[SI-LIST] Re: Remove Ground underneath Differential signal isdeservedor not?

Perry,

Absolutely.  Mike Conn is the true advocate of this approach.  He's been 
using this technique for years. I've also found it to be quite useful, 
so that the overall Q of the resonance peaks is reduced.  The same can 
also be done on multi-drop busses, where the stub length to the 
receivers can be "dithered" randomly.  When all stubs are the same 
length, some very nasty resonance peaking can occur.  This randomization 
can be done on the cards or on the connection to the backplane 
connector, but will help to increase the overall usable bandwidth of the 
bus.

regards,

scott


-- 
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com



Perry Qu wrote:

>Scott:
>
>I find your recommendation on "random interval" via stitching interesting.
>This can be applied not only on guard trace but other cases when we need to do
>via stitchings. I call it a "spread spectrum" technique, as we reduce the
>peak amplitude of one sharp resonance and spread the energy a little bit.
>
>Regards
>
>Perry
>
>Scott McMorrow wrote:
>
>  
>
>>Lee,
>>
>>    
>>
>>>What I show in my class is that guard traces are always LC networks that
>>>resonate at some frequency and can and do turn into bandpass filters
>>>at some
>>>frequencies.  I demonstrate this will actual failed circuits.
>>>
>>>
>>>      
>>>
>>This is exactly why Mike Conn and myself recommend stitching guard
>>traces to ground at random intervals across the length.  The average
>>spacing of the via sites should be 1/10 of the wavelength of the fast
>>signal frequency or equivalent risetime that will be present on this
>>trace.  These stitch vias to ground will eliminate the problems which
>>you have alluded to.  They are backed by extremely good analytical and
>>experimental science.
>>
>>Best regards,
>>
>>Scott
>>
>>--
>>Scott McMorrow
>>Teraspeed Consulting Group LLC
>>2926 SE Yamhill St.
>>Portland, OR 97214
>>(503) 239-5536
>>http://www.teraspeed.com
>>
>>--
>>Scott McMorrow
>>Teraspeed Consulting Group LLC
>>2926 SE Yamhill St.
>>Portland, OR 97214
>>(503) 239-5536
>>http://www.teraspeed.com
>>
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>
>--
>Perry Qu
>
>Product Integrity         |      600 March Road
>Alcatel Canada            |      Ottawa, ON K2K 2E6, Canada
>
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>
>
>  
>


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