[SI-LIST] Re: Ring back
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: leeritchey@xxxxxxxxxxxxx
- Date: Mon, 22 May 2006 19:44:20 -0400
As long as I remember in my world, ringback was defined to be the
voltage excursion of the ringing that follows a transition of an
underdamped system. For a low to high transition it is the minimum
value of the ringing that occurs after positive overshoot. For a high
to low transition it is the maximum value of the ringing that occurs
after negative overshoot (sometimes called undershoot).
Since I was in the Intel processor world for many years, it would not be
surprising to find that similar definitions are used by the manufacture
IA processors. For those that are interested, here's the definition of
Ringback from a Pentium II processor specification.
3.3.2. RINGBACK SPECIFICATION
Ringback refers to the amount of reflection seen after
a signal has switched. The ringback specification is
the voltage that the signal rings back to after
achieving its maximum absolute value.
And here's the definition from the AMD K6 processor I/O model specification
Ringback ---In the case of a rising waveform, the difference
between the nominal I/O VCC voltage and the minimum
voltage of a signal after that signal has reached its maximum
value. In the case of a falling waveform, ringback is the
difference between the maximum voltage of a signal after
that signal has reached its minimum value and ground (See
Figures 4 and 5). Excessive ringing can cause the destination
receiver to falsely switch if the signal traverses the switching
threshold of the receiver
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
Lee Ritchey wrote:
> Doug,
>
> I refer you to my reply of earlier where I cite pages in a book by Hall,
> Hall and McCall that gives a printed definition of ringback. Perhaps there
> are others.
>
>
>
>> [Original Message]
>> From: Douglas Burns <dburns@xxxxxxxxxx>
>> To: <leeritchey@xxxxxxxxxxxxx>; Madhusudhan Kulkarni
>>
> <madhusudhan@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
>
>> Date: 5/22/2006 12:26:27 PM
>> Subject: RE: [SI-LIST] Re: Ring back
>>
>> Lee,
>>
>> I would argue that overshoot and undershoot are specifying the same thing,
>> while ringback is it's own issue. Overshoot is how much a signal exceeds a
>> desired voltage level and is generally associated with VDD and VSS. Thus a
>> signal is in an overshoot condition when it exceeds VDD (or VSS). I see
>> people call the event overshoot when the signal exceeds VDD and undershoot
>> when it exceeds VSS...but in reality.. The signal is overshooting the
>>
> target
>
>> voltage, independent of VDD or VSS)
>>
>> Many vendors specifications specify AC and DC overshoot. The max DC
>>
> voltage
>
>> a device can accept (example VDD+0.3V or VSS -0.3v) would be a DC
>>
> overshoot
>
>> limit. In addition, some vendors provide a time and with another max
>>
> voltage
>
>> spec (ie VDD + 1v for <= 2ns). This second spec would be an AC overshoot
>> spec.
>>
>> Ringback on the otherhand does not require a signal to overshoot. Ringback
>> occurs when a signal makes multiple crossings of a voltage threshold and
>> affects timing margins. Use some standard LVTTL logic. Thresholds are 0.8V
>> and 2.0V. If a rising signal exceeds 2.0V, the signal is said to have
>> switched. If however, the signal crosses 2.0V, rises to 3.0V (below VDD of
>> 3.3)and then falls below 2.0 and then some time later crosses 2.0V and
>> settles out, when is the signal valid from a timing perspective. Based
>>
> upon
>
>> worst case, it would be the second crossing. The ring between the 1st and
>> 2nd crossing is called ringback. Ringback occurs on both rising and
>>
> falling
>
>> edges.
>>
>> To help reduce the uncertainty in timing points caused by ringback,
>>
> vendors
>
>> have added AC and DC switching levels. A signal must than cross the AC
>> level, but is allowed to ringback to the DC level without effecting the
>> device timing.
>>
>> The IBIS specification does a good job documenting these events.
>>
>> Douglas J Burns
>> Vice-President, Consulting Services
>> Signal Integrity Software, Inc. (SiSoft)
>> 6 Clock Tower Place
>> Suite 250
>> Maynard, MA 01754
>> 978-461-0449 x14
>> dburns@xxxxxxxxxx
>>
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>>
> On
>
>> Behalf Of Lee Ritchey
>> Sent: Monday, May 22, 2006 11:02 AM
>> To: Madhusudhan Kulkarni; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Ring back
>>
>>
>> Ringback is just another name for undershoot. I don't know why someone
>>
> had
>
>> to invent another name for something that already had a name.
>>
>> When you have undershoot and you use series terminations, the terminator
>> value it too high or the output impedance of the driver is too high. When
>> you have undershoot and you use parallel terminations, the value of the
>> terminator is too low. Fix which ever problem you have by changing the
>> value appropriately.
>>
>>
>>
>>> [Original Message]
>>> From: Madhusudhan Kulkarni <madhusudhan@xxxxxxxxxx>
>>> To: <si-list@xxxxxxxxxxxxx>
>>> Date: 5/22/2006 9:28:26 AM
>>> Subject: [SI-LIST] Ring back
>>>
>>> Hi,
>>> How to solve ringback problem and what is the disadvantages of
>>> ringback
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