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In a recent paper, it has been shown that, if an N‐port network fulfills the condition of (geometrical) unconditional stability at a given frequency, then its scattering parameters will also necessarily satisfy N easily computable bounds, one per port. In order to complete that picture, this contribution investigates whether a tighter bound can be obtained by combining the N$$ N $$ bounds into just one. The answer is in general negative, except that the 3‐port case does indeed exhibit a peculiar behavior: this can be exploited to reduce the upper bound when the diagonal elements of the scattering matrix are limited in magnitude up to some α$$ \alpha $$, and in particular for α=0$$ \alpha =0 $$ (simultaneous conjugate match). [ABSTRACT FROM AUTHOR]

A new indicator of unconditional stability is proposed, which is well suited to $N$ -port networks called the stability radius. When compared to previous work on this subject, the new indicator is unique, irrespective of $N$ , and has a clear geometrical interpretation in terms of allowed reflectances in the termination planes. The latter aspect endows it with the ability to describe the (unconditional) stability margin quantitatively. The case for general $N$ needs to be addressed, as in the previous literature, with numerical techniques, but closed-form expressions are derived for $N \leq 2$. The present work brings to light a subtle error in a previous publication and provides a way to correct it. [ABSTRACT FROM AUTHOR]

This article addresses the classical problem of determining the extrinsic resistances ($R_{G}$ , $R_{S}$ , and $R_{D}$) of field-effect transistors (FETs) and, in particular, of high-electron-mobility transistors (HEMTs). The presented approach relies on small-signal measurements of open-channel transistors, as often proposed both for traditional metal–semiconductor FETs (MESFETs) and HEMTs. Unlike what is common practice with HEMTs, the method proposed here does not oversimplify the model of the active channel. On the contrary, we retrieve from the literature a possible analytical model for the open-channel HEMT and use it to determine the triplet of extrinsic resistances without the need of stressing the gate junction with too high currents. Another result of the approach, valid both for MESFETs and HEMTs, is a deterministic way to remove the contribution of the gate junction from the small-signal parameters of the measured devices. All extractions process data that are available on suitable ranges in frequency or in bias voltage, without taking to the limit the sweep parameters or seeking specific resonances. Also, optimizations are only allowed to refine the nominal values, not as the main technique of extraction. These goals are achieved by setting up different subproblems in the form of overdetermined linear systems and then solving by pseudoinversion. The validity of the approach is demonstrated on the measurements of devices from advanced HEMT technologies realized by OMMIC, both GaAs-based (40-nm gate length) and GaN-based (100 and 60 nm). [ABSTRACT FROM AUTHOR]

This paper is focused on the extraction of the noise parameters of a linear two-port network by exploiting both forward and reverse noise power measurements, thus extending the universally adopted approach in which only forward measurements are involved. The analytical derivation of the constituting relations is detailed and the application to an exemplifying measurement context is reported. A fuller exploitation of the approach may in the future simplify the direct extraction of black-box noise models at very high frequencies, where the difficulty in synthesizing a number of different terminations is the most prominent limiting factor. [ABSTRACT FROM PUBLISHER]

This present study investigated the temporal effects of type 1 diabetes mellitus (T1DM) on adolescent skeletal muscle growth, morphology and contractile properties using a 90% partial pancreatecomy (Px) model of the disease. Four week-old male Sprague-Dawley rats were randomly assigned to Px (n = 25) or Sham (n = 24) surgery groups and euthanized at 4 or 8 weeks following an in situ assessment of muscle force production. Compared to Shams, Px were hyperglycemic (>15 mM) and displayed attenuated body mass gains by days 2 and 4, respectively (both P<0.05). Absolute maximal force production of the gastrocnemius plantaris soleus complex (GPS) was 30% and 50% lower in Px vs. Shams at 4 and 8 weeks, respectively (P,0.01). GP mass was 35% lower in Px vs Shams at 4 weeks (1.24±0.06 g vs. 1.93±0.03 g, P<0.05) and 45% lower at 8 weeks (1.57±0.12 vs. 2.80±0.06, P<0.05). GP fiber area was 15-20% lower in Px vs. Shams at 4 weeks in all fiber types. At 8 weeks, GP type I and II fiber areas were ∼25% and 40% less, respectively, in Px vs. Shams (group by fiber type interactions, P,0.05). Phosphorylation states of 4E-BP1 and S6K1 following leucine gavage increased 2.0- and 3.5-fold, respectively, in Shams but not in Px. Px rats also had impaired rates of muscle protein synthesis in the basal state and in response to gavage. Taken together, these data indicate that exposure of growing skeletal muscle to uncontrolled T1DM significantly impairs muscle growth and function largely as a result of impaired protein synthesis in type II fibers. [ABSTRACT FROM AUTHOR]

