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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]

The stability analysis of nonlinear circuits is a central problem in the framework of microwave design, as applied to high-power amplifiers, oscillators, frequency dividers, and multipliers. However, reliable, user-friendly tools for the stability analysis of such components seem to be quite scarce, even within the very commercial suites for high-frequency circuit simulation. This contribution addresses the problem by generalizing Ohtomo’s test—a popular tool born in the context of linear circuits—to the nonlinear case. Specifically, the new technique allows to analyze the characteristic zeros of a linearized large-signal solution resulting from a harmonic-balance (HB) simulation. As well known, the location of these zeros with respect to the imaginary axis of the complex plane is critical in relation to the qualitative nature of the solution, i.e., to its stability. To the best of the authors’ knowledge, for the first time, a large-signal stability test based on the system determinant but not requiring direct access to the nonlinear elements is implemented completely within a commercial circuit simulator (i.e., without requiring an external mathematical environment for data postprocessing). Some limitations still present are discussed. The generalized Ohtomo test was validated against other methods and circuits from the literature. [ABSTRACT FROM AUTHOR]

A theoretical analysis is carried out of the problem of checking the unconditional stability of a linear $N$ -port with arbitrary $N$ , explaining at length its inherent difficulties. To overcome the algebraic roadblock, an optimization-based method is proposed; the main novelty is that notwithstanding the use of optimization, the problem formulation is specifically chosen so as to guarantee convergence to the global minimum. In particular, recent advancements in the field of convex optimization, mostly unknown to the high-frequency engineering community, are exploited to that end. The result is a method suitable for checking the unconditional stability of linear $N$ -ports with $N$ up to 4. Higher numbers of ports, although allowed in principle, are not viable with the current combination of hardware resources and software implementation. Several examples of applications are provided, both purely illustrative and from actual circuit designs. [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]

A novel result is presented concerning the locus, on the source reflection coefficient plane, of the optimum tradeoff between noise factor and available gain. Although this locus has been discussed and exploited in previous contributions, here, it is shown in a simple manner that it must be an arc of a circumference with center $C_{\mathrm{ tc}}$ and radius $\rho _{\mathrm{ tc}}$ (tangency circle). A handy transformation (a reversible, conformal one) of two-port networks is adopted to study the problem in a simplified, yet general, representation. Properties of the tangency circle are observed in this “noise-centered” representation which are preserved under the conformal transformation, thus providing two equivalent, closed-form approaches to computing $C_{\mathrm{ tc}}$ and $\rho _{\mathrm{ tc}}$. The second method presented lends itself to being easily implemented in commercial circuit simulators, thus serving as the basis of a simple design method for single-stage low-noise amplifiers. [ABSTRACT FROM AUTHOR]

A novel technique for characterizing reciprocal three-port networks is proposed. The approach is an extension of the conventional unterminating method for characterizing two-port networks: on the one hand, the latter extracts the parameters of a (reciprocal) two-port network from one-port measurements, and on the other hand, the presented generalization extracts the parameters of a (reciprocal) three-port network from two-port measurements. The technique is believed of interest particularly for those which occasionally need to perform three-port vector-corrected measurements of three-port test-bench components such as baluns and directional couplers but do not have access to multiport equipment and software. [ABSTRACT FROM AUTHOR]

This letter presents an improved circuit topology to minimize the number of external control voltages that are required to set the state of an N‐bit microwave digital attenuator. An alternative method to connect the control signal is proposed. Typically, the control signal is connected to the gate terminal of the field effect transistor while the source terminal is DC grounded. Here, the control signal is applied to the source terminal of the field effect transistor while the gate is connected to a fixed reference voltage. In this way, only one control voltage is necessary to set the state of single attenuator cell vs two control voltages required in the typical case. The proposed method becomes particularly beneficial as the number of bits increases (ie, >4). The topology has been validated through design, realization, and testing of a 5‐bit Monolithic Microwave Integrated Circuit (MMIC) attenuator operating over the full C‐band (4‐8 GHz). [ABSTRACT FROM AUTHOR]

