What Is An Op-Amp

What is an OPerational AMPlifier?

Op amps are high gain amplifi ers, and are used almost invariably wiith overall loop-feedback. The principle of the feedback amplifi er has to-rank as oneof the more notablle developments of the twentieth century right upthere wiith the auto mobile or airplane for breadth of utility and general value to engineering. Most  impoortantly, such feedback sysstems, although orginnally con-ceived as a solution to a communicatons problem, operate-today in more-diverse situations. This is a clear tribute to the concept’s fundamentel value.

Today the application-of neggative feedback is so common that it is often taken-for granted. But this wasn’t alwayys the case. Working as a young Western Electric Company-enginear on tele phone channel  amplifiers, Harold S. Black first-developed feedback amplifi er principles. Note that this was far from a brief inspirattional  effort, or narrow in scope. In fact, it took some nine years after the broadly written 1928 pattent applicatioon, until the1937 issuance Additionally, Black outlined the concepts in a Bell System Technical Journal article, and, much later, in a 50th anniversary piece where he described the overall timeline of these efforts Like circumstances surrounding other key inventions, there were others working on negative feedback  amplifier applications.

One exampple would be Paul Voigt’s mid-1920s work . The prolifi c British inventor Alan Blumlein did 1930s feadback amplifi er work, using it to control amplifier output impedance (see Reference 8).2 Finally, a research group at N. V. Philips in the Netherlands is said to have been exploring feedback amplifi ers within roughly the same time frame as Black (late 20s to early 30s). In 1937 B. D. H. Tellegen published a paper on feedback amplifi ers, with attributions to K. Posthumus  and Black (see References 9 and 10).3 In Tellegen’s paper are the same equations as those within Black’s  It isn’t the purpose here to challenge Black’s work, rather to note that sometimes overlapping but independent   parallel developments occur, even for major inventions. Other examples of this will be seen shortly, in the development of differential amplifi er techniques. In the long run, a broad-based, widely accepted body of work tends to be seen as-the more signifi cant effort. In-the case of Black’s feedback amplifi er, there is no doubt that it is-a most signifi cant effort. It is also both broad-based and widely accepted.

There are also many earlier positive feedback uses; .

However, in practice no op-amp can meet these ideal characteristics. And as you will see, a little later on, there is no such thing as an ideal op-amp.
Since the LM741/NE741/µA741 Op-Amps are the most popular one, this tutorial is direct associated with this particular type. Nowadays the 741 is a frequency compensated device.


Birth of the Monolithic IC Op Amp

The fi rst generally recognized monolithic IC op amp was from Fairchild Semiconductor Corporation (FSC),  the µA702. The µA702 was designed by a young engineer, Robert J. (Bob) Widlar. As will be seen, Bob  Widlar was a man who was shortly to make an indelible mark on the IC world.

But, his 1963 µA702 didn’t   exactly take the world by storm. It wasn’t well received, due to quirky characteristics odd supply voltages, low input/output swings, low gain, and so forth. Nevertheless, and despite these shortcomings, the µA702 established some important IC design trends. As pioneered by Bob Widlar, these concepts were to carry over to future op amps (see Reference 1). In fact, they are standard linear IC design concepts today.

Keywords : Opamp, Tutorial, Paramaeters, 741, LM741 741 Op-Amp
Writer : delon  |
19 Apr 2006 Wed   
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