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A new approach is presented that allows a Vector Network Analyzer to be operated as a Large Signal Network Analyzer without the need for a harmonic phase reference generator. The mode of operation exploits the architecture of a Rohde and Schwarz ZVA-67, which incorporates internal signal and local oscillator sources based on direct digital synthesis [1]. This unique capability leads to a Vector Network Analyzer based Large Signal Network Analyzer configuration that provides for time coherent receivers. This feature combined with a modified calibration procedure, allows the instrument, to provide error corrected RF current and voltage waveform measurements, requiring only the internal signal sources and an external phase (time) meter [2-5]. This approach simplifies the Large Signal Network Analyzer architecture and removes the complexities and bandwidth limitations introduced when employing a harmonic phase reference generator.

This paper combines the advantages of accurate measurement based non-linear behavioral look-up table transistor models with passive embedding networks to develop a scalable large signal model. This approach provides for a more robust utilization of measurement based data models in X-band MMIC design by providing accurate performance predictions as a function of gate periphery and at power levels beyond the limitations of high frequency measurement systems. An example is provided where a 1 W Gallium Nitride reference device, characterized in Class B at 9 GHz, delivering over 70% efficiency, is used to accurately predict the behavior of devices with up to 5 times larger gate periphery.

As circuit element losses increase with frequency and availability of power amplifiers reduces also, active control of harmonics by means of a traditional filter and hybrid diplexer becomes problematic. In this paper a technique is presented that allows the reflective filters to be removed, and lower loss couplers to be used, resulting in much less power being needed to control the second harmonic, and also a useful reduction in the fundamental load-pull power. The effectiveness of the method is demonstrated using a GaN based HEMT device, and then some of the extensions possible are presented.

A small signal S-parameter and noise model for the cascode MODFET has been validated up to 120 GHz, allowing predictable monolithic microwave integrated circuit (MMIC) design up to W-band. The potential of coplanar waveguide technology to build compact, high performance system modules is demonstrated by means of passive and active MMIC components. The realized passive structures comprise a Wilkinson combiner/divider and a capacitively loaded ultra miniature branch line coupler. For both building blocks, very good agreement between the measured and modeled data is achieved up to 120 GHz. Based on the accurate design database, two versions of compact integrated amplifiers utilizing cascode devices for application in the 90-120 GHz frequency range were designed and fabricated. The MMICs have 26.3 dB and 20 dB gain at 91 GHz and 110 GHz, respectively. A noise figure of 6.4 dB was measured at 110 GHz. The 90-100 GHz amplifier was integrated with an MMIC tunable oscillator resulting in a W-band source delivering more than 6 dBm output power from 94 to 98 GHz.

A simple analogue technique called auxiliary envelope tracking, or AET, is presented, which is shown to be capable of improving the efficiency of a radio frequency power amplifier (RFPA). This AET signal is an amplified envelope signal that supplies the drain port of the RFPA. The concept of AET is explained and a theoretical background for the technique is presented. The main feature of this technique lies in the separation of the DC and AC components of the tracking signal. This allows for a very simple and low-cost tracking generator design that consists of a simple source follower amplifier and an RF broadband transformer. A practical system has been implemented and the measured results are obtained for WCDMA signals. A measurement on the realised system shows a 50% improvement in the drain efficiency at average output power of 33 dBm of a 25 W GaN. This substantial improvement is achieved at a competitive WCDMA signal with peak-to-average envelope power ratio of 9.17 dB.

Characterisation, test and modelling of microwave devices and transistors are becoming the pre-requisite for the utilization in the design of modern wireless power amplifies. This serves dual purpose; on one hand it saves the effort and investment due to the possible anomaly in the expected performance of the design while on the other hand it provides a reliable performance estimation of the transistors and devices apriori. Design of matching circuit is one of the most important stages in the overall performance investigation and analysis of the Power Amplifiers (PAs). Load-pull techniques are extensively used in the synthesis of required load impedance, and in turn the design of matching circuit. This paper discusses some unique features of the Envelope Load-Pull technique and demonstrates usefulness of such features in high speed device characterization.

