Subcircuit Model Research Articles

A SPICE model for multiconductor transmission lines excited by an incident electromagnetic field

This paper describes a SPICE model that may be used for predicting the time-domain or frequency-domain voltages and currents induced at the terminations of a multiconductor transmission line (MTL) by an incident electromagnetic held. Explicit results for the entries in the SPICE circuit model are obtained for an incident uniform plane wave that may represent sources such as radio and television transmitters, radars, lightning, etc. The result relies on the transformation of the MTL equations into uncoupled modal lines by similarity transformations. The entries in the similarity transformations are provided for lossless lines. The model is implemented using controlled sources to implement the modal transformations and delay lines to implement the modal lines. If the model is implemented as a SPICE subcircuit model, the time-domain form of the incident field can be implemented as a source external to that subcircuit model so that changes in the line responses due to changes In the incident field waveform can be simulated without changing the subcircuit model. In order to avoid negative line delays, the result is restricted to incident waves having components of the propagation vector in the positive direction along the line. This restriction can be removed by simply reversing the line. The paramount advantages of the model are that both time-domain and frequency-domain results can be easily obtained with the existing SPICE code, and nonlinear loads, such as transistors and digital devices, as well as dynamic loads, such as inductors and capacitors, may be easily incorporated using the existing elements in the SPICE code. Predicted results for MTL's using the method are compared to those of the time-domain to frequency-domain transformation and finite difference-time-domain (FDTD) methods. >

Computational models of transmission lines with skin effects and dielectric loss

We present circuit models of a length of transmission line with skin effect and frequency-dependent dielectric loss, treating the ordinary RLGC line as a special case. The line is modeled as a characteristic two-port in which the characteristic impedance is approximated as the input impedance of a lumped circuit and the propagation function is approximated as the transfer function of a second lumped circuit plus an ideal delay. A unified approach based on frequency matching is presented to form the model. In the approximation, the skin effect is represented as the impedance of an RL ladder, and the complex dielectric parameter as the admittance of an RC ladder. A table of the rms error of the approximation is derived from which the complexity of the model can be found for a desired accuracy. The model is guaranteed to be stable, and since it consists entirely of lumped circuit elements and ideal delay lines and since the model parameters can be easily computed, it can be incorporated as a subcircuit model in a general circuit simulator, and the solution can be obtained by integrating the circuit equations in the usual manner. No FFT or convolution is required. >

A circuit simulation model for high-frequency power MOSFETs

A circuit simulation model suitable for modeling the static and dynamic switching characteristics of high-frequency power MOSFETs is reported. The model parameters were obtained from physical device layout, silicon doping, and measured electrical characteristics of power MOSFETs. Accurate voltage dependencies of the interelectrode capacitances were obtained from extensive two-dimensional device simulations. The voltage dependence of gate-drain capacitance was modeled using an analytic expression. The measured static current-voltage and transient-switching responses under resistive switching conditions are in excellent agreement with simulation results obtained from SPICE. The MOSFET subcircuit model was used to accurately predict the performance of a series-parallel resonant DC-DC converter using a multilevel system simulator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>