qpss vco phase noise simulation
Hi,
I have tried the 2nd method with Cadence 4.55 and here is the report:
I did it for 4 times with different numbers of harmonic in PSS of 400,120,80,40
I specify the 'tstab' as 1u, which is long enough for my PLL to be stable.Please See The Figure below.
I specify the 'integration method' as 'Gear2only' for efficient convenge and the 'maxacfrequency' as 10G to increase the iteration number.
I set accuracy to 'moderate' or 'liberate'.
The result is: For larger harmonics (400,120,80) PSS fails to converge .For smaller harmonics (40) the PSS converges after 5 iterations.
However,I think the harmonic number of 40 is too small for an accurate phase noise analysis.Because the noise near the multiple frequency of 2GHz (For Example,4GHz, 6GHz,8GHzand higer) will be folded down to the phase noise near 2GHz. So I think if I want to analyse the phase noise more accurately,the harmonics in PSS should be specified at least as 200 so that in PNOISE I can take the the noise near 10GHz into account.Then the circuit is too complicated for PSS to converge.
By the way,gunturikishore,I think the first method is only valid for analysing phase noise at a frequency offset higher than the PLL bandwidth as VCO noise will dominate at that frequency.However,below the PLL bandwidth,charge pump noise will dominate.So I did not try the first method.But thank u all the same.
I think I will use some behavior model to take the place of the block,such as Divider and PFD,which are not so important to the phase noise contribution.
Other suggestion will be appreciated.