A representation of an actual electric circuit or electronic device by a simple circuit whose behavior is very near to that of the actual circuit over a specified range of conditions. When these conditions are satisfied, the equivalent circuit may be said to constitute a macromodel of the actual circuit. The use of equivalent circuits is important in many of the analysis and design operations associated with electronic circuits. For example, a frequently used electronic device is the operational amplifier. One of the better-known operational amplifiers, the μA 741, is realized as an integrated circuit containing over 20 transistors. Many electric circuits, for example, active-RC (resistance-capacitance) filters, require the use of large numbers of operational amplifiers. In such applications, the use of equivalent circuits greatly simplifies analysis and design operations.