[SI-LIST] Re: characteric impedance
- From: Brian Rautio <brian@xxxxxxxxxxxxxxxxxx>
- To: "<long.0.yang@xxxxxxxxx>" <long.0.yang@xxxxxxxxx>
- Date: Tue, 4 Dec 2012 17:54:04 +0000
All,
S-parameters and Z-parameters are most certainly different ways to represent
the same thing. The conversions are trivial and are implemented in most
software packages that deal with such things. The main difference is that
S-parameters are normalized to a characteristic impedance, typically but not
necessarily 50 Ohms, whereas Z-parameters are not. Y-, H-, T- and ABCD- are
additional standardized formats to represent the same thing. Each has strengths
and weaknesses and is more or less convenient for a given task.
Converting an S-parameter file to a spice model is NOT a trivial task, as you
are converting from frequency domain to time domain. There are a number of ways
to solve this problem, again, each with strengths and weaknesses. There are
also a number of serious pitfalls, mostly centered around bandwidth and
causality.
For bandwidth, one might naively think that for a 1 GHz signal they need
S-parameters with a range of 800-1200 MHz. In reality, the transients for a 1
GHz clock might be from 200 MHz up to 3 or 4 GHz--broadband models are a
requirement.
Casualty is another issue. In employing a transform to go from frequency domain
to time-domain, it is possible to end up with a less-than-causal model. There
are a number of ways to "force" causality, and this can work very well. At
Sonnet, what we actually do is use a curve fit with RLC networks, which is
guaranteed to be causal from the start. You can find more information here --
http://www.sonnetsoftware.com/products/sonnet-suites/bb_spice.html.
Thanks,
Brian
On Dec 4, 2012, at 12:37 PM, Long Yang <long.0.yang@xxxxxxxxx>
wrote:
> Long time ago, I derived the S2S conversion, shown as below
> Sy = { [Zx/Zy * (U-Sx)^-1] + (U+Sx)^-1 }^-1 * { [Zx/Zy * (U-Sx)^-1]
> - (U+Sx)^-1 }
>
> where
> Zx --- Reference impedance matrix X
> Zy --- Reference impedance matrix Y
> Sx --- S-parameter matrix with ref impedance Zx
> Sy --- S-parameter matrix with ref impedance Zy
>
> For example, there is one transmission line S-parameter derived with
> reference impedance 100ohm, but we want to know the corresponding
> S-parameter with 85ohm as reference impedance. If this transmission line is
> designed with 85ohm as Zc, we will see resonance in 100ohm S-matrix, but no
> resonance in 85ohm S-matrix.
>
> thanks
> Long
>
> On Wed, Dec 5, 2012 at 1:26 AM, Long Yang <long.0.yang@xxxxxxxxx> wrote:
>
>> Does it work to use the conversion between Z-parameter and S-parameter? I
>> doubt...
>> S-parameter is a behavioral model. You can not recognize what the
>> S-parameter stand for, transmission line, or waveguide, or something
>> else////
>>
>> Here is my thought, point out if something wrong.
>> If you are very sure that this S-parameter is for one dimension non-ideal
>> (or ideal) TEM-dominant transmission line, in the other words uniform
>> transmission line, then this S-parameter is kind of equivalent to
>> W-element, the characteristic impedance is ready to solve. And I do think
>> S2Z or Z2S conversion can be directly used to estimated Zc, though they can
>> be used to do.
>>
>> By the definition of S-parameter, reflection is zero when the reference
>> impedance is matched characteristic impedance, so we can derive the formula
>> of S2S conversion, and sweep Zc to see when reflection tends to zero.
>>
>> thanks
>> Long
>>
>> On Tue, Dec 4, 2012 at 8:23 PM, Zhang Tony <tonywai34@xxxxxxxxx> wrote:
>>
>>> Hi
>>> If I got a s-parameter file, how can I calculate its characteric
>>> impedance at some frequency range?
>>> is there any tools can help on this?
>>> thanks
>>> tony
>>> ------------------------------------------------------------------
>>> To unsubscribe from si-list:
>>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>>
>>> or to administer your membership from a web page, go to:
>>> //www.freelists.org/webpage/si-list
>>>
>>> For help:
>>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>>
>>>
>>> List forum is accessible at:
>>> http://tech.groups.yahoo.com/group/si-list
>>>
>>> List archives are viewable at:
>>> //www.freelists.org/archives/si-list
>>>
>>> Old (prior to June 6, 2001) list archives are viewable at:
>>> http://www.qsl.net/wb6tpu
>>>
>>>
>>>
>>
>
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List forum is accessible at:
> http://tech.groups.yahoo.com/group/si-list
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
