Implementation of direct current to direct current converter exploiting 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.

During the last decade, the implementation of wireless power transfer (WPT) technology has been penetrating in many applications. One of essential issues in wireless power transfer is how to acquire high efficiency of power transferred wirelessly. In this paper, a high gain E-class radio frequency (RF) power amplifier is designed in 2-stage using MOSFETs and characterized for wireless power transfer application. The use of class-E RF power amplifier driven by 2 cascaded MOSFETs of IRF510 and IRF620 types is aimed to attain high efficiency of RF power amplifier with high gain amplification. Some attempts to achieve high output power of the RF power amplifier are performed through a circuit & EM simulator software. Based on the optimum design result, the proposed RF power amplifier is then realized and experimentally characterized. The result shows that the realized RF power amplifier has gain achievement more than 38 dB suitable for wireless power transfer application.

When amplifying signals with a high peak to average power ratio, the efficiency of linear radio frequency (RF) power amplifiers (PA) is reduced to about 30%. This flaw can be noticeably corrected by using envelope tracking technology. However, using switched mode PAs of envelope signal (ES) is accompanied by the emergence of nonlinear distortions, which can appear as undesirable components in the RF PA signal spectrum. One of the ways to reduce the negative influence of the switched mode is to use ES PA of multicell structure. The paper covers the issues of the ES PA number of cells influence on its efficiency and output signal distortion, as well as its influence on the efficiency and output signal distortion of the RF PA. It is shown that rational choice of the number of cells allows to increase the efficiency of ES PA from 94 through 98% and to reduce the level of intermodulation components in the envelope signal spectrum by 20 … 25 dB.

The drift in radiofrequency (RF) power amplifiers (RFPAs) is assessed and several contributing factors are investigated. Two approaches for prospective correction of drift are proposed and their effectiveness is evaluated. RFPA drift assessment encompasses both intra-pulse and inter-pulse drift analyses. Scan protocols with varying flip angle (FA), RF length, and pulse repetition time (TR) are used to gauge the influence of these parameters on drift. Directional couplers (DICOs) monitor the forward waveforms of the RFPA outputs. DICOs data is stored for evaluation, allowing calculation of correction factors to adjust RFPAs' transmit voltage. Two correction methods, predictive and run-time, are employed: predictive correction necessitates a calibration scan, while run-time correction calculates factors during the ongoing scan. RFPA drift is indeed influenced by the RF duty-cycle, and in the cases examined with a maximum duty-cycle of 66%, the potential drift is approximately 41% or 15%, depending on the specific RFPA revision. Notably, in low transmit voltage scenarios, FA has minimal impact on RFPA drift. The application of predictive and run-time drift correction techniques effectively reduces the average drift from 10.0% to less than 1%, resulting in enhanced MR signal stability. Utilizing DICO recordings and implementing a feedback mechanism enable the prospective correction of RFPA drift. Having a calibration scan, predictive correction can be utilized with fewer complexity; for enhanced performance, a run-time approach can be employed.

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.

An envelope tracking (ET) radio frequency (RF) power amplifier (PA) is described intended for handsets and applications where a large number of PAs are needed. Instead of the usual split frequency architecture, a linear tracking charge pump structure is proposed. This allows the supply voltage of an RF PA to increase during the peaks of a high peak-to-average power ratio signal. When combined with an LDMOS RF PA, 42.9% efficiency was achieved at 31.3 dBm output power (POUT) when amplifying a 5 MHz bandwidth 8 dB PAPR 3rd Generation Partnership Project (3GPP) long term evolution signal. The first channel adjacent power ratio (ACPR) without digital pre-distortion was −30.4 dBc, meeting the 3GPP handset emission mask. The ACPR could be improved to −32.5 dBc by adopting a curved envelope shaping function at a reduced efficiency of 38.9%.

Many radio frequency (RF) power amplifiers (PAs) behavioral models have been developed in the past decades. Typical among them are Wiener model, Hammerstein model, Wiener-Hammerstein model, memory polynomial model, Volterra-based model, neural networks model. All these models have become powerful tools in modeling the RF PAs and the PAs linearization. Yet their formulations appear to be unrelated. We use memory polynomial and Volterra series to generalize all these different behavioral models. The significance of this paper is twofold: 1) all the RF PAs behavioral models can be unified by memory polynomial and Volterra series and 2) any other new models may be developed with memory polynomial and Volterra series framework.

This article presents a high-performance radio frequency (RF) power amplifier (PA) module for which an optimum chip-level packaging structure is proposed to reduce the operating temperature of the RF PA monolithic microwave integrated circuit (MMIC). Because the output power ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> ) and the efficiency of an RF PA module are strongly affected by the thermal characteristics of the PA MMIC, various types of heat spreader materials and thermal interface materials have been examined to implement the PA chip-level packaging structure, and the optimum combination is proposed for a performance enhancement of the PA module in this article. In addition, the optimum form-factor of the heat spreader was suggested based on a thermal simulation. To verify the proposed PA chip-level packaging structure, a 10 W 6–18 GHz RF PA MMIC using a commercial 0.25- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m gallium nitride high electron mobility transistor process was designed and implemented for radar applications. The operating temperature of the PA MMIC on the proposed chip-level packaging structure shows a dramatic reduction of 24.8 °C, and accordingly, the average <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> and average power-added efficiency are enhanced by up to 9.2% and 2.8%, respectively, when compared with a PA module using the conventional chip-level packaging structure.

