Characterization of Memory Effects in Power Amplifiers Using Digital Two-Tone Measurements

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a quantitative metric for memory effects in power amplifiers (PAs) and applies it to various active device technologies and wireless system contexts. The proposed metric is mathematically founded in the dynamic two-tone distortion response, has a clear physical meaning in the important field of PA linearization and can be easily evaluated from either harmonic balance simulations or measurement data gathered in a microwave laboratory. In addition, a memoryless PA linearizer, optimum for reducing the integrated intermodulation distortion (IMD) power in the operation bandwidth for a two-tone excitation, is derived, providing a rigorous figure-of-merit of PA linearizability under static IMD compensation. The application of this figure-of-merit is then illustrated for three different PA prototypes based on Si LDMOS, InGaP/GaAs heterojunction bipolar transistors, and GaN high electron-mobility transistors, designed for 900-MHz (global system for mobile communications), 2.1-GHz (wideband code division multiple access), and 3.5-GHz (WiMax) wireless systems, respectively. </para>

Radio frequency power amplifier (PA) is an important part of the transmitter system, which can drive numerous output devices. However, the nonlinear characteristics of PA will cause serious harmonic interference, which leads to electromagnetic interference (EMI) problems. In this article, the nonlinear characteristics and the memory effect of PA are analyzed. The strong nonlinearity region and the weak nonlinearity region are divided according to the strength of the nonlinearity. For the strong nonlinearity, an encoder–decoder-based (E-D-based) artificial neural network model is proposed to predict the harmonic interference of PA. To promote the prediction of high-order harmonics when the input signal is small, a multilayer perceptron model is used for the weak nonlinearity region. The models can effectively predict the first five harmonics of PA, in which the mean absolute error of the fundamental wave is about 0.1 dB, the one of the second-order and the third-order harmonics is about 0.5 dB. Since transfer learning (TL) can simplify the training of the model based on the similarity of different tasks, TL based on model transfer is used to predict the harmonic interference of other PAs according to the existing models. The amount of data required for the modeling of PA can be greatly reduced and the accuracy of prediction can be guaranteed by applying TL. Ultimately, the proposed method can predict the harmonic interference rapidly and accurately according to the known excitation signal so that corresponding measures can be taken to avoid the influence of radiated spurious emission on the use of the sensitive receiving devices in the same electromagnetic environment.

The application of digital predistortion in base band signal is an extended method of amplifier linearization to reduce the adjacent channel interference (ACI) in those systems in which a varying envelope modulation scheme like OFDM and MQAM is used. Digital baseband predistortion is a highly cost-effective way to linearize power amplifiers (PAs), but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA) or wideband orthogonal frequency-division multiplexing (W-OFDM), PA memory effects can no longer be ignored. In this paper we proposed a new technique for adaptation of digital predistorter that considers memory effects in power amplifiers. This method is a combination of two techniques, memory polynomial predistortion and slope-dependent method. This new technique is validated by using a 1.9 GHz 60W LDMOS power amplifier and various signals such as 2-carrier and 3-carrier CDMA.

This paper presents a hardware implementation of a digital predistorter (DPD) for linearizing RF power amplifiers (PAs) for wideband applications. The proposed predistortion linearizer is based on a nonlinear auto-regressive moving average (NARMA) structure, which can be derived from the NARMA PA behavioral model and then mapped into a set of scalable lookup tables (LUTs). The linearizer takes advantage of its recursive nature to relax the LUT count needed to compensate memory effects in PAs. Experimental support is provided by the implementation of the proposed NARMA DPD in a field-programmable gate-array device to linearize a 170-W peak power PA, validating the recursive DPD NARMA structure for W-CDMA signals and flexible transmission bandwidth scenarios. To the best of the authors' knowledge, it is the first time that a recursive structure is experimentally validated for DPD purposes. In addition to the results on PA efficiency and linearity, this paper addresses many practical implementation issues related to the use of FPGA in DPD applications, giving an original insight on actual prototyping scenarios. Finally, this study discusses the possibility of further enhancing the overall efficiency by degrading the PA operation mode, provided that DPD may be unavoidable due to the impact of memory effects.

In this paper, an efficient method to characterize electrical memory effects arising from the interaction between the static nonlinearity and the frequency response is proposed using a multi-tone measurement. A transmitter system with nonlinear power amplifier (PA) is modeled with two box Wiener structure that consists of a static Saleh model and a linear filter. A nonlinear least square method with a multi-tone measurement is used to extract frequency response and nonlinear characteristics. The proposed method is verified with a simulation and experiment with a 10W class AB gallium-nitride (GaN) HEMT PA.

Power amplifiers (PAs) are inherently nonlinear devices and are used in all transmitters of a communications equipment. To improve the performance of telecommunication channels, digital baseband predistortion is employed to compensate for PA nonlinearities. But most existing architectures base on the memoryless PA model. For wideband signal transmission, PA memory effects can no longer be ignored and memoryless predistortion has poor performance. In this paper, a predistortion scheme based on the indirect learning architecture is proposed and analyzed with application to the wideband wireless transmitter. Then the performance of overall transmitter system is verified by simulation results. The measurement shows that, when inputting a single carrier WCDMA signal with 5 MHz bandwidth, good AM-AM and AM-PM performance and roughly 20 dB improvement of out-of-distortion at an offset frequency of 5 MHz were achieved, after adding the proposed predistortion method.

