[SI-LIST] Re: AC/DC impedance spec for floppy and 40Pin-IDE cables.

John,

I've calculated and measured the characteristic impedance matrix for the 40
pin IDE cable.  The 80 pin IDE cable is a ground-signal-ground (mostly,
there are a few extra grounds) configuration so each signal line is near a
nominal characteristic impedance.  The 40 pin IDE cable has only 7 grounds
in it, with all 16 data lines together without any grounds inbetween.  In
terms of the RLGC matrices, there is a lot of inductive coupling amongst the
data lines, and significant capacitive coupling as well.  Consequently, the
characteristic impedances of a single data line are quite higher than the 80
pin case, vary with distance from the ground lines, approaching a maximum
the furthest away from the ground lines.  Moreover, the coupling makes each
data dependent on the others.  This coupling dramatically increases ringing
after an edge due to the large stored energy and low damping factor (the
characteristic impedance is high).  That is one reason for the series
resistors now used in IDE.  Parallel ATA is essentially a series terminated
interface.


Charles Hill, consultant

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of John Lin (ªL´Â·×)
Sent: Friday, September 13, 2002 11:45 PM
To: 'SI-List'
Cc: John Lin (ªL´Â·×)
Subject: [SI-LIST] AC/DC impedance spec for floppy and 40Pin-IDE cables.


Dear all SI gurus,

Are there any AC/DC impedance spec for floppy cable and 40pin-IDE cable?
ATAPI-6 spec. doesn't mention ac impedance for 40pin-IDE but 80pin-IDE
cable. Can somebody tell the reason?


Regards,

John Lin

Quanta Computer Inc.,Taiwan, R.O.C.
Email: John@xxxxxxxxxxxx
Tel: 886+3+3272345 ext. 5183






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