Electronics is unthinkable without amplifiers, so the sooner we address the subject, the better. The internal structure of any amplifier has its complications, but all amplifiers can be viewed largely as dependent sources—active circuit elements in contrast to passive elements such as resistors or transformers—that can deliver substantial power to a load while drawing virtually none from their controlling inputs.
By accepting such a functional description for now, leaving questions of physical structure for later chapters, and focusing on the particularly versatile class of operational amplifiers, we will go far toward acquiring a language applicable to all amplifiers and at the same time acquaint ourselves with circuits of great practical value.
Integrated operational amplifiers are exceedingly easy to use and have gained in speed and precision to the point that they are what first comes to mind when contemplating a new design. Focusing on operational amplifiers will thus have the further advantage of leading us into the mainstream of electronics.
A discussion of operational amplifiers necessarily involves feedback, a notion that has many aspects and is thus hard to define in few words without limiting its scope. We will therefore introduce feedback gradually by means of specific examples, with the intent of achieving enough familiarity to suit our purposes while implicitly acknowledging that much remains to be explored.