model is constructed to simulate. Simulation results show that the proposed method can effectively compensate for the nonlinear distortion and memory effects of RF power amplifiers. The model's accuracy is used to evaluate power amplifiers memory effects by the enormalized mean square error (NMSE). In the end, simulation and evaluation of this pre-distortion system proceeded, and the power spectral density estimation was also applied to calculate the adjacent channel power ratio.

Two differential radio frequency (RF) power amplifier (PA) architectures are presented in this paper both of which can be used to implement a wideband Doherty PA. Classic PA architecture is compared to a SB (SB) PA in order to determine an architecture that offers the widest input impedance match without external component tuning. Both amplifiers presented in this paper have been designed to output an average of 10.5 dBm of continuous wave (CW) power with 1.8 V supply. The classic PA architecture is tuned to 1.9 GHz central frequency by external components and has a bandwidth of 500 MHz at S11=−10 dB. The SB PA architecture has an operating range spanning from 0.8 GHz to 2.2 GHz at S11=−10 dB. SB PA has a higher power added efficiency (PAE) at output compression point (OR-P1dB) in the whole 1.2 GHz–2.4 GHz range by 3 %–7 % with a peak efficiency of 31 %. The presented results indicate that a SB RF PA architecture can be implemented designing a wideband Doherty PA.

In this paper a new approach is proposed to decompose the basis functions in a piece-wise modeling technique for nonlinear radio frequency (RF) power amplifiers. The proposed technique treats the discontinuity problem of the model output at the joint points between different operating points, whereas preserves the linear and nonlinear properties of the original model within each region. Experimental results show that the proposed technique outperforms the conventional piece-wise model in terms of model errors.

The design of a temperature compensating bias circuit applicable to GaAs HBT radio frequency (RF) power amplifiers (PAs) is presented. It is developed by adding a simple voltage-compensation circuit to the existing base bias circuit. It is applied to a stage bypass RF PA and the experimental results show that the quiescent current (Q-current) remains nearly unchanged over a temperature range between −30–85°C, which markedly improves the linearity of the PA at low temperatures.

In this paper, a novel frequency component controllable digital predistortion (DPD) for radio frequency (RF) power amplifiers (PAs) is proposed. The detailed analysis and experimental results demonstrate that the target band or frequency component to be linearized can be arbitrarily chosen according to user's demand by employing the proposed approach, which makes digital predistortion much more flexible in future wireless communication systems.

Dynamic load modulation (DLM) is a technique for increasing radio frequency (RF) power amplifier (PA) efficiency when amplifying amplitude modulated signals. It does this by manipulating a tuneable matching network (TMN) between the PA and the antenna in harmony with the envelope of the transmitted signal. The TMN is usually based on varactor diodes, requiring control voltages with up to 100 V peak-to-peak swing. Conventional off-the-shelf op-amps cannot produce a big enough voltage swing at sufficient speed, especially when amplifying modern communications standards like the 3GPP 4G Long Term Evolution (LTE). The discrete current mirror driver amplifier described here capable of producing 50V peak-to-peak voltage swing. When the driver amplifier was combined with a suitable RF PA and TMN, 46.0% DC-to-RF efficiency was achieved at 33.9 dBm output power (POUT) with a 1.4 MHz LTE signal. The adjacent channel power ratio (ACPR) was -40 dBc, confirming that the current mirror amplifier is suitable for LTE use.

It has been challenging for a wireless sensor node to realize long-range real-time information feedback in the low power harvesting scenarios, due to the limited power budget. In this article, a sensor node powered by low radio frequency (RF) power harvesting is proposed with long-communication capability without using an RF power amplifier or external power source. The proposed sensor node is capable of rectifying input RF power as low as −20 dBm at 433 MHz, while simultaneously generating a 866 MHz second harmonic during the harvesting process. To address problems of long-range data transmission, the generated harmonic is amplified by a tunnel diode powered by rectified dc power, while carrying sensor data of temperature, humidity, and CO2 concentration. The fabricated sensor node shows an output power of around −14.75 dBm for the second harmonic, even with an injecting RF power as low as −20 dBm. It enables a long range exceeding 40 m for indoor communication scenarios with a low energy consumption of just 20.7 mJ. The sensor node demonstrates a great potential for future internet of things (IoT) applications in low RF power harvesting scenarios.

The burst-mode transmitter has been proposed as an efficiency enhancement technique for signals with high peak-to-average-power ratios (PAPRs), where appropriate modulation schemes such as pulse-width modulation (PWM) are used to generate a switching signal to drive the radio frequency (RF) power amplifier (PA). Ideally, a PWM signal is of infinite bandwidth, however, high-frequency spectral components are attenuated, e.g., by the bandlimitation of the PA matching network or the PWM circuit itself. Bandlimitation introduces ripples in the signal amplitude, which might reduce the PA efficiency in burst-mode operation. In this paper, we show that a bandlimited PWM signal does not necessarily degrade the overall transmitter efficiency because of the higher coding efficiency. The coding efficiency of bandlimited PWM signals, i.e., PWM signals with a finite number of harmonics, is derived analytically and verified by measurements. Additionally, from the measurements, we exemplarily determine the number of harmonics for bandlimited PWM signals with the best transmitter efficiency-linearity trade-off, and therefore demonstrate the excellence of bandlimited PWM for burst-mode transmitters in terms of transmitter efficiency as well as transmission signal quality.

