Vijai K. Tripathi

Asymmetric Coupled Transmission Lines in an Inhomogeneous Medium

Terminal characteristic parameters for a uniform coupled-line four-port for the general case of an asymmetric, inhomogeneous system are derived in this paper. The parameters (impedance, admittance, etc.) are derived in terms of two independent modes that propagate in two uniformly coupled propagating systems. The four-port parameters derived are of the same form as those obtained for the symmetric case resulting in similar port equivalent circuits for various circuit configurations considered by Zysman and Johnson. The results obtained should be quite useful in designing asymmetric coupled-line circuits in an inhomogeneous medium for various known applications.

CAD-oriented equivalent-circuit modeling of on-chip interconnects on lossy silicon substrate

A new, comprehensive CAD-oriented modeling methodology for single and coupled interconnects on an Si-SiO/sub 2/ substrate is presented. The modeling technique uses a modified quasi-static spectral domain electromagnetic analysis which takes into account the skin effect in the semiconducting substrate. Equivalent-circuit models with only ideal lumped elements, representing the broadband characteristics of the interconnects, are extracted. The response of the proposed SPICE compatible equivalent-circuit models is shown to be in good agreement with the frequency-dependent transmission line characteristics of single and general coupled on-chip interconnects.

On the Analysis of Symmetrical Three-Line Microstrip Circuits

The immittance parameters for the case of symmetrical coupled three-line microstrip or other inhomogeneous six-port structures are derived in terms of the normal modes of the coupled system. The analytical results obtained reduce to the heretofore known results when the line parameters are interrelated in a specified manner, and should be useful in the study and accurate design of three-line couplers and other microwave circuit elements.

Compact folded line rat-race hybrid couplers

A new, compact folded line configuration for rat-race hybrid couplers is proposed. Simple design equations are presented for the single and double C-section folded line structures. The new configuration exhibits a four- to fivefold reduction in footprint as compared to the conventional rat-race configuration. The design is validated both by using the full-wave electromagnetic simulator and with measurement.

Spectral-domain computation of characteristic impedances and multiport parameters of multiple coupled microstrip lines

A numerical procedure based on the spectral-domain techniques is formulated to compute all the frequency-dependent normal-mode parameters of general multiple coupled line structures in an inhomogeneous medium. In addition to the phase and attenuation constants for all the normal modes, these parameters include the line-mode and decoupled line modal impedances and the current and equivalent voltage eigenvector matrices of the coupled system. The multiport admittance (and impedance) matrices and coupled line equivalent-circuit model parameters are evaluated in terms of these normal-mode parameters. Numerical results for these normal-mode parameters for typical asymmetric two-, three-, and four-line microstrip structures are included to demonstrate the procedure and the frequency dependence of these parameters. >

Analysis and modeling of quantum waveguide structures and devices

A complete description of the numerical analysis of quantum waveguide structures and devices is given. Modal expansions of the wave function together with a mode‐matching technique are utilized to calculate the generalized scattering matrices (GSMs) of junctions or discontinuities and uniform waveguide sections. The different GSMs are combined via an extended generalized scattering‐matrix technique to obtain the scattering parameters of composite quantum waveguide structures. Results for cascaded right‐angle bends and periodic multiwaveguide structures in a split‐gate configuration are presented. A sharp transition to a plateau of zero conductance is observed for the double‐bend configuration. For the periodic multiwaveguide structures, strong resonant behavior similar to that in resonant tunneling diodes is found. Calculated current‐voltage characteristics for the special case of a double constriction are shown, exhibiting a region of negative‐differential resistance (NDR) for temperatures up to approxim...

Equivalent circuit modeling of interconnects from time domain measurements

A technique for the equivalent circuit modeling of interconnects having discontinuities such as bends, steps, and junctions in high-speed circuits and packages is developed. The circuit models are extracted from time domain reflection (TDR) measurements. The simulated results for the circuit models are compared with the measured data to validate the accuracy of the circuit model. The proposed method can be used to help validate circuit models based on field-theoretic techniques as well as used as an independent tool to synthesize circuit models for general nonuniform or interacting two- and three-dimensional interconnects. >

Time-domain characterization of interconnect discontinuities in high-speed circuits

Experimental techniques to characterize typical interconnect discontinuities such as bends and steps, based on time-domain reflection (TDR) measurements, are formulated. These interconnect discontinuities are characterized in terms of general lumped/distributed circuit models which are compatible with CAD simulation tools such as SPICE. The results for the model element values are shown to be consistent with frequency-domain lumped equivalent models for microstrips derived from S-parameter measurements and electromagnetic computations based on the excess inductance and capacitance concepts. The models are also validated by simulating their step response on SPICE and comparing them with the TDR data. >

Analysis of discontinuities in quantum waveguide structures

We have used the modal expansion of the wave function in the discontinuity region based on the superposition principle together with a mode‐matching technique to investigate the transmission characteristics of semiconductor quantum wire structures with discontinuities. Our calculations compare quite well with published results for the theoretical transmission coefficient and experimental conductance of a T‐stub and split‐gate geometry, respectively. We apply this technique to analyze the effect of right‐angle bends in narrow quantum wires which show strong resonant behavior due to the presence of discontinuities in this geometry.

An efficient algorithm for the three-dimensional analysis of passive microstrip components and discontinuities for microwave and millimeter-wave integrated circuits

A numerical technique for the full-wave analysis of shielded, passive microstrip components on a two-layer substrate is presented. The distinct feature of the technique is an efficient formulation for establishing the system matrix in the moment method procedure which allows the derivation of the elements of any large matrix by a linear combination of elements in a precomputed index table. The table is obtained from a two-dimensional discrete fast Fourier transform. In the moment method procedure, the two-dimensional surface current is represented by locally defined rooftop functions. The effect of the resonant modes associated with the metallic enclosure on the numerical procedure is examined. In order to demonstrate the features and the accuracy of the technique, numerical results for a microstrip open end and for a right-angle bend with and without the compensated corner are computed by using the resonant technique and are compared with other published computational and experimental data. >