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Simulators >> RF Simulators >> how can i setup sampled pxf smoothly?
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Message started by hiSkill_11 on Apr 23^rd, 2012, 2:18am

Title: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 23^rd, 2012, 2:18am

Hi, I am puzzled in setting up the sampled pxf analysis. I am a newer to use pxf. I encountered a error hint which shown in attached file. How can I fix it? In fact, I want to simulate a crystal osc using pxf to see the tf from power supply to output clk. Does someone introduce the meaning of probe, Maximum samples, sample delay, additional timepoints? How does they pose effects on the simulation result?
Thanks very much.

Title: Re: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 23^rd, 2012, 7:38pm

I also show the simualtion result with none specialized analysis(say, not check either modulated or sampled). Does the result make sense in evaluating the jitter effect from power supply for 40M crystal? Can someone guide me to distinguish the moudlated analysis and sampled analysis and none specilized analysis? Thanks very much.

Title: Re: how can i setup sampled pxf smoothly?
Post by Frank Wiedmann on Apr 24^th, 2012, 2:39am

You might want to get a more recent version of the Cadence software. I have attached an image of the form in IC6.1.5 ISR9. There it is more clear that the two fields are for the nets that define the voltage that triggers the sampling. The sample delay field is also gone in this version.

Samples are taken when the voltage specified by the two nets (or by the probe component) crosses the threshold value. If there are many of these crossings during the pss period, you can specify a maximum number of samples that will be taken. Usually, you do not need to specify any additional timepoints.

Title: Re: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 24^th, 2012, 6:43pm

Hi, Frank, you are very nice, Thanks for your very kind help :)

Title: Re: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 24^th, 2012, 6:49pm

More a question, could you help me distinguish the difference among the three specialized analysis (none, modulated, sampled)? Thanks.

Frank Wiedmann wrote on Apr 24^th, 2012, 2:39am:

Title: Re: how can i setup sampled pxf smoothly?
Post by Frank Wiedmann on Apr 25^th, 2012, 12:58am

The standard mode ("none") works in a way that is similar to a spectrum analyzer. The sampled mode is typically used to determine the jitter of a signal edge. The modulated mode gives you amplitude and phase modulation and assumes a filtered output signal (only one sideband at each side of the output signal is evaluated).

You can find additional information about sampled analysis in http://www.designers-guide.org/Analysis/sc-filters.pdf. Chapter 4 "Time Domain Analysis: Shooting Newton" of the manual "Virtuoso Spectre Circuit Simulator and Accelerated Parallel Simulator RF Analysis User Guide" also has some information about and examples for the different pxf analysis modes. Further resources are the forum at http://www.cadence.com/community/forums/33.aspx and the Cadence support site at http://support.cadence.com/.

Title: Re: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 25^th, 2012, 1:26am

Ok, I go there for further study. Thank you very much.

Title: Re: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 25^th, 2012, 10:30pm

Hi Frank, I simulated pxf with two specialized analysis. one in none mode, the other in sampled mode. I post the results for comparision.
I found that there is big difference between them. To my opinion, the none mode make sense beacuse the low frequency gain of the tf is about 0.5 since the power is used to power supply the common inverter which is output buffer of the xosc. The sampled result seems much worse than none mode. which is correct for evaluating effect of the power supply noise for measuing the jitter performance of the xosc? why they have so big difference? please correct me. Thanks a lot.

Frank Wiedmann wrote on Apr 25^th, 2012, 12:58am:

Title: Re: how can i setup sampled pxf smoothly?
Post by Frank Wiedmann on Apr 26^th, 2012, 1:01am

You should use the sampled pxf result to determine the jitter. Divide the result by the slope of the output signal at the transition in order to obtain the transfer function from the power supply disturbance to the output jitter.

Most circuits are much more sensitive to disturbances during signal transitions (which is where you are sampling). If you doubt your results, you can always perform a transient simulation with a small sinusoidal signal on the supply and compare the results to those of your sampled pxf analysis.

Title: Re: how can i setup sampled pxf smoothly?
Post by hiSkill_11 on Apr 26^th, 2012, 2:26am

Ok, Thanks very much.