[SI-LIST] : ATA source termination

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From: Rehm, Dennis (Dennis.Rehm@lsil.com)
Date: Fri Apr 28 2000 - 10:00:16 PDT


I am coming up to speed on the ATA spec and have found a point where the
spec seems inconsistent.

Regarding the source termination resistors at a device, I quote from D.2.2.6

"Ideal termination at each connector is when the impedance seen looking back
toward the source matches the cable impedance in the forward direction. For
devices, this means that the sum of driver output impedance and termination
resistance match the cable impedance(typically 80 to 85 ohms), minus 5 to 10
% to allow for attenuation due to the capacitive loading of other devices on
the cable."

However in Table 6 of section 4.2.2.2 the device termination impedance
specified varies from 22 to 82 ohms. I assume that 82 represents matching to
the cable impedance which would actually disagree with D.2.2.6 above as you
should match to 5 -10 % less. To be consistent with D.2.2.6 this table
should have all entries be the same at about 70 to 75 ohms. But I guess I am
missing something.

Dennis

-----Original Message-----
From: Sean Murray [mailto:seandm@mmspec.com]
Sent: Friday, April 28, 2000 8:58 AM
To: 'si-list@silab.eng.sun.com'
Subject: [SI-LIST] : RF boards
Importance: High

Anyone have any feelings on what subtle differences when fabricating a
board can do to an RF board. Such as going from FR-4 to Getek; 50/200
gold/nickle vs. 30/100 gold/nickle. Is there any books out there that
deal with strictly the layout of RF boards??

Regards,
Sean Murray
Sales Manager
 
M&M Specialties Inc.
1236 W. Southern Ave. #106
Tempe, AZ. 85282-4518
Phone: (480) 858-0393 x105
Cell: (602) 684-7859
Fax: (480) 858-1882
Email: seandm@mmspec.com
WWW.mmspec.com
                  
                  

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