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I'm taking an introductory electronics class, the first chapter is about amplifiers, controlled sources, gain, stuff like this. They mention "small AC signal" a few times but never explain what small mean and why there is the need to talk about "small" signals in the first place.

Anyone knows?

Thank you very much

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2 Answers 2

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Small signal is relative term. When non-linear device (for e.g. transistor) is DC biased, it stays fairly linear in small region around the bias point. Small signal is the one that fits in the linear region.

http://en.wikipedia.org/wiki/Small-signal_model

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  • \$\begingroup\$ Sounds pretty solid to me. You could even think about it as approaching zero. \$\endgroup\$ May 15, 2013 at 0:18
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You could ask your instructor - he should know best how such terms are used in your course.

Generally, I'd consider a small signal to be under 1 volt peak-to-peak, but I think the term also has implications that transistors are not driven into cutoff or saturation, or op-amps outputs driven to the rails - generally that the circuit is operating in a linear region.

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