The theory of inverse Doherty has been introduced. An experimental optimization technique has verified that the current requirement for inverse load modulation is less than classical load modulation in three different implementations where the peak is smaller than the carrier. The drain efficiency performance of inverse Doherty outperforms most recently published Doherty publications at large output power back-off levels. The 2.05GHz configuration achieves 48%, 33% and 17% at 10, 15 and 20dB output power back-off. The efficiency results can be improved by designing a dedicated inverse Doherty PA.

New analytical behavioral model formulations based on the polyharmonic distortion (PHD) model have been successfully used to describe the nonlinear behavior of transistors and circuits. In this paper, the PHD model and its associated analytical X -parameters formulation will be utilized to provide an analytical design procedure for use in nonlinear microwave circuit design. For RF oscillator design, the negative-resistance method based on the analytical manipulation of scattering parameters is very popular due to its high rate of success in oscillation frequency prediction. However, it cannot be used to accurately predict the oscillator performance because it is based on linear parameters. To overcome this limitation, new analytical expressions based on large-signal X -parameters have been developed for use in transistor-based oscillator circuit design. The robustness of this new approach has been validated by designing and manufacturing a 5-GHz microwave oscillator. Ministerio de Ciencia e Innovación | Ref. TEC2008-06874-C03-02 Ministerio de Ciencia e Innovación | Ref. TEC2008- 02148 Ministerio de Ciencia e Innovación | Ref. TEC2011-29264-C03-03

The introduction and formulation of the "Continuous" modes of transistor operation has provided an alternative design route for the realization of high efficiency power amplifiers (PA's) over a wide bandwidth (approaching an octave). The formulation of the "Continuous" modes provides a mathematical framework for extending the fundamental/harmonic impedance space over which the power and efficiency performance of the traditional PA modes, i.e. Class, B, Class F, etc, can be maintained. This mathematical framework has been experimentally validated using RF I-V waveform engineering measurements systems and the realization of demonstrator PA prototypes.

Theory and measurements are presented comparing Class B amplifier performance of a 0.5 W GaAs pHEMT driven with (a) a sinusoidal signal or (b) using 2nd harmonic input injection. Engineering the input waveform in this way leads to a class B operating mode requiring 3.4 dB less input drive at 9 GHz. This increases power gain and maintains the output power. The 2nd harmonic injection case then shows a 5.9% PAE improvement over the class B case.

This paper presents for the first time the broadband Continuous-ClassF3 mode power amplifier (PA) extended to include a variable reactance third harmonic impedance. It will be demonstrated that by proper manipulation of the voltage and current waveforms different optimum impedance solutions can be identified. When designing PAs, the harmonic impedances cannot easily be constraint to open-circuit and/or short-circuit points with varying frequency. Therefore, the possibility to vary the third harmonic reactance as well as the second harmonic and fundamental reactance with frequency would allow for an easier, more flexible and achievable design requirement. Measurements on a GaN power transistor have delivered around 34.5–35.9 dBm of output power, 80–85 % of drain efficiency and 13.7–15.5 dB of available gain at 1 GHz of fundamental frequency for the various combination of first three load solutions. The measurements demonstrate that constant or greater output performance can be obtained over a wide PA design space when varying properly the first three harmonic loads. The different reactive impedance solutions carried out at the single frequency can then be translated into frequency domain, allowing the design of high power-efficiency broadband power amplifiers.

A modified piece-wise polynomial pre-distortion is proposed, investigated and compared against classic memoryless polynomial pre-distortion. The proposed enhanced piece-wise polynomial pre-distortion uses the overlap between segments to ensure continuity in the total pre-distortion function. The implementation of overlap allows the use of a simple error estimation algorithm to minimise hand over error. The classic and proposed piece-wise pre-distortion performances are assessed and compared for several sets of polynomial coefficients. The proposed method is shown to consistently outperform classical polynomial pre-distortion in terms of required coefficients and linearity improvement. The method is applied for the linearisation of an envelope tracking Class-J PA at 1.7GHz, under a 1.4MHz LTE signal with a 14.4dB PAPR.

