@IanB, thanks for the explanation & illustration, I'm somehow get "part of it"
, pardon for noobness. I guess I will try this out my self once I had the chance, circuit wise should be easy enough looking at the component counts.
now there's the problem. where can you find two "equal" resistors? let alone three.
Google for resistor pairing manually, its relatively easy to sort a pair out from a bunch of resistors from the same batch down to 0.1% accuracy or even better, as long you have the required and good enough resolution, like bench-top dmm class.
is it worth it to match or exact the value of 2 or more precision resistors?
Again, find the articles on resistor pairing method manually, its a piece of cake Cik Shafri.
you may as well complicate things further unnecesarily. btw what the amperage we talking about? in OP its "small current" how small? power engineer will consider 1A is small
This thread is created for learning purpose, hence its in Beginner section, even its not practical. Just really curious of the concept of low drop out current measurement.
About the current scale, it depends heavily on the op-amp's current capability of course, looking at common precision op-amps spec, I'd say this is only suitable for sub mA measurement, CMIIW.