Electronics > Projects, Designs, and Technical Stuff
Very low bias current Op-amp to buffer a Kelvin Varley divider
Gyro:
Just for completeness, here is the later input circuit used on the Datron 1041 / 1051.
It uses a LM394 dual matched transistor and an LF355 in place of the LM312. Quite a lot of added complexity for very little gain in stability (Instrument specs are identical in fact). The bootstrap supplies are on a different sheet but are identical to the previous one.
XFDDesign:
The Analog Devices AD8616 might be a good candidate if you apply some bootstrapping. 0.2pA typ, 1pA max. The typ CMRR is only 100dB so you would have to wrap some bootstrapping around it to get the extra 40dB and use it as a buffer stage.
poorchava:
As far as I know LMC6001 offers lowest guaranteed bias current at 25fA. It was even featured in 'what is this femtoampere stuff anyway' with Bob Pease. Arcane stuff going on there...
Wys?ane z mojego HTC One M8s przy u?yciu Tapatalka
dom0:
10 µV/K offset drift and +-1 mV offset...
Marco:
--- Quote from: Gyro on June 16, 2015, 01:29:53 pm ---0.2uV/'C
--- End quote ---
Which is still 10 times as much as an auto-zero.
Just use a AD8638 or a LTC1052 and throw an aggressive low pass filter at it to get rid of the noise and eat the slightly slow response on a setting change (maybe use some nonlinearity to speed it up a bit for large changes).
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