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

This mail was sent from ELTA SYS LTD.


 

Feb-25th-03

 

Hello,

 

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

 




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