A question about "the negative resistance of cross-coupled pair"

[pablomarco]

Dear edaboard community,

I would like to ask you a question about the following figure.

Could you please help me derive the impedance seen through the source terminal of the pair? I wanted to derive it by myself (using the small signal model), but I could not achieve a result.

The result is --> Zin2 = -Z2 +2/gm

Thank you very much,
Best regards,
Pablo Marco

 

[G4BCH]

These might help

 

[pablomarco]

I have seen these videos, but they are not related to my issue because in my question I am trying to find the impedance seen through the source, In the videos, the impedance seen through the drain is studied.

Thank you for your response.

So I am still looking for help for deriving it.

 

[FvM]

I think it's simple. Inject a current difference, measure the voltages.

 

[pablomarco]

Yes thank you for your reply, it was what I have been doing. I just realized that I have been missing a point. I would like to share the solution for the community's disposal.

Best regards,
Pablo Marco

 

[BigBoss]

Z2 is Open Circuit @ Resonance so it shouldn't be taken into account.

 

[pablomarco]

Z2 is Open Circuit @ Resonance so it shouldn't be taken into account.

But this is for the case when we have a parallel LC tank oscillator, right?

 

[BigBoss]

But this is for the case when we have a parallel LC tank oscillator, right?

Sure.
This is a typical Oscillator configuration and Negative Resistance is used to compensate the losses in the Tank Circuit.