current amplifier recommendations?

[clas004]

Hello,

Looking for a vendor recommendation. 

I'm trying to measure nanoamps to picoamps (i.e., 10^-9 A to 10^-12 A) and so am seeking a low-noise current amplifier.

Was wondering if anyone here had some cost-effective recommendations. Something like this would be nice but I'm not paying over $2,000 US for a glorified op-amp circuit 🙂

In case anyone asks - yes, we've made some ourselves, but they're finnicky and I'd prefer a commercial solution that works out of the box...

Thanks! 

[AnalogKid2DigitalMan]

Have you looked at Femto? I do not know costs offhand.

http://www.femto.de/index.html?../products/ddpca.html

 How much bandwidth do you need? For $2000, that SRS unit seems like a heck of a deal.

As you have found out first hand, trying to design and fabricate your own is a challenging endeavor. At these levels material selection, shielding, trace routing, guarding, and residual contamination all come into play. Much more than a glorified op-amp circuit.

-AK2DM

Message Edited by AnalogKid2DigitalMan on 10-01-2009 08:33 AM

[Henrik_Volkers]

Clas004 ,

still in measuring salty water(s) ? High impedances? 

I don't have a recommendation for an amplifier, but I seems that you are measuring in DC mode and request low noise. Ever thought about a AC measurement schemes? (Lock In Amps, sync rectifiers...... )

Just like what you and AK2DM said, it's not the schematic, it's the experience (blood&sweat&time) that you pay 😉 

Played around with LTC6240s and LMP7721s myself... gained experience... burned my fingers 😕  ...will try again 🙂

[AnalogKid2DigitalMan]

Henrik:

I was in a similar situation trying to build a high gain transimpedance amp for a photodiode. Many weeks of playing around with SMT components soldered onto copper clad with traces cut with an Xacto knife 😞 Never got near the gain-BW product I needed and the noise level was not good.

Finally convinced management to spend the money on a Femto unit, it was cheaper than all the time I spent trying to build my own.

-AK2DM

[Henrik_Volkers]

AK2DM,

I prefer pure dead bug and air as isolator 😉

Do you know AN47 from Jim Williams/linear? Appendix F give an idea 🙂

[AnalogKid2DigitalMan]

Henrik:

I do now:) Thanks for the link. I can relate to some of those methods. I am afraid such work is becoming a lost art nowdays.

-AK2DM

[CWolf]

The NI-4071 DMM measures down to a resolution of 1 pA, so you could use that to measure your current, and there would be no need for an external amplifier. 

-Christina

[clas004]

Thanks for the good discussion guys and gals, got some interesting ideas from this thread 🙂