A high-efficiency push-pull power amplifier has been designed and measured across a bandwidth of 250MHz to 3.1GHz. The output power was 46dBm with a drain efficiency of above 45% between 700MHz and 2GHz, with a minimum output power of 43dBm across the entire band. In addition, a minimum of 60% drain efficiency and 11dB transducer gain was measured between 350MHz and 1GHz. The design was realized using a coaxial cable transmission line balun, which provides a broadband 2∶1 impedance transformation ratio and reduces the need for bandwidth-limiting conventional matching. The combination of output power, bandwidth and efficiency are believed to be the best reported to date at these frequencies.

On-wafer measurements of the frequency-dependent impedance, modulation response, and RIN power spectra of ultra-high-speed p-doped In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers are presented and analyzed. The experimental results are shown to be accurately modeled by an equivalent circuit which accounts for both the carrier transport/capture dynamics and the junction space-charge capacitance. We find that the carrier escape time out of the QW's in our laser structure is much larger. Than the carrier capture time, and therefore the interplay between carrier capture and re-emission is not affecting the high-speed modulation dynamics. On the other hand, the absolute values of both the carrier capture time and the space-charge capacitance still limit the modulation bandwidth. >

Typically performance maxima in terms of output power, efficiency, etc. are determined from analyzing, effectively “data mining”, load-pull measurements. This approach while identifying relevant design information provides no insight into the origin or location of the relevant maxima. However, if during load-pull measurements the RF I-V waveforms are also measured this insight is available. Measured RF I-V waveform load-pull information from a 10×75μm Gallium Arsenide transistor operating in class-B at 8GHz is used to correctly identify the effect of the knee region of the transistor I-V characteristic on power and efficiency. As a consequence the location of the drain efficiency contours on the Smith Chart are explained in terms of V min and current waveform compression.

This paper demonstrates how the Poly Harmonic Distortion (PHD) modelling framework is effective in its ability to interpolate or extrapolate non-linear measured data and thereby improve the quality and speed of measurement systems. Fundamental interpolation was verified and demonstrated using a 7-coefficient model extracted from a sparse set of fundamental impedances (19 points). It was shown that a relatively low order polynomial was required to capture the second harmonic space. Interpolation accuracy was however increased by including more coefficients. Second harmonic extrapolation was carried out on measured data and shown to be accurate to an average confidence of 99% when 6 model coefficients were extracted on a 0.7 reflection coefficient circle and then used to predict data on a 1.0 reflection coefficient circle. Measurements were carried out using an open loop active load-pull system operating at a fundamental frequency of 9GHz, on a 0.5W 10×75μm GaAs PHEMT device.

It is often desirable to measure device characteristics under non-continuous operation, perhaps to better simulate actual operating conditions, to reduce the thermal loading or to investigate RF operation going beyond the CW safe operating region. In this paper a measurement solution is presented that allows for the concept of experimental RF waveform engineering to be undertaken under such conditions. The system is demonstrated by using it to investigate the feasibility of operating GaAs based HEMT technology under pulsed conditions in high efficiency modes that required high RF voltage swings that extend beyond their rated CW safe operating region.

This paper presents a methodology that provides rapid estimation of the parameters necessary for the high-speed characterization of transistor devices used in modern microwave power amplifiers. The key in achieving this significant measurement speed improvement is the use of a systematic waveform postulation methodology in combination with an active harmonic load-pull measurement system. The methodology is based on a rapid and systematic procedure that initially requires only a few DC measurement parameters to approximate the device's transfer characteristic and boundary conditions. Using these parameters, it is then possible to accurately estimate or ‘postulate’ the idealized output current and voltage waveforms, in this case for a three harmonic Class-F mode. These waveforms are rich in information and provide harmonic load impedances as well as other key postulated parameters that can then be used to ‘guide’ the harmonic active load-pull measurement system resulting in a very time-efficient characterization process.

