Real op-amps Apr 13, 2016

Operational amplifiers are the work horses of analog. The standard notation for it is:

There are lots of low-cost op-amps available these days. Easy-to-use 8- or 14-pin chips, with 1, 2, or 4 op-amps in a single package.

The principle of an op-amp can be described concisely as (see Chris Gamell’s website):

The op-amp always “wants” both inputs […] to be the same value. If they are not […], the op amp output will go positive or negative, depending on which input is higher than the other.

But real op-amps have imperfections. Last week’s articles used them for a voltmeter setup which is able to handle -25V to +25V and feed that to a µC’s ADC, and I already mentioned a few limitations.

This week extends that series a bit with an example of where things aren’t working out quite as expected, some key parameters to keep in mind when choosing an op-amp, and an improved voltmeter setup:

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