Re: Book Signal Integrity for PCB Designs available on net

John Larkin a écrit :
> On Thu, 11 Mar 2010 10:51:27 -0800, "Joel Koltner"
> <(E-Mail Removed)> wrote:
>
>> "Additya" <(E-Mail Removed)> wrote in message
>> news:86c70eaf-2b15-4a4d-b1a6-(E-Mail Removed)...
>>> http://www.ezdia.com//Signal-Integri...ent.do?id=1435
>>From the above:
>> ---
>>
>> Tom - I was reading this rise time and knee frequency stuff. It says that the
>> rise time is a significant thing and determines the highest frequency content.
>> Does it mean that if I have a 1 KHz square wave that has a rise time of 100
>> ps, it should be treated as a high frequency signal with spectral frequency of
>> or 3.5 GHz?
>>
>> Bob - Ideally, yes, this 1 KHz signal should be treated as a 3.5 GHz signal at
>> least from some of the SI angle, e.g., EMI. But Tom tell me why will anyone
>> design a circuit with 1 KHz frequency with such a fast rise edge? Does it make
>> sense? A very fast rising edge makes sense only when you want to achieve high
>> data rate.
>>
>> ---
>>
>> Seems like that needs a bit more qualification... more like, "while not too
>> many applications require super-fast edges but have low repetition rates,
>> sometimes this will occur..."
>
> 3.5 GHz is the 3.5 millionth harmonic of 1 KHz. So the power spectral
> density up there will be zilch.
>

Let's push it a bit further...

350MHz is still 350Kth harmonic of 1kHz and there's still almost nothing
there. So we can safely ignore this part of the spectrum...

.... and, once provided the signal fundamental frequency is low enough we
can design a rather band limited channel while still achieving fast rise
time.

Cute!


--
Thanks,
Fred.

Fred Bartoli wrote:
> John Larkin a écrit :
>> On Thu, 11 Mar 2010 10:51:27 -0800, "Joel Koltner"
>> <(E-Mail Removed)> wrote:
>>
>>> "Additya" <(E-Mail Removed)> wrote in message
>>> news:86c70eaf-2b15-4a4d-b1a6-(E-Mail Removed)...
>>>
>>>> http://www.ezdia.com//Signal-Integri...ent.do?id=1435
>>>>
>>> From the above:
>>> ---
>>>
>>> Tom - I was reading this rise time and knee frequency stuff. It says
>>> that the rise time is a significant thing and determines the highest
>>> frequency content. Does it mean that if I have a 1 KHz square wave
>>> that has a rise time of 100 ps, it should be treated as a high
>>> frequency signal with spectral frequency of or 3.5 GHz?
>>>
>>> Bob - Ideally, yes, this 1 KHz signal should be treated as a 3.5 GHz
>>> signal at least from some of the SI angle, e.g., EMI. But Tom tell me
>>> why will anyone design a circuit with 1 KHz frequency with such a
>>> fast rise edge? Does it make sense? A very fast rising edge makes
>>> sense only when you want to achieve high data rate.
>>>
>>> ---
>>>
>>> Seems like that needs a bit more qualification... more like, "while
>>> not too many applications require super-fast edges but have low
>>> repetition rates, sometimes this will occur..."
>>
>> 3.5 GHz is the 3.5 millionth harmonic of 1 KHz. So the power spectral
>> density up there will be zilch.
>>
>
> Let's push it a bit further...
>
> 350MHz is still 350Kth harmonic of 1kHz and there's still almost nothing
> there. So we can safely ignore this part of the spectrum...
>
> ... and, once provided the signal fundamental frequency is low enough we
> can design a rather band limited channel while still achieving fast rise
> time.
>
> Cute!
>

Even better. Since you have now determined that we no longer need the
range from 350MHz to 3.5GHz we could auction that off and issue revenue
anticipation bonds to plug some pressing holes in the budget. Since the
money will have been spent by the time the auction happens we could
already look at whether the 35kth harmonic is good enough so we can pay
the interest :-)

--
SCNR, Joerg

http://www.analogconsultants.com/

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