[SI-LIST] Re: 22.1 Ohm vs 50 Ohm Termination
- From: Robert_Washburn@xxxxxxxx
- To: kevinlfitzgerald@xxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Fri, 30 Aug 2002 12:20:02 -0500
The value of the series terminating resistor is chosen such that the output
impedance of the driver in series with it equals the characteristic
impedance of the interconnect. So, in your case...if 22 ohms is the ideal
value for series termination (and Zo=50 ohms), then the output impedance of
your driver must be 28 ohms. If it's not, then 22 ohms isn't the ideal
value.
The series resistor can be varied higher or lower than the ideal case to
help slow or speed, respectively, the edge rates along the line.
robert
Robert M Washburn
Signal Integrity Group
Dell Computer Corporation
512.723.6025
robert_washburn@xxxxxxxx
-----Original Message-----
From: kevinlfitzgerald [mailto:kevinlfitzgerald@xxxxxxxx]
Sent: Friday, August 30, 2002 8:40 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] 22.1 Ohm vs 50 Ohm Termination
Hi,
I am wondering what the reason for the use of 22.1 Ohm series
termination on a 50 Ohm line, as opposed to matching it with 50 Ohm.
I have simulated signals with both, and both look reasonable. Is
there an electrical reason for using 22.2 Ohm or is it just lab
experience.
Thanks,
kevin
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