[volt-nuts] How to measure micro-amp currents and have low impedance?

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Sep 27 00:03:31 UTC 2009

Bob Paddock wrote:
> On Sat, Sep 26, 2009 at 6:56 PM, Bruce Griffiths
> <bruce.griffiths at xtra.co.nz> wrote:
>> Use the Patterson transdiode connection with npn and pnp transistors as
>> feedback elements.
> I'm not familiar with Patterson's work, and Google was not much help.
> Will you point me to a specific paper or schematic please?
Its not particularly new, you have probably seen the circuit many times
(the name has been around for at least 50 years or so) see:


The problem is that transistor bulk resistance and opamp output
limitations restrict the maximum operating current to 10mA or less.


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