To NIC or not to NIC

[featherpillow]

I've been studying a bit about negative impedance converters, and I'm interested on hearing some other people's thoughts about them. I find them to be a curious thing...

Yamaha uses them to enhance damping in their amplifiers. Soundcraft uses them in their mixer pan-pot circuits instead of using a pull-up resistor to enhance L/R tracking.

Have you used them in applications?

What are the benefits/drawbacks in your opinion?

And yes, this is my first post after lurking for quite some time...

 

[gyraf]

Negative-impedance drive is a fine idea for driving output transformer stages with very small distortion/error figures by compensating for copper resistance:

http://www.lundahl.se/pdfs/papers/feedbck.pdf

http://img.photobucket.com/albums/v172/gyraf/LL1517_output_stage_calrecUA8000.gif

Jakob E.

 

[featherpillow]

Negative-impedance drive is a fine idea for driving output transformer stages with very small distortion/error figures by compensating for copper resistance

So optimum R in the Lundahl application should be roughly equal to R primary times Rin divided by Rf--is R primary the DC resistance or the AC impedance?

As I understand it, the circuit works best when the source impedance is greater than the negative impedance resistor (which would be Rr in the Lundahl app, correct?).

 

[bcarso]

There is a tricky aspect to the copper compensation, which is that you can overcompensate and get instability. If the copper gets cool it will be ...err...uncool.

AP I believe has a patent, possibly expired by now, that uses a non-inductive winding in the trafo as part of the driver feedback loop to take the copper temperature into account and adjust the negative Z accordingly. UREI used to license it.

As such, NIC's (actually an abbreviation for negative immittance, meaning impedance and admittance, converters) are useful circuit blocks and part of the somewhat larger class of GIC's (general i.c.). They are generally realized with voltage input/output op amps but can use the other three flavors of amplifier as well.

 

[featherpillow]

There is a tricky aspect to the copper compensation, which is that you can overcompensate and get instability.

I've read that if the value of compensation gets too high, the output distorts and eventually locks at one of the rails. At this point the output would be prevented from swinging to the other polarity, I'm guessing?

...actually an abbreviation for negative immittance, meaning impedance and admittance, converters...

I didn't know that--thanks for the information.