[sdiy] current conveyor?

[ASSI]

On Monday 06 February 2012, 12:47:39, David G Dixon wrote:
> Do any gurus here know of a circuit to convey a current from a virtual
> ground point to another point at any voltage?

Not claiming guru status, but these things are indeed called current 
conveyors... they come in several types and generations.  While they are 
convenient to synthesize network functions with, their implementation can be 
fantastically complicated.  The "diamond transistor" from Burr-Brown 
actually can be used as a current conveyor.

> Essentially, I'm trying to
> feed the current output from a 2164 (which must feed to virtual ground) to
> an integrator with a voltage of -5V at its + input.

That's actually an easier thing to do, since you simply want to level shift 
that current signal from 0V down to -5V — use a FET cascode transistor.  For 
an nMOS (enhancement, not JFET), the gate would be kept one Vth above -5V 
and everything else takes care of itself.  Now, Vth changes with temperature 
and is different for each transistor, so you'll have to put on a regulator 
that keeps the drain side at 0V to keep the 2164 happy.

Since the compliance of the 2164 does in fact goes slightly above and below 
0V, a crude but effective solution might be to level shift with a 5V 
(selected) Zener diode.  These have nearly no temperature coefficient, so 
this might actually work if the current range is not too large.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf rackAttack V1.04R1:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada