Difference between revisions of "Real electronics"
Steven Nagle (Talk | contribs) (Created page with "Real electronics sometimes behave significantly different than the idealized models presented in lecture. ==Real op-amps== Image:Real_op-amp.png Amplifiers using op-amps u...") |
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Revision as of 00:04, 23 August 2013
Real electronics sometimes behave significantly different than the idealized models presented in lecture.
Real op-amps
Amplifiers using op-amps unfortunately do not follow the golden rules. The open-loop gain is not infinite. Therefore the difference between the input voltages is not zero and the current into or out of the inputs is not zero. A realistic model of an op-amp must incorporate a specification for the input offset voltage VOS, an internal voltage that adds to whatever voltage is externally applied to the input terminals V- and V+. The model also incorporates a bias current IB for each input. Normally these are well matched in real op-amps and the average is specified on the datasheet. However they are not perfectly matched and the difference is called the input offset current IOS. All of these non-idealities have the net effect of causing a non-zero voltage, sometimes large, at the output in a negative feedback implementation even when the input is zero. Luckily there are corrective actions available.
