# Amplifying small non-linear signals

Discussion in 'The Projects Forum' started by blah2222, Jun 6, 2011.

1. ### blah2222 Thread Starter Well-Known Member

May 3, 2010
565
33
Hello, I am working on a project where I am receiving a very small current signal (~100 pA - 10 nA) and I would like to convert this into a voltage signal and amplify it up to something that is more reasonable.

Firstly, to convert this into a voltage signal, is the best method just to pass the current through a resistor and take the voltage drop as the new input voltage signal?

Secondly, I will be dealing with an electrochemical signal current that is far from sinusoidal, as you can imagine. I am just curious if my previous knowledge of small-signal analysis and amplifier design will be sufficient to process this signal.

Any advice would be greatly appreciated!
JP

2. ### #12 Expert

Nov 30, 2010
16,664
7,311
40 years ago we did this with a j-fet input stage. There is probably something better now. What's your frequency range?

3. ### blah2222 Thread Starter Well-Known Member

May 3, 2010
565
33
Hm, from what I understand these signals are not periodic. Basically my job is going to be to produce a realtime plot of current levels with time. This electrochemical sensor can have a potential placed between its electrodes to simulate a response in the current.

The plots that I have seen from articles show current spikes based on events that occur at the electrodes, so there is no periodic nature to these signals. So I can't really give a frequency range.

J

Aug 21, 2008
2,753
665
5. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
This might also be useful ....

File size:
135.3 KB
Views:
23
6. ### wayneh Expert

Sep 9, 2010
12,371
3,224
What you need is also called an instrument amplifier, one with very high input impedance. A pH meter is an example, although even a pH meter might not be able to deal with currents that small. You'll need an op-amp with an extremely high input impedance. Last time I went looking, I found the LMC6035 or LMC660.

7. ### #12 Expert

Nov 30, 2010
16,664
7,311
I see you need a DC amplifier in the picoamp range and output recording. In today's world, recording is childs play. As for the amp, now you know what to look for.

Actually, the stuff I worked on in '73 would be perfect for you. Just get in your Wayback machine and buy a Ph meter from Unilock Inc. in Irvine Ca. It comes with a DC coupled picoamp level preamp, alarm point switching, and 4-20ma recording output...or find something similar in the 21st century. It's probably cheaper now.

8. ### wayneh Expert

Sep 9, 2010
12,371
3,224
Don't buy one. Most labs I've worked it will throw out old meters from time to time. #12's right; everything you need is all there.