Development of an RF IV waveform based stress test procedure for use on GaN HFETs

This paper reports on the development of an RF IV waveform based stress test procedure. DC and low-voltage RF characterisation was carried out before and after high power RF stress. RF waveform measurements showed that the exact change in the RF load line induced during RF degradation cannot be directly inferred from the DC or low power RF measurement. The RF degradation takes the form of a knee-walkout, a small pinch-off shift consistent with charge trapping and defect generation, and in addition gate leakage occurs once the RF voltage exceeds a critical voltage

Effect of impedance variation around the fundamentals on PA distortions characteristics under wideband multi-tone stimulus

Characterisation of modern wireless power transistors and amplifies requires wideband-modulated stimuli for realistic performance evaluation. Normally power transistor performance is evaluated using passive load-pull techniques. However, these have some physical realization constraints that influence the amplitude and the phase of the presented impedance at the DUT plane as across the modulated bandwidth. The problem becomes more apparent as modulation bandwidth is increased beyond few MHz. It has been shown recently that a digitally controlled active envelop load-pull (ELP) system can completely address this problem [1], thus allowing for a more systematic investigation of the parameters that may affect the performance of power transistors under wideband-modulated stimuli. In this paper, non ideal multi-tone impedance conditions are purposely introduced for demonstrating their effects on power amplifier performance in order to illustrate the DUT sensitivity to measurement system imperfections at higher modulation bandwidths in excess of few MHz

Design of injection‐locked oscillator circuits using an HBT X‐parameters™‐based model

A load independent X-parameters-based heterojunction bipolar transistor (HBT) model has been used for the first time in the design and behaviour prediction of injection-locked oscillator circuits. This model has been extracted from load-pull measurements with a large-signal network analyser and, in order to obtain a high oscillator RF power, targeting a load impedance close to the optimum one for HBT maximum output power. A methodology is given to obtain robust injection-locked oscillator circuits with a high-synchronisation bandwidth. Several injection-locked oscillator prototypes have been designed and fabricated, and their measurements compared with the simulations obtained using the X-parameters model. Satisfactory results were obtained when the prototypes were operated as free-running and synchronised oscillators.Ministerio de Ciencia e Innovación | Ref. TEC2011-29264-C03-03Xunta de Galicia | Ref. 2012/26

Hot-Electron Electroluminescence under RF Operation in GaN-HEMTs::A Comparison Among Operational Classes

Electroluminescence microscopy and spectroscopy are used to compare the average hot-electron concentration and temperature under radio frequency (RF) operation class A, class B, and class F modes. From the results obtained, class A results, on average, in the highest hot-electron concentration, while class F is the mode with the lowest concentration due to its “L”-shaped load line. The electron temperature extracted from the electroluminescence spectra is reduced with increasing RF power, reflecting the dominance of electroluminescence from the portion of the load line in the semi-on region. The electroluminescence method is not able to give substantial information on the portion of the load line with high field and low current density which will be responsible for the potentially damaging hottest electrons present in the channel

Stretching the design: extending analytical circuit design from the linear to the nonlinear domain

In the design of most electronic circuits and systems, designers use computer-aided design (CAD) tools to guide the design flow. They exploit the ability of CAD tools to perform algebraic operations to compute/ predict circuit and system performance. This is possible because, in most electronic circuits and systems, linear operation can be assumed. The behavior of microwave components, circuits, and systems can, for example, be described in terms of "behavioral" parameters, such as Z-parameters, Y-parameters, and S-parameters. Transformation from one parameter to another is achieved by simple linear algebraic operations [1]. The performance of more complex circuits can be computed via linear matrix operations using the relevant parameters, i.e., Y-parameters for parallel connections and Z-parameters for series connections. More significantly, performance predictions can also be obtained via linear algebra transformations, i.e., the maximum gain, minimum noise figure, potential instability, etc., along with design insight, i.e., gain circles, noise circles, optimum input/output match requirements, and so on [1], [2].Ministerio de Ciencia e Innovación | Ref. TEC2011-29264-C03-03Ministerio de Ciencia e Innovación | Ref. TEC2011-28683-C02-0

Characterising the baseband impedance of supply modulators using simple modulated signals

Envelope tracking is one of the promising technologies for 5G power amplifiers, providing high power efficiency over a wide output power range by modulating the supply voltage. Although the baseband impedance, the output impedance of the supply modulator, plays a crucial role in the linearity of the PA, it is often not measured or considered during the modulator design. This paper presents a new, simplified approach to characterising this impedance using a PA with a simple multi-tone modulation as a load. It describes the measurement setup and verifies the results by characterising the baseband impedance of a state-of-the-art buck converter and comparing this to its static model. The results demonstrate that multi-tone signals and complex modulations yield comparable results and are both suitable for measuring and modelling the baseband impedance. This shows that using simple multi-tone measurements and basic equipment, the full static impedance characteristic can be obtained

Evaluation of admittance domain behavioural model complexity requirements for Power Amplifier design

In the framework of Power Amplifier (PA) design for communications, frequency domain non-linear behavioural models have shown their potential as efficient complementary modelling tools when Field Effect Transistor compact models are not available or sufficiently accurate. The Admittance behavioural model, formulated in the V-I domain, is especially suitable for device size and fundamental frequency scaling. It is important to note that the direct extraction of this model, from the Nonlinear Vector Network Analyser (NVNA) load-pull (LP) measurements, requires some extra processing since it necessitates a Look-up-Table indexed to |V11| rather than |A11|. When using such models in PA design, there is the need for the user to select the necessary model complexity. To address this requirement, in this paper, a systematic analysis methodology, to guide the user, is presented and validated in different PA design scenarios. The methodology was tested using NVNA LP measurements of GaN Heterostructure FETs. A fifth order Admittance model formulation showed good accuracy in the studied PA design scenarios.Agencia Estatal de Investigación | Ref. TEC2017‐88242‐C3‐2‐RXunta de Galicia and European Regional Development Fund - ERDF| Ref. "Centro singular de investigación de Galicia accreditation 2019-2022, atlanTTic