[Show abstract][Hide abstract] ABSTRACT: Extensive GaAs field-effect-transistor noise measurements are used
to compare noise models with the aim of recommending the most useful one
for monolithic-microwave integrated-circuit design. The evaluation is
based on noise and S-parameter measurements of metal-semiconductor
field-effect transistors and high electron-mobility transistors with
different gatewidths in the frequency range of 0.05-26 GHz. The models
under investigation differ in the number of independent coefficients
necessary to calculate the four noise parameters of the device. The
broad frequency range including radio-frequency frequencies down to 50
MHz requires two different noise measurement systems with special
modifications for optimum performance. In conclusion, the two-parameter
Pospieszalski model turns out to be the most suitable one
Preview · Article · Mar 1999 · IEEE Transactions on Microwave Theory and Techniques
[Show abstract][Hide abstract] ABSTRACT: This article presents a physics-based varactor-diode model for exponentially graded doping profiles. The capacitance-voltage characteristic and the bias dependence of the series resistance are discussed in detail. The model is validated by frequency and time domain measurements on GaAs varactors. The optimum design for nonlinear transmission () line NLTL applications is discussed. Q 1997 John Wiley & Sons, Inc. Int J Microwa'e Millimeter-Wa'e CAE 7: 278-288, 1997.
Preview · Article · Aug 1997 · International Journal of Microwave and Millimeter-Wave Computer-Aided Engineering
[Show abstract][Hide abstract] ABSTRACT: A time-domain model for the formation of picosecond voltage transients on a Nonlinear Transmission Line is presented. Physics-based models for varactors and coplanar lines are used for the numerical calculations. The varactor model is validated by measuring the voltage shape reflected from a single varactor. The modelling results for the output voltage of a Nonlinear Transmission Line are compared with electro-optical measurements and with on-wafer sampling circuit measurements. The measured waveforms are in excellent agreement with the model calculations.
[Show abstract][Hide abstract] ABSTRACT: A new physical model of millimeter-wave Schottky varactors with hyperabrupt doping profile is presented. The bias dependent capacitance and series resistance can be calculated from technological parameters. Analytical formulas for C(V) and Rs(V) for exponentially graded profiles have been verified for varactors of different size and doping profiles which are designed for the integration in coplanar nonlinear transmission lines. The modeling results are compared in detail with on-wafer impedance measurements of a 280Â¿m2 GaAs Schottky diode in reverse and forward bias range up to 110GHz.
[Show abstract][Hide abstract] ABSTRACT: A new method of measuring MMIC transmission-line parameters is presented. The characteristic impedance ZL(Â¿) and the propagation constant Â¿L(Â¿) are extracted from the admittance matrix that can be easily obtained from a two-port S-parameter measurement. For lines longer than half a wavelength, resonances occur that are utilized to determine the line parameters from an analytical model of the resonance behaviour. The main advantages of this method are: 1. Long lines can be measured, which provides better accuracy for attenuation and phase velocity. 2. At resonant frequencies the elements of the admittance matrix are only weakly disturbed by the networks embedding the line under test (this applies to both on-wafer and test-fixture measurement systems). 3. All parameters can be extracted from one line. Examples of coplanar transmission-line parameters for frequencies up to 110 GHz are given.
[Show abstract][Hide abstract] ABSTRACT: The determination of transmission-line characteristic impedance
and propagation constants from two-port S-parameter measurements is
disturbed by half-wavelength resonances. We demonstrate this effect for
on-wafer measurements of coplanar lines. Two networks representing end
effects embed the line and strongly enhance the resonant effect. The
de-embedding consists in determining these networks and subtracting them
from the measured chain matrix. It is shown that simple shunt
admittances are sufficient for modeling of the end effects. Three
methods of de-embedding are presented
[Show abstract][Hide abstract] ABSTRACT: A noise model based on an equivalent circuit is applied to an HEMT. Besides the frequency dependence of the most important noise parameters (F<sub>min</sub>, R<sub>opt</sub>, X<sub>opt</sub>, R<sub>N</sub>) two apparent experimental facts are explained: the limited R<sub>opt</sub>, X<sub>opt</sub> and the increase of R<sub>N</sub> with decreasing frequency.
No preview · Article · Apr 1992 · Electronics Letters
[Show abstract][Hide abstract] ABSTRACT: The noise properties of GaAs field effect transistors in the microwave frequency range are described by a theoretical model. The calculation of the four noise parameters Fm, Rm, Gopt and Bopt, based upon an equivalent circuit The influence of the drain current noise source is separately investigated by one-port measurements with short circuited gate. The channel noise in the upper GHz range (f > 10GHz) is thermal. For low currents (Id/Ids < 0.2) it corresponds to the ambient temperature, for higher currents heating of the electron gas leads to an increasing noise figure. The increase of the effective noise temperature with decreasing frequency is striking in the values of the noise resistance Ra, it is explained by traps.
