[SI-LIST] Re: Series termination greater than the characteristic impedance?
- From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
- To: <aminotg@xxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 17 Jan 2006 09:07:55 -0700
Gilles,
Your understanding of theory is correct. Doesn't make sense to me either.
However, sometimes a series 10 ohm is used to dampen the ringing if the Mem
Contoller has high package/pin inductance and faster rise/fall times than
what is required for that data rate. For DDR2 at 533MBs that equates to a
risetime of ~560ps (20%-80%), or ~750ps (10% - 90%). This could be what
they are talking about.
Ken
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of aminotg@xxxxxxx
Sent: Tuesday, January 17, 2006 8:13 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Series termination greater than the characteristic
impedance?
Hi All,
I was wondering if there is ever a case where a series termination should be
higher than the characteristic impedance of a trace?
We had an SI analisys performed on our DDR2 interface and the conclusion was
to change the series terminations of our data bus to 60ohms. The
characteristic impedance of the traces on our board is 50ohms.
I always thought that a series termination was added to match the driver to
the characteristic impedance of the trace, now I am confused, because the
analysis on our board doesn't agree with this thinking.
Kindest Regards,
Gilles
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