The Designer's Guide Community Forum https://designers-guide.org/forum/YaBB.pl Design >> RF Design >> Question on Hajimiri-Lee model https://designers-guide.org/forum/YaBB.pl?num=1549266425 Message started by iVenky on Feb 3rd, 2019, 11:47pm

 Title: Question on Hajimiri-Lee model Post by iVenky on Feb 3rd, 2019, 11:47pm I am reading the Hajimiri-Lee phase noise model, and got a question on that. If you have an LC tank circuit that is free-running and I inject a current i(t) (dirac current) at instants either t1 or t2 (shown in the figure), depending on when you inject the phase of the output changes (as shown). If I inject it at t1, then phase of the output changes while if I inject it at t2 only the amplitude changes but not the phase. What I don't understand here is when I inject the current i(t) at instant t1, shouldn't the amplitude also change just by superposition of oscillation waveform and the input i(t) energy? This is the part that's confusing to me. And what happens if I inject a really large i(t) that the delta voltage step at t1 exceeds the initial peak voltage to begin with, would the amplitude still change?In the dV/dt and V plot, t1 corresponds to 'b' and t2 corresponds to 'a'.

 Title: Re: Question on Hajimiri-Lee model Post by Ken Kundert on Feb 4th, 2019, 1:10am You are correct. The Hajimiri-Lee model is not to be taken too literally. It is more a conceptual/intuitive explanation. The impulses are assumed to be small.-Ken

 Title: Re: Question on Hajimiri-Lee model Post by Geoffrey_Coram on Feb 6th, 2019, 6:51am It's intuitive, but not always right:https://ieeexplore.ieee.org/abstract/document/933331/

 Title: Re: Question on Hajimiri-Lee model Post by iVenky on Feb 6th, 2019, 8:09am Thanks for the replies.

 Title: Re: Question on Hajimiri-Lee model Post by iVenky on Feb 21st, 2019, 10:41pm 1) While reading about the model again, the author mentions that the ISF is a dimensionless quantity. If you consider this expression (attached), I feel that ISF function Γ(ωτ) has a unit of radians otherwise, I don't see the equation balance on both sides. Is this right?2) Also, does the ISF change with the Q factor of LC tank? It's interesting that the expression that the author derives is only for an ideal lossless tank.