[SI-LIST] Re: Electrical length

Gaurav,

The electrical length is the property of the transmission line, it
tells us what is the phase shift through the line at any given frequency.
The rise time is the property of the signal you may want to push through 
the transmission line. one DOES NOT depend on the other, but there are
rules you cited that you want to obey when using a transmission line
for signal transmission.  For the line to operate in the lumped mode, so
that you dont need to apply termination to dampen reflections, the 
propagation delay through the line should be a small fraction of the 
rise time.  if you cannot keep the above rule, the transmission still
may work very well in transmitting your signal, just you need some 
sort of termination to suppress reflections.

Hope this helps

Regads,

Istvan Novak
SUN MIcrosystems



Gaurav MATHUR wrote:

>Hello All,
>  Can anybody tell me :
>1. Is electrical length of a line is related to its wavelength and rise =
>time both. Literature tells that a line is long (or short) depending =
>upon=20
>  its physical length with respect to its quarter wavelength. But when =
>we talk about PCB systems; we talk about rise time (we generally don't=20
>  bother about frequency). Johnson & Graham(Handbook of Black magic) =
>showed a relationship l =3D Tr/D; l is electrical length, Tr is rise =
>time and D is      propagation delay. Book says line length should be =
>less than l/6 for lumped systems.  =20
>  So is there any relationship of rise time and wavelength to correlate =
>the two texts?? =20
>Gaurav.
>
>  
>

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