DESIGN VIEW is the summary of the complete DESIGN SOLUTION contributed article, which begins on Page 2.
In today's quest for simplicity in "ready-to-use" EDA tools, understanding what's under the hood of a Spice circuit-simulation engine can be helpful, particularly for designs that challenge the conventional limits of Spice. Analog-centric designers will get the most out of Spice simulation by combining their knowledge and experience with an understanding of how their Spice design tool works.
Stepping back to Analog 101, Spice (Special Programs with Integrated Circuit Emphasis) is essentially an equation solver, in compliance with Kirchhoff's Current Law (KCL). The KCL matrix is modified by Spice to analyze the current through voltage sources, and with digital components (e.g., as with XSpice), it uses state variables in model extensions. For linear time-invariant circuits, the equation matrix creates a unique solution. Nonlinear circuits and operations involving integration require inserting a Norton equivalent circuit with the large-signal current summed into the matrix's right-hand side (RHS) and the small-signal conductance summed into the matrix.
That summation process is applied to the "matrix stamp" of a Spice model. Interestingly, during a Spice simulation, each model sums its contributions without knowing what the other models are doing.
The article discusses the Spice options for operating-point control to attain successful convergence and transient simulation control. Design tips are provided with various options to help make the process more efficient.
Full article begins on Page 2