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GCF in the PSS settings

Clidre over 9 years ago

Hello,

I'm setting a PSS simulation for my DDS.

The produced frequency is fCK/(2^N)*step, where step is a parameter that I control from the ADE, and N=10.

I would like to set the beat frequency of the PSS as a function of my parameter. In particular, I would like the beat frequency to be

fCK/(2^N)*GCF(2^N,step)

where I called GCF the greatest common factor between 2^N and step.

Is there a GCF function? I didn't find anything similar in the Virtuoso Visualization and Analysis XL User Guide. I really need a GCF function to keep my PSS settings correct for every value I assign to my parameter.

I hope you can help me.

Thanks a lot!

Frank Wiedmann over 9 years ago

I did not find any documented GCF (or GCD) function although it has to exist internally in Virtuoso for the "Auto Calculate" option of the "Beat Frequency" in the pss setup form.

You could define the function trGCD (and the functions it uses) from http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:TechPubDocs;src=pubs;releaseName=;DocumentType=manuals;q=/sklanguser/sklanguserIC6.1.7/chap17.html#1008369 in your environment. If you are using ADEXL, you should also take a look at http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;DocumentType=tbshtng;solutionNumber=11821730.
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Andrew Beckett over 9 years ago

The simplest might be to set autofund=yes in the additional parameters field in the PSS options form (it's not available as a checkbox - partly that was because we changed the "auto calculate" many years ago to use the new autofund=yes parameter and then I pointed out that this was fine until you had a divider in the circuit because it didn't take that into account; put another way, autofund=yes tells the simulator to figure out the fundamental based on the sources alone). It probably should have been added back as a separate option on the UI, but it hasn't been so far.

I wrote some SKILL using Euclid's method to compute the GCD - see below. This is assuming integer arguments though:

/* abGCD.il

Author     A.D.Beckett
Group      Custom IC (UK), Cadence Design Systems Ltd.
Language   SKILL
Date       Sep 24, 2001 
Modified   
By         

Euclid's algorithm for finding Greatest Common Divisor.

***************************************************

SCCS Info: @(#) abGCD.il 09/24/01.15:15:30 1.1

*/

/***************************************************************
*                                                              *
*                          abGCD(a n)                          *
*                                                              *
*     Finds the greatest common divisor of two integers..      *
*                                                              *
***************************************************************/

procedure(abGCD(a n "x")
    while(a!=0
        n=prog1(a a=mod(n a))
    )
    n
)

Regards,

Andrew

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