[SI-LIST] Re: How do you perform a frequency sweep of a differential coupled line model in Hspice ?
- From: "Muranyi, Arpad" <arpad.muranyi@xxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 18 Feb 2004 12:21:22 -0800
Chris,
What acout does is it selects between the two calculation methods.
a) magnitude of the difference
b) difference of the magnitude
Both methods are "correct". What you want to see is another story.
Your statement to which I responded to in my previous message came
across to me as if you were saying that HSPICE had a bug in its math,
which is not the case for either calculation methods.
Arpad
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Betz
Sent: Wednesday, February 18, 2004 11:03 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: How do you perform a frequency sweep of a
differential coupled line model in Hspice ?
Hello Arpad,
What is obviously incorrect to me is that the magnitude of the=20
differential signal between nodes 1 and 2 is 0. The problem is not with=20
the equation, but with how HSpice is set up.
You are correct in that HSpice does what the equation states, but it is=20
important to note it does so with respect to the setting of acout. With=20
acout=3D 1 HSpice will return the subtraction of the magnitudes of the=20
voltages vectors at those 2 nodes. With acout=3D0 HSpice will return the =
magnitude of the subtraction of the voltage vectors of those 2 nodes.
What is necessary is to make sure you ask HSpice for what you want which =
sometimes includes more than just the single calculation line.
What I was trying to show was that the .option acout will change how=20
HSpice does the calculations.
Chris
Muranyi, Arpad wrote:
>Chris,
>
>I disagree with your statement "obviously incorrect".
>HSPICE does what the equation says correctly, gives
>you the difference of the magnitudes (1-1=3D3D0).
>
>The problem with HSPICE is that it doesn't do complex
>algebra, you have to "do it out" by hand using the
>real/im or mag/ph components, which is what is ugly.
>
>Arpad
>=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D
>=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D
>=3D3D=3D3D=3D3D
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Betz
>Sent: Wednesday, February 18, 2004 6:43 AM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: How do you perform a frequency sweep of a
>differential coupled line model in Hspice ?
>
>
>We have seen the same issues and a coworker figured this out:
>See our following info:
>Consider the voltage on 2 nodes:
>
>node 1 : magnitude=3D3D1 phase=3D3D0
>node 2 : magnitude=3D3D1 phase=3D3D180.
>
>Imagine we wish to measure the voltage between these 2 nodes.
>The HSPICE default calculation for the magnitude of this voltage is
>
>VM(N1,N2) =3D3D VM(N1,0) - VM(N2,0)
>
>which for this example gives the signal as a magnitude of 0.
>This is obviously incorrect.
>
>If you need to deal with voltages as vectors (magnitude and phase) =
like=3D20
>the example above, you need to set .options acout=3D3D0
>The default method for AC analysis (acout=3D3D1) makes sense for system =
=3D
>gain=3D20
>calculations.
>
>Hope this helps
>
>Chris Betz
>
>Vadim Heyfitch wrote:
>
> =20
>
>>Hello Jon,
>>
>>without answering your question, let me point out
>>something about Hspice transmission line model.=3D20
>>
>>There is a difference in the way W-element model
>>behaves in the ac- analysis and the time-domain
>>(TD)simulation. In case of the former, the exact
>>solution is used (the one for the closed form eq'n).
>>In case of the TD, on the other hand, the W-element
>>algorithm is used. The two approaches are radically
>>different. Therefore, if you compare analysis results
>>of even a *single* W-line model at some (high)
>>frequency you should see a difference. Similar
>>difference should be seen for a diff pair. Therefore,
>>the exercise you are trying to go thru is not going to
>>be predictive of TD simulation results, if that's what
>>you expect. I may be mistaken about the purpose of
>>your planned simulation. Then, please, ignore all of
>>the above.
>>
>>-Vadim Heyfitch
>>
>>
>>--- Jon Stahl <jstahl@xxxxxxxxx> wrote:
>>=3D20
>>
>> =20
>>
>>>Hi All,
>>>
>>>I would really appreciate a suggestion on the proper
>>>way to perform a
>>>frequency sweep of a differential coupled line model
>>>I have using
>>>Hspice. I would like to determine the insertion
>>>loss vs. frequency for
>>>the line when being driven by differential stimulus.
>>>
>>>For a single line, it seems trivial to do the
>>>following:
>>>Vinput input 0 ac=3D3D1
>>>.print ac vdb(output, input)
>>>
>>>However, I have had understanding how to peform the
>>>equivalent for
>>>a coupled lines. For stimulus I have tried all of
>>>the following:
>>>
>>>Vin_p in_p 0 ac=3D3D0.2
>>>Vin_n 0 in_n ac=3D3D0.2
>>>
>>>---
>>>
>>>Vin_p in_p 0 ac=3D3D0.2
>>>Vin_n in_n 0 ac=3D3D-0.2
>>>
>>>---
>>>
>>>Vin_p in_p 0 ac=3D3D0.2
>>>Vin_n in_n 0 ac=3D3D0.2,180
>>>
>>>---
>>>
>>>.print ac decibels=3D3DPAR('20 * log(v(out_p,
>>>out_n)/v(in_p, in_n))')
>>>
>>>However, when I do this I always get ZERO for the
>>>differential input
>>>voltage v(in_p, in_n) (???), which of course messes
>>>up the result.
>>>
>>>I have even tried the following:
>>>
>>>Vstim in_p in_n 0 ac=3D3D1
>>>
>>>Which just produces bizarre results.
>>>
>>>Any insights into how to do this would be greatly
>>>appreciated ...
>>>
>>>Thanks,
>>>Jon Stahl
>>>Avici Systems, Inc.
>>>
>>> =3D20
>>>
>>> =20
>>>
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>>
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>
>--=3D20
>Christopher Betz Integrated Device Technology
>Test Engineer 11555 Medlock Bridge Road
>Atlanta Design Center Suite 200 =3D20
>Phone: 678/775-2978 Duluth, GA 30097
>Fax: 678/775/2801
>
>
>
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--=20
Christopher Betz Integrated Device Technology
Test Engineer 11555 Medlock Bridge Road
Atlanta Design Center Suite 200 =20
Phone: 678/775-2978 Duluth, GA 30097
Fax: 678/775/2801
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