[Show abstract][Hide abstract] ABSTRACT: Noise figure measurements of GaAs-MESFETs at 1.5 GHz show an increase of Fmin with increasing reverse gate current, whereas at 12 GHz this effect is absent. The noise is caused by the shot effect of the gate current and can be included in an equivalent circuit as a current source in parallel to the gate-drain capacity. In that case the model predicts a noise figure Fmin-1-1/ω. Physical reasons are tunneling of electrons through the depletion layer between gate and drain and the generation of carriers by avalanches. In the latter case a strongly enhanced shot effect is observed.
No preview · Article · Apr 1989 · Frequenz -Berlin-
[Show abstract][Hide abstract] ABSTRACT: The equilibrium of a magnetized Helium plasma is disturbed by a pulsed Trivelpiece-Gouldwave. The electrons obtain the energy by linear collisionless wave absorption. The relaxation phenomena of density and energy are explained in terms of two relaxation times τE, τ1 and a quantity giving the additional ionization. These quantities are derived from a small signal fluid model based upon energy and particle balance equations. In the experiment they are taken from the transient curves of Langmuir-probe current, optical line radiation and the noise power at the electron cyclotron frequency.The experimental conditions are: Helium-gas, p = 1 … 5 Pa, Te = 4 eV, n = 1 … 5 · 1010 cm−3, B = 6,5 · 10−2 T, 27 MHz rf plasma source, low frequency fluctuation level < 1%, classical losses. The energy relaxation time …E = 10 … 15 μs is given by inelastic collision losses. The ionization time constant τ1 is related to the instantaneous ionization frequency during the transient state. It shows a high value at the very beginning of the pulse which must be explained by a tail formation in the distribution function and enhanced radial losses becoming Bohm-like in the transition phase.
No preview · Article · Jan 1982 · Beiträge aus der Plasmaphysik
[Show abstract][Hide abstract] ABSTRACT: Transport processes in magnetized low temperature plasmas have been
investigated during the past two decades up to the present. They are
stimulated by the dominant role of anomalous transport in fusion
devices, where the concept of wave induced perpendicular losses gives a
promising model for physical explanation. A disturbance of the plasma
equilibrium distributed nearly homogeneous along the plasma column is
used. The propagating density perturbation in radial direction is
observed. It was found that the perturbation propagates in an anomalous
way with enhanced perpendicular transport, caused by a discrete spectrum
of correlated drift-like modes. From the field equations for electrons
and ions a rectangular slab model introduced by Aldrige and Keen has
been derived which gives the dispersion of dissipative drift wave modes
(Ellis, et al., 1980).
[Show abstract][Hide abstract] ABSTRACT: Two wide spreaded methods for the measurement of plasma fluctuations are investigated both theoretically and experimentally. In limited regions of frequency and wave number, the fluctuation amplitudes obtained by probes and optical line radiation show sufficient good agreement; in general, however, different effects must be eliminated in order to obtain quantitative values. As an application, a transition from isothermal ion acoustic turbulence to a hybrid turbulent state including temperature fluctuations in a low pressure d.c. plasma has been discovered.
No preview · Article · Jan 1978 · Beiträge aus der Plasmaphysik
[Show abstract][Hide abstract] ABSTRACT: Experiments on the propagation of TG-modes in a weakly inhomogeneous plasma are reported. The modes travel from the high density part (ω < ωpe) to that of lower density (ω > ωpe). The wavelength decreases as expected but an increase of the longitudinal fieldstrength predicted by collisionless theory could not be observed. Two nonlinear effects appear one after another with increasing wave amplitude. These are the sideband instability and a decay into the drift frequency range occuring in the whole plasma column. Neither the region ω ≈ ωpe nor the very vicinity of the exciter antenna are distinguished. The second instability is accompanied by effective electron heating.
No preview · Article · Jan 1978 · Beiträge aus der Plasmaphysik
[Show abstract][Hide abstract] ABSTRACT: The parametric decay process in inhomogeneous layers existing near the plasma boundaries or in front of antennas and probes in a plasma has been investigated. The linear enhancement of the pump field near ω = ωp, the threshold fieldstrength, the wavenumber selection rules and the influence of spontaneous low frequency fluctuations are discussed in detail using a one-dimensional model of the inhomogeneous plasma capacitor. According to this model the instabilities appear in the layers with maximum linear transformation and (linear) absorption. In addition, a strong nonlinear part of absorption in the presence of the instability has been observed.
The level of the spontaneous low frequency fluctuations influences strongly the spectrum of the parametrically excited ion waves. The experiments show a redistribution of the transferred ion acoustic wave energy over the whole wave continuum up to ωpi, if a sufficient strong spontaneous fluctuation level exists in the plasma. It is impossible, however, to excite ion acoustic turbulence by the decay of the high frequency pump field under the present conditions. The conditions for the linear field enhancement are disturbed by the action of the ponderomotive forces changing the density profile near the critical point before reaching the strong pump amplitude being necessary for the excitation of a cascade of decay processes.
No preview · Article · Jan 1977 · Beiträge aus der Plasmaphysik
[Show abstract][Hide abstract] ABSTRACT: The present work describes the results of some linear scattering experiments in a high-frequency plasma and in a dc plasma. The behavior of the plasma as the intensity of the incident field is increased was studied, and abrupt transition to a strongly fluctuating plasma was observed when the power of the incident wave exceeded a well-defined threshold value.