This paper demonstrates, for the first time, that the Class B to Class J concept can be successfully extended to X-band operation. X band power amplifiers with >30% bandwidth are required for a wide range of emerging applications where achieving optimal electrical efficiency is a key system driver. High efficiency is ordinarily achieved using circuit elements resonant at harmonic frequencies that are inherently narrowband in operation. The Class B to Class J continuum of modes, exploited here, offers Class B levels of efficiency over a continuum of impedance matching conditions, making wider bandwidth designs more feasible. This paper presents measurements of devices and MMIC designs which were undertaken to systematically use the continuum of modes for the first time at X-band. The 0.5W MMIC fabricated using a GaAs pHEMT process yields above 65% drain efficiency over >30% bandwidth.

A new technique called Auxiliary Envelope Tracking (AET) is proposed, which demonstrates substantial improvement in linearity of RF power amplifiers. A small amplitude envelope-tracking voltage is superimposed on the fixed DC bias of a specially designed 25W GaN HEMT Class AB RF power amplifier (RFPA). A large improvement in third-order intermodulation (IM3) distortion has been observed while maintaining low fifth-order intermodulation (IM5). The overall drain efficiency of the RFPA is also observed to improve, even when the power consumption of the envelope tracking generator is included. The AET concept uses a simple and easily integrated system that consists of an RFPA, a diplexer and an envelope amplifier.

A novel, highly efficient and broadband RF power amplifier (PA) operating in “continuous class-F” mode has been realized for first time. The introduction and experimental verification of this new PA mode demonstrates that it is possible to maintain expected output performance, both in terms of efficiency and power, over a very wide bandwidth. Using recently established continuous class-F theory, an output matching network was designed to terminate the first three harmonic impedances. This resulted in a PA delivering an average drain efficiency of 74% and average output power of 10.5W for an octave bandwidth between 0.55GHz and 1.1GHz. A commercially available 10W GaN HEMT transistor has been used for the PA design and realization.

This paper demonstrates how the linearity performance of a 10W GaN HEMT can be dramatically improved by actively engineering the baseband impedance environment around the device. An important refinement to existing active load-pull measurement capability is proposed that allows the precise and independent control of all significant baseband and RF components that result from the amplification of a complex 9-carrier multi-sine modulation. The synthesis of constant, modulation frequency independent negative baseband impedances, resulting in specific baseband voltage waveforms has delivered a 24dB improvement in ACPR compared to the classical baseband short case, even when the device is operating with RF components terminated into a non-optimal 50Ω RF environment. This linearization concept is further investigated through the broadband emulation of a class-J impedance environment around a single device. Using this enhanced system and a two-tone modulated excitation, optimum baseband loads are identified that result in a 18.5dB and 24dB improvement in IM 3 and IM 5 inter-modulation products respectively, again relative to the case of a traditional IF short circuit. The significance of this last observation is that unlike the 50Ω case, the optimum class-J IM 3 and IM 5 baseband impedances disperse, becoming reactive and moving away from the real axis.

This paper outlines a non-linear measurement approach suitable for wafer mapping and technology screening applications. It is shown how rapid characterization and uniformity investigations of non-linear devices is possible through the development of an intelligence driven, open-loop active harmonic load pull measurement system, where localized behavioral models are exploited to dramatically improve measurement system speed and to improve utilization efficiency. The load pull measurement results obtained were then used to extract 5th order behavioral models for robust CAD integration. Device variations can now be included within the CAD tool. Technique demonstration involved the measurements of 10×75 μm GaAs pHEMT devices, operating at 9 GHz, biased in Class-AB on four different wafers. An example CAD investigation comparing the variation of the measured and modeled current and voltage waveforms is discussed.

