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Simulators >> Circuit Simulators >> Why Spectre noise-aware PLL flow give huge PSF output?
https://designers-guide.org/forum/YaBB.pl?num=1253257577

Message started by bluestatic on Sep 18^th, 2009, 12:06am

Title: Why Spectre noise-aware PLL flow give huge PSF output?
Post by bluestatic on Sep 18^th, 2009, 12:06am

we are trying to follow the spectre RF noise-aware PLL sim flow. Using MMSIM71 and IC5141(with latest hotfix), and the PLL is running at 2.5GHz.

It goes well at the beginning, the divider ,CP and VCOmodel was
extracted sucessfully, though we can not view it since the model was encrypted. We don't see much problem since it is a general PLL structure and the flow very straightfoward too. We set the ChargPump load voltage (Vload) to 0.45~0.75.

The transient simulation also goes well at first, untill the chargepump load voltage gradually reached 0.45V, ie, the lower boundary of the voltage range we set previouse in CP model extraction. Now the simulation become very slow, the simulation step is 0.01 fs. It takes 6 hours to simulate 3us. And after the simulation run to 60us, the result psf data has become 65G bytes, which is not possible to be handled by wavescan.

Can anyone please tell me what's happening here? Thanks a lot

Title: Re: Why Spectre noise-aware PLL flow give huge PSF output?
Post by macrohan on Sep 22^nd, 2009, 2:03am

Hi, bluestatic
When I run PLL Noise-aware flow, I have confronted the same problem with you, the simulation step sunddenly change very small.

The reason of this problem is that pfd extracted model from testbench, the setting is not correctly, such as tstab, if you
config wrongly, the step issue may be appear.

I suggest you fixed the cp load voltage, such as fixed to 1/2*VDD.

Title: Re: Why Spectre noise-aware PLL flow give huge PSF output?
Post by bluestatic on Sep 22^nd, 2009, 7:16pm

hi macrohan,
Thanks a lot for the suggestion. According to the simulation result of recent few days, we also suspect this is a problem to do with CP. We found in the extracted CP model, the Iup(max)=2uA, and Idn(max)=0.2uA, which of course is not right. The target value of Iup and Idn are both 100uA, so I guess the extraction is not right anyway.

thanks agian, will try to advice soon.