High RF Power Amplifier Research Articles

AlGaN/GaN power amplifiers for ISM applications

In this paper, we report on the development of an RF high power amplifier, based on normally-on AlGaN/GaN Heterostructure Field-Effect Transistors (HFETs) on semi-insulating SiC substrates. The amplifier is derived from a transistor with a total gate periphery of 120mm that exhibits a breakdown voltage better than 420V. The transistor yields pulsed drain current levels of up to 53A and therefore is found suitable for the ISM frequency band (industrial, scientific, medical) power applications at 13.56MHz. The realized amplifier shows good performance in cw mode with an output power of 139W and an efficiency of 71%, respectively. In pulsed mode, the amplifier exhibits an output power of 431W for a duty cycle of 10% at a frequency of 13.56MHz, which emphasizes the high potential of the III–V-compound semiconductor AlGaN/GaN for ISM applications. The comparison of the obtained values with standard silicon based semiconductor devices used for this frequency range furthermore shows the impressive advantages of AlGaN/GaN based devices for parameters like current density and power density that are at least by a factor of 10 higher. In a next step, the ruggedness of the realized amplifier was investigated. Operating the amplifier up to a VSWR of more than 15:1, no damage was observed. The junction temperature during VSWR mismatch was calculated to be more than 249°C.

Digital Predistortion Using Stochastic Conjugate Gradient Method

This paper is concerned with digital predistortion for linearization of RF high power amplifiers (HPAs). An iterative stochastic conjugate gradient (SCG) method is used in computing the predistorter in the digital predistortion. We also propose an adaptive scheme for selecting basis functions in the SCG computations. The adaptive scheme with SCG has the advantage of reducing the complexity and, at the same time, increasing the convergence rate and stability of iteration. We present some results of using the SCG in a hardware platform with a solid state HPA.

Reliability study of AlGaN/GaN HEMT under electromagnetic, RF and DC stress

In the context of studying the reliability of RF High Power Amplifiers (HPA) in their real environment, a study of the behavior of AlGaN/GaN HEMTs performances under electromagnetic stress is presented in this paper. The DUT has undergone several stress combinations (electromagnetic stress, electromagnetic and RF stress, electromagnetic and DC stress, …). The near field setup is used to disturb with electromagnetic field the device under test (DUT). Degradations in DC and power characteristics are observed for all stress types. This could be associated with electron trapping within the AlGaN barrier and AlGaN surface leading depletion of the 2-DEG.

Digital Predistortion for Power Amplifiers Using Separable Functions

This paper is concerned with digital predistortion for linearization of RF high power amplifiers (HPAs). It has two objectives. First, we establish a theoretical framework for a generic predistorter system, and show that if a postdistorter exists, then it is also a predistorter, and therefore, the predistorter and postdistorter are equivalent. This justifies the indirect learning methods for a large class of HPAs. Secondly, we establish a systematic and general structure for a predistorter that is capable of compensating nonlinearity for a large variety of HPAs. This systematic structure is derived using approximation by separable functions, and avoids selection of predistorters based on the assumption of HPA models traditionally done in the literature.

Reliable procedure for electrical characterization of MOS-based devices

Contemporary models of MOSFET are very complicated, especially the BSIM and EKV ones. Therefore, an identification of many parameters of these models is quite a difficult task from both algorithmic and numeric points of view. Moreover, the complexity of the models makes an optimization of MOS-based functional blocks too difficult. This paper suggests several improvements of both mono-objective and multi-objective optimization methods to enhance the reliability of extraction of the model parameters and to find the most achievable properties of the MOS-based functional blocks. In the mono-objective optimization, we use a faster version of the Levenberg–Marquardt method which does not require a one-dimensional minimization. Moreover, we propose a novel way for normalizing the Jacobian matrix, which makes the algorithm more robust especially in the cases of huge differences of magnitudes of the Jacobian-matrix elements. In the multi-objective optimization, an enhancement of an existing method known as GAM (Goal attainment method) is suggested. In our proposal, the GAM algorithm is combined with a mechanism which automatically provides a set of parameters (weights, coordinates of the reference point) for which the method generates noninferior solutions uniformly spread over a suitably selected part of the Pareto front. The resulting set of solutions is then presented in an appropriate graphic form so that the solution representing the most satisfactory tradeoff can easily be selected by designers. The modified algorithms have been used for characterization of a wide class of MOS-based devices. Utilizing the mono-objective optimization, the model parameters have been determined for both depletion- and enhancement-mode transistors of various types – from submicron to high-power ones. Moreover, we have used the procedures for identifying the parameters of three types of the MOSFET model – the semiempirical, EKV, and BSIM ones, which shows their appropriateness for various transistors. Furthermore, the whole multi-objective optimization algorithm has been implemented as a program and tested on various RF design examples. One of them – a multi-objective optimization of a last stage of a high-power RF amplifier with VMOS for a narrow-band signal with an analog modulation – is also presented.

