[SI-LIST] Re: AC series capacitor position in high speeddifferential signals
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
- Date: Thu, 13 May 2010 10:44:48 -0700
The risk in trusting any two things that agree is that they may share
underlying false assumptions. The importance of null tests cannot be
overstated.
It is a bit out of the signal integrity field, but a good study of false
confirmations is the Air New Zealand Flight 901 crash into Mt. Erebus.
A series of optical illusions confirmed to the very experienced pilot he
was right on his planned (simulated?) course over McMurdo sound, instead
of 27 miles to the west directly into 13,000' Mt. Erebus.
Best Regards,
Steve.
Lee Ritchey wrote:
> I don't trust either if they don't agree.
>
>
>
>> [Original Message]
>> From: Muranyi, Arpad <Arpad_Muranyi@xxxxxxxxxx>
>> To: <si-list@xxxxxxxxxxxxx>
>> Date: 5/13/2010 10:09:45 AM
>> Subject: [SI-LIST] Re: AC series capacitor position in high
>>
> speeddifferential signals
>
>> Hmmm... I wonder how many of us trusts their measurements
>> (blindly) without validating those? We all know that
>> probing will have an effect on the results, especially at
>> high speeds, right? Should I continue?
>>
>> Arpad
>> =============================================================
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Lee Ritchey
>> Sent: Thursday, May 13, 2010 11:28 AM
>> To: Istvan Novak
>> Cc: fei xue; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: AC series capacitor position in high
>> speeddifferential signals
>>
>> I would maintain from my measurements that the reflections are
>> negligibly
>> small.
>>
>> I would also maintain that simulation results, no matter what the tool
>> or
>> operator, should not be trusted until they are validated by measurements
>> to
>> insure the modelling is accurate. I've seen too many simulations done
>> incorrectly which were used to develop design rules that were either
>> ineffective or caused problems that I, for one, will not use the results
>> of
>> unvalidated simulations.
>>
>> Each engineer can make up his or her own mind on this, but my experience
>> says validate simulation results before betting any money on them.
>>
>> I'm not trying to offend anyone who does simulations, just advising
>> proceed
>> with caution.
>>
>> Lee
>>
>>
>>
>>> [Original Message]
>>> From: Istvan Novak <istvan.novak@xxxxxxx>
>>> To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
>>> Cc: fei xue <harrison_cls@xxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
>>> Date: 5/12/2010 8:55:32 PM
>>> Subject: Re: [SI-LIST] Re: AC series capacitor position in high
>>>
>> speeddifferential signals
>>
>>> Lee,
>>>
>>> As it was pointed out in earlier threads, location does make a
>>> difference unless reflections are
>>> negligibly small. Assuming linearity, when we move components around,
>>>
>>> reciprocity prevails,
>>> but voltage transfer function from source to load will change, which
>>>
>> in
>>
>>> turn impacts eye
>>> parameters.
>>>
>>> Regards,
>>>
>>> Istvan Novak
>>> Oracle-America
>>>
>>>
>>> Lee Ritchey wrote:
>>>
>>>> This has been answered before on this forum. Since the circuits are
>>>> linear, it does not matter from a signal integrity point of view.
>>>>
>>>> Lee
>>>>
>>>>
>>>>
>>>>
>>>>> [Original Message]
>>>>> From: fei xue <harrison_cls@xxxxxxxxxxxx>
>>>>> To: <si-list@xxxxxxxxxxxxx>
>>>>> Date: 5/12/2010 11:35:49 AM
>>>>> Subject: [SI-LIST] AC series capacitor position in high speed
>>>>>
>>>>>
>>>> differential signals
>>>>
>>>>
>>>>> Hello all,
>>>>> We often can get different guideline of placing capacitor position
>>>>>
>> when
>>
>>>>>
>>>>>
>>>> placing AC series capacitor on high speed differential signals, like
>>>>
>> PCIe,
>>
>>>> SAS or LVDS signals. sometimes we followed the guideline to put
>>>>
>> capacitors
>>
>>>> near driver, sometimes near multi-connection connectors or sometimes
>>>>
>> put it
>>
>>>> near receivers.
>>>>
>>>>
>>>>> Could anybody tell me what is the consideration of capacitor
>>>>>
>> placing
>>
>>>>>
>>>>>
>>>> position? Thanks!
>>>>
>>>>
>>>>> Harrison
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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--
Steve Weir
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