What do you understand by device modeling ?Ripunjay Tiwari
Ans. The aim in device modeling is to get the functional relationship between the terminal electrical variables of the device which is to be modeled. These electrical characteristics based on a parameter set containing geometric variables and variables dependent upon the device physics. Design parameters or process are all variables which appear in the equations. The design parameters controlled by the circuit designer. The characteristic of the semiconductor process are process parameters itself and are not at the control of the circuit designer once the process has been specified. At best only a good approximation to the real relationship of the electrical variables can be found, for5 most physical electrical devices. There are tradeoffs between the quality of the approximation and its complexity. The factors that the engineer considers when marking these tradeoffs are the needed accuracy and the intended use of model. A simple model is normally require to give insight for design and facilitate symbolic hand manipulations where a more accurate and correspondingly more sophisticated model is normally preferred for computer simulation of circuits employing these devices. The beginning point for modeling the MOSFET and BJT discussed here will be a dc model. A linear small single model and equivalent simplified ac and dc circuit will be derived. The better agreement among the experimental result and theoretical for use in computer simulation shown in fig. 2.1.