Implementation of electrothermal system-level model for RF power amplifiers in Scilab/Scicos environment

This paper presents a behavioral electrothermal model implementation for high RF power amplifiers dedicated to the simulation of radar application in the Scilab/Scicos environment. This model, based on the direct coupling between a behavioral electrical model and a physics-based reduced thermal model, allows to predict nonlinear effects, high-frequency memory effects, and thermal effects due to the amplifier self-heating. System model implementation in Scilab/Scicos platform allows fast time domain simulation with very good convergence properties.

AlN 기판을 이용한 RF 고전력 증폭기 모듈

In this paper, a high power RF amplifier module using AlN substrate of high thermal conductivity has been proposed. This RF amplifier module has the advantage of compact size and effective heat dissipation for the packaging of high power chip. To fabricate the thru-hole and scribing line on AlN substrate, the key parameters of <TEX>$CO_2$</TEX> laser were experimented. And then, microstrip lines and spiral planar inductors were fabricated on an AlN substrate using the thin-film process. The fabricated microstrip lines on the AlN substrate has an attenuation value of 0.1 dB/mm up to 10 GHz. The fabricated spiral planar inductor has a high quality factor, a maximum of about 62 at 1 GHz for a 5.65 nH inductor. Packaging of a RF power amplifier was implemented on an AlN substrate with thru-hole. From the measured results, the gain is 24 dB from 13 to 15 GHz and the output power is 33.65 dBm(2.3 W).

Design Considerations for High-Power RF Amplifiers with MOS-FET's

Design Considerations for High-Power RF Amplifiers with MOS-FET's

Equalization of Multiuser Wireless CDMA Downlink Considering Transmitter Nonlinearity Using Walsh Codes

Transmitter nonlinearity has been a major issue in many scenarios: cellular wireless systems have high power RF amplifier (HPA) nonlinearity at the base station; satellite downlinks have nonlinear TWT amplifiers in the satellite transponder and multipath conditions in the ground station; and radio-over-fiber (ROF) systems consist of a nonlinear optical link followed by a wireless channel. In many cases, the nonlinearity is simply ignored if there is no out-of-band emission. This results in poor BER performance. In this paper we propose a new technique to estimate the linear part of the wireless downlink in the presence of a nonlinearity using Walsh codes; Walsh codes are commonly used in CDMA downlinks. Furthermore, we show that equalizer performance is significantly improved by taking into account the presence of the nonlinearity during channel estimation. This is shown by using a regular decision feedback equalizer (DFE) with both wireless and RF amplifier noise. We performestimation in amultiuser CDMA communication system where all users transmit their signal simultaneously. Correlation analysis is applied to identify the channel impulse response (CIR) and the derivation of key correlation relationships is shown. A difficulty with using Walsh codes in terms of their correlations (compared to PN sequences) is then presented, as well as a discussion on how to overcome it. Numerical evaluations show a good estimation of the linear system with 54 users in the downlink and a signal-to-noise ratio (SNR) of 25 dB. Bit error rate (BER) simulations of the proposed identification and equalization algorithms show a BER of 10-6 achieved at an SNR of ∼25 dB.

