運算放大器學習資料

The Op Amp’s Place In The World Ron Mancini In 1934 Harry Black［1］ commuted from his home in New York City to work at Bell Labs in New Jersey by way of a railroad/ferry. The ferry ride relaxed Harry enabling him to do some conceptual thinking. Harry had a tough problem to solve; when phone lines were extended long distances， they needed amplifiers， and undependable amplifiers limited phone service. First， initial tolerances on the gain were poor， but that problem was quickly solved with an adjustment. Second， even when an amplifier was adjusted correctly at the factory， the gain drifted so much during field operation that the volume was too low or the incoming speech was distorted. Many attempts had been made to make a stable amplifier， but temperature changes and power supply voltage extremes experienced on phone lines caused uncontrollable gain drift. Passive components had much better drift characteristics than active components had， thus if an amplifier’s gain could be made dependent on passive components， the problem would be solved. During one of his ferry trips， Harry’s fertile brain conceived a novel solution for the amplifier problem， and he documented the solution while riding on the ferry. The solution was to first build an amplifier that had more gain than the application required. Then some of the amplifier output signal was fed back to the input in a manner that makes the circuit gain （circuit is the amplifier and feedback components） dependent on the feedback circuit rather than the amplifier gain. Now the circuit gain is dependent on the passive feedback components rather than the active amplifier. This is called negative feedback， and it is the underlying operating principle for all modern day op amps. Harry had documented the first intentional feedback circuit during a ferry ride. I am sure unintentional feedback circuits had been built prior to that time， but the designers ignored the effect！