What techniques are used for analyzing nonlinear circuits?

Nonlinear circuit analysis techniques include: load-line analysis (graphical intersection with device characteristics), piecewise-linear approximation (different linear models per region), small-signal analysis (linearization around operating point), harmonic balance (steady-state with multiple frequencies), and SPICE-type numerical simulation. Describing functions approximate nonlinear elements for frequency-domain analysis. Newton-Raphson iteration solves nonlinear algebraic equations. Choice depends on circuit complexity and required accuracy.