floating inductor

Don Tillman don at till.com
Thu Nov 30 17:41:22 CET 1995

The morning after...

   Date: Wed, 29 Nov 1995 21:08:53 -0800
   From: Don Tillman <don at till.com>

   You can implement a floating inductor with three OTAs and a cap
   like this:

Note that this is yet another reason OTAs are cool.  The original 4
opamp floating inductor circuit needed two opamps to make a
differential integrator and one opamp and a bunch of resistors for
each of two current sources.  Messy at best.  The OTAs shine because
these pieces can be implemented more directly.

   Cool, eh?  But not good enough.  Still too many components.  How about
   a single JFET:

Note that I simplified this circuit a lot for presentation.  Probably
far too much.  The FET needs to be forward biased (it's not working as
a variable resistor as a glance at the ascii schematic would suggest)
and you'll need an extra cap in series with the R decouple the gate
from said bias.  For a delay line you'd probably want to alternate
polarites along the way.  I haven't thought about these issues enough

Also, you'll need to juggle the R, C and gm so that the effective
series resistance of this virtual inductor is not a problem.

Ie., this is a vague sketch, not an actual schematic.

  -- Don

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