Re: negative impedance generation

Yes, you can analyze the tapped coil of the Hartley oscillator as ideal (auto) transformer with windings ratio n1:n2. Then you get a frequency independent negative input resistance

Vgs = Vin*n1/(n1+n2)
Is = -gm*Vgs
Iin = Is*n2/(n1+n2)

=> Rin = Vin/Iin = -(n1+n2)2/(gm*n1*n2)

File:Hartley osc.svg - Wikipedia, the free encyclopedia

Dear FvM
Again Hi
Thank you for your patience and guide. now i can understand your mean.
Respect
Goldsmith

Hi Goldsmith,
just for clarification (and in addition to FvM's explanation):

* Each 4-pole oscillator (with pos. feedback) can be analyzed also based on the negative resistance concept
* Each oscillator that - at a first look - works as a negative-resistance oscillator can be seen (by alternative interpretation) also as an oscillator exhibiting a positive feedback loop - as long as the negative resistor is realized by an active device (transistor, opamp).
* Obviously, this excludes all circuits using passive devices (gunn or tunnel diodes), which can be analyzed only based on the negative resistance principle (as already explained by FvM).

The statement recalls a previous discussion about classification of diodes as active or passive devices. https://www.edaboard.com/thread196336.html

ok.thanks for your vast replies
I'm simulating some circuit in microwave office.I've placed a resistance in some part of circuit and manipulate it for tuning.with some negative value for resistor the parameters of circuit goes better.
so can I situated your suggestions in that place to make better my parameters?
the tuned value is -1 ohm