[SI-LIST] Re: Antwort: Re: 90 degree turn in PCB tracks

The paper published by Ultracad tests the effects of right angle bends in a
logic signal trace with an 18 pSec edge which is equivalent to about 20
GHz.  There is no detectable effect.  These tests were conducted by Todd
Hubing of UMR in a well equipped lab and are to be trusted.  There have
been amy other similar tests done with the same result.

I believe the notion that right angle bends are a source of problems stems
from an error in the Motorola ECL handbook published in 1974 and still in
print with the error.  Now O Semiconductor publishes it.

This may be one of those cases where simulation shows a change in the field
distribution around the right angle bend, which we expect.  The question is
whether the change is significant.  One of our jobs is to distinguish
between visible and significant.

Once again, we have lies, damn lies and simulations.  Simulations without
validation may well be more dangerous than no simulations at all in some
cases. 


> [Original Message]
> From: Matthias Bergmann <MBergmann@xxxxxxxxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 7/25/2006 1:42:10 AM
> Subject: [SI-LIST] Antwort: Re: 90 degree turn in PCB tracks
>
> Hello,
>
> Following the advices I read the article about 90 degree bends on
> ultracad.com as well as the appropriate chapter in Eric Bogatins book.
> I am quite surprised about the conclusion that 90 degree corners don't
> matter. I remember that once in a simulation of a 50 ohm microstrip-lin=
> e
> with
> a chamfered 90=B0 corner in ADS Momentum, I never got a S11 better than=
>  15 dB
> at frequencies higher than 15 GHz, even 10 GHz made problems.
> The mentioned articles don't consider the frequency respectively just
> consider designs where the right-angle bend is electrically smaller tha=
> n a
> rising edge.
> Would be interesting to know how two 45 degree corners behave at higer
> frequencies.
>
> Regards, Matthias
>
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