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[SI-LIST] Re: time-constant=2.3*Z0*CL
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <venki.pras@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 14 Dec 2007 11:54:39 -0800
Pras
If you let a capacitor charge up through a resistor the voltage on the
capacitor will increase in a Vin(1 - e^-t/RC) rate. Any good book on EE101
electrical theory will cover this very well. Risetime in many systems is
defined at the time it takes for a signal to go from the 10% value to the
90% value of the 0 to 100% amplitude of the signal. So, if you start a
stopwatch when the signal passes the 10% point and stop it at the 90% point
it will take about 2.2 time constants or 2.2*RC to make that transition.
The 10% point will occur at about 0.1RC and the 90% point will occur at the
2.3RC point.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Pras venki
Sent: Friday, December 14, 2007 10:42 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] time-constant=2.3*Z0*CL
Hello there,
In the equation for "time constant of the rise-time", when a trace is
terminated by a load capacitance-
time-constant=2.3*Z0*CL
what does the factor 2.3 stand for and when should it be used? How is it
derived?
Thanx in advance.
-Pras
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