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group delay calculation in Cadance (Read 2117 times)

raja.cedt Senior Fellow Offline Posts: 1516 Germany	group delay calculation in Cadance Nov 08^th, 2011, 8:24am hello all, Generally i find group delay through calculatorin spectre , but i have tried with finding the derivative of the Phase, both are not matching. can any one please tell me why this is happening to me. Thanks, raj.
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buddypoor Community Fellow Offline Posts: 529 Bremen, Germany	Re: group delay calculation in Cadance Reply #1 - Nov 8^th, 2011, 8:49am Raj, there are two possible error sources: * The x-axis (frequency) must be w not f * This axis must scaled linear There is a 3rd error source: The phase must be scaled in rad (not degrees).
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: group delay calculation in Cadance Reply #2 - Nov 8^th, 2011, 8:53am hello buddypoor, I have taken care of W by diving by 2*pi, but why axis must be linear? Thanks, raj.
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buddypoor Community Fellow Offline Posts: 529 Bremen, Germany	Re: group delay calculation in Cadance Reply #3 - Nov 8^th, 2011, 9:20am Dividing by 2Pi ??? For my opinion: w=2Pi*f It must be linear because the program calculates the differential quotient of the function to be analyzed.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: group delay calculation in Cadance Reply #4 - Nov 8^th, 2011, 11:33am hello buddypoor, it's 2*pi becaz when you find derivative you will get dΦ/df, si want to find dΦ/dω, so divided with 1/6.28. Thanks, Raj.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: group delay calculation in Cadance Reply #5 - Nov 8^th, 2011, 12:47pm hello buddypoor, One intersting thing, i have calculated the ration of group delay given by simulator and my method(mean derivative of the phase), interstingly it is 360, i am expecting 2*3.14 ... Thanks, raj.
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buddypoor

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Re: group delay calculation in Cadance
Reply #6 - Nov 8^th, 2011, 3:02pm

raja.cedt wrote on Nov 8^th, 2011, 12:47pm:

hello buddypoor,
One intersting thing, i have calculated the ration of group delay given by simulator and my method(mean derivative of the phase), interstingly it is 360, i am expecting 2*3.14 ...
Thanks,
raj.

Is this a question?
Sorry, but I do not understand the content of your posting.
The result must be in seconds (or mikroseconds).
And - what do you mean with "mean derivative"?
The derivative of the phase function again is a function of frequency.
Please, clarify.

LvW (buddypoor: In memory of the great late Buddy Rich)

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rfidea Senior Member Offline Posts: 159 Europe	Re: group delay calculation in Cadance Reply #7 - Nov 12^th, 2011, 6:49am The relationship is simple. Eg. Virtuoso from CDS is using degrees for phase and Hertz for frequency. This gives Tg = -d(fi,rad)/dw = - d(fi,deg2PI/360)/d(2PIf) = -d(fi,deg)/df / 360 So, you should divide the derivative from Virtuoso with 360 to get the group delay.
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raja.cedt Senior Fellow Offline Posts: 1516 Germany	Re: group delay calculation in Cadance Reply #8 - Nov 12^th, 2011, 9:42am hello rfidea, thanks a lot, i forgot this!!!! Thanks, Raj.
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rfidea Senior Member Offline Posts: 159 Europe	Re: group delay calculation in Cadance Reply #9 - Nov 12^th, 2011, 11:25am Yeah, sometime the answer is to simple...
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Mikay

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Re: group delay calculation in Cadance
Reply #10 - Jan 22^nd, 2014, 8:20am

I noticed this is a quite old topic. But this will be unaccurate if the phase response is not linear. The group delay can be calculated in the spectre: (fi,deg)/f/360.

Mikay

rfidea wrote on Nov 12^th, 2011, 6:49am:

The relationship is simple. Eg. Virtuoso from CDS is using degrees for phase and Hertz for frequency. This gives

Tg = -d(fi,rad)/dw = - d(fi,deg*2*PI/360)/d(2*PI*f) = -d(fi,deg)/df / 360

So, you should divide the derivative from Virtuoso with 360 to get the group delay.

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