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Yes, instrumention amps are often used for low-voltage amplification...primarily because the topology enables the elimination of impedance-matched input termina
by metaphor 7y ago
Yes, instrumention amps are often used for low-voltage amplification...primarily because the topology enables the elimination of impedance-matched input termination with the distinct benefit of minimizing parasitic load on the UUT. Apparently, readily-available integrated instrumentation amps on the market are designed for relatively low-bandwidth applications as a quick DigiKey parametric search suggests, but the canonical topology itself isn't fundamentally bandwidth-constrained...which is part of the reason why I pointed to max GBW results from the search and left it at that.
No, that's not what I'd be looking for, especially in response to your question with the specific constraint of "an integrated version of a differential amp"; given the sensitivity of the in-circuit measurement application being considered, this effectively suggests integrated instrumentation amp. With your suggestion of what I should be looking for, how would you go about input termination without loading the UUT to the detriment of SI?
The author does indeed briefly discuss his prototypes and even released his Eagle design on GitHub[1] with still more notes.
For the record, I didn't downvote on first response, but your "oh-so-brillant-ones" snark may have earned one.
[1] https://github.com/wingel/diff-probe https://github.com/wingel/diff-probe
- bsder 7y agoI actually did originally go back to the GitHub repo, but I missed this in the README: "So far I have only built the B variant of the probe, that is, the probe with separate OP amps for the inputs." So, that's why he doesn't discuss the others. He never built them. > With your suggestion of what I should be looking for, how would you go about input termination without loading the UUT to the detriment of SI? I would almost certainly want to grab the LMH6552 which is a fully-differential. It's input bias current isn't dramatically worse (110uA (about 10K Ohm) vs 34uA (about 30K Ohm)) than the LMH6702 that he used and likely wins by being matched/same temperature because same die/no PCB routing mismatch/etc.