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Motivation behind Single Stage Amplifiers

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Junior Member level 3
Jul 2, 2013
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Context: I'll be teaching a second year EE class that covers circuit analysis including the basics of transistor amplifiers. When I took these courses, I remember I couldn't keep any of the configurations in my head without resorting to memorization in the beginning. I really didn't know why a common collector vs. common base was used other than "one is harder," "this one is a current buffer because I was told it was," and I often wondered why was I studying these single stage amplifiers other than "to build bigger and better amplifiers." And though amps with high GBP sounded cool, I had no idea why they were useful.

Of course, the more advanced material gave great context to why I would use one stage vs. another, how to chain them together, etc., but I'd like to make this class and subject matter exciting without throwing harder topics at them. Does anyone have any ideas on ways to motivate students in this material? Also, just as important: what didn't work?

Thanks in advance for any suggestions!

In regard to common emitter/ collector/ base...

There is a difference as to where the input signal is applied, and where the load is placed (or alternately, where the output signal is taken).

Common base: Can measure resistance of very low-ohm components. Device under test is installed in the emitter leg.

Common emitter gives extreme sensitivity to changes in input, if you do not put any resistance in the emitter leg.

Common emitter inverts signal. Common collector does not.

It's fun to see how a transistor responds when you touch a bare bias wire, while operating it at maximum sensitivity. Our bodies can pick up ambient mains hum from nearby, which is amplified by the transistor. An oscilloscope displays the 60 cycle waveform, as a sine or square wave.

I would suggest a crystal microphone feeding a transistor amplifier with the choice of CE, CB, CC input stages. the sound quality should be memorable! The main claim to fame of a CB amp is its frequency response and linearity. Perhaps the experiment could be repeated with a ultra low impedance micro phone ( ribbon? ). Or using an audio type transistor as a RF amplifier. I am old enough to have seen common base amplifiers used in a 240 MHZ walkie talkie.
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