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A generalized impedance converter

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jasmin_123

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In the GIC below one can change the OpAmps polarities and also do some other modifications without changing the impedance Z=(Z1*Z3*Z5)/(Z2*Z4).

So, why the conventional circuit is always as shown in the diagram and not a different one?
 

You can not simply change polarity because local loop does not have phase shift of 180 deg ... i.e unstable.
 

Hi, pixel,

It is nice hearing from you again!

I also thought about local loops, but what is unclear for
me is that if the equation for the total Z remains stable then
the entire system should be stable. Is this wrong?

Jasmine
 

ok... if the polarities are changed then the question that you have asked is gonna arise.... there is gotta be a particular way in which the circuit has to be given right????
 

Hello,

I understand that you are referring to "ideal" gyrators that can reverse an impedance without introducing additional unwanted elements, e. g. series resistance, provided the non-ideal amplifier properties can be ignored so far.

If so, the single amplifier circuits must be excluded from consideration. Alternative "ideal" two amplifier circuits can be found in literature. The question could be regarding advantages of different solutions. The presented circuit has minimum part count, don't know if alternative "4 auxilary R" circuits exist. Another circuit from a popular german electronics textbook allows for a ground referenced Z2 but needs 7 auxilary R.

Do you think that the presented circuit has inherent limitations that could be possibly avoided in a different approach? What should be exactly the circuit with reversed OP polarity? The last time, I built a Gyrator circuit was about 35 year ago.

Regards,
Frank
 

jasmin_123 said:
Hi, pixel,

It is nice hearing from you again!

I also thought about local loops, but what is unclear for
me is that if the equation for the total Z remains stable then
the entire system should be stable. Is this wrong?

Jasmine
Sometimes you can use positive feedback to increase speed, but it has to be weaker than negative... If you connect ressitor across Vin+ and out it will be certainly unstable.. I prefer system where all local loops are stable and global also...
 

I am sorry, but I cannot agree with you, pixel.
A local loop can be unstable, but the whole system
can be stable as a rock. Is not it???
 

jasmin_123 said:
I am sorry, but I cannot agree with you, pixel.
A local loop can be unstable, but the whole system
can be stable as a rock. Is not it???

Is it so easy to make stable global loop with unstable local loops? It can maybe be mathematically true.
If local loop is is unstable than amplifier is ussually in saturation (positive feedback) i.e works like a comparator... Output can be stable as a rock? Answer is yes- gnd or vdd...
 

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