The technology, design procedure and measurements of an E‐band (71‐86 GHz) high performance gallium arsenide (GaAs) low‐noise amplifier (LNA) are presented. The latter provides a gain in excess of 20 dB, an average in‐band noise figure (NF) of 2.3 dB, absorbing 60 mW DC bias power. A European space‐qualified technology (OMMIC's GaAs 70 nm process) has been selected to demonstrate the feasibility of employing the proposed LNA for production‐ready wireless backhaul point‐to‐point communication systems. A possible installation scenario has been depicted, in order to verify the maximum distance at which TX and RX antennas can be placed and employing the proposed LNA as first amplifying stage of the receiver chain. [ABSTRACT FROM AUTHOR]

A geometrical test for the unconditional stability of three-port networks is presented. The derivation is presented in full detail, starting from the concept of input mapping region as an indicator of unconditional stability. A novel set of (equivalent) parameters is then defined, which can serve to rapidly check the unconditional stability of a three-port network under test. Although the derivation is rather lengthy, the final part of the contribution shows that the practical application of the test is actually straightforward. [ABSTRACT FROM AUTHOR]

The design, realization, and tests of an S-band gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) single-chip front end (SCFE) is presented. The MMIC, realized on the 250-nm gate length GaN process available from the united monolithic semiconductor, integrates high-power and low-noise amplification together with the transmit (Tx)-receive (Rx) switch in a $7\times 7$ mm2 chip area. The SCFE has been conceived for active electronically scanned antenna applications in S-band. In the Rx mode, noise figure (NF) lower than 1.75 dB and gain better than 30 dB have been measured. In the Tx mode, output power and power added efficiency better than 45 dBm and 42%, respectively, have been achieved, with an associated gain higher than 35 dB. Such performance has been measured over a 13% fractional bandwidth in S-band. To the best of the authors’ knowledge, this is the first GaN SCFE operating in S-band. [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]

An optimization-based method allowing a straightforward extraction of scalable small-signal equivalent-circuit models for high-frequency active devices is proposed. The approach only requires a set of devices with a fixed number of fingers and scaling unit gate widths: no dummy structures or bias conditions potentially harmful for the devices are needed. The extraction method is then demonstrated by presenting in full a sample extraction, carried out on a 0.25 GaN-on-SiC HEMT technology provided by Selex-ES. The example also includes the extraction of a noise model, by means of a well-known noise-temperature approach. Both the small-signal and noise models agree well with the experimental data. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This contribution presents an original mathematical method for numerically evaluating the noise parameters of a transmission line subject to an arbitrary thermal gradient. Compared with previous methods, this procedure permits to easily take into account possible variations of line parameters along the propagation direction due to very high thermal excursions. The principal application of the proposed method is coaxial cable modeling in noise figure measurement setups under cryogenic conditions: the connection cable or waveguide from the outside to the inside of the cryogenic vacuum chamber are subject to non-negligible thermal excursions. Under these conditions, significant de-embedding errors may arise if the cables are not correctly modeled, given the very low values of noise figure, which are commonly exhibited by in cryo-cooled devices. The behavior of transmission lines subject to thermal gradients is investigated through extensive 3D thermal and electromagnetic simulations. Simulated data are then input to a numerical algorithm for efficiently determining both scattering and noise parameters of coaxial cables actually used in a cryogenic probe station developed and realized in the facilities of the University of Rome Tor Vergata. A measurement campaign has been performed to validate the simulation-based approach. Subsequently, the numerical model has been used to de-embed the noise contribution of the coaxial cables from cryogenic NF50 measurements of a 70 nm metamorphic high electron mobility transistor (mHEMT). Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The present work is focused on the modeling of the noise performance of GaAs HEMTs under laser illumination. The model is straightforwardly extracted by using a polynomial approximation of the noise correlation parameters without the need for determining an equivalent circuit representation. The validity of the model is confirmed by the observed good agreement between model simulations and noise measurements with and without light up to 26 GHz. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the framework of silicon (Si) technology, evolution towards high-frequency analog applications - which involves innovative solutions such as SiGe BiCMOS and FinFET devices - wide bandgap semiconductors grown on Si substrates are likely to represent a valid option in those cases wherever high-power handling and low noise figures are required. Although such active devices have been extensively investigated in the last years, much of interest has been devoted in developing nonlinear models for high-power applications, whereas reliable noise models still lack, in particular, the validity of traditional (i.e. equivalent temperature-based) approaches for noise modeling of wide bandgap devices has not been sufficiently probed yet. In this contribution, a quite general, black box noise model of active devices is proposed and applied to a family of gallium nitride-on-Si high-electron-mobility transistors fabricated by Selex ES. The model is based on a polynomial approximation of the device correlation matrix and does not require that an accurate small-signal equivalent circuit is available; instead, it can be extracted from multifrequency source pull data. Experimental results demonstrate that a typical behavior of the noise parameters is obtained, both versus frequency and gate periphery. [ABSTRACT FROM AUTHOR]

