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

 
From another dated (and gray-haired) one -
(repeating this because I forgot to include Mark's comments)
 
From Mark's email -
 
>Lee wrote:

>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.

>************************************************************************
 
>You're dating several of us Lee :) =20

>Motorola MECL  SYSTEM DESIGN HANDBOOK

>Page 144, Figure 7-17: Reflections Caused by  Signal-Line Shape
>Variations

>What always puzzled me, was if  you look closely at the figure, you'll
>see what looks like a VIA at the  right angle bend, but nothing at the
>smooth curve.  I was always  wondering if the test setup actually had a
>VIA at the bend  :)

>Mark




Mark - I believe that what you think might be vias in Fig. 7-17  are  simply 
dots placed in the drawing to indicate locations of the  reference  numbers 
for 
the various discontinuities in the plots.   There are no  dots in the radius 
bends because there are no  discontinuities in the second  plot (c) to be 
referenced to trace  locations.

Take a look at  Fig.7-15, for example.  The  dots  1, 2,  and 3 tie locations 
in the trace layout to  discontinuities in the  waveform; in particular. in 
this figure there  is no rationale for  interpreting the dot designated "2" 
as a  
via.  
Regards -  Bill

Dr. F. Williams Sarles   Tel:  781-862-0607
Consulting  Engineer     Fax:  781-861-7518
FWS  ENGINEERING   Email:  DrFWS@xxxxxxx
54 Ledgelawn  Avenue
Lexington MA  02420-3449





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