Re: [SI-LIST] : MECL System Design Handbook

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From: David Instone ([email protected])
Date: Fri May 11 2001 - 04:45:45 PDT

   What CAD tools do you have in mind? As far as I know the
Cadence/Allegro PCB layout software for one does not, unless of course
there is a little known command to make it do so. Then of course you
are dependent on the layout to gerber conversion. Remember most lines
are laser photoploted using a round mask, to plot a chamfer on say a 6
mil trace using a round laser mask would take some doing, probably
beyond the resolution in X and x of the photo plotter itself. I suppose
it could be photoplotted at some higher magnification and then photo
reduced but that adds cost.


Dave Instone. Compliance Engineer Storage Systems Development, MP24/22 Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK. Tel: +44 (0)23-92-496862 (direct line) Fax: +44 (0)23-92-496014 Tel: +44 (0)23-92-496000

Scott McMorrow wrote: > > Everyone, > > The best discussion of right angle bend effects is in the > the book, Microstrip Lines and Slot Lines by Gupta. > > There is a very good compilation of S-parameter measurements made > of loss versus bend radius and frequency. > > I have seen very few boards in recent history where right angle > bends were ever used. CAD tools now automatically chamfer the > edge at 45 degrees and it comes for free. This reduces the > corner effect at high frequencies drastically, such that for digital > applications up to the low gigahertz region it is a non-issue. If you > want better performance, the book shows an optimal chamfer that > gives the best performance. It is used extensively in the Microwave > world, because it will reduce the reflection to the -60dB level with > a little extra CAD effort. Radiused bends can be used, but they > are extremely difficult to perform in most CAD systems. They should > be avoided. > > For most cases and most designs on this reflector, as long as > 45 degree chamfering is used on the corners (as is normal > practice for most layout tools, anyway) then this is all that is > necessary up to 2.5GBPS. At 10GBPS, more optimal bends > should be investigated. > > regards, > > scott > > -- > Scott McMorrow > Principal Engineer > SiQual, Signal Quality Engineering > 18735 SW Boones Ferry Road > Tualatin, OR 97062-3090 > (503) 885-1231

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