How can I do a current source controlled by voltage?

[bomba]

I need to do a current source controlled by voltage, with an excursion in Amp (peak to peak) 20nA. I need to have the load grounding. Using OP-AMPS.
Precision current source.

Any suggestions are welcome

 

[goodboy_pl]

refer to "OpAmp cook book" and u will find at least 3 ckts for VCCS.
BTW I think the current range u need is so small thus requires precision/low noise opamps like OP-07 and even with them u need to use dynamic offset cansellation of the opamp( only for feedback path) or something like that to measure very low voltages.

also at this range of current u need shield for the ckt to remove EMI.

BEST!

 

[bomba]

thanks!!!

where can i find this ebook?
Or link to this ebook.

 

[electronics1981]

I think you use ICL 7650

 

[bomba]

very nice IC thanks.
Have anybody an ckt schematic?

 

[michel95]

Hi,

You can use a current source like these used in HiOhm multimeter circuit. I have designed some years ago this kind of high precision low current source. You need two precision OPamp and N and P jfet.
The file I wrote (in french, sorry) will give you all the informations. Use PTFE stand-off for output connexion.

Regards

Michel

 

[bomba]

I tried a OPAMP ckt with the RL (impedance) in the feedback loop, a ckt with positive an negative feedback (OP Amps cookbook, bidirectional current source), but I had problems because the impedance value are between 1 to 6 MOhms, and this configurations can't regulate the current at this RL values.

I found this link today in the morning, related to the topic.
https://arxiv.org/ftp/physics/papers/0209/0209038.pdf