[sdiy] Interpreting four-pole-w-feedback circuits

René Schmitz uzs159 at uni-bonn.de
Thu Mar 6 19:22:54 CET 2008

Ian Fritz schrieb:
> At 09:53 AM 3/6/2008, Aaron Lanterman wrote:
>> BUT... I'm bewildered by the four-pole arp patent circuit. The stages
>> look inverting (since the opamp-cap-in-feedback is an inverting
>> configuration), the four of them in casecade should give total
>> noninverting behavior, that's OK... but... it looks to be like the
>> feedback loop is POSITIVE. I'd expect the input to either go through
>> an inverting opamp before being fed back, or for it to go to the
>> negative terminal of the first OTA (so that first stage would be
>> noninverting, but the other three inverting, so it would all go
>> through with a minus sign).
>> What am I missing? Where is my thinking going wrong?
> Aren't the transconductors inverting?

It doesn't really matter if they are, if you have an even number of them.

I think that this might be simply a "flaw" in the patent drawing.
Its only an illustrative drawing, it doesn't really matter if it would 
work that way or not for legal purpose.

I mean nobody at the USPTO would have breadboarded that circuit
anyway. :)


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