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Design >> Analog Design >> why i cannot see the tran noise
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Message started by zteic on Feb 26^th, 2004, 4:45am

Title: why i cannot see the tran noise
Post by zteic on Feb 26^th, 2004, 4:45am

Hi,all
I driver a inv with a vpulse source .
the simulator I use is spectre.
the model I use has noise parameter.
I set reltol=1e-6,vabstol=1e-9,iabstol=1e-12 and
maxsetp=1ps.
when tran simulation finish. I use function eyeDiagram to see
the peak-to-peak jitter. but there is no jitter!
I think the noise parameter will cause some different in tran simulation.
Could any one tell me why?

Title: Re: why i cannot see the tran noise
Post by Mighty Mouse on Feb 26^th, 2004, 7:58am

The noise sources are not active during a transient analysis. You can get what you want using the PNoise analysis in SpectreRF. See sections 6.1, 6.3, and 9.1 in Predicting the phase noise and jitter of PLL-based frequency synthesizers, which can be found at http://www.designers-guide.com/Analysis/ for information on how to do this. With this approach, you would not view the noise using an eye diagram. Rather you would see the power spectral density of the noise sampled at the threshold crossing. This approach has two significant advantages over transient noise. First, you get the noise spectrum rather than just the noise power. Second, you can view the individual contributions of each of the noise source using the noise contributor summary.

- MM -

Title: Re: why i cannot see the tran noise
Post by ywguo on Feb 28^th, 2004, 7:27am

Hi, Mighty Mouse,

SpectreRF is a harmonic simulator. Does it suit to simulate inverter? I thought SpectreRF is more suitable for RF circuit.

zteic,

Are you a IC designer from ZTE? ;) Just a guess. The noise parameters in SPICE model are used for .noise analysis which always acompanies AC analysis. So you can not see any jitter due to random noise in a transient analysis.

But if you want to analyze data dependent jitter (ISI) of your inverter, apply a stimulus with a data pattern such as 10111101000001.... Then sweep the start time of the data patten.

I hope it is helpful.

Yawei Guo

Title: Re: why i cannot see the tran noise
Post by Mighty Mouse on Feb 28^th, 2004, 11:09am

SpectreRF is useful for all kinds of non-RF circuits. Documents on this website show how to apply it to predict jitter of digital circuits (such as phase/frequency detectors and frequency dividers) and switched-capacitor filters. People are also using it for ADCs, switching-power supplies, and digital audio amplifiers.

It is really changing analog simulation.

- MM -

Title: Re: why i cannot see the tran noise
Post by Shiva on Aug 1^st, 2004, 11:54am

Hello,

just a quick note: the Eldo simulator (Mentor) does allow
a transient noise analysis (.noisetran).

Kind Regards

Title: Re: why i cannot see the tran noise
Post by Eugene on Aug 4^th, 2004, 1:27pm

If the earlier comment about SpectreRF being a "harmonic" simulator refers to harmonic balance, the comment is not true. SpectreRF is a not harmonic simulator, it is a shooting Newton simulator, which is very different and makes SpectreRF a better option when devices produce waveforms with sharp edges.