| Elliott Sound Products | Amplifier Basics - How Amps Work (Part 6) |
Copyright (c) 1999 - Rod Elliott (ESP)
Page Last Updated 06 Apr 2005
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Amp Basics IndexSection 5 finalises this series - at least until such time as I find (or someone points out) a mistake or major omission that I will then have to fix, there will be no further updates.
The articles in this series describe the essential building blocks of nearly all circuits in common use today. There are others (of course) but they are most often combinations of the above - for example, a LTP stage can be built using two cascode circuits, a current source and a current mirror. The resulting circuit looks complex, but is simply a combination of common circuits such as those shown.
Other circuits are modification of the basic stages to exploit what might otherwise be seen as a deficiency - for example circuits that deliberately exploit the temperature dependency of a BJT can be used as high gain thermal sensors, or to stabilise the quiescent current in a power amplifier.
There are also some bizarre combinations possible. A valve and BJT operating in cascode would be interesting, and would no doubt have some desirable characteristics (I haven't seen this particular combination, but there is no reason that it would not work). Likewise, a valve with a transistor current source instead of the load resistor would have far better linearity and more gain than a simple resistor loaded version.
In many cases, ICs are available to accomplish many of the functions described. Opamps are an obvious one, but there are also IC current sources, transistor arrays (ideal for current mirror applications because of the excellent thermal tracking), plus quite a few others.
I hope that I have shed some light on the subject, and that you get some benefit from my musings.
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