Linear amplification using nonlinear components (LINC) is a method of vector summing two constant amplitude phase-modulated signals to achieve power amplification. The theoretical efficiency of the LINC power amplifier has been reported as 100% since highly efficient nonlinear constant amplitude amplifiers can be used. However, the 100% efficiency performance is only possible at one or two loads along the power output curve. The bulk of the papers regarding LINC has focused on clever implementations of the signal vector decomposition as well as methods to achieve highly linear signal separation. There has been little regard in the literature to the signal combiner implementation necessary to achieve the high power-added efficiency (PAE) of the LINC radio frequency (RF) power amplifier. Efficiency is not an intrinsic property of the combiner implementations, however, the combiner method is the single biggest contributor to efficient performance of a LINC RF power amplifier. This paper develops an analysis method that determines the efficiency of the LINC power amplifier as a function of the amplitude modulation statistics. This can be employed to design the RF communication system amplitude modulation characteristics and to tradeoff and optimize the RF transmitter PAE.

In this work a design flow for class C radiofrequency (RF) power amplifiers (PA) with on-chip output networks in nanometric technologies is presented. This is a new parasitic-aware method intended to reduce time-consuming iterations which are normally required in fully-integrated designs. Unlike other methods it is based on actual transistors DC characteristics and inductors data both extracted by simulation. Starting from the output power specifications a design space map is generated showing the trade-offs between efficiency and components sizing, thus enabling the selection of the most appropriate design that satisfies the harmonic distortion requirements. As a proof of concept of the proposed method, a design example for an IEEE 802.15.4 2.4 GHz PA in a 90 nm CMOS technology is presented.

A new dynamic behavioral modelling technique, based on support vector regression (SVR), is presented in this paper. As an advanced machine learning technique, the SVR method provides an effective option for behavioral modeling of radio frequency (RF) power amplifiers (PAs) including the nonlinear and memory effects. In this paper, the basic theory of the proposed SVR modelling method is provided, along with details on model implementation of RF PAs. Experimental test example for a LDMOS PA is presented, revealing that the new modelling methodology provides a very efficient and extremely accurate prediction.

In this work, a new particle swarm optimization (PSO) method with dynamic nonlinear self-adaptive hyperparameters (DNSHs) (PSO-DNSHs) is proposed for radio frequency (RF) power amplifier (PA) design. The theory and advantages of this method are described and analyzed. Based on the proposed PSO-DNSH method, a multioctave PA and a broadband pseudo-Doherty load-modulation balance amplifier (PD-LMBA) are designed. The multioctave single-ended PA achieves an output power exceeding 40.3 dBm, a drain efficiency greater than 60.9%, and a gain of over 10.3 dB between 0.5 and 3.6 GHz. While the broadband PD-LMBA shows a saturated output power of 41.1–43 dBm, a saturation drain efficiency of 57.7%–77.6%, a 6-dB output power back-off (OBO) DE of 47.3%–64.6%, and a 10-dB OBO DE of 51.2%–68.4%. Compared with other existing PSO-based methods, the results demonstrate that the proposed method not only achieves better performance for both PAs, but also shows faster convergence capability. Modulated signal tests along with the digital predistortion (DPD) are also conducted for both PAs, 20-MHz 5G new radio (NR) signal with 6- and 10-dB peak-to-average power ratios (PAPRs) are used for single-ended PA and PD-LMBA, respectively. Excellent linearity is achieved for both PAs.

Three-layer perceptron (TLP) is one of the approaches to the behavioral modeling of radio frequency (RF) power amplifiers (PAs) for wireless communication systems. A low-pass equivalent PA behavioral modeling should be able to represent the AM-AM and AM-PM characteristic curves, besides generating only useful contributions. This work shows that adapting a complex-valued activation function toencompass the strict characteristics from the AM-AM and AM-PM curves at the same time fulfilling the bandpass constraint gives better results in terms of network complexity and accuracy. Besides that, a novel TLP-based model for a multimode PA is proposed. This type of PA has characteristics that add difficulty to its inverse modeling. A modification in the ascendant method is also proposed for application with TLP-based PA models. This method simplifies the models in terms of operations needed for implementation. In a scenario of same number of network parameters, a significant reduction in modeling error is achieved when a complex-valued TLP that accounts for both AM-AM and AM-PM is used instead of a complex-valued TLP that accounts only for AM-AM. Such reduction is quantified by up to 5.73 dB (-35.53 dB to -41.26 dB) improvements in normalized mean square error (NMSE) metric. Moreover, when applying the ascendant method a 67% reduction in active parameters is achieved (36 to 12 active parameters), deteriorating the NMSE by less than 0.5 dB.

This study presents a feedforward linearizer, in order to reduce the intermodulation distortion (IMD) caused by the nonlinear properties of the radio frequency (RF) power amplifier (PA) in orthogonal frequency-division multiplexing (OFDM) systems. The design procedure and validation of OFDM system and feedforward linearizer have been carried out by Agilent-ADS. In order to evaluate the performance of the feedforward linearizer, sweeping back-off power has been used. Adjacent channel power ratio (ACPR) levels versus back-off power results are investigated to evaluate the performance of the linearization technique. Efficiency improvement is figured out by investigating the power added efficiency (PAE) versus back-off power. Simulation results have been shown that ACPR improvements were acceptable for OFDM system when the PA is utilized together with feedforward linearizer.