Re: [SI-LIST] : BLVDS Hot Swap - Connectors

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From: Fred Rosenberger (fred@ee.wustl.edu)
Date: Tue Apr 25 2000 - 07:27:47 PDT


I believe it. I measured something similar about 30 years ago when looking
at contact bounce in toggle switches.

Regards,

Fred

----- Original Message -----
From: DAmbrosia, John F <john.dambrosia@tycoelectronics.com>
To: <si-list@silab.eng.sun.com>
Sent: Tuesday, April 25, 2000 8:27 AM
Subject: RE: [SI-LIST] : BLVDS Hot Swap - Connectors

> Francis,
> Thanks for your response. I apologize for the lateness of my response,
but
> I have been traveling for the last week.
>
> First, let me say that I understand the overall skepticism of your
response.
> The phenomenon of "nanosecond" discontinuities" has just been recently
> discovered, and AMP has been working to resolve the issue, which has
> resulted in the introduction of our Quiet MateTM Contact technology.
> Nanosecond discontinuities should not be so quickly dismissed, however, as
> only two of our customers have seen the phenomenon, which was discovered
> while evaluating a system for high availability. Just because it is not
> being seen in a controlled lab environment, does not mean that it will not
> be seen in the field. It is unclear how rigorous the test environment was
> used to test your devices. Furthermore, it is very difficult to measure
> the resulting glitch. What equipment did you use to detect and measure
the
> glitch? Can you further describe the glitch? duration/width, frequency of
> occurrence during hot-swaps, specific levels (20mV/50mV/100mV?), etc.
>
> There are several comments that need discussed -
>
> 1. We know that there will be "discontinuities" during Live Insertion,
> it is NOT "microsecond discontinuities" we are investigating BUT any data
> errors in BLVDS during Live Insertion.
> We agree that the area of concern is for any data errors
> during any Live Insertion. High availability systems demand it! It has
> been proven that in a CPCI environment nanosecond discontinuities can
cause
> data errors.
>
> 2. The occurence of abnormalities on the signals are COMMON on both
> signals, thus data was not impacted.
>
> Based on test data taken in our labs, we do not agree with
> this statement. 'Glitches' occurring during live insertion events do not
> and will not happen at EXACTLY the same points in time. If the resolution
> is not accurate enough, they may appear to be occurring at the same time,
> but will actually be offset from one another at some distinct point in
time.
> If the resolution is not that accurate enough, the measured glitch is
> probably resulting from something other than nanosecond discontinuities.
> They are extremely difficult to observe, even with the most advanced
> equipment. We are not sure what was seen. Even the initial 'glitch',
> resulting from the potentials on the card and backplane coming together
> (assuming no nanosecond discontinuities occur) would never happen at
EXACTLY
> the same time. Can you measure any distinct separation in time of the
> "glitch" on each leg of the differential pair?
>
> 3. The National parts were designed better than the industry
> specifications which means the thresholds for high and the threshold for
low
> have a higher noise margin as specified in the data book. On top of
> this,there are internal filters in the receiver that will further take
care
> of the glitches.
>
> This very issue came up at PICMG last week, where it was realized by
> committee members that higher margins / tighter thresholds can actually be
> worse in a hot swap environment.
>
> This issue is related to the system application. I suggest you contact me
> directly, and we can discuss your logic and the hot-swap / nanosecond
> discontinuity issue and the potential impact on systems. My contact info
is
> listed below.
>
> Have a nice day!
>
> John D'Ambrosia
> AMP Circuits & Design
> Program Manager, Strategic Accounts
> Tel (717) 986-5692
> Fax (717) 986-5095
> Email: john.dambrosia@tycoelectronics.com <mailto:john.dambrosia@amp.com>
> URL: http://www.amp.com/simulation <http://www.amp.com/simulation>
>
>
> -----Original Message-----
> From: Francis Chiu [SMTP:Francis.Chiu@nsc.com]
> Sent: Friday, April 14, 2000 7:28 PM
> To: si-list
> Subject: Re: [SI-LIST] : BLVDS Hot Swap - Connectors
>
> Hi, John,
>
> Thank you for your information. I did go through the file you
> attached. Actually, I am busy working on other projects, but I will spend
> sometime on
> the BLVDS Hot Swap issues.
>
> First of all, I have to stay the emphasis for our Hot Swap tests
> which we did one year ago - 0 data error in Live Insertion.
>
> We know that there will be "discontinuities" during Live
> Insertion, it is NOT "microsecond discontinuities" we are investigating
BUT
> any data errors in BLVDS
> during Live Insertion.
>
> The tests were performed on multichannel BLVDS (9 channels per
> chip), the speed of theTektronix tester is 100Mb/sec, coded data.
> The BLVDS common mode range is +/-1V. The signal swing is a
> typical 300mV transition centered around +1.25V. Note the differential
swing
> is twice the
> magnitude of the single-ended.
>
> When a card is being hot-plugged into the system, that transceiver