In wireless communications, it is often desirable to transmit a signal as efficiently as possible to achieve low power dissipation. In the meantime, it is necessary to keep signal distortion small. Unfortunately, these two desirable features contradict each other. For example, it is well known that the radio frequency (RF) power amplifier (PA) in wireless transmitters is inherently nonlinear, and when operated near saturation, it causes inter-modulation products that interfere with adjacent channels. To reduce distortion, a common method is to “back-off” the output power of the PA to ensure that signal peaks do not exceed the saturation point of the amplifier to permit distortion-free transmission. This “back-off” has not been a big concern in narrowband systems, e.g. GSM/EDGE systems, where the modulation exhibits a modest few dB peak-to-average power ratio (PAPR), which degrades efficiencies by around 30 percent that is deemed acceptable. However, the “back-off” could dramatically degrade the PA efficiency in wideband systems because, for example, 3GPP LTE (Long Term Evolution) signals often exhibit PAPRs in excess of 10 dB. Backing off an amplifier to operate within its linear region with these waveforms rapidly forces highly inefficient operation, which can lead to typical efficiencies of less than 10%. That is not acceptable in practical situations.

This paper presents a spurious emission suppression technique for RF power amplifiers using frequency-hopping DC-DC converters. The frequency-hopping technique changes the switching frequency of the DC-DC converter dynamically and reduces the peak spur created by using a DC-DC converter with a radio frequency power amplifier. The use of this technique can also reduce the size of the external passive components used for reducing the ripple voltage of the DC-DC converter, which creates the radio frequency spurs. A prototype system using a cellular band power amplifier operating at 836.5 MHz and a commercial DC-DC converter was built to verify this technique. Measurement results show by frequency-hopping between eight frequencies, the maximum radio frequency spur can be reduced by more than 11 dB.

Radio frequency (RF) power amplifiers (PA) are the most power consuming components of a mobile communications unit. They are used to convert the DC power from the battery into RF power delivered to the antenna. In a cell phone it becomes very important to use highly efficient power amplifiers, such as Class C and Class E PAs, to increase the talk time which is directly proportional to the battery life. On the other hand, these RF PAs are inherently nonlinear and produce spectral regrowth and other undesirable effects. Therefore, to exploit their high efficiency, it is desirable to employ linearization techniques to linearize their overall response. Linear model matching linearization techniques are investigated in this work to compensate for PA nonlinearities. The application of these techniques results in a controller architecture that delivers excellent linearity performance of compensated Class C PA models, making them very suitable in wideband digital communication systems that transmit multiple signals at high data rates, assuring that intermodulation distortion and spectral regrowth are minimized at the output of the power amplifier.

ABSTRACTThe single-carrier frequency-division multiple access (SC-FDMA) is used in the uplink of the long-term evolution (LTE) and LTE-advanced systems because of the lower peak-to-average-power ratio (PAPR) compared with the widely used orthogonal frequency-division multiplexing (OFDM) scheme. However, the non-linearity caused by the characteristic of the radio frequency (RF) power amplifiers (PAs) is still a critical problem, and there are few researches about the linearisation for the SC-FDMA signals. The digital predistorter is widely applied by employing digital baseband distortion ahead of the amplifier to compensate for the non-linearity effects and provide efficiency enhancements for high PAs in the different communication systems. This letter presents an efficient and flexible inverse autoregressive moving-average (ARMA) model-based digital predistorter to linearise the PA distortion with memory in the LTE uplink system. The proposed digital predistortion (DPD) algorithm is for the first time applied to SC-FDMA signals and verified with a series of experimental measurements. The spectrum regrowth of SC-FDMA signals is improved by up to 12 dB from both simulation and measurement. The proposed predistorter has been shown to solve the distortion problem caused by the memory effect effectively in RF PA.

The research of radio-frequency (RF) power amplifier model has always been one of the most important breakthroughs in the emitter feature extraction and specific emitter identification. Through the establishment of RF power amplifier model, we can extract feature parameters of the specific emitter. In this paper, we discuss the research issues of the specific emitter feature extraction and individual identification based on RF power amplifier nonlinear model, summarize the nonlinear distortion and modeling method of the power amplifier. Furthermore, we analyzed the applicability of these models.

The road towards the reduction in the carbon footprint associated with power-hungry wireless communication devices will require a holistic design approach to ensure that energy saving can be achieved throughout the entire system. The information and communication technology today accounted for 3 and 2% global power consumption and global CO2 emissions, respectively, where a significant portion is a result of the power consumption in the radio frequency (RF) power amplifier device. Moreover, tomorrow amplifiers will need to be reconfigurable and host a plethora of modulated signals to support effective signal processing. Therefore performance metrics such as linearity, power efficiency and their trade-off should be at the forefront of the RF power amplifier design. This study proposes an energy-efficient power amplifier design based on the Doherty configuration as part of a green RF front end for mobile WiMAX. The authors extend the classical Doherty to incorporate a three-stage load modulation design with a proposed new output power combiner. The performance of the three-stage load modulation RF power amplifier is compared with the legacy two-stage load modulation technique. The experimental results show that 30 dBm output power can be achieved with 67% power-added efficiency, which represents a 14% improvement over the current state-of-the-art system while meeting the power output requirements for mobile WiMAX.

In radio frequency (RF) power amplifiers (PA), power efficiency, linearity and cost are contradictory requirements. In the Long Term Evolution (LTE) and LTE-Advanced (LTE-A) standards by the Third Generation Partnership Project, maximum power reduction (MPR) is used to relax RF PA requirements in user equipment. In this paper, we analyze the gating factors that determine the MPR in multicluster transmission, a new feature in LTE-A that significantly changes the way unwanted emissions are distributed in the spectrum. The analysis can help in devising more advanced MPR formulas and in development of RF PA linearizers.