[SI-LIST] Re: Rise-time of Cascaded Lossy T- Lines

The RSS approximation of risetimes of cascaded elements is just that ...
an approximation.  It seems to work pretty well in most cases, but it is
not exact.

One assumption that I believe goes into this approximation, is that each
cascaded section is effectively isolated from the others.  In other
words, connecting component B to component A doesn't affect the response
of component A itself.  The frequency response of the whole system would
be the product of each individual section.

But that is not the case when cascading passive elements like lossy
t-lines without repeaters.  I think this is where the assumption breaks
down.


> I've been reading Mr. Eric Bogatin's "Lossy Transmission Lines: Plain
> and Simple" paper and have a question, which I hope those of you who
> have also read it could answer (The same reasoning I present here also
> follows, to my understanding, from Mr. Howard Johnson's "Black Magic"
> book, App. B):
> 
>  
> 
> On page 21 of his paper, Mr. Bogatin presents the
> Root-of-Sum-of-Squares
> equation for calculating the rise-time at the end of a lossy
> transmission line, as a function of the driver rise-time and the 3-dB
> rise-time of the interconnect.
> 
>  
> 
> It seems from this paper as if one can cascade several interconnects
> and
> get the total effective rise-time of the whole interconnect by using
> the
> equation as follows: Take the individual 3dB-rise-times of the
> individual interconnects and take the square-root of their sum of
> squares.
> 
>  
> 
> But it seems there is a problem with this use of the equation. One can
> take a long interconnect, and calculate its effective rise-time using
> 2
> methods: as an un-divided interconnect, or sub-divide it to (e.g.)  2
> identical halves, and do the arithmetic again. Using the 2nd method
> one
> gets a result which is (1/square-root of 2) of the "undivided"
> calculation rise-time.
> 
>  
> 
> This is a strange result, so I must be missing something, but what? 
> 
>  
> 
> Thanks for anyone who can help
> 
>  
> 
> Itzhak Hirshtal
> 
> Elta Systems
> 
> Israel
> 
>  
> 
> 
> 
> 
> 

------------------------------------------------------------------
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:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: