ABSTRACT
Any lumped network obeys three basic laws: Kirchhoff ’s voltage law (KVL), Kirchhoff ’s current law (KCL), and the elements’ laws (branch characteristics). For filter applications, we write the frequencydomain instead of the time-domain network equations. Three general methods for writing network equations are described in Chapter 18.1. They are the node equations, the loop equations, and the hybrid equations. This section outlines another method, the signal flow graph (SFG) method of characterizing a linear network. The basic definitions of terms and theorems related to signal flow graphs are presented in Chapter 8.4. The concepts of tree, co-tree, loop, and cutset, required for the present discussion, are introduced in Chapter 7. Note that the terms loop, tree, and co-tree refer to directed circuit, spanning tree, and co-spanning tree defined in Chapter 7.