> would be disabled, the impedance should be around 300K Ohm (?)
> Under these circumstances, the glitch we observed was around
> several millivolts and this will not create any problem. The occurence of
> abnormalities on the signals are COMMON on both signals, thus data
> was not impacted.
>
> The National parts were designed better than the industry
> specifications which means the thresholds for high and the threshold for
low
> have a higher
> noise margin as specified in the data book. On top of this,there
> are internal filters in the receiver that will further take care of the
> glitches.
>
>
> Actually, I like to find out whether anybody did the Hot-Plug test
> at a data rate higher than 100MBits/sec with BLVDS.
>
>
> Up to this minute, I still have not hear any complaint from the
> Telco guys who use the BLVDS in their 3G wireless basestation designs,
> Hot-Plug
> is a MUST requirement for the wireless basestations.
>
>
> Regards.
>
>
>
> Francis
>
>
>
>
>
>
> john.dambrosia@tycoelectronics.com on 04/14/2000 01:30:00 PM
> To: si-list@silab.eng.sun.com@Internet
> cc:
>
> Subject: [SI-LIST] : BLVDS Hot Swap - Connectors
>
> In the past few days there have been some questions regarding BLVDS
> and HOT
> SWAP applications. I am with AMP, and we have been very busy
> investigating
> glitches that have been seen in applications requireing HOT SWAP.
> It was
> questioned whether this was an issue in a BLVDS application, or
> would the
> differential nature make it a non-issue. A comment was made that
> the
> phenomenon would not be seen since it was seen on both signals of
> the
> differential pair simulatenously.
>
> The testing we have done in our labs (for 2mm HM product, as well as
> any
> other separable conductive interface) has shown that we ALMOST NEVER
> connect
> the multiple beams of the contact at the same point in time. For
> typical
> card insertion speeds (this also includes all speeds within certain
> specifications), we have measured the time between these connections
> (of
> different contact beams ON THE SAME PIN) on the order of
> micro-seconds.
>
> For different pins within the same connector, the time between these
> connections can be much longer. This separation time depends highly
> on the
> tolerances and design of the mechanical cage supporting the inserted
> cards,
> the tolerancing in the alignment and guidance of the connector
> housings, and
> the human factor (operators or maintenance personnel will insert
> cards at
> different speeds, sometimes not insert them fully, insert them
> partially
> before finishing the insertion, etc., etc.).
>
> Sooo...we have definitely seen (during live insertion scenarios)
> occurrences
> of inserted cards impacting the individual legs of a differential
> pair
> separately. This impact could be separated by micro-seconds or
> longer.
>
> In addition to these relatively long (with respect to a high-speed
> waveform)
> micro-second separations, we have also recently discovered a much
> faster
> discontinuity in our labs. This new phenomenon also occurs during
> hot-swap
> events and occurs right at the initial time when the conductive
> interfaces
> come in contact with one another. The connections/disconnections
> between
> backplane contact and card contact happen as quickly as nanoseconds
> and as
> slow as micro-seconds. We have been referring to the phenomenons as
> nanosecond discontinuities. We have also seen this occur at any
> highly
> conductive separable interface.
> The nanosecond discontinuities are extremely erratic and never seem
> occur
> at the same positions or in the same timeframes consistently (even
> for the
> same contact, let alone discrete contacts within the same
> connector).
>
> The combination of mechanical tolerancing and nanosecond
> discontinuities
> provides us with an extremely wide range of time with which we can
> separate
> the impacts of a hot-swapped card on the individual legs of a
> differential
> waveform. Depending on the logic family you are using, opposing
> potential
> levels (i.e. 0.0-5.0V, 0.0-3.3V, 0.5-1.5V, etc) during an insertion
> can
> resulting in significant current flow to/from the backplane from the
> inserted card. The capacitive loading, termination, topology,
> driver
> capabilities, and sampling of the system will all play key roles in
> the
> worst-case analysis of such 'glitches'. We have measured (on 5V
> systems)
> voltage disruptions as high as ~2 V (on a logic level 'low'
> waveform). On
> lower voltage systems (like LVDS or ECL or GTL), we can measure
> similar
> percentages of voltage alteration to an operating waveform.
>
> For those who are interested in a presentation we gave on this
> phenomenon,
> go to www.amp.com/simulation <http://www.amp.com/simulation> . Go
> to the
> "documents" section, and choose "Conference Presentations." Select
> "Nanosecond Discontinuity Impact on Hot Swap."
>
> Have a nice day!
>
> John D'Ambrosia
> AMP Circuits & Design
> Program Manager, Strategic Accounts
> Tel (717) 986-5692
> Fax (717) 986-5095
> Email: john.dambrosia@tycoelectronics.com
> <mailto:john.dambrosia@amp.com>
> URL: http://www.amp.com/simulation <http://www.amp.com/simulation>
>
>
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