additional a/d converter for measuring nano-ampere

is it possible to use a DDC 114 a/d converter with 20 bit with the adruino? Are where examples of additional a/d converters attaced to the ardino?

The simple answer is yes it is possible to use this device with an Arduino.

However, this is a surface mount device so you must use a PCB and with a proper layout if you are going to see all 20 bits. Also you need an op amp buffed reference voltage, and a separate digital and analogue power supply. Best bet is to see the data sheet.

These are not cheap costing in the UK more than an Arduino board. I doubt if anyone has ever used one with this processor before. It's not something you can just lash up on a bit of bread board.

Thanks for the quick answer. So it should be possible. Can I use a 1 battery for powering both prozessors? I think i have to clean the peaks... i case of the DDC 114 maybe something like this....
http://sxm4.uni-muenster.de/stm-de/Plan1.gif

Can I use a 1 battery for powering both prozessors

Not sure what you mean.

Do you mean for powering the Arduino and the analogue side of the A/D? If so, then you can, but you will not achieve the full 20bits resolution if you do.

That circuit is like a pulse stretcher with the second op amp being an integrator. I don't know what your application is so it is hard to say. It will slow down the attack and decay of the pulse though. Can you live with that?

okey my elektronic skills are not very good, actually i just started 2 weeks ago.
The first problem i have that i have a biochemical process which is generating a current which is in nano ampere. This will be very hard to measure because of noise etc.

The second Problem is that I have to measure not only 1 current but 4 / 8 / 16 currents at a time. So I thougt this Chip is the right solution for that problem. But actually I have no clou. Maybe there are other solutions which are better. The resolution is not so importent. I think for my puropse lower resolution is ok. Do you mean oversampling by not archiving 20 bits?

Yes I meant powering the Arduino and the analoge side of the A/D. But maybe there is a solution to filter the peaks of the powering by some circuits. ( Sorry for my bad english and eletronic skills )

Maybe there is a solution on the analog side which is giving me a clear signal to convert to digital... maybe a op-amp array is a good solution

Do you mean oversampling by not archiving 20 bits?

No, over sampling refers to taking more samples of a waveform that is strictly necessary to reconstruct the original waveform. It is nothing to do with the amplitude resolution. What I meant was that the noise would amount to say 5 or 6 bits worth of data and so you would not get the full resolution.

my elektronic skills are not very good, actually i just started 2 weeks ago

This is a hard protect for someone with good skills, I am not sure you can cope with this. As I said it will require a PCB and knowledge of how to lay it out for low noise. It's not a first time project thing.

The second Problem is that I have to measure not only 1 current but 4 / 8 / 16 currents at a time

Form that point of view the input arrangements are good. There are two actual converters each one having one of two inputs switched to it. However not as good as some others with multiple converters. What is the time resolution or sample rate you are after. If it is a biological process I imagine this will be quite slow.

But maybe there is a solution to filter the peaks of the powering by some circuits

This is known as supply decoupling:- http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
but you will not be able to achieve enough isolation between supplies for this sort of resolution.

I would advise that you try and get physical help for this project, maybe a collage or University department. It is the sort of thing I used to have my MSc instrumentation students tackle.

I always start with the hard stuff... but maybe this needs really some professional help...
or maybe this can work SparkFun Current Sensor Breakout - ACS723 (Low Current) - SEN-14544 - SparkFun Electronics in combination with a normal multichannel A/D converter

Thx for the link.. this is really helping me.

Not sure which of the three types of sensor is used in the Spark Fun board but this is a whole couple of orders of magnitude less sensitive that what you were looking at before. Looking at the data sheet the most sensitive one (the 05B) produces 185mA per Amp with 21mV noise. A quick sum 21 / 185 = 0.1 which means it can only measure currents to an accuracy of 100mA no matter how much you amplify its output.
While they say:-

The bandwidth on the ASC712 Low Current Sensor Breakout has been set to 34Hz to reduce noise when using at high gains

This can only mean it could measure current down to 10mA which is still way outside your requirements I think.