Microampere current source

Since you only want a high output impedance then put a resistor in series with the voltage.

you would only need an active solution if you wanted a low impedance output.

Am i misreading the question and you have a 'high impedance voltage' .. try http://www.google.com.au/search?hl=en&q=voltage+to+current+&btnG=Google+Search&meta=

This is of course possible, but first you must tell us what you mean by "...very accurate and stable..."

Without knowing what accuracy or stability you require, your question is impossible to answer....

A fet with its gate connected to its source would do the job, but it may not be stable or accurate enough...

Please advise?

John.

Many thanks for your comments

I will use it to supply stable and accurate DC curent ( independent of the load connected to it). The load can vary from 1k to 700k

Regards

I'm afraid you haven't told us what accuracy or stability you require?

Is it to calibrate 6½ digit digital multimeters? 3½ digit or a moving coil meter?

Is it just to give a 1% stable current over a few minutes or over a whole year?

There are just too many reasons for wanting an 'accurate and stable' current source that we could sit here all week designing some extremely expensive high accuracy and stable current source when all you might need is a lower accuracy one.

John.

+V pin of the op amp will be connected to the V and -V pin to gnd. That mess should be read V-V_A and the current I_L is given by (V-V_A)/R_E

What is inadequate with a constant current diode available cheap from any catalogue? He did not say.

look up a howland current source. it can push and pull current.