In this paper, an overview of recently reported low-noise amplifiers (LNAs), designed, and fabricated in GaN technology is provided, highlighting their noise performance together with high-linearity and high-robustness capabilities. Several SELEX-ES GaN monolithic technologies are detailed, providing the results of the noise characterization and modeling on sample devices. An in-depth review of three LNAs based on the 0.25-\mum GaN HEMT process, marginally described in previous publications, is then presented. In particular, two robust and broadband 2–18-GHz monolithic microwave integrated circuit (MMIC) LNAs are designed, fabricated, and tested, exhibiting robustness to over 40-dBm input power levels; an X-band MMIC LNA, suitable for synthetic aperture radar systems, is also designed and realized, for which measurement results show a noise figure \sim2.2~dB with an associated gain >25~dB and robustness up to 41-dBm input power level. [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]

The first realizations of S-band hybrid amplifiers based on hydrogenated-diamond (H-diamond) FETs are reported. As test vehicles of the adopted H-diamond technology at microwave frequencies, two designs are proposed: one, oriented to low-noise amplification, the other, oriented to high-power operation. The two amplifying stages are so devised as to be cascaded into a two-stage amplifier. The activities performed, from the technological steps to characterization, modelling, design and realization are illustrated. Measured performance demonstrates, for the low-noise stage, a noise figure between 7 and 8 dB in the 2–2.5 GHz bandwidth, associated with a transducer gain between 5 and 8 dB. The OIP3 at 2 GHz is 21 dBm. As to the power-oriented stage, its transducer gain is 5–6 dB in the 2–2.5 GHz bandwidth. The 1-dB output compression point at 2 GHz is 20 dBm whereas the OIP3 is 33 dBm. Cascading the measured S-parameters of the two stages yields a transducer gain of 15 ± 1.2 dB in the 2–3 GHz bandwidth. [ABSTRACT FROM AUTHOR]

Source degenerative feedback is extensively applied in the low-noise amplifier design. The beneficial effects of this technique are well established in the open literature. However, the designer is often left to trial-and-error or optimization procedures to identify the adequate amount of feedback when other linear requirements, such as signal matching, come into play. This issue is even more relevant in multistage designs. In this article, we present a synthesis procedure and the relevant design chart to identify the optimum feedback inductor value on all transistors of an N-stage amplifier to obtain a perfect match at its external ports in conjunction with amplifier noise figure minimization and a specified gain requirement. It is shown that the method is applicable to arbitrary N values although it becomes more elaborate for N greater than 6. The method is deterministic as opposed to optimization or trial-and-error-based procedures. The design flow is illustrated at first through a four-stage design with ideal matching elements and subsequently validated by an monolithic microwave integrated circuit (MMIC) test vehicle designed and realized in the WIN foundry’s Gallium Arsenide PIH1-10 process. The measured performance of the test vehicle is NF = 1.9 dB, 26 dB gain, typical I/O return loss of 15 dB in the 26.5–29.5-GHz bandwidth, and practically ideal behavior at the design frequency of 28 GHz. [ABSTRACT FROM AUTHOR]

