[sdiy] current question

[ASSI]

On Thursday 26 July 2007 19:56, John Mahoney wrote:
> We're all familiar with voltage dividers, but what if I want to take
> the output from a varying current source and split it into 2 signals:
> one supplying the original current and another supplying, say, half
> that current. Is this easy to do?

The canonical way to do that is a tapered current mirror.  In your case 
you'd need to use two input transistors and three to mirror to, all 
matched.  Problem with mirroring is that (using npn) the current needs 
to come "from above", but is mirrored to be sunk "into the ground".  If 
you source the current into the virtual ground of opamps anyway, a 
current division is easily accomplished by chosing the input impedance 
of each.


Achim.
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