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

Identification of atropine-and P2X1 receptor antagonist-reistant, neurogenic contractions of the urinary bladder

Acetylcholine and ATP are excitatory cotransmitters in parasympathetic nerves. We used P2X1 receptor antagonists to further characterize the purinergic component of neurotransmission in isolated detrusor muscle of guinea pig urinary bladder. In the presence of atropine (1 μm) and prazosin (100 nm), pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS) (0.1–100 μm) and suramin (1–300 μm) inhibited contractions evoked by 4 Hz nerve stimulation in a concentration-dependent manner (IC50 of 6.9 and 13.4 μm, respectively). Maximum inhibition was 50–60%, which was unaffected by coadministration of the ectonucleotidase inhibitor ARL67156 (6-N,N-diethyl-d-β,γ-dibromomethyleneATP) (100 μm). The remaining responses were abolished by tetrodotoxin (1 μm). PPADS and suramin also reduced contractions to exogenous ATP (300 μm) by 40–50%, but abolished those to the P2X1 agonist α,β-methyleneATP (α,β-meATP) (1 μm). The P2X1 antagonists reactive blue 2, NF279 (8,8′-[carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)] bis-1,3,5-naphthalenetrisulfonic acid), MRS2159 (pyridoxal-α5-phosphate-6-phenylazo-4′-carboxylic acid) (100 μm), and NF449 [4,4′,4,4-(carbonylbis(imino-5,1,3-benzenetriylbis(carbonylimino)))tetrakis-benzene-1,3-disulfonic acid] (3 μm) abolished contractions to α,β-meATP (1 μm; n = 4–5), but only reduced contractions evoked by 4 Hz nerve stimulation by ∼40–60% (n = 4–6) and ATP by 30–60% (n = 4–7). However, prolonged exposure to α,β-meATP (50 μm) abolished contractions evoked by all three stimuli (n = 5–12). PPADS (100 μm) and suramin (300 μm) reduced the peak neurogenic contraction of the mouse urinary bladder to 30–40% of control. At the same concentrations, the P2X1 antagonists abolished the nonadrenergic, purinergic component of neurogenic contractions in the guinea pig vas deferens (n = 4–5). Thus, P2X1 receptor antagonists inhibit, but do not abolish, the noncholinergic component of neurogenic contractions of guinea pig and mouse urinary bladder, indicating a second mode of action of neuronally released ATP. This has important implications for treatment of dysfunctional urinary bladder, for which this atropine- and P2X1 antagonist-resistant site represents a novel therapeutic target

Medición de las formas de onda en la caracterización de dispositivos de microondas: impacto en el diseño de amplificadores de potencia

This paper describes an example of a measurement setup enabling waveform measurements during the load-pull characterization of a microwave power device. The significance of this measurement feature is highlighted showing how waveform engineering can be exploited to design high efficiency microwave power amplifiers.Este artículo describe un ejemplo de setup, para la medición de las formas de onda durante la caracterización load-pull de un dispositivo de microondas con alta capacidad de potencia. La significancia de está característica de la medición, se resalta al estudiar la forma en la cual puede ser utilizada, en el diseño de amplificadores de microndas con altas potencias de salida y alta eficiencia

Value co-creation in the delivery of outcome-based contracts for business-to-business service

Working paperThis study introduces the concept of outcome-based contracting (OBC) as the mechanism for firms to focus on delivering value-in-use, and as the driver for value co-creation as the firm would need to jointly deliver outcomes with the customer. The paper analyses two OBC-type contracts between the UK Ministry of Defence and two of its industrial partners. We find that in delivering to outcomes and achieving value-in-use, the state-dependent nature of value in usage „pushes back‟ into the organization, requiring the firm to re-evaluate the way they are structured to receive changes from customer state-dependencies so as to deliver a better service. Our analysis presents seven generic attributes of value co-creation (AVCs) essential for the capability to deliver value-in-use. These are behavioral alignment, process alignment, congruence in customer expectations, congruence in firm expectations, empowerment and perceived control, behavioral transformation, and complementary competencies. The attributes discovered through qualitative data were matched with previous academic literature and operationalized and a measurement instrument was developed. The instrument was then validated by performing an exploratory and second order confirmatory factor analysis.This research was made possible through the joint funding of the Engineering & Physical Science Research Council (UK) and BAE Systems on the Support Service Solutions: Strategy & Transition (S4T) project consortium led by the University of Cambridge. The authors gratefully acknowledge the staff of BAE Systems and MBDA as well as members of the ADAPT IPT, 16th Regiment, ATTAC IPT, MoD and the RAF who have all contributed substantially towards this research

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

Supply modulator ripple in envelope tracking systems - effects and countermeasures

Envelope tracking power amplifiers (ET PAs) are one of the promising architectures to provide high efficiency amplification for future wireless communication systems. This is due to their ability to offer high efficiency over a wide output power range, by modulating the supply voltage applied to the PA. Generating this dynamic supply voltage with switching-mode modulators is highly efficient, but filtering the output remains a challenge, resulting in a residual `ripple' on the supply voltage. This paper presents an experimental investigation into the interaction between a PA and a supply modulator in the presence of this ripple. By adding a varying ripple magnitude to the modulated drain voltage of a 2.14 GHz GaN ET PA with a 10 MHz LTE signal, the effects on the linearity of the RFPA can be observed and analysed to allow the system designer an insight into the amount of ripple that is tolerable, while still being able to achieve linearity and efficiency targets. The mixing products of the ripple and RF signal are shown to be a potential issue in ET PAs. This paper shows, for the first time, the full impact of the ripple voltage magnitude on the output spectrum. Further more, the ripple sensitivity of two different ET PA linearisation approaches are explored; firstly applying generic memory polynomial digital pre-distortion (DPD) and secondly optimising the ET tracking signal shaping function to improve linearity. Measurements show that for the case where the ripple and RF are not synchronized, neither approach is able to significantly mitigate the ripple effect on the PA linearity

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

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