Active Devices and Modeling

Accurate device modeling is an extremely important procedure in circuit design, especially in monolithic integrated circuits. Better approximations of the final design can only be achieved if the nonlinear device behavior is described accurately. Once a device model has been incorporated into a circuit simulator, it requires the parameters to specify the device characteristics according to the model equations. The next step is to provide a procedure for adequate extraction of S-parameter data. This poses the problem of how to extract the device parameters from the measurement results accurately, rapidly, and without unnecessary measurement complexity. The best way is to minimize the device bias points under S-parameter measurements and to combine the analytical approach with a final optimization procedure to provide the best fitting of the experimental curves and empirical equation-based model curves. Numerical optimization is often used to fit the model S-parameters to the measured parameters since the resulting device element values depend on the starting values and are not unique. The analytical approach incorporates a derivation of the basic intrinsic device parameters from its equivalent circuit based on S- to Y- or Z-parameter transformations using sufficiently simple equations. However, it is crucial to choose an appropriately large-signal model that is most suitable for a specific active device, accurately describes the nonlinear behavior ...

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