[SI-LIST] Re: Electrical Length?
- From: "Carrier, Patrick" <Patrick_Carrier@xxxxxxxxxx>
- To: "aaditya.kandibanda@xxxxxxxxx" <aaditya.kandibanda@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 30 May 2012 16:47:25 +0000
Hello Aaditya--
I would say electrical length is the length in terms of time.
For instance, on a PCB, your "physical length" might be 1 inch, but the
electrical length could be 159ps on an outer layer or 175ps on an inner layer.
Signals move faster on an outer layer since the dielectric consists partially
of air.
I find that it is more useful to describe things in terms of "electrical
length" when dealing with signal integrity, since it is the time it takes for a
signal to propagate that really matters.
Now, that is not to confuse "electrical length" with what is often called
"flight time" or "simulated delay". The overall "delay" of the signal
travelling through the PCB, in terms of system timing, will depend mostly on
the electrical length, but since we measure timing at specific thresholds of
voltage, the shape of the signal will also matter. The signal gets shaped by
things like the transmission line impedance and the impedance of the load.
I discuss both these concepts in greater detail in our SI Basics Webinar Series:
http://www.mentor.com/products/pcb-system-design/series/si-basics-series
You can select which ones you want to view (in this case the 2nd and 3rd ones)
and click the "Register" button on the bottom to access them.
--Pat
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Aaditya Kandibanda
Sent: Tuesday, May 29, 2012 5:29 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Electrical Length?
Hello Everyone,
I came across this concept called Electrical length, Could anyone please
explain me when, how and why is electrical length used?
Thank you!
Aaditya
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