A new methodology is presented for designing baluns exhibiting multi-decade bandwidths at microwave frequencies. Simulations show that resistors terminating the outer transmission line suppress the half-wavelength resonance and greatly extend the bandwidth. Using linear measurements at microwave frequencies, ferrite beads have been shown to behave as resistors with a small reactance, suitable for terminating the outer transmission line. This paper shows that ferrite beads can perform the dual role of improving magnetic coupling at low frequency and suppressing resonance at higher frequencies. The design methodology was applied to produce a balun that operates between 30MHz and 6GHz, displays less than 1dB of power loss up to 4.4GHz, and delivers an impedance transformation of 2∶1.

Recently there has been a renewed interest in improving power amplifier performance via input waveform engineering. In order to support this development it is important that non-linear behavioral device models can accurately describe and fully account for the high levels of input harmonic signal injection necessary. The work presented in this paper introduces an adapted mixing model formulation, which was used to extract input second harmonic model coefficients from a set of simultaneous active fundamental load-pull and harmonic source-pull measurements at 9 GHz. It was observed that a fourth order model was sufficient to capture the response of the scattered travelling b 2,1 and b 2,2 waves to a confidence of 99.46% and 97.62% respectively of the measured data. Hereafter the behavioral model was used to accurately generate the full fundamental output impedance space and the respective port current and voltage waveforms within a CAD environment.

This paper describes a design methodology based on waveform engineering within a harmonic active load-pull system and utilizing the Cardiff Direct Look-Up Table (DLUT) model. The process seeks to address some of the key issues facing designers when using nonlinear simulation of high power microwave amplifiers: model validity, boundary conditions and yield. The application of this process to the design of a 0.5 W, 5–10 GHz GaAs pHEMT with good PAE is detailed.

This paper reports that significant linearity improvement can be obtained in gallium nitride (GaN) RF power amplifiers (RFPAs) in comparison to laterally diffused metal oxide semiconductor (LDMOS) RFPAs through the use of a modulated drain supply. It is shown that the gain characteristic of a GaN RFPA has significant variation with the drain bias voltage and this results in a 10–20dB reduction in intermodulation (IM) levels. The LDMOS RFPA was measured and the result showed that the gain of LDMOS did not change substantially with drain bias voltage. As a consequence, when the LDMOS RFPA is measured using modulated drain bias, the IM levels showed only a much smaller improvement. These results appear to indicate that GaN devices have an important advantage over LDMOS in linear RFPA applications.

Recently analytical behavioral model formulation based on the PHD model has been introduced and successfully used to describe the nonlinear behavior of transistors and components [1–3]. The next important advance would be to utilize this formulation, constraint to load-independent X parameters, to enable analytical non-linear microwave circuit design procedures. For this purpose, in this paper a blind iterative process is presented and validated in order to obtain the appropriate load-independent X parameters, focused around the chosen optimum impedance condition, necessary to enable accurate analytical non-linear circuit design to be undertaken [4].

Modulation doped Al0.2Ga0.8As/In0.3Aa0.3As high electron mobility transistors (HEMT) were statistically characterized at μ-wave frequencies. The results provided information to optimize transistor fabrication technology and as well to investigate transistor reliability and reproducibility to allow the design of multi stage low noise amplifiers (LNAs) [1].

Utilizing small-signal direct modulation and relative intensity noise measurements, the authors investigate changes in the modulation response, the differential gain delta g/ delta n, the nonlinear gain coefficient in , and the damping factor K, which result from three structural modifications to GaAs-based multiple quantum well lasers: the addition of strain in the quantum wells; and increase in the number of quantum wells; and the addition of p-doping in the quantum wells. These modifications are assessed in terms of their potential for reducing the drive current required to achieve a given modulation bandwidth, for increasing the maximum intrinsic modulation bandwidth of the laser, and for improving the prospects for monolithic layer/transistor integration. It has been possible to simultaneously increase delta g/ delta n and decrease K, yielding very efficient high-speed modulation (20 GHz at a DC bias current of 50 mA) and the first semiconductor lasers to achieve a direct modulation bandwidth of 30 GHz under DC bias. >