We present a highly accurate measurement setup and related methods for the efficient characterization of inductive rotary position sensors. The test bench is designed to measure analog sine/cosine output signals of the device under test (DUT) under nominal conditions as well as deliberate misalignment, such as offset and tilt tolerances- enabling analysis of DUT performance w.r.t. the angle deviation, the harmonic decomposition, and tolerance sensitivities. The uncertainty of measurements with the proposed test bench setup is quantified with a repeatability study and an effort is made to determine the systematic deviation. By means of laser-guided positioning, the printed circuit board (PCB) of the DUT is automatically positioned relative to the rotary axis (runout ±5 μm) in airgap and radial direction (repeatability 5 μm, total deviation 30 μm). The setup is capable of high-speed measurements at a rotation speed of at least 2000 min−1. The proposed measurement setup is flexible to accommodate a wide range of rotary position sensors and enables fast (less than 3 s per tolerance scenario) and automated characterization of the DUT angle deviation with excellent accuracy better than 10′′ (0.003∘).

This paper proposes a new high efficiency power amplifier configuration injecting envelope components. The proposed configuration has the saturated power amplifier for continuous wave and the liner amplifier for extracted envelope signal from the input signal to the proposed configuration. The envelop component is extracted from the input signal, while that is injected to the input signal in the input side of the saturated power amplifier. The linear power amplifier attains the same gain of the saturated power amplifier for the extracted envelope component. At the output port of the saturated power amplifier, the extracted envelope component is injected into the output signal of the saturated power. From this process, the proposed power amplifier can achieve high efficiency amplification with acceptable the out-of-band distortion level. The calculation results show that validity of the proposed configuration. In ideal case, the proposed power amplifier can attain the efficiency of about 64% at the third-order intermodulation component to the fundamental component of -45 dBc, when the saturated efficiency of saturated power amplifier is 80%. These results show the potential of proposed configuration.

In this letter, a novel model is proposed for modeling the nonlinearity and memory effects of power amplifiers. The classical Volterra model is modified through a function of the sum of nonlinearity order with sum of memory length. The parameters of this model can be extracted in digital domain since the model is analyzed based on the envelope signals. The model we proposed enables a substantial reduction in the number of coefficients involved, and with excellent accuracy.

Digital predistortion (DPD) is one of the most effective techniques that can compensate for the distortions caused by the nonlinearities and memory effects of power amplifiers (PAs). In this paper,...

The decomposed vector rotation (DVR) model is proposed for digital predistortion (DPD) to compensate for the nonlinearities and memory effects of Power Amplifiers (PA). In this paper, we propose a new neighborhood definition for the DVR model that allows to extend the hill climbing (HC) algorithm to find the optimal structure of DVR model which provides the best compromise between modeling accuracy and complexity. The convergence of the algorithm has been verified and validated using real measurements from Class-AB PA.

Self-interference (SI) cancellation is one of the most important techniques for full duplex wireless communication. As an indispensable component, the active analog canceller (AC) needs to mitigate the analog SI to ensure it meets the analog-to-digital converter (ADC) sampling requirement. However, the active AC cancellation performance is often restricted by the nonideal electronic components, e.g., the tunable attenuator, the phase shifter and associated circuits, which introduce nonlinear distortions to the residual SI signal that enters the receive chain, as the transmit power increases. This paper presents a full duplex architecture with AC nonlinearity modeling and suppression by including an extra feedback loop right after the power amplifier and an AC nonlinear distortion modeling and cancellation process followed by SI channel estimation and digital SI cancellation. By analyzing the feedback signal feeding the AC and the residual signal after AC cancellation, the AC nonlinear distortion can be estimated and subsequently suppressed by subtracting its estimates from the received samples. The distortion-suppressed signal is then processed by the refined digital SI cancellation with channel estimation and mitigation to further improve the cancellation performance. Experiments are performed on 20-MHz Long Term Evolution-advanced signals to demonstrate the effectiveness of the proposed full duplex architecture with signal power ranging from -5 dBm to 23 dBm at the PA output while from -23 dBm to 5 dBm at the receiver front end.

In this paper, an innovative approach to achieve broadband linear power amplifier (PA) with a continuous broadband is presented. The proposed method mainly depends on the theory of control of intermodulation products and harmonics. This method results in a continuous sweet spots over a wide bandwidth. Based on the continuous sweet spots, a suboptimal solution is derived for improving the efficiency and linearity of broadband PAs. To verify the effectiveness of this method, one broadband PA operating over 4.5–5.5[Formula: see text]GHz is developed and measured, it indicates that the peak output power of the PA is 35–57[Formula: see text]dBm for a small signal input with a gain of 12[Formula: see text]dB, and the peak drain efficiency (DE) of the PA is larger than 57% over the whole working band. However, when the PA is stimulated by a 5[Formula: see text]MHz two-tone signal input, we observe that the DE keeps above 38% under the condition of the measured third-order intermodulation distortion (IMD3) is not larger than [Formula: see text][Formula: see text]dBc.

The methods reported for the measurement of distance and medium velocity using ultrasound are based on the principles of pulse radar, pulse Doppler radar, and continuous- wave radar. In this paper, the use of frequency-modulated sonic/ultrasonic radiations for such measurements has been proposed. The required measurement setup has been described, and the mathematical model needed for extraction of distance/medium velocity from the electrical output signal has been developed. The proposed measurement setup has been implemented for distance measurement with commonly used ICs.

This paper presents a compact dehydration measurement method, keeping in mind a system integration in a wristwatch housing. In contrast to the conventional measurement approach using two measurement antennas, the proposed measurement setup uses only one antenna and one metallic reflector. Measurements have been performed using a patch antenna immersed in a steel basin filled with a tissue-equivalent liquid. The microstrip antenna has been optimized for an application in the 2.45GHz ISM band and features a biocompatible passivation layer and a rigid aluminum housing. The tissue-equivalent liquid mimicks dielectric tissue properties over a hypotonic hydration change. The steel basin acts as a liquid retainer and as a metallic reflector for the measurement setup. Measurements with the proposed setup have shown, that a clear distinction of physiologically relevant hydration levels is possible.