Envelope-domain time series (ET) behavioral model of a Doherty RF power amplifier for system design

In this paper, we present an envelope-domain behavioral model of a high-power RF amplifier. In this modeling approach, we use the signal envelope information, and the behavioral model is generated using an established nonlinear time-series approach to create a time-domain model that operates in the envelope or signal domain. We have generated a model of a 200-W Doherty amplifier from measured IQ data taken using a wideband code-division multiple-access excitation; the amplifier was driven from the linear regime into saturation. The time-series model was created using a time-delay embedding identified from auto-mutual information analysis, and an artificial neural network was used to fit the multivariate transfer function. The model has been validated using measured and simulated data, and it has been used in the development of a system-level design of a digital pre-distorter

Experimental study of a single tube high RF power amplifier for ICRF heating system

A concept of a single tube high RF power amplifier was developed for ion cyclotron range of frequency (ICRF) plasma heating system. In the concept, a tetrode was used with a grounded cathode and input power to drive a control grid of the tetrode was provided by a switching circuit. As the new amplifier arrangement can eliminate a low power (10 kW level) and an intermediate power (100 kW level) tetrode amplifiers, their high voltage DC (HVDC) power supplies, and control and monitor system for these amplifiers and HVDC power supplies in a conventional high RF power source of the ICRF heating system, this new high RF power source is more flexible on frequency change and more mechanically reliable than the conventional one. A test amplifier composed of the tetrode and a field effect transistor (FET) switching circuit was constructed. The FET switching circuit was so compact that it could be mounted close to the tetrode socket. The maximum output RF power of 8.5 kW was obtained with a plate efficiency of 82% at 70 MHz. The feasibility of the single tube high RF power amplifier was experimentally proved. The plate efficiency of 82% could not be explained by the standard class-C amplification but by high efficiency amplification under assumptions of a flat-topped plate current pattern and double resonance of an output cavity at the fundamental frequency and the third higher harmonic frequency.

A new simplified high radio frequency power amplifier

In order to simplify a present standard high rf power amplifier of ion cyclotron range of frequency plasma heating system, a new amplifier arrangement composed of a tetrode with a grounded cathode and a field effect transistor (FET) switching circuit providing an input rf power is proposed. The FET switching circuit is so small that it can be installed close to the tetrode in one cubicle. It might be called a single tube high rf power amplifier. A test amplifier composed of the tetrode (8F76R) and the FET (2SK-1310) switching circuit is constructed. The maximum output rf power of 8.5 kW was stably obtained at 70 MHz. The feasibility of the single tube high rf power amplifier was experimentally proved.

ION IMPLANTED SiC STATIC INDUCTION TRANSISTOR WITH 107 W OUTPUT POWER AND 59% POWER ADDED EFFICIENCY UNDER CW OPERATION AT 750 MHZ

There are many commercial applications which require high RF CW power in the kilowatt to megawatt range. To date, these high RF power requirements can only be accomplished by incorporating traveling wave tubes (TWT) or inductive output tubes (IOT). However, recent advances in the output power capability of SiC power devices for radar systems now suggest that high power SiC static induction transistors (SIT) can be used to develop a 10 kW solid state RF power amplifier. From analysis of existing high power RF amplifiers, development of a transistor cell that can produce 10 W CW output power would provide the necessary building block for assembly of a 10 kW power amplifier. As a first step in this development, existing ion implanted SiC SIT device cells fabricated at Northrop Grumman were packaged and tested for CW operation at 750 MHz. Identical transistor die from a single wafer of ion implanted SIT devices were selected, each having a layout of 10 device cells per die, with each cell having a gate periphery equal to 1.30 cm, and an active area of 2.92 /spl times/ 10/sup -4/ cm/sup 2/. To minimize heating under CW operation, only 10 cells were bonded into a transistor package. This was accomplished by attaching only 2 die to a package, and wire bonding every other cell in each die. In this manner, only 5 cells from each die were connected together, and the remaining 5 cells were not used, thus allowing for improved heat spreading.