This paper outlines the formulation of a mixing based behavioral model, capable of capturing the nonlinear response of microwave transistors to fundamental and harmonic load pull effects for use in Computer Aided Design tools. The key to the model formulation was the experimental identification of the dominating mixing terms. The model is able to accurately compute the voltage and current waveforms present at a Transistors Terminals. The formulation lends itself to economical use of measured data, reducing data storage required within the CAD environment. In this paper the modeling approach has been demonstrated on a 10×75µm GaAs HEMT operating at 9 GHz.

A rigorous, systematic, measurement-founded approach is presented that enables the design of highly efficient power amplifiers. The identified process allows the designer to quickly identify the parameters necessary for completion of a design whilst ascertaining their flexibility and impact on performance degradation. The investigation continues to consider the impact of the higher harmonics and gate bias as design tools on the performance of the design and proposes a strategy that utilizes their positive effect as well as considering the subsequent impact on device scaling. This was carried out on GaAs pHEMT devices from commercial processes that obtained measured peak efficiencies of 90.1% at P1dB in a class-B bias.

In this paper, the efficiency of a GaN HEMT transistor and its intrinsic waveforms are measured at 0.9 GHz and investigated for load- and supply-modulation applications. The results show that both techniques perform equally well for back-off levels ≤6.5 dB. At higher back-off levels, the efficiency improvements achieved by supply modulation outperform load modulation. At 10 dB back-off, supply, and load modulation provide a power-added efficiency (PAE) of 68%, and 58%, respectively. Using measured intrinsic waveforms, it is shown that PAE degradations in load modulation can be mainly attributed to parallel losses rather than series losses, which are dominant in supply modulation. The harmonic contents of the intrinsic waveforms, in both techniques, are equally strong in back-off and peak power operations. There is, therefore, a great potential for further efficiency enhancement by circuit-level optimization of harmonic terminations for back-off.

This paper describes how the application of the PHD model can add intelligence to an open loop active loadpull system. This intelligence driven approach by providing for an improved prediction of the operating conditions required to emulate a specified load speeds up the load emulation convergence process by minimizing the number of iterations to predict the injected signal, therefore making more efficient use of a measurement system. The results were validated by carrying out loadpull measurements on the fundamental tone of a 10×75um GaAs HEMT, operating at 3 GHz.

This paper introduces a novel approach for the realization of wide band (>octave) high-efficiency (>95%) high Power Amplifiers (PAs). The proposed concept utilizes active harmonic injection to achieve the appropriate waveform shaping of the voltage/current waveforms necessary to deliver simultaneously both high power and high efficiency operation. The new PA structure thus consists of two parallel PAs where the main PA generates fundamental power and an auxiliary PA injects a harmonic signal at the output of the main PA to perform waveform shaping. An active harmonic injection PA circuit designed around the 10 W GaN transistor is demonstrated, along with the basic mathematical analysis and computer simulation of this new mode of operation. The measured performance of the PA demonstrator realized at 0.9 GHz provided a drain efficiency of 74.3% at P1dB, validating the concept and its potential.

Low-frequency, baseband effects in Power Amplifiers can become particularly important when steps are taken to improve operational efficiency through the application of `envelope' based approaches such as Envelope Elimination and Restoration (EER) and Envelope Tracking (ET). The aim of this paper is to demonstrate how a broadband modulated time-domain measurement system, when used in combination with active IF load-pull, can be employed to gain valuable insight into the behaviour of high-frequency power transistors whilst operating under modulated conditions. Also considered is the interesting idea of how PA linearity can be improved using the very mechanisms that are employed to improve efficiency. Low-frequency, baseband effects in Power Amplifiers can become particularly important when steps are taken to improve operational efficiency through the application of `envelope' based approaches such as Envelope Elimination and Restoration (EER) and Envelope Tracking (ET). The aim of this paper is to demonstrate how a broadband modulated time-domain measurement system, when used in combination with active IF load-pull, can be employed to gain valuable insight into the behaviour of high-frequency power transistors whilst operating under modulated conditions. Also considered is the interesting idea of how PA linearity can be improved using the very mechanisms that are employed to improve efficiency.

