How to use the phaseMargin function?

I

irun2

Guest
Hi,all.
I am just a freshman to Cadence, and now I encounter a problem: if I want
to figure the phaseMargin of a circuit output, how can I write the
expression?(I don't have the help manaual!)Do I have to do the AC analyse
first? phaseMarin(VF("/outnode")), the outnode must be in voltage unit?
Thx in advance!

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seems no one interested in this thread....:(

irun2 wrote:
Hi,all.
I am just a freshman to Cadence, and now I encounter a problem: if I want
to figure the phaseMargin of a circuit output, how can I write the
expression?(I don't have the help manaual!)Do I have to do the AC analyse
first? phaseMarin(VF("/outnode")), the outnode must be in voltage unit?
Thx in advance!

--
Message posted using http://www.talkaboutcad.com/group/comp.cad.cadence/
More information at http://www.talkaboutcad.com/faq.html
Click to expand...
 
I think you already got it.

1. run a ac ananlysis
2. measure pm by phaseMargin(VF("/out"))
3. if it is differential output phaseMargin(VF("/outp") - VF("/outn"))

JD

On Jan 23, 7:45 am, irun2 <yeahgr...@gmail.com> wrote:
seems no one interested in this thread....:(

irun2 wrote:
Hi,all.
I am just a freshman to Cadence, and now I encounter a problem: if I want
to figure the phaseMargin of a circuit output, how can I write the
expression?(I don't have the help manaual!)Do I have to do the AC analyse
first? phaseMarin(VF("/outnode")), the outnode must be in voltage unit?
Thx in advance!

--
Message posted usinghttp://www.talkaboutcad.com/group/comp.cad.cadence/
More information athttp://www.talkaboutcad.com/faq.html
Click to expand...
 
On Wed, 23 Jan 2008 06:45:16 -0800 (PST), JD <Jiandong.Ge@gmail.com>
wrote:

I think you already got it.

1. run a ac ananlysis
2. measure pm by phaseMargin(VF("/out"))
3. if it is differential output phaseMargin(VF("/outp") - VF("/outn"))

JD
Click to expand...
And an even better approach is to use spectre's "stb" (stability)
analysis. With this you don't have to open the loop being analyzed.

Regards,

Andrew.
 
On Jan 23, 5:33 pm, andrewb <andr...@DcEaLdEeTnEcTe.HcIoSm> wrote:
On Wed, 23 Jan 2008 06:45:16 -0800 (PST), JD <Jiandong...@gmail.com
wrote:

I think you already got it.

1. run a ac ananlysis
2. measure pm by phaseMargin(VF("/out"))
3. if it is differential output phaseMargin(VF("/outp") - VF("/outn"))

JD

And an even better approach is to use spectre's "stb" (stability)
analysis. With this you don't have to open the loop being analyzed.

Regards,

Andrew.
Click to expand...
May I add here a question? stability and ac analysis are all based on
ac. But what if your phase margin is degraded by strong transient
signals (assume your OPAMP input is influenced by some strong signals
on top of your AC signal). A stb or AC yields here deceiving results
as it does not take account of the interference. So far a transient
analysis will give you a good result (but of course slow). Is there
maybe a more elegant and safe way to take account of interference with
a AC like analysis (thus faster)?

Regards,

Klaus
 
On Jan 24, 12:33 am, andrewb <andr...@DcEaLdEeTnEcTe.HcIoSm> wrote:
On Wed, 23 Jan 2008 06:45:16 -0800 (PST), JD <Jiandong...@gmail.com
wrote:

I think you already got it.

1. run a ac ananlysis
2. measure pm by phaseMargin(VF("/out"))
3. if it is differential output phaseMargin(VF("/outp") - VF("/outn"))

JD

And an even better approach is to use spectre's "stb" (stability)
analysis. With this you don't have to open the loop being analyzed.

Regards,

Andrew.
Click to expand...
Thanks Andrew and JD.
But after reading you reply I raise a question: what is "stb"
analysis? Is it on the ADE->Analysis menu? Or should it be a function
of the OCEAN script ?
 
On Thu, 24 Jan 2008 02:45:04 -0800 (PST), irun2 <yeahgreat@gmail.com>
wrote:

On Jan 24, 12:33 am, andrewb <andr...@DcEaLdEeTnEcTe.HcIoSm> wrote:
On Wed, 23 Jan 2008 06:45:16 -0800 (PST), JD <Jiandong...@gmail.com
wrote:

I think you already got it.

1. run a ac ananlysis
2. measure pm by phaseMargin(VF("/out"))
3. if it is differential output phaseMargin(VF("/outp") - VF("/outn"))

JD

And an even better approach is to use spectre's "stb" (stability)
analysis. With this you don't have to open the loop being analyzed.

Regards,

Andrew.

Thanks Andrew and JD.
But after reading you reply I raise a question: what is "stb"
analysis? Is it on the ADE->Analysis menu? Or should it be a function
of the OCEAN script ?
Click to expand...
It's on the ADE Choose Analysis form (provided you're using a release
from the last 4 years or so). You can also use it with the
analysis('stb ...) function in OCEAN.

It's covered in the spectre documentation, of course.

Regards,

Andrew.
 
On Thu, 24 Jan 2008 01:05:29 -0800 (PST), klaus.vongehr@googlemail.com
wrote:

On Jan 23, 5:33 pm, andrewb <andr...@DcEaLdEeTnEcTe.HcIoSm> wrote:
On Wed, 23 Jan 2008 06:45:16 -0800 (PST), JD <Jiandong...@gmail.com
wrote:

I think you already got it.

1. run a ac ananlysis
2. measure pm by phaseMargin(VF("/out"))
3. if it is differential output phaseMargin(VF("/outp") - VF("/outn"))

JD

And an even better approach is to use spectre's "stb" (stability)
analysis. With this you don't have to open the loop being analyzed.

Regards,

Andrew.

May I add here a question? stability and ac analysis are all based on
ac. But what if your phase margin is degraded by strong transient
signals (assume your OPAMP input is influenced by some strong signals
on top of your AC signal). A stb or AC yields here deceiving results
as it does not take account of the interference. So far a transient
analysis will give you a good result (but of course slow). Is there
maybe a more elegant and safe way to take account of interference with
a AC like analysis (thus faster)?

Regards,

Klaus
Click to expand...
Large-signal stability is quite hard to assess, because you can't use
the linearisation approaches that allow ac or stb (or pz) analyses to
run quickly.

You can use the "actimes" and "acnames" parameters of a transient to
run an occasional ac or stb analysis through a transient - so you
could vary some large signal and occasionally do a stability analysis
about the point at which it reached - that's still not really
"sufficient" though to find all potential stability problems.

Regards,

Andrew.
 
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