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| Very low bias current Op-amp to buffer a Kelvin Varley divider |
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| Echo88:
Just like Santa i made a list, to check which OP behaves naughty or nice. Maybe someone else finds it useful. If i made an error please point it out, the prices mentioned may not be all accurate or for the particular op-amp-grade. Anyway, at the moment im lacking the knowledge to make a better voltage follower than the one made by Jim Williams. So i continue looking at Datron DMM-service manuals (1051 and 1061 for example) for info on supply bootstrapping and the infos from AoE3 and Bob Peases articles about femtoampere- and teflon-stuff. |
| Cicada:
Might be worth your while using TI's paramateric search. Just select Vos, Offset driftand Input Bias current tick boxes. Sort by Vos and scroll down to where you see the input bias is below 1 pA. https://www.ti.com/amplifier-circuit/op-amps/products.html Maybe? https://www.ti.com/product/opa2320 https://www.ti.com/product/lmp2232 You can Analog devices as well http://www.analog.com/en/parametricsearch/11070 |
| danadak:
A related topic - http://www.electronicdesign.com/test-amp-measurement/whats-all-femtoampere-stuff-anyhow Regards, Dana. |
| chuckb:
There are some examples of Bootstrapping the power supplies for improved op amp performance in this old Burr Brown App note. |
| MisterDiodes:
Just be very careful picking an op-amp from a parametric list looking at input bias current alone - usually low Ib means higher voltage noise in an IC amp. By the same token be aware that the typical AZ amp input current noise datasheet spec is generally hundreds of times lower than the -actual- gate current injection noise spikes that occur at the switching freq. That's not a deal breaker but you have to be ready for it - keep that switching noise current on AZ amp inputs and power rails contained in a safe way inside small area current loops. Be aware that the ancient '1010 that shows up in old LT app notes: Even though it gives you some current drive, that comes at the expense of some relatively strong noise density. It all depends on what your acceptable noise level is on the final output, and how many of those KVD dials are you -really- planning on using? |
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