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Modeling >> Behavioral Models >> modeling flicker noise in vco model
https://designers-guide.org/forum/YaBB.pl?num=1425902933

Message started by josef_sous on Mar 9^th, 2015, 5:08am

Title: modeling flicker noise in vco model
Post by josef_sous on Mar 9^th, 2015, 5:08am

hi all ,
i want to add a flicker noise to an vco verilog A based model(for modeling close loop pll with noise contribution).
i have read ken kundert "modeling jitter in pll- based frequency synthesizers" and it was very helpful.
ken offers there this way for adding accumulating jitter:
code: freq = freq*(1 + dT*freq);
.....
....
where dT= 1.414*jitter*$rdist_normal(seed,0, 1);
now , i did noise analysis simulation, i modeled the vco as 2*pi*kvco/s with svcvs block and i use veriloga driver with flicker noise.the plot out put with noise analysis was the same plot i got after simulating pss & pnoise analysis on the vco schamtic so i'm understanding that thus parameters are the correct parameters for flicker noise . now i want to use the parameters i put in phase domain vco simulation and put it on time domain vco simulation use tran noise and simulating an close loop pll .
so i've 2 questions:
1)i tried to use the idea ken offered except that i changed dT as
--> f_n=flicker_noise(flickerPSDat1Hz,1);
dT=1.414*f_n;
but i don't really see any impact on the phase noise which is strange.
is that correct to do it .
2) if there is anyone who can give me an idea how to do it. maybe what i trying to do is not correct way to do it?
bay the way i did phase domain simulation with noise in tran noise and in noise analysis and the seems logical .so now i want to add time domain simulation for the get the whole picture.
thanks

Title: Re: modeling flicker noise in vco model
Post by Geoffrey_Coram on Mar 19^th, 2015, 6:55am

flicker_noise() is a small-signal noise generator that works in small-signal ac noise analysis (like Spice's .noise). You will not get anything in transient analysis unless you use something like Ken's approach.