Differential current source

So that the current through E1 doesn't run through the load and invalid the equation io = (E1-E2)/R

It says the OP80 maintains 250fA max input current allowing Io to be less than 1pA.

Without the buffer perhaps use Io >>> IE1

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

On a sunny day (Wed, 14 Jan 2009 23:23:23 -0800 (PST)) it happened snipped-for-privacy@gmail.com wrote in :

The purpose is to create a very high impedance. It actually says that in the text, that talks about 1pA output currents, so Rsense will then be very high (to get any voltage over it). And that means you need a very high input impedance.

As an aside, this kind of circuit topology is also used in old B&K differential charge amplifers. Brings back some memories.

Dave.