Re: gEDA-user: terminators

[carzrgr8@xxxxxxxxxxxxx]

----- Original Message -----
From: John Griessen 

> [jg]I think HJ might have meant length of the ramp up or ramp 
> down when he said "edge".
> 	I can't see how length of a square wave half cycle translates 
> to fractions of wavelengths  at some resonance...which is where "1/4 * 'length of the 
edge'"   must come from.


Yep, it's the edge not the cycle.  A 1ns edge has 500 MHz component.  That's true even 
if the square wave were 1 kHz.  If you think you don't have a transmission line for that 
example, you'd be wrong.  That 1nS edge will rattle around on a long trace if not 
terminated.  You'd see it as ringing.  By saying 1/4 length of the edge is the longest you 
can go without termination means that all the ratling due to reflections is damped out long 
before the edge reaches it's full value.


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