Plasma source ion implantation using high-power pulsed RF plasma

In plasma source ion implantation of molecular gases such as nitrogen, oxygen, etc., the ratio of atomic and molecular ionic species is very important from the standpoint of implanted ion energy. Hence, it is very beneficial to produce more atomic ion species rather than molecular ones to achieve deep implant profiles. The high RF power has been known to be an efficient way to produce atomic ion species along with high ionization rate of molecular gases. A large-scale plasma source ion implantation system has been built, in which a high-power pulsed RF amplifier and a water-cooled internal antenna were used to produce high-density inductively coupled RF plasma. The pulsed RF amplifier, aiming at the higher generation rate of atomic ion species, was constructed based on a 4CX5000A RF tetrode and turned out to give output of up to 50 kW PEP and 2 kW average at 13.56 MHz. The 4CX5000A RF tetrode tube was series-connected with an RF MOSFET to form an electron tube-MOSFET cascode circuit. The Ar plasma density at 30 kW pulsed RF power was measured to reach 7.5×10 11/cm 3 at 0.13 Pa (1 mTorr) of Ar pressure. The pulsed RF amplifier was used to produce an inductively coupled N 2 plasma and plasma source ion implantation was performed on Si using a hard-tube type HV pulse modulator at 55 kV of implantation voltage. The Auger depth profile results showed that the pulsed high-power RF plasma was more advantageous in plasma source ion implantation to achieve a deeper ion implantation, which was resulted from the increased atomic ion species compared to the continuous wave (CW) mode operation.

Trenched-Sinker LDMOSFET (TS-LDMOS) Structure for 2 GHz Power Amplifiers

This paper proposes a new LDMOSFET structure with a trenched sinker for high-power RF amplifiers. Using a low-temperature, deep-trench technology, we succeeded in drastically shrinking the sinker area to one-third the size of the conventional diffusion-type structure. The RF performance of the proposed device with a channel width of 5 mm showed a small signal gain of 16.5 dB and a maximum peak power of 32 dBm with a power-added efficiency of 25% at 2 GHz. Furthermore, the trench sinker, which was applied to the guard ring to suppress coupling between inductors, showed an excellent blocking performance below -40 dB at a frequency of up to 20 GHz. These results confirm that the proposed trenched sinker should be an effective technology both as a compact sinker for RF power devices and as a guard ring against coupling.

Analog predistortion linearizer for high-power RF amplifiers

We have developed an analog predistortion linearizer for a high-power amplifier of a code-division multiple-access (CDMA) base station. To effectively suppress the spectral regrowth in the adjacent channels, the odd-order intermodulation distortions (IMDs) should be cancelled. To accomplish this purpose, we employed a predistorter, which can cancel the third and fifth IMDs independently. The implemented predistorter linearized the RF amplifier with an average power of 45 dBm at 2.37-2.4-GHz band. A 9-dB suppression of spectral regrowth, from 33 to 42 dBc, was achieved for the CDMA signal with an 8.192-Mc/s chip rate over a 30-MHz bandwidth.

Power amplifier linearisation using post-distortion error canceller based on complex envelope transfer characteristics

A new linearisation technique for an RF high-power amplifier (HPA) using a post-distortion error canceller (PDEC) is presented. The PDEC generates an error signal based on the complex envelope transfer characteristics of the HPA, which is combined at the output of the HPA. Therefore, the stability of the system is guaranteed.

Digital linearizer for RF amplifiers

Broadcast technology is at the beginning of a new era. It is characterized by the intensive use of the most advanced digital modulation formats (8VSB, QAM, OFDM) in combination with high power RF amplifiers. To date the linearity required for these digital formats has only been accomplished in cumbersome low efficiency class A amplifier or even more cumbersome feed-forward systems. A potentially more efficient and cost effective approach is the combination of nonlinear power amplifiers and a predistortion technique capable of compensating for the nonlinear amplifiers. Digital predistortion will provide a highly linear output and improved efficiency. Itelco has developed a digital adaptive base band predistorter to provide for improved performance and cost. The technique is independent of the modulation type, the output frequency, or the signal bandwidth. Furthermore the capability of automatic adaptive predistortion to compensate for the environment (temperature, power supply variations, aging, and even operation during replacement of a faulty module) is highly desirable.

Residual phase noise measurements of VHF, UHF, and microwave components

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new, high efficiency, digital, modulation technique for AM or SSB sound broadcasting applications

Saturated pulse-width modulation (SPWM), a form of modulator control signal that uses a flash converter for analog-to-digital conversion, is discussed. SPWM is used to modulate high-power RF amplifiers. The operations of a flash converter, formed from a plurality of comparators, and a ring modulator, an address rotation circuit that performs a controlled sequence defining which comparator commands a particular power switch, are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>