The present paper presents the transistor modeling work achieved in the GaN European project KorriGaN (“Key Organisation for Research in Integrated Circuits in GaN technology”). The KorriGaN project (2005–09) has released 29 GaN circuits such as high-power amplifiers (HPAs), low-noise amplifiers (LNAs), and switches. Modeling is one of the main key to reach successful designs. Therefore, nonlinear models of European GaN HEMT models have been developed. This work deals with characterization tools such as pulsed IV, pulsed [S] parameters, load-pull measurements, and measurement-based methods to perform GaN HEMT compact models parameters extraction. The present paper will describe the transistor modeling activities in KorriGaN for HPA designs (nonlinear models including trapping and/or self-heating effects) and LNA designs (nonlinear models and noise parameters). [ABSTRACT FROM PUBLISHER]

This letter describes a new approach for determining the scaling properties of Field Effect Transistors (FETs). Unlike typical equivalent circuit-based scaling techniques, we propose to scale the electrical parameters at the ports of the device. The scaling rules are extracted by performing an exhaustive analysis of the scaling features of all the measured parameters. All possible scaling expressions are considered limited only by the number of available device samples with different dimensions. The analysis is completely automated. [ABSTRACT FROM PUBLISHER]

This article presents the design, measurement, and test of a MMIC for the front-end section of a composite multielement radiating system. The MMIC is composed of a 3-BIT modified constant phase digital attenuator, a switch, and a pair of amplifiers for TX/RX operation. A uniform linear array can be realized attaching 15 MMICs to the T/R radiating elements. The so obtained array's co-polarisation pattern is presented. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1667–1673, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23443 [ABSTRACT FROM AUTHOR]

In this paper, the design, fabrication, and test of high-efficiency, high-power C-band harmonic-tuned power amplifiers in GaN technology is reported. The amplifier has been designed utilizing second-harmonic tuning for high-efficiency operation, thus exploiting the high-breakdown voltage peculiarity of GaN-based devices. Realized in a hybrid form, the amplifier has been characterized in terms of small-signal, power, and intermodulation (IMD) performance. An operating bandwidth over 20% around 5.5 GHz, with 33-dBm minimum output power, and 60% drain efficiency at center frequency is demonstrated, together with low IMD. [ABSTRACT FROM AUTHOR]

The conversion matrix, usually represented in a conventional complex-number form, assumes a nonanalytic, real-imaginary form when the frequency of the small signal fs is equal to one-half the local oscillator (LO) frequency f0. This is due to interference phenomena between the input small signal at fs = f0/2 and the converted signal again at f0 - fs = fs = f0/2; the interference is dependent on the phase relation between the input small signal and the LO. The conversion matrix with fs = f0/2 is used in the design of frequency dividers by two. The conversion equations have been rewritten for the case of fs = f0/2, and the conversion matrix has been found to assume a real-imaginary form. Consequently, Barkhausen's criterion has been reassessed for this case. Experiments are performed that confirm this formalism, and computer simulations based on a nonlinear model for the nonlinear device are presented, showing similar results. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [ABSTRACT FROM AUTHOR]

A fast and accurate method to determine the noise parameters of microwave FETs, based on a new expression of the device noise figure as a function of the Y-parameters and two equivalent noise temperatures, is presented. The method requires only the measured small-signal parameters and 50Ω noise figure, thus avoiding the extraction of the small-signal equivalent circuit. It is particularly suitable for noise characterization of coplanar devices. Good agreement with the results of more conventional methods is demonstrated in a wide frequency range. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 565–569, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20698 [ABSTRACT FROM AUTHOR]

This paper is focused on the extraction of the noise parameters of a linear active device by exploiting both forward and reverse noise power measurements associated with different terminations. In order for load-pull measurements to yield a significant marginal improvement (as compared to forward measurements only) it is expected that the device under test should appreciably deviate from unidirectionality. For this reason, the source/load-pull technique is applied to frequencies at which the considered devices are still usable but their reverse noise factor exhibits a measurable dependence on the output terminations. Details on the test bench set up to the purpose, covering the 20–40 GHz frequency range, are provided. A characterization campaign on a 60 nm gate length, 4 × 35 µm GaN-on-Si HEMT fabricated by OMMIC is illustrated. [ABSTRACT FROM AUTHOR]

Low‐noise amplifier (LNA) designers often struggle to simultaneously satisfy gain, noise, stability, and I/O matching requirements. In this article, a novel design technique, tailored for two‐stage low‐noise amplifiers, is presented. The proposed design method is completely deterministic and exploits inductive source degeneration to obtain a two‐stage LNA featuring perfect input and output match together with low noise figure (NF) and a pre‐determined gain, including stability analysis. A novel flowchart is provided together with the corresponding design chart that contains gain, matching, and stability information, therefore addressing all key figures‐of‐merit of a linear amplifier. The design chart is easily implementable in commercial Electronic Design Automation software, to aid designers in the difficult task of selecting the appropriate source degeneration inductor value. The noise performance, on the other hand, is the best possible since the matching networks are designed to provide the input of the two Field Effect Transistors with the optimum termination for noise. The design method is validated with two separate test vehicles operating respectively at Ka‐band (26.5‐31.5 GHz) and K‐band (20.0‐24.0 GHz). The realized Monolithic Microwave Integrated Circuits exhibit 18 dB gain for both versions, NF of 1.5 and 1.2 dB, respectively for the Ka‐band and K‐band version. Input and output matching are typically better than 12 and 15 dB. [ABSTRACT FROM AUTHOR]