The inter-modulation distortion products can vary both in terms of amplitude and asymmetry due to the effects of baseband and 2nd harmonic impedance. This paper presents an investigation into the relationship between the IMD asymmetries caused by baseband impedance variation and the looping or hysteresis that can sometimes appear in the dynamic transfer characteristics of microwave power devices when subjected to modulated excitation. The investigation is carried out using a 2W GaN HFET bare die device characterized at 2.1GHz, and using IF active load-pull to clarify the role of baseband impedance on observed hysteresis in the dynamic transfer characteristics. Analysis is performed using the envelope domain in order to more effectively reveal the DUT's sensitivity to impedance environments and specifically electrical baseband memory effects. The inter-modulation distortion products can vary both in terms of amplitude and asymmetry due to the effects of baseband and 2nd harmonic impedance. This paper presents an investigation into the relationship between the IMD asymmetries caused by baseband impedance variation and the looping or hysteresis that can sometimes appear in the dynamic transfer characteristics of microwave power devices when subjected to modulated excitation. The investigation is carried out using a 2W GaN HFET bare die device characterized at 2.1GHz, and using IF active load-pull to clarify the role of baseband impedance on observed hysteresis in the dynamic transfer characteristics. Analysis is performed using the envelope domain in order to more effectively reveal the DUT's sensitivity to impedance environments and specifically electrical baseband memory effects.

The use of active load-pull techniques in the design of high efficiency microwave amplifiers has been well documented. This paper describes how it has been applied to the design of a wideband RFIC gain stage. The technique is particularly relevant in new and developing processes where accurate device models are not available and designers otherwise are often forced to use multiple iterations of a design to attempt to encompass the variability in the process. Often in RFIC design, components operate outside of the ideal operating impedance. A look-up table model technique based on measured data which can be used by conventional CAD programs is used to analyse behaviour. This paper shows how the design process and capabilities of the system can be combined to improve the cost effectiveness and performance of RFIC development and with a stable manufacturing process a “first pass” design methodology. The use of the measurement system as an analysis tool is described.

A study in the optimization of ultrathin planar doped barriers (PDB) for use as hot‐electron/ballistic electron launchers in vertical field effect spectrometer structures was conducted. A comparison was made of results for an all‐PDB (PDB launcher/PDB analyzer) versus a PDB launcher/graded AlGaAs spectrometer. Previous work involving PDB launchers and vertical field effect structures predicted little to no enhancement of electron current density. This study conclusively refutes these predictions. A new analyzer‐up‐top design scheme as well as optimization experiments involving varying PDB layer and associated drift region thickness were developed. This work shows previously unobserved hot electron/ballistic spectra for these structures. Moreover, high current densities in excess of 105 A/cm2 were observed for the all‐PDB and for the ultra‐thin PDB launcher/graded AlGaAs spectrometers under conditions involving both thermionic emission and tunneling.

An accurate database for active and passive MMIC components valid up to millimeter-wave frequencies has been established. The CAE models for the transistors and the passive CPW-components; which include the coplanar T-junction, are derived from on-wafer S-parameter measurements up to 63 GHz. For noise modeling of the MODFETs up to millimeter-wave frequencies, an approach based on the temperature noise model reported by M.W. Pospiezalski (1989) has been used. The parameter T/sub d/, which is required for the temperature model, is extracted from on-wafer noise parameter measurements up to 18 GHz. Using this database, the authors have designed and fabricated low-noise V-band two-stage amplifiers, using pseudomorphic MODFETs on a GaAs substrate, which have a performance of 10.5-dB gain and 5.2-dB noise figure at 58.5 GHz. Very good agreement between simulated and measured MMIC gain and noise performance is achieved up to V-band. >

RF I-V waveform measurement and engineering systems are finally enabling practical waveform engineering to be directly undertaken within the RF power amplifier (RFPA) design cycle. RFPAs are a critical component in many systems; e.g. mobile communications, satellite communications and radar systems.

