[SI-LIST] Re: Right Angle Bends
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: Julian Ferry <julian.ferry@xxxxxxxxxx>
- Date: Fri, 15 Jul 2011 17:02:05 -0400
It depends on who you ask.
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
On 7/15/2011 4:53 PM, Julian Ferry wrote:
> That's a good point.
>
> Who's that guy who always says "It depends?".....
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Scott McMorrow
> Sent: Friday, July 15, 2011 4:39 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Right Angle Bends
>
> Julian
>
> Actually, it depends on the frequency and the trace thickness, since
> capacitive coupling on the sidewall of the trace at the corner can cause
> a net decrease in capacitance at some frequencies.
>
>
> 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(r) is the registered service mark of
> Teraspeed Consulting Group LLC
>
>
> On 7/15/2011 4:05 PM, Julian Ferry wrote:
>> OK, looks like I made one little not-so minor mistake in my previous email:
>>
>> The capacitance goes UP, the inductance goes DOWN.
>>
>> Sorry for any confusion I might have caused!
>>
>> Julian Ferry
>> High Speed Engineering Manager
>> Samtec, Inc
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>> Behalf Of Julian Ferry
>> Sent: Friday, July 15, 2011 3:48 PM
>> To: Brad Brim; 'Jeff Walden'; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Right Angle Bends
>>
>>
>> I think one of the problems here is that like with most myths or urban
>> legends, there is a kernel of truth to it.
>>
>> It is pure, unarguable physics that the capacitance will go down and the
>> inductance will go up in a right angle bend. The question is whether that
>> change matters in a particular application.
>>
>> For some applications, like in high power microwave or RF applications, this
>> effect can be significant enough relative to other factors that it is
>> definitely worth worrying about.
>>
>> But in the grand scheme of things in the current SI world, this change is
>> way down on the list of potential problems. It is effectively swamped out by
>> many other effects (like our relatively crappy connectors, for one
>> example...)
>>
>> I think these guys wrote a pretty decent little paper with some math that
>> can help determine whether you might need to worry about bends.
>>
>> http://www.millertechinc.com/pdf_files/mti_tn063_microstrip_right_angle_bends.pdf
>>
>>
>> Also keep in mind that we in the SI world are mostly dealing with pulsed
>> signals, where a large portion of the energy is contained in the lower
>> frequency components. The excess capacitance will only affect the very high
>> frequency components. But in the microwave environment, it's all about the
>> high frequency signal, so a bend can be a much greater concern.
>>
>>
>>
>> Julian Ferry
>> High Speed Engineering Manager
>> Samtec, Inc
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>> Behalf Of Brad Brim
>> Sent: Friday, July 15, 2011 2:57 PM
>> To: 'Jeff Walden'; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Right Angle Bends
>>
>> exactly, Jeff ... and the traces that connect to the bends are also MUCH
>> longer than typical for the RF/microwave case.
>>
>> In RF/mw ckt sim libraries/layouts a bend is a separate "component". The
>> reference planes (i.e. where the traces connect to the bend) are at the edge
>> of this component. For example, the 90-degree bend reference planes are at
>> the edge of the square representing the area of the bend. For most SI
>> applications the bend is NOT a separate component and the two traces simply
>> meet at a single node. Having worked way too many hours to implement and
>> test RF/mw ckt sim bend models over a dozen years ago I observed the
>> parasitics are a delay of length on the order of the node-to-node distance
>> with additional capacitive parasitics for sharp bends and inductive
>> parasitics for aggressively chamfered bends. For a 90 degree bend the
>> different definitions of reference plane imply 2*(W/2) additional length
>> trace for the SI case. Given approximate parasitic delay of sqrt(2)*W/2, all
>> implies doing nothing for SI applications is still on the order of only 30%
>> phase delay error versus a much more precise parasitic model (for an already
>> small parasitic). The phase delay dominates because bend capacitive
>> parasitics are small for SI apps relative to other capacitive parasitics not
>> modeled throughout the system.
>>
>> Therefore, if the trace are not wide (low impedance) and their lengths
>> coming in/out of the bend are long relative to the linewidth, then ignoring
>> the bend is obviously the correct choice.
>>
>> Where SI apps might not always want to ignore bends is for tight meander
>> structures used to accumulate phase delay and balance skew. These geometries
>> sometimes have short distance between bends and could therefore lose some
>> accuracy from ignoring bend parasitics. In these cases it is probably more
>> important to include coupling amongst the parallel traces. As we all might
>> guess, if you need to know a meander behavior accurately you may wish to
>> model it as a single component with more detailed simulation rather than
>> treat it as a collection of traces (with or without bend parasitics).
>>
>> cheers,
>> -Brad
>>
>>> -----Original Message-----
>>> From: si-list-bounce@xxxxxxxxxxxxx
>>> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Jeff Walden
>>> Sent: Friday, July 15, 2011 10:55 AM
>>> To: si-list@xxxxxxxxxxxxx
>>> Subject: [SI-LIST] Re: Right Angle Bends
>>>
>>> The difference is that today's SI traces are significantly
>>> narrower than the typical "RF" microstrip of 30 years ago.
>>> -Jeff
>>>
>>>
>> ------------------------------------------------------------------
>> To unsubscribe from si-list:
>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>> or to administer your membership from a web page, go to:
>> //www.freelists.org/webpage/si-list
>>
>> For help:
>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>> List technical documents are available at:
>> http://www.si-list.net
>>
>> List archives are viewable at:
>> //www.freelists.org/archives/si-list
>>
>> Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
>> ------------------------------------------------------------------
>> To unsubscribe from si-list:
>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>> or to administer your membership from a web page, go to:
>> //www.freelists.org/webpage/si-list
>>
>> For help:
>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>> List technical documents are available at:
>> http://www.si-list.net
>>
>> List archives are viewable at:
>> //www.freelists.org/archives/si-list
>>
>> Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
>> ------------------------------------------------------------------
>> To unsubscribe from si-list:
>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>> or to administer your membership from a web page, go to:
>> //www.freelists.org/webpage/si-list
>>
>> For help:
>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>> List technical documents are available at:
>> http://www.si-list.net
>>
>> List archives are viewable at:
>> //www.freelists.org/archives/si-list
>>
>> Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
