[sdiy] Combining currents from different OTA outputs

[Aaron Lanterman]

Howdy gang,

Suppose I have several OTAs with current outputs, and I would like to  
add those currents and turn that sum into a voltage.

A) Could I tie all the OTA outputs together, and run that output down  
a resistor to ground, and then buffer it with an op amp?

B) Could I tie all the OTA outputs together, run that into the  
negative terminal of an op amp with a a resistor in a feedback loop,  
with the + tied to ground (this would be an inverting current-to- 
voltage conversion.

Assuming A and B are valid...

C) Could I add some of the currents with a plus sign and some of the  
currents with a minus sign by combining A and B above using the  
principle of linear superposition?

If I can, I think I can do something rather cool.

In theory, if the OTA outputs act as ideal current sources, the above  
should work... but I don't think I've ever seen OTA outputs ganged up  
like that in practice.

I'm worried that there may be some "in practice" reason why OTAs might  
not like having their output currents summed in such a direct fashion.

- Aaron