RE: [SI-LIST] : ATA source termination

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From: Chuck Hill (chuckh@altaeng.com)
Date: Thu May 04 2000 - 13:10:48 PDT


Dennis,

Sorry for the delay. 22-33 ohms at the driver, but 82 ohms at receive only
inputs.

Chuck

At 01:19 PM 4/28/00 -0600, you wrote:
>
>Chuck:
>
>Thanks for the clarification of input only lines vs lines that can be driven
>from the "device" side.
>However the DD15 thru DD0 lines list 33 ohms and the DMARQ,INTRQ, and
>DSTROBE lines list 22 ohms.
>I know the on resistance range of the pad driver(for all lines) and if the
>pad driver is the same for these 4 lines then I intend to make the resistor
>value 82-.1*(82) - nom pad driver on resistance. That would agree with
>section D.2.2.6.
>Do you concur?
>
>
>Dennis
>
>
>-----Original Message-----
>From: Chuck Hill [mailto:chuckh@altaeng.com]
>Sent: Friday, April 28, 2000 12:32 PM
>To: si-list@silab.eng.Sun.COM; 'si-list@silab.eng.Sun.COM'
>Subject: Re: [SI-LIST] : ATA source termination
>
>
>Dennis,
>
>Perhaps I can clarify this. On the source (driving) end, it is necessary
>to provide some series resistance to dampen ringing that occurs after the
>driver has switched. The on resistance of the device and the series
>resistor combine to provide this damping. The ATA spec calls for this
>resistive damping to be 1.0 times the characteristic impedance of the
>line--my opinion is the ideal value is slightly less than that since the
>ringing can still be well controlled and risetime slightly faster (LC model
>instead of distributed transmission line, we are in an in-between frequency
>range). Typical drivers have 10-20 ohms of ON resistance so series
>resistors should be 33 to 47ohms. Higher resistance values make it harder
>to achieve good DC margin on the low level (0.8v).
>
>The 82 ohms apply to those lines which are input only. Even CMOS inputs
>have some series resistance along with the capacitance. This combined
>resistance on the input should be near the line impedance.
>
>Remember, this is not a precision system. There is a lot of tolerance
>allowed for. When adjusting components, look for good edge speed and not
>too much ringing and crosstalk and reflection noise which gets closer to
>switching thresholds.
>
>
>Chuck Hill, consultant
>
>
>At 11:00 AM 4/28/00 -0600, Rehm, Dennis wrote:
>>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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>
>
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