A generalized filter block may consist of inductors, capacitors, resistors, and possibly active elements such as operational amplifiers and transistors. The terminations shown are a voltage source Es, a source resistance Rs, and a load resistor RL. The circuit equations for the network can be written by using circuitanalysis techniques. Modern network theory solves these equations to determine the network values for optimum performance in some respect.

Reproduced from the book Electronic Filter Design Handbook. Copyright © 2006 The McGraw-Hill Companies. Reproduced by permission of The McGraw-Hill Companies. Written permission from The McGraw-Hill Companies is required for all other uses.