M.J. Howes

Improved calibration and measurement of the scattering parameters of microwave integrated circuits

A novel procedure for the calibration of microwave integrated circuit test fixtures, based on a generalization of the through-reflect-line (TRL) algorithm, is presented. Its advantages compared with previous methods, namely bandwidth of validity and standards availability, are discussed. The approach is verified through the characterization of a particular microstrip verification standard using both the generalized TRL and precision 7-mm calibration techniques. Comparison of the results obtained from these schemes indicates that both the effective directivity and the source/load match are better than 30 dB. >

A large-signal physical MESFET model for computer-aided design and its applications

A quasi-static, large-signal MESFET circuit model is presented. It is based on a comprehensive quasi-two-dimensional, semiclassical, physical device simulation, and its unique formulation and efficiency make it suitable for the computer-aided design of nonlinear MESFET subsystems. Using this approach the semiconductor equations are reduced to a consistent one-dimensional approximation requiring substantially less computing resources than a full two-dimensional simulation. CPU time is typically reduced by a factor of 1000. A single/two-tone harmonic balance analysis procedure which uses the describing frequency concept is also developed and combined with the MESFET model. Numerical load-pull contours as well as intermodulation distortion contours have been simulated; their comparison with measured results validates the approach taken. >

A large-signal physical HEMT model

This paper reports a new, efficient physical HEMT model capable of accurately predicting DC, small- and large-signal performance. It has been interfaced to an industry standard simulator which allows for accurate, large-signal simulation to be integrated into the design process. Large-signal results demonstrate the models suitability for MMIC CAD.

Ka-band and MMIC pHEMT-based VCO's with low phase-noise properties

Two pseudomorphic high electron-mobility transistor (pHEMT)-based Ka-band voltage-controlled oscillators (VCOs), which have exhibited novel close-to-carrier phase-noise properties in conjunction with output powers greater than previously reported heterojunction bipolar transistor (HBT) based oscillators, are presented in this paper. Good low phase noises of at least -70 and -75 dBc/Hz at an offset of 100 kHz around 38 GHz have been measured for the two different VCO designs over reasonable frequency tuning ranges with flat or linear output-power tuning in these ranges. Both designs show a strong dependence between phase noise and tuning-element bias conditions.

Scattering parameter characterization of microwave optoelectronic devices and fiber-optic networks

A microwave fiber-optic network analyzer test set is proposed that will allow the application of two-port calibration theory to the measurement of optical and optoelectronic components in high frequency fiber-optic links. Formulae for the optoelectronic calibration are presented. A unified approach to optical and optoelectronic two-port calibration theory is covered.<<ETX>>

Efficient computation of the steady-state response of periodic nonlinear microwave circuits using a convolution-based sample-balance technique

The authors describe an efficient and robust approach to the computation of the steady-state response of periodic nonlinear microwave circuits. The problem of solving a set of differential equations is converted into that of solving a system of nonlinear algebraic equations using a technique called convolution-based sample balance. Although exact in all cases for which harmonic-balance techniques are exact, this technique does not require the use of discrete Fourier transforms, and calculating the Jacobian is straightforward. For the solution of the resulting system of nonlinear equations, an efficient and yet robust algorithm has been developed. In the examples given, savings in computational effort of over 85% are reported when this algorithm is compared with Newtons method. >

Circuit considerations in the design of wide-band tunable transferred-electron oscillators

A theoretical and experimental investigation into a particular type of tunable microwave circuit commonly used for LSA operation of GaAs layers is reported. It is shown that certain effects which often impose severe limitations on the performance of wide-band transferred-electron oscillators (TEOs) such as frequency saturation, fixed frequency operation, resonance switching, deterioration of efficiency, and high FM noise may, in many instances, be attributed directly to the interaction of the equivalent circuit of the encapsulated device and the microwave circuit. The theoretical result are used to deduce design criteria for a J-band (11 to 19 GHz) waveguide circuit in order to optimize the performance of the oscillator with respect to tunning range, efficiency, and FM noise performance. In particular the results of the investigation indicats that, for continuous tuning combined with low FM noise over the tuning range, the parallel resonant frequency associated with the encapsulated device should be less than the minimum operating frequency, and that, by suitable design of the oscillator, frequency deviation due to fluctuation in the magnitude of the device capacitance can, in principle, be reduced to zero over a narrow bandwidth.

Nonlinear circuit analysis of harmonic and intermodulation distortions in laser diodes under microwave direct modulation

A microwave nonlinear circuit analysis technique which can account for all known steady-state responses has been developed and applied to the large-signal characterization of directly modulation laser diodes. An equivalent circuit derived from the rate equations is used to model the laser diode. The proposed technique is based on a harmonic balance algorithm which represents two-tone inputs by describing frequencies. Second-harmonic and third-order intermodulation distortion results for a single-mode GaAlAs diode have been compared with corresponding measured data to validate the method. Aperiodic responses are detected by means of bifurcation theory prior to the harmonic balance analysis and are simulated in the time domain. Simulated results are shown to agree well with published measurements, and indicate the capability of using this approach for the computer-aided design of microwave fiber-optic transmitters. >

Contact degradation of GaAs transferred electron devices

Abstract The migration of contact material into GaAs devices may degrade the device performance (noise, power output) 1 ) and can shorten the mean time to failure of operational adevices. In order to understand contact degradation the interdiffusion of gold/germanium contacts on gallium arsenide has been studied using Rutherford backscattering, ion microprobe ∗ (SIMS) and microbeam 2 ) techniques. Both the depth profiling and imaging properties of the ion microprobe have been used. The microbeam was used for focused Rutherford backscattering giving a lateral resolution ∼ 10 μm. When used in conjuction with angle lapped samples it allows analysis to be conducted to greater depths and hence one may use thicker contact films. The use of these techniques has enabled both the lateral and depth distributions of gold, germanium, gallium and arsenic to be obtained. These distributions have revealed gold and germanium spike formation beneath the contact. The information obtained provides insight into the mechanisms involved in the formation of ohmic contacts to gallium arsenide. The degradation of such contacts as a result of thermal and electrical effects is discussed.

Electroforming and dielectric breakdown in thin aluminium oxide films

Abstract Experiments are described which compare the electroforming of thin film metal-oxide-metal structures with dielectric breakdown in the same materials. Experiments indicate that forming is initiated by local high fields at irregularities at the metal-oxide interface. At low voltages, the electrical breakdown and heating of the material results in the formation of conducting channels of different electrical behaviour from the bulk of material resulting in the current-voltage characteristics expected from such filamentary conduction.