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Measurements >> Phase Noise and Jitter Measurements >> huge spike in PLL CP noise current simulation
https://designers-guide.org/forum/YaBB.pl?num=1170199979

Message started by rfic on Jan 30^th, 2007, 3:32pm

Title: huge spike in PLL CP noise current simulation
Post by rfic on Jan 30^th, 2007, 3:32pm

hi, i'm simulating PLL phase noise contribution from CP. when i use PLL+Pnoise to simulate the CP/PFD noise current output, i see a huge spike at comparison frequency.

how this spike generated? is there any relationship to reference spur (or i should ask: can i use this spike to simulate reference spur)

thanks

Title: Re: huge spike in PLL CP noise current simulation
Post by Visjnoe on Jan 30^th, 2007, 11:55pm

Dear rfic,

what you see in your simulation is most likely the reference spur.

It can be caused by:

1) mismatch between CP UP/DOWN currents
2) CP/LF leakage current
3) timing mismatch between UP/DOWN signals

I would guess that the spur you see will be largely caused by (1)...

Kind Regards

Peter

Title: Re: huge spike in PLL CP noise current simulation
Post by rfic on Jan 31^st, 2007, 10:06am

hi, peter,

thanks for reply. I fully agree with the cause of reference spur.

In fact, my concern is:

1. as u say, the reference spur is caused by mismatach/leakage CURRENT, in stead of CURRENT NOISE ; but the spike i see is in Pnoise result (i check the current noise); do u think these 2 are in fact same thing?

2. i normally use CP current noise (simulate with PSS+Pnoise) to calculate pn due to CP, i have compared simulation to measurement, they're reasonablely close; but i never check current noise at comparison frequency until recently I happen to see this spike.

mathmatically, this spike is due to convolution of huge flicker noise value at 0-frequency with square wave; but physically, what it mean?

thanks

Title: Re: huge spike in PLL CP noise current simulation
Post by David Lee on Feb 1^st, 2007, 11:59pm

This is usually due to 1/f noise up converted to the comparison frequency.
Is the top noise contributor a 1/f noise source?