[sdiy] Combining currents from different OTA outputs

[David G. Dixon]

Aaron,

Here's another thought.  If you connect the combined current sources into
the centre tap of a potentiometer and the + terminal of an opamp follower,
connect one end of the potentiometer to ground, and connect the other end to
the - input of a unity-gain opamp inverter, you will have what I envisaged
in my last post.

Of course, I misspoke in my last post, as the idea of buffered
resistors-in-parallel is nonsense.  It is just resistors in parallel in the
Thevenin (or Norton) sense looking in from the current source, with buffered
outputs of + and - the source voltage equal to I*(RA||RB) where RA is the
resistor to ground at the follower, RB is both the input and feedback
resistors of the inverter, and RA||RB = RA*RB/(RA + RB).