How to simulate gm vs freq in LC VCO

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davidwong

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When I use ideal inductor(with 5ohm series resistor), and ideal capactor.
LC VCO can be oscillated
But when I use te process kit to simulate my LC VCO.
I find that the VCO can not be oscillated.
I think it may be due to the parasitic component in varactor and inductor.
and the gm of the NMOS transistor is too low at high freq.
How can I simulate gm vs freq in LC VCO?

Note : large signal gm is large enough for oscillating.
 

Scan frequence under tran. analyse and achieve the gm through I/V, then gm/frequency plot is achieved, right?
 

when design LC VCO , always assume a startup factor 3 or more , he startup factor mean that the gm of the gernrated by the active element is 3 times larger than the resistance of the tank circuit

about the gm it can be calcualted from the DC operating point


khouly
 

I use the attached schematic to simulate gm vs freq.
Is it correct?
 

gm will the the ids of the NMOS
 

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