This paper presents, for the first time, a multi-harmonic active envelope load-pull system allowing for the robust, high-speed characterization of devices used in modern microwave power amplifiers. Measurements of a commercially available 1W GaAs FET device demonstrate at least an eight-fold improvement in the measurement speed when compared to existing open-loop solutions. The developed active load-pull system, which instantly reacts, via baseband feedback, has the ability to set load impedances that are independent of changing device conditions. Thus it is similar to passive systems, but without the associated loss. This system is shown to be valuable in allowing the utilization of rapid, experimental, measurement driven optimization within the power amplifier design and yield analysis process.

Modulation doped Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures for device application have been grown using molecular beam epitaxy. Initially the critical layer thickness for InAs mole fractions up to 0.5 was investigated. For InAs mole fractions up to 0.35 good agreement with theoretical considerations was observed. For higher InAs mole fractions disagreement occurred due to a strong decrease of the critical layer thickness. The carrier concentration for Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures with a constant In x Ga1−x As quantum well width was investigated as a function of InAs mole fraction. If the In x Ga1−x As quantum well width is grown at the critical layer thickness the maximum carrier concentration is obtained for an InAs mole fraction of 0.37. A considerable higher carrier concentration in comparison to single-sided δ-doped structures was obtained for the structures with δ-doping on both sides of the In x Ga1−x As quantum well. Al0.3Ga0.7As/In x Ga1−x As/GaAs high electron mobility transistor structures with InAs mole fractions in the range 0–0.35 were fabricated for device application. For the presented field effect transistors best device performance was obtained for InAs mole fractions in the range 0.25–0.3. For the field effect transistors with an InAs mole fraction of 0.25 and a gate length of 0.15 μm a f T of 115 GHz was measured.

In this paper a time domain waveform measurement system with active harmonic load-pull has been used to enhance the design cycle of RF power amplifiers (PAs). Wave-shaping (waveform engineering) techniques using Cardiff University's high power waveform measurement system have yielded optimum device conditions enabling a rapid PA realisation with a first-pass success. The resulting inverse class-F design, based on a 10W GaN HEMT device, is operating at 0.9GHz, and achieving 81.5% drain efficiency in both the load-pull emulated state and also in the directly realised PA. The value of measured waveforms, and the ability to engineer optimum waveforms to a specific amplifier mode, is demonstrated in this study.

This paper presents, for the first time, a new active load-pull approach capable of supporting wideband multi-tone modulation based on the active envelope load-pull architecture. The new solution utilizes a digital control unit, implemented on a reconfigurable FPGA platform with high-speed signal processing capability, in the feedback loop to track the time varying amplitude and phase envelope of modulated RF communication signals. This novel approach enables a loop delay compensation scheme to be successfully implemented allowing for synchronization of the transmitted and the reflected signals over wide (>5 MHz) bandwidths. Initial, proof of concept, measurements on this active load-pull system have demonstrated that it can provide constant, frequency independent control of load impedances for signal excitations that are relevant for communication systems.

This paper outlines the use of a measurement based waveform CAD tool for enhanced PA design. Two measurement based models have been used to simulate a complete Doherty power amplifier together with output matching. The output matching network and auxiliary bias were optimised to produce a region of high efficiency typical of Doherty power amplifiers. Through the incorporation of a large signal de-embedding network, the current and voltage waveforms were accessed at the current generator plane. This allowed for the confirmation of Doherty operation on an individual device basis. This powerful tool allows for further optimisation of power amplifiers using well established waveform design procedures, previously not possible at high power levels.