Approach to Device Modeling
The fundamental goal in device modeling is to obtain the functional relationship between the electrical variables or characteristics of the device that is to be modeled. These electrical characteristics depend upon a set of parameters including geometric variables and variables dependant upon the device physics.
The starting point for modeling both the BJT and MOSFET is the DC model. From this DC model, a linear small signal model and equivalent simplified ac and dc circuits can be derived. The models can then be expanded upon to provide better agreement between the theoretical and experimental results for use in computer simulations.