A recently presented implementation of the current‐reuse concept, specifically devised for microwave cascaded single‐ended amplifiers, is applied to the design of a three‐stage medium‐power low‐noise amplifier (LNA) operating in X‐band. The LNA is realized on a GaN‐on‐SiC 0.25 µm technology supplied by Leonardo S.p.A.'s internal foundry and achieves a transducer gain (GT) of 24 dB, a noise figure (NF) better than 2.5 dB and an output power at 1 dB gain compression (Pout,1dB) higher than 20 dBm over the whole X‐band. The first two stages of the LNA are stacked and share the same current while requiring, as a pair, a doubled external supply voltage, which corresponds to that of the third, medium‐power stage. The versatility of the adopted current‐reuse concept is exemplified by the fact that the two low‐noise stages are initially designed in a conventional single‐ended topology: only in a second step are they converted into a current‐sharing stage pair with no significant effect on RF performance. Nonconventional approaches to low‐noise design and small‐signal stability analysis developed by the Authors and adopted in this design are referred to the Reader. [ABSTRACT FROM AUTHOR]

Abstract: Designing wideband low noise amplifiers (LNAs) at millimeter wave frequencies (>30 GHz) is rather challenging due to trade‐offs that need to be achieved between often contrasting goals such as noise figure, gain, impedance matching, stability, DC power consumption, and chip size. In this paper, a low noise design procedure at 50 GHz is presented, proving the feasibility of a 2 dB Noise Figure LNA at Q/V band. Such performance is enabling for future (but imminent) satellite communication systems operating in the 47‐52 GHz frequency band. Repeatability and reliability are key requirements for satellite operations and therefore an Industrial Grade—Space Qualified technology has been selected. [ABSTRACT FROM AUTHOR]

In this paper, an analysis of gate–source and gate–drain scaling effects in MESFETs fabricated on hydrogen-terminated single-crystal diamond films is reported. The experimental results show that a decrease in gate–source spacing can improve the device performance by increasing the device output current density and its transconductance. On the contrary, the gate–drain distance produces less pronounced effects on device performance. Breakdown voltage, knee voltage, and threshold voltage variations due to changes in gate–source and drain–source distances have also been investigated. The obtained results can be used as a design guideline for the layout optimization of H-terminated diamond-based MESFETs. [ABSTRACT FROM AUTHOR]

Constant input and output mismatch circles in the output load plane are introduced as the basis for low-noise amplifier design methodology. Optimum tradeoff between input and output matching levels results as the application of a design chart providing, at the same time, the corresponding stage transducer gain. The role of degenerative series feedback is studied and systematically embedded in the design procedure, thus providing a direct way to evaluate its optimum level. [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]

We report for the first time on the dc and RF performance of novel MISFETs fabricated on hydrogen-terminated (H-terminated) single crystal diamond film using vanadium pentoxide (V2O5) as insulating material. The active devices were characterized in terms of static $I$ – $V$ characteristics and static transconductance as well as of S-parameters for the calculation of the maximum cutoff frequency and the maximum oscillation frequency. Time stability of the drain current was evaluated overnight observing a maximum fluctuation of 7%. Investigations on temperature dependence of diamond-based MISFET were also performed up to 130 °C. The experimental results were compared with the better established diamond MESFET technology. Finally, the surface transfer doping of H-terminated diamond by very thin V2O5 insulator was also investigated in terms of conductivity, stability in air, and resistance to high temperatures. [ABSTRACT FROM PUBLISHER]