previous OP AMP BASICS
As a precursor to more detailed sections following, this introductory portion considers the most basic points of op amp operation. These initial discussions are oriented around the more fundamental levels of op amp applications. They include: Ideal Op Amp Attributes, Standard Op Amp Feedback Hookups, The Non-Ideal Op Amp, Op amp Common Mode Dynamic Range(s), the various Functionality Differences of Single and Dual-Supply Operation, and the Device Selection process.
Before op amp applications can be developed, some first requirements are in order. These include an understanding of how the fundamental op amp operating modes differ, and whether dual-supply or single-supply device functionality better suits the system under consideration. Given this, then device selection can begin and an application developed.
The ideal op amp and its attributes
Figure 1-1: The ideal op amp and its attributes
First, an operational amplifier (hereafter simply op amp) is a differential input, single ended output amplifier, as shown symbolically in Figure 1-1. This device is an amplifier intended for use with external feedback elements, where these elements determine the resultant function, or operation. This gives rise to the name "operational amplifier," denoting an amplifier that, by virtue of different feedback hookups, can perform a variety of operations (The actual naming of the operational amplifier occurred in the classic Ragazinni, et al paper of 1947 (Reference 1: John R. Ragazzini, Robert H. Randall and Frederick A. Russell, "Analysis of Problems in Dynamics by Electronic Circuits," Proceedings of the IRE, Vol. 35, May 1947, pp. 444-452). However analog computations using op amps as we know them today began with the work of the Clarence Lovell led group at Bell Labs, around 1940 (acknowledged generally in the Ragazinni paper)). At this point, note that there is no need for concern with any actual technology to implement the amplifier. Attention is focused more on the behavioral nature of this building block device.
An op amp processes small, differential mode signals appearing between its two inputs, developing a single ended output signal referred to a power supply common terminal. Summaries of the various ideal op amp attributes are given in the figure. While real op amps will depart from these ideal attributes, it is very helpful for first-level understanding of op amp behavior to consider these features. Further, although these initial discussions talk in idealistic terms, they are also flavored by pointed mention of typical "real world" specifications— for a beginning perspective.
It is also worth noting that this op amp is shown with five terminals, a number that happens to be a minimum for real devices. While some single op amps may have more than five terminals (to support such functions as frequency compensation, for example), none will ever have less. By contrast, those elusive ideal op amps don’t require power, and symbolically function with just four pins (Such an op amp generates its own power, has two input pins